Version: 2.0.0

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The pop_alerts() function on session is the main interface for retrieving alerts (warnings, messages and errors from libtorrent). If no alerts have been posted by libtorrent pop_alerts() will return an empty list.

By default, only errors are reported. settings_pack::alert_mask can be used to specify which kinds of events should be reported. The alert mask is a combination of the alert_category_t flags in the alert class.

Every alert belongs to one or more category. There is a cost associated with posting alerts. Only alerts that belong to an enabled category are posted. Setting the alert bitmask to 0 will disable all alerts (except those that are non-discardable). Alerts that are responses to API calls such as save_resume_data() and post_session_stats() are non-discardable and will be posted even if their category is disabled.

There are other alert base classes that some alerts derive from, all the alerts that are generated for a specific torrent are derived from torrent_alert, and tracker events derive from tracker_alert.

Alerts returned by pop_alerts() are only valid until the next call to pop_alerts(). You may not copy an alert object to access it after the next call to pop_alerts(). Internal members of alerts also become invalid once pop_alerts() is called again.

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alert

Declared in "libtorrent/alert.hpp"

The alert class is the base class that specific messages are derived from. alert types are not copyable, and cannot be constructed by the client. The pointers returned by libtorrent are short lived (the details are described under session_handle::pop_alerts())

struct alert
{
   time_point timestamp () const;
   virtual int type () const noexcept = 0;
   virtual char const* what () const noexcept = 0;
   virtual std::string message () const = 0;
   virtual alert_category_t category () const noexcept = 0;

   static constexpr alert_category_t error_notification  = 0_bit;
   static constexpr alert_category_t peer_notification  = 1_bit;
   static constexpr alert_category_t port_mapping_notification  = 2_bit;
   static constexpr alert_category_t storage_notification  = 3_bit;
   static constexpr alert_category_t tracker_notification  = 4_bit;
   static constexpr alert_category_t connect_notification  = 5_bit;
   static constexpr alert_category_t status_notification  = 6_bit;
   static constexpr alert_category_t ip_block_notification  = 8_bit;
   static constexpr alert_category_t performance_warning  = 9_bit;
   static constexpr alert_category_t dht_notification  = 10_bit;
   static constexpr alert_category_t session_log_notification  = 13_bit;
   static constexpr alert_category_t torrent_log_notification  = 14_bit;
   static constexpr alert_category_t peer_log_notification  = 15_bit;
   static constexpr alert_category_t incoming_request_notification  = 16_bit;
   static constexpr alert_category_t dht_log_notification  = 17_bit;
   static constexpr alert_category_t dht_operation_notification  = 18_bit;
   static constexpr alert_category_t port_mapping_log_notification  = 19_bit;
   static constexpr alert_category_t picker_log_notification  = 20_bit;
   static constexpr alert_category_t file_progress_notification  = 21_bit;
   static constexpr alert_category_t piece_progress_notification  = 22_bit;
   static constexpr alert_category_t upload_notification  = 23_bit;
   static constexpr alert_category_t block_progress_notification  = 24_bit;
   static constexpr alert_category_t all_categories  = alert_category_t::all();
};
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timestamp()

time_point timestamp () const;

a timestamp is automatically created in the constructor

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type()

virtual int type () const noexcept = 0;

returns an integer that is unique to this alert type. It can be compared against a specific alert by querying a static constant called alert_type in the alert. It can be used to determine the run-time type of an alert* in order to cast to that alert type and access specific members.

e.g:

std::vector<alert*> alerts;
ses.pop_alerts(&alerts);
for (alert* a : alerts) {
        switch (a->type()) {

                case read_piece_alert::alert_type:
                {
                        auto* p = static_cast<read_piece_alert*>(a);
                        if (p->ec) {
                                // read_piece failed
                                break;
                        }
                        // use p
                        break;
                }
                case file_renamed_alert::alert_type:
                {
                        // etc...
                }
        }
}
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what()

virtual char const* what () const noexcept = 0;

returns a string literal describing the type of the alert. It does not include any information that might be bundled with the alert.

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message()

virtual std::string message () const = 0;

generate a string describing the alert and the information bundled with it. This is mainly intended for debug and development use. It is not suitable to use this for applications that may be localized. Instead, handle each alert type individually and extract and render the information from the alert depending on the locale.

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category()

virtual alert_category_t category () const noexcept = 0;

returns a bitmask specifying which categories this alert belong to.

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dht_routing_bucket

Declared in "libtorrent/alert_types.hpp"

struct to hold information about a single DHT routing table bucket

struct dht_routing_bucket
{
   int num_nodes;
   int num_replacements;
   int last_active;
};
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num_nodes num_replacements
the total number of nodes and replacement nodes in the routing table
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last_active
number of seconds since last activity
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torrent_alert

Declared in "libtorrent/alert_types.hpp"

This is a base class for alerts that are associated with a specific torrent. It contains a handle to the torrent.

struct torrent_alert : alert
{
   std::string message () const override;
   char const* torrent_name () const;

   torrent_handle handle;
};
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message()

std::string message () const override;

returns the message associated with this alert

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handle
The torrent_handle pointing to the torrent this alert is associated with.
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peer_alert

Declared in "libtorrent/alert_types.hpp"

The peer alert is a base class for alerts that refer to a specific peer. It includes all the information to identify the peer. i.e. ip and peer-id.

struct peer_alert : torrent_alert
{
   std::string message () const override;

   aux::noexcept_movable<tcp::endpoint> endpoint;
   peer_id pid;
};
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endpoint
The peer's IP address and port.
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pid
the peer ID, if known.
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tracker_alert

Declared in "libtorrent/alert_types.hpp"

This is a base class used for alerts that are associated with a specific tracker. It derives from torrent_alert since a tracker is also associated with a specific torrent.

struct tracker_alert : torrent_alert
{
   std::string message () const override;
   char const* tracker_url () const;

   aux::noexcept_movable<tcp::endpoint> local_endpoint;
};
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tracker_url()

char const* tracker_url () const;

returns a 0-terminated string of the tracker's URL

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local_endpoint
endpoint of the listen interface being announced
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torrent_removed_alert

Declared in "libtorrent/alert_types.hpp"

The torrent_removed_alert is posted whenever a torrent is removed. Since the torrent handle in its base class will always be invalid (since the torrent is already removed) it has the info hash as a member, to identify it. It's posted when the alert_category::status bit is set in the alert_mask.

Even though the handle member doesn't point to an existing torrent anymore, it is still useful for comparing to other handles, which may also no longer point to existing torrents, but to the same non-existing torrents.

The torrent_handle acts as a weak_ptr, even though its object no longer exists, it can still compare equal to another weak pointer which points to the same non-existent object.

struct torrent_removed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   info_hash_t info_hashes;
   client_data_t userdata;
};
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userdata
'userdata` as set in add_torrent_params at torrent creation. This can be used to associate this torrent with related data in the client application more efficiently than info_hashes.
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read_piece_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the asynchronous read operation initiated by a call to torrent_handle::read_piece() is completed. If the read failed, the torrent is paused and an error state is set and the buffer member of the alert is 0. If successful, buffer points to a buffer containing all the data of the piece. piece is the piece index that was read. size is the number of bytes that was read.

If the operation fails, error will indicate what went wrong.

struct read_piece_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::storage;
   error_code const error;
   boost::shared_array<char> const buffer;
   piece_index_t const piece;
   int const size;
};
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file_completed_alert

Declared in "libtorrent/alert_types.hpp"

This is posted whenever an individual file completes its download. i.e. All pieces overlapping this file have passed their hash check.

struct file_completed_alert final : torrent_alert
{
   std::string message () const override;

   file_index_t const index;
};
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index
refers to the index of the file that completed.
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file_renamed_alert

Declared in "libtorrent/alert_types.hpp"

This is posted as a response to a torrent_handle::rename_file() call, if the rename operation succeeds.

struct file_renamed_alert final : torrent_alert
{
   std::string message () const override;
   char const* new_name () const;
   char const* old_name () const;

   static constexpr alert_category_t static_category  = alert_category::storage;
   file_index_t const index;
};
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new_name() old_name()

char const* new_name () const;
char const* old_name () const;

returns the new and previous file name, respectively.

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index
refers to the index of the file that was renamed,
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file_rename_failed_alert

Declared in "libtorrent/alert_types.hpp"

This is posted as a response to a torrent_handle::rename_file() call, if the rename operation failed.

struct file_rename_failed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::storage;
   file_index_t const index;
   error_code const error;
};
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index error
refers to the index of the file that was supposed to be renamed, error is the error code returned from the filesystem.
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performance_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a limit is reached that might have a negative impact on upload or download rate performance.

struct performance_alert final : torrent_alert
{
   std::string message () const override;

   enum performance_warning_t
   {
      outstanding_disk_buffer_limit_reached,
      outstanding_request_limit_reached,
      upload_limit_too_low,
      download_limit_too_low,
      send_buffer_watermark_too_low,
      too_many_optimistic_unchoke_slots,
      too_high_disk_queue_limit,
      aio_limit_reached,
      deprecated_bittyrant_with_no_uplimit,
      too_few_outgoing_ports,
      too_few_file_descriptors,
      num_warnings,
   };

   static constexpr alert_category_t static_category  = alert_category::performance_warning;
   performance_warning_t const warning_code;
};
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enum performance_warning_t

Declared in "libtorrent/alert_types.hpp"

name value description
outstanding_disk_buffer_limit_reached 0 This warning means that the number of bytes queued to be written to disk exceeds the max disk byte queue setting (settings_pack::max_queued_disk_bytes). This might restrict the download rate, by not queuing up enough write jobs to the disk I/O thread. When this alert is posted, peer connections are temporarily stopped from downloading, until the queued disk bytes have fallen below the limit again. Unless your max_queued_disk_bytes setting is already high, you might want to increase it to get better performance.
outstanding_request_limit_reached 1 This is posted when libtorrent would like to send more requests to a peer, but it's limited by settings_pack::max_out_request_queue. The queue length libtorrent is trying to achieve is determined by the download rate and the assumed round-trip-time (settings_pack::request_queue_time). The assumed round-trip-time is not limited to just the network RTT, but also the remote disk access time and message handling time. It defaults to 3 seconds. The target number of outstanding requests is set to fill the bandwidth-delay product (assumed RTT times download rate divided by number of bytes per request). When this alert is posted, there is a risk that the number of outstanding requests is too low and limits the download rate. You might want to increase the max_out_request_queue setting.
upload_limit_too_low 2 This warning is posted when the amount of TCP/IP overhead is greater than the upload rate limit. When this happens, the TCP/IP overhead is caused by a much faster download rate, triggering TCP ACK packets. These packets eat into the rate limit specified to libtorrent. When the overhead traffic is greater than the rate limit, libtorrent will not be able to send any actual payload, such as piece requests. This means the download rate will suffer, and new requests can be sent again. There will be an equilibrium where the download rate, on average, is about 20 times the upload rate limit. If you want to maximize the download rate, increase the upload rate limit above 5% of your download capacity.
download_limit_too_low 3 This is the same warning as upload_limit_too_low but referring to the download limit instead of upload. This suggests that your download rate limit is much lower than your upload capacity. Your upload rate will suffer. To maximize upload rate, make sure your download rate limit is above 5% of your upload capacity.
send_buffer_watermark_too_low 4

We're stalled on the disk. We want to write to the socket, and we can write but our send buffer is empty, waiting to be refilled from the disk. This either means the disk is slower than the network connection or that our send buffer watermark is too small, because we can send it all before the disk gets back to us. The number of bytes that we keep outstanding, requested from the disk, is calculated as follows:

min(512, max(upload_rate * send_buffer_watermark_factor / 100, send_buffer_watermark))

If you receive this alert, you might want to either increase your send_buffer_watermark or send_buffer_watermark_factor.

too_many_optimistic_unchoke_slots 5 If the half (or more) of all upload slots are set as optimistic unchoke slots, this warning is issued. You probably want more regular (rate based) unchoke slots.
too_high_disk_queue_limit 6 If the disk write queue ever grows larger than half of the cache size, this warning is posted. The disk write queue eats into the total disk cache and leaves very little left for the actual cache. This causes the disk cache to oscillate in evicting large portions of the cache before allowing peers to download any more, onto the disk write queue. Either lower max_queued_disk_bytes or increase cache_size.
aio_limit_reached 7  
deprecated_bittyrant_with_no_uplimit 8  
too_few_outgoing_ports 9 This is generated if outgoing peer connections are failing because of address in use errors, indicating that settings_pack::outgoing_ports is set and is too small of a range. Consider not using the outgoing_ports setting at all, or widen the range to include more ports.
too_few_file_descriptors 10  
num_warnings 11  
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state_changed_alert

Declared in "libtorrent/alert_types.hpp"

Generated whenever a torrent changes its state.

struct state_changed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   torrent_status::state_t const state;
   torrent_status::state_t const prev_state;
};
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state
the new state of the torrent.
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prev_state
the previous state.
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tracker_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated on tracker time outs, premature disconnects, invalid response or a HTTP response other than "200 OK". From the alert you can get the handle to the torrent the tracker belongs to.

struct tracker_error_alert final : tracker_alert
{
   std::string message () const override;
   char const* failure_reason () const;

   static constexpr alert_category_t static_category  = alert_category::tracker | alert_category::error;
   int const times_in_row;
   error_code const error;
   operation_t op;
};
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failure_reason()

char const* failure_reason () const;

if the tracker sent a "failure reason" string, it will be returned here.

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times_in_row
This member says how many times in a row this tracker has failed.
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error
the error code indicating why the tracker announce failed. If it is is lt::errors::tracker_failure the failure_reason() might contain a more detailed description of why the tracker rejected the request. HTTP status codes indicating errors are also set in this field.
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tracker_warning_alert

Declared in "libtorrent/alert_types.hpp"

This alert is triggered if the tracker reply contains a warning field. Usually this means that the tracker announce was successful, but the tracker has a message to the client.

struct tracker_warning_alert final : tracker_alert
{
   std::string message () const override;
   char const* warning_message () const;

   static constexpr alert_category_t static_category  = alert_category::tracker | alert_category::error;
};
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warning_message()

char const* warning_message () const;

the message associated with this warning

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scrape_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a scrape request succeeds.

struct scrape_reply_alert final : tracker_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::tracker;
   int const incomplete;
   int const complete;
};
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incomplete complete
the data returned in the scrape response. These numbers may be -1 if the response was malformed.
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scrape_failed_alert

Declared in "libtorrent/alert_types.hpp"

If a scrape request fails, this alert is generated. This might be due to the tracker timing out, refusing connection or returning an http response code indicating an error.

struct scrape_failed_alert final : tracker_alert
{
   std::string message () const override;
   char const* error_message () const;

   static constexpr alert_category_t static_category  = alert_category::tracker | alert_category::error;
   error_code const error;
};
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error_message()

char const* error_message () const;

if the error indicates there is an associated message, this returns that message. Otherwise and empty string.

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error
the error itself. This may indicate that the tracker sent an error message (error::tracker_failure), in which case it can be retrieved by calling error_message().
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tracker_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is only for informational purpose. It is generated when a tracker announce succeeds. It is generated regardless what kind of tracker was used, be it UDP, HTTP or the DHT.

struct tracker_reply_alert final : tracker_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::tracker;
   int const num_peers;
};
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num_peers
tells how many peers the tracker returned in this response. This is not expected to be greater than the num_want settings. These are not necessarily all new peers, some of them may already be connected.
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dht_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated each time the DHT receives peers from a node. num_peers is the number of peers we received in this packet. Typically these packets are received from multiple DHT nodes, and so the alerts are typically generated a few at a time.

struct dht_reply_alert final : tracker_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht | alert_category::tracker;
   int const num_peers;
};
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tracker_announce_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated each time a tracker announce is sent (or attempted to be sent). There are no extra data members in this alert. The url can be found in the base class however.

struct tracker_announce_alert final : tracker_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::tracker;
   event_t const event;
};
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event

specifies what event was sent to the tracker. It is defined as:

  1. None
  2. Completed
  3. Started
  4. Stopped
  5. Paused
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hash_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a finished piece fails its hash check. You can get the handle to the torrent which got the failed piece and the index of the piece itself from the alert.

struct hash_failed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   piece_index_t const piece_index;
};
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peer_ban_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is banned because it has sent too many corrupt pieces to us. ip is the endpoint to the peer that was banned.

struct peer_ban_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
};
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peer_unsnubbed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is un-snubbed. Essentially when it was snubbed for stalling sending data, and now it started sending data again.

struct peer_unsnubbed_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
};
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peer_snubbed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is snubbed, when it stops sending data when we request it.

struct peer_snubbed_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
};
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peer_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer sends invalid data over the peer-peer protocol. The peer will be disconnected, but you get its ip address from the alert, to identify it.

struct peer_error_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
   operation_t op;
   error_code const error;
};
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op
a 0-terminated string of the low-level operation that failed, or nullptr if there was no low level disk operation.
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error
tells you what error caused this alert.
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peer_connect_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted every time an incoming peer connection both successfully passes the protocol handshake and is associated with a torrent, or an outgoing peer connection attempt succeeds. For arbitrary incoming connections, see incoming_connection_alert.

struct peer_connect_alert final : peer_alert
{
   std::string message () const override;

   enum direction_t
   {
      in,
      out,
   };

   static constexpr alert_category_t static_category  = alert_category::connect;
   direction_t direction;
   socket_type_t socket_type;
};
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enum direction_t

Declared in "libtorrent/alert_types.hpp"

name value description
in 0  
out 1  
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direction
Tells you if the peer was incoming or outgoing
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peer_disconnected_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer is disconnected for any reason (other than the ones covered by peer_error_alert ).

struct peer_disconnected_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::connect;
   socket_type_t const socket_type;
   operation_t const op;
   error_code const error;
   close_reason_t const reason;
};
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socket_type
the kind of socket this peer was connected over
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op
the operation or level where the error occurred. Specified as an value from the operation_t enum. Defined in operations.hpp.
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error
tells you what error caused peer to disconnect.
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reason
the reason the peer disconnected (if specified)
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invalid_request_alert

Declared in "libtorrent/alert_types.hpp"

This is a debug alert that is generated by an incoming invalid piece request. ip is the address of the peer and the request is the actual incoming request from the peer. See peer_request for more info.

struct invalid_request_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
   peer_request const request;
   bool const we_have;
   bool const peer_interested;
   bool const withheld;
};
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request
the request we received from the peer
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we_have
true if we have this piece
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peer_interested
true if the peer indicated that it was interested to download before sending the request
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withheld
if this is true, the peer is not allowed to download this piece because of super-seeding rules.
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torrent_finished_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a torrent switches from being a downloader to a seed. It will only be generated once per torrent. It contains a torrent_handle to the torrent in question.

struct torrent_finished_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
};
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piece_finished_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted every time a piece completes downloading and passes the hash check. This alert derives from torrent_alert which contains the torrent_handle to the torrent the piece belongs to. Note that being downloaded and passing the hash check may happen before the piece is also fully flushed to disk. So torrent_handle::have_piece() may still return false

struct piece_finished_alert final : torrent_alert
{
   std::string message () const override;

   piece_index_t const piece_index;
};
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piece_index
the index of the piece that finished
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request_dropped_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a peer rejects or ignores a piece request.

struct request_dropped_alert final : peer_alert
{
   std::string message () const override;

   int const block_index;
   piece_index_t const piece_index;
};
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block_timeout_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request times out.

struct block_timeout_alert final : peer_alert
{
   std::string message () const override;

   int const block_index;
   piece_index_t const piece_index;
};
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block_finished_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request receives a response.

struct block_finished_alert final : peer_alert
{
   std::string message () const override;

   int const block_index;
   piece_index_t const piece_index;
};
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block_downloading_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request is sent to a peer.

struct block_downloading_alert final : peer_alert
{
   std::string message () const override;

   int const block_index;
   piece_index_t const piece_index;
};
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unwanted_block_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block is received that was not requested or whose request timed out.

struct unwanted_block_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
   int const block_index;
   piece_index_t const piece_index;
};
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storage_moved_alert

Declared in "libtorrent/alert_types.hpp"

The storage_moved_alert is generated when all the disk IO has completed and the files have been moved, as an effect of a call to torrent_handle::move_storage. This is useful to synchronize with the actual disk. The storage_path() member return the new path of the storage.

struct storage_moved_alert final : torrent_alert
{
   std::string message () const override;
   char const* old_path () const;
   char const* storage_path () const;

   static constexpr alert_category_t static_category  = alert_category::storage;
};
[report issue]

old_path() storage_path()

char const* old_path () const;
char const* storage_path () const;

the path the torrent was moved to and from, respectively.

[report issue]

storage_moved_failed_alert

Declared in "libtorrent/alert_types.hpp"

The storage_moved_failed_alert is generated when an attempt to move the storage, via torrent_handle::move_storage(), fails.

struct storage_moved_failed_alert final : torrent_alert
{
   std::string message () const override;
   char const* file_path () const;

   static constexpr alert_category_t static_category  = alert_category::storage;
   error_code const error;
   operation_t op;
};
[report issue]

file_path()

char const* file_path () const;

If the error happened for a specific file, this returns its path.

[report issue]
op
this indicates what underlying operation caused the error
[report issue]

torrent_deleted_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a request to delete the files of a torrent complete.

This alert is posted in the alert_category::storage category, and that bit needs to be set in the alert_mask.

struct torrent_deleted_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::storage;
   info_hash_t info_hashes;
};
[report issue]
info_hashes
The info-hash of the torrent that was just deleted. Most of the time the torrent_handle in the torrent_alert will be invalid by the time this alert arrives, since the torrent is being deleted. The info_hashes member is hence the main way of identifying which torrent just completed the delete.
[report issue]

torrent_delete_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a request to delete the files of a torrent fails. Just removing a torrent from the session cannot fail

struct torrent_delete_failed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::storage
   | alert_category::error;
   error_code const error;
   info_hash_t info_hashes;
};
[report issue]
error
tells you why it failed.
[report issue]
info_hashes
the info hash of the torrent whose files failed to be deleted
[report issue]

save_resume_data_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated as a response to a torrent_handle::save_resume_data request. It is generated once the disk IO thread is done writing the state for this torrent.

struct save_resume_data_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::storage;
   add_torrent_params params;
};
[report issue]
params
the params structure is populated with the fields to be passed to add_torrent() or async_add_torrent() to resume the torrent. To save the state to disk, you may pass it on to write_resume_data().
[report issue]

save_resume_data_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated instead of save_resume_data_alert if there was an error generating the resume data. error describes what went wrong.

struct save_resume_data_failed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::storage
   | alert_category::error;
   error_code const error;
};
[report issue]
error
the error code from the resume_data failure
[report issue]

torrent_paused_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated as a response to a torrent_handle::pause request. It is generated once all disk IO is complete and the files in the torrent have been closed. This is useful for synchronizing with the disk.

struct torrent_paused_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
};
[report issue]

torrent_resumed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated as a response to a torrent_handle::resume() request. It is generated when a torrent goes from a paused state to an active state.

struct torrent_resumed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
};
[report issue]

torrent_checked_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when a torrent completes checking. i.e. when it transitions out of the checking files state into a state where it is ready to start downloading

struct torrent_checked_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
};
[report issue]

url_seed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a HTTP seed name lookup fails.

struct url_seed_alert final : torrent_alert
{
   std::string message () const override;
   char const* server_url () const;
   char const* error_message () const;

   static constexpr alert_category_t static_category  = alert_category::peer | alert_category::error;
   error_code const error;
};
[report issue]

server_url()

char const* server_url () const;

the URL the error is associated with

[report issue]

error_message()

char const* error_message () const;

in case the web server sent an error message, this function returns it.

[report issue]
error
the error the web seed encountered. If this is not set, the server sent an error message, call error_message().
[report issue]

file_error_alert

Declared in "libtorrent/alert_types.hpp"

If the storage fails to read or write files that it needs access to, this alert is generated and the torrent is paused.

struct file_error_alert final : torrent_alert
{
   std::string message () const override;
   char const* filename () const;

   static constexpr alert_category_t static_category  = alert_category::status
   | alert_category::storage;
   error_code const error;
   operation_t op;
};
[report issue]

filename()

char const* filename () const;

the file that experienced the error

[report issue]
error
the error code describing the error.
[report issue]
op
indicates which underlying operation caused the error
[report issue]

metadata_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when the metadata has been completely received and the info-hash failed to match it. i.e. the metadata that was received was corrupt. libtorrent will automatically retry to fetch it in this case. This is only relevant when running a torrent-less download, with the metadata extension provided by libtorrent.

struct metadata_failed_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   error_code const error;
};
[report issue]
error
indicates what failed when parsing the metadata. This error is what's returned from lazy_bdecode().
[report issue]

metadata_received_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when the metadata has been completely received and the torrent can start downloading. It is not generated on torrents that are started with metadata, but only those that needs to download it from peers (when utilizing the libtorrent extension).

There are no additional data members in this alert.

Typically, when receiving this alert, you would want to save the torrent file in order to load it back up again when the session is restarted. Here's an example snippet of code to do that:

torrent_handle h = alert->handle();
if (h.is_valid()) {
        std::shared_ptr<torrent_info const> ti = h.torrent_file();
        create_torrent ct(*ti);
        entry te = ct.generate();
        std::vector<char> buffer;
        bencode(std::back_inserter(buffer), te);
        FILE* f = fopen((to_hex(ti->info_hashes().get_best().to_string()) + ".torrent").c_str(), "wb+");
        if (f) {
                fwrite(&buffer[0], 1, buffer.size(), f);
                fclose(f);
        }
}
struct metadata_received_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
};
[report issue]

udp_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when there is an error on a UDP socket. The UDP sockets are used for all uTP, DHT and UDP tracker traffic. They are global to the session.

struct udp_error_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   aux::noexcept_movable<udp::endpoint> endpoint;
   operation_t operation;
   error_code const error;
};
[report issue]
endpoint
the source address associated with the error (if any)
[report issue]
operation
the operation that failed
[report issue]
error
the error code describing the error
[report issue]

external_ip_alert

Declared in "libtorrent/alert_types.hpp"

Whenever libtorrent learns about the machines external IP, this alert is generated. The external IP address can be acquired from the tracker (if it supports that) or from peers that supports the extension protocol. The address can be accessed through the external_address member.

struct external_ip_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   aux::noexcept_movable<address> external_address;
};
[report issue]
external_address
the IP address that is believed to be our external IP
[report issue]

listen_failed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when none of the ports, given in the port range, to session can be opened for listening. The listen_interface member is the interface that failed, error is the error code describing the failure.

In the case an endpoint was created before generating the alert, it is represented by address and port. The combinations of socket type and operation in which such address and port are not valid are: accept - i2p accept - socks5 enum_if - tcp

libtorrent may sometimes try to listen on port 0, if all other ports failed. Port 0 asks the operating system to pick a port that's free). If that fails you may see a listen_failed_alert with port 0 even if you didn't ask to listen on it.

struct listen_failed_alert final : alert
{
   std::string message () const override;
   char const* listen_interface () const;

   static constexpr alert_category_t static_category  = alert_category::status | alert_category::error;
   error_code const error;
   operation_t op;
   lt::socket_type_t const socket_type;
   aux::noexcept_movable<lt::address> address;
   int const port;
};
[report issue]

listen_interface()

char const* listen_interface () const;

the network device libtorrent attempted to listen on, or the IP address

[report issue]
error
the error the system returned
[report issue]
op
the underlying operation that failed
[report issue]
socket_type
the type of listen socket this alert refers to.
[report issue]
address
the address libtorrent attempted to listen on see alert documentation for validity of this value
[report issue]
port
the port libtorrent attempted to listen on see alert documentation for validity of this value
[report issue]

listen_succeeded_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the listen port succeeds to be opened on a particular interface. address and port is the endpoint that successfully was opened for listening.

struct listen_succeeded_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   aux::noexcept_movable<lt::address> address;
   int const port;
   lt::socket_type_t const socket_type;
};
[report issue]
address
the address libtorrent ended up listening on. This address refers to the local interface.
[report issue]
port
the port libtorrent ended up listening on.
[report issue]
socket_type
the type of listen socket this alert refers to.
[report issue]

portmap_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a NAT router was successfully found but some part of the port mapping request failed. It contains a text message that may help the user figure out what is wrong. This alert is not generated in case it appears the client is not running on a NAT:ed network or if it appears there is no NAT router that can be remote controlled to add port mappings.

struct portmap_error_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::port_mapping
   | alert_category::error;
   port_mapping_t const mapping;
   portmap_transport map_transport;
   aux::noexcept_movable<address> local_address;
   error_code const error;
};
[report issue]
mapping
refers to the mapping index of the port map that failed, i.e. the index returned from add_mapping().
[report issue]
map_transport
UPnP or NAT-PMP
[report issue]
local_address
the local network the port mapper is running on
[report issue]
error
tells you what failed.
[report issue]

portmap_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a NAT router was successfully found and a port was successfully mapped on it. On a NAT:ed network with a NAT-PMP capable router, this is typically generated once when mapping the TCP port and, if DHT is enabled, when the UDP port is mapped.

struct portmap_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::port_mapping;
   port_mapping_t const mapping;
   int const external_port;
   portmap_protocol const map_protocol;
   portmap_transport const map_transport;
   aux::noexcept_movable<address> local_address;
};
[report issue]
mapping
refers to the mapping index of the port map that failed, i.e. the index returned from add_mapping().
[report issue]
external_port
the external port allocated for the mapping.
[report issue]
local_address
the local network the port mapper is running on
[report issue]

portmap_log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated to log informational events related to either UPnP or NAT-PMP. They contain a log line and the type (0 = NAT-PMP and 1 = UPnP). Displaying these messages to an end user is only useful for debugging the UPnP or NAT-PMP implementation. This alert is only posted if the alert_category::port_mapping_log flag is enabled in the alert mask.

struct portmap_log_alert final : alert
{
   std::string message () const override;
   char const* log_message () const;

   static constexpr alert_category_t static_category  = alert_category::port_mapping_log;
   portmap_transport const map_transport;
   aux::noexcept_movable<address> local_address;
};
[report issue]

log_message()

char const* log_message () const;

the message associated with this log line

[report issue]
local_address
the local network the port mapper is running on
[report issue]

fastresume_rejected_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a fast resume file has been passed to add_torrent() but the files on disk did not match the fast resume file. The error_code explains the reason why the resume file was rejected.

struct fastresume_rejected_alert final : torrent_alert
{
   std::string message () const override;
   char const* file_path () const;

   static constexpr alert_category_t static_category  = alert_category::status
   | alert_category::error;
   error_code error;
   operation_t op;
};
[report issue]

file_path()

char const* file_path () const;

If the error happened to a specific file, this returns the path to it.

[report issue]
op
the underlying operation that failed
[report issue]

peer_blocked_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when an incoming peer connection, or a peer that's about to be added to our peer list, is blocked for some reason. This could be any of:

  • the IP filter
  • i2p mixed mode restrictions (a normal peer is not allowed on an i2p swarm)
  • the port filter
  • the peer has a low port and no_connect_privileged_ports is enabled
  • the protocol of the peer is blocked (uTP/TCP blocking)
struct peer_blocked_alert final : peer_alert
{
   std::string message () const override;

   enum reason_t
   {
      ip_filter,
      port_filter,
      i2p_mixed,
      privileged_ports,
      utp_disabled,
      tcp_disabled,
      invalid_local_interface,
   };

   static constexpr alert_category_t static_category  = alert_category::ip_block;
   int const reason;
};
[report issue]

enum reason_t

Declared in "libtorrent/alert_types.hpp"

name value description
ip_filter 0  
port_filter 1  
i2p_mixed 2  
privileged_ports 3  
utp_disabled 4  
tcp_disabled 5  
invalid_local_interface 6  
[report issue]
reason
the reason for the peer being blocked. Is one of the values from the reason_t enum.
[report issue]

dht_announce_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a DHT node announces to an info-hash on our DHT node. It belongs to the alert_category::dht category.

struct dht_announce_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
   aux::noexcept_movable<address> ip;
   int port;
   sha1_hash info_hash;
};
[report issue]

dht_get_peers_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a DHT node sends a get_peers message to our DHT node. It belongs to the alert_category::dht category.

struct dht_get_peers_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
   sha1_hash info_hash;
};
[report issue]

cache_flushed_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the disk cache has been flushed for a specific torrent as a result of a call to torrent_handle::flush_cache(). This alert belongs to the alert_category::storage category, which must be enabled to let this alert through. The alert is also posted when removing a torrent from the session, once the outstanding cache flush is complete and the torrent does no longer have any files open.

struct cache_flushed_alert final : torrent_alert
{
   static constexpr alert_category_t static_category  = alert_category::storage;
};
[report issue]

lsd_peer_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when we receive a local service discovery message from a peer for a torrent we're currently participating in.

struct lsd_peer_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
};
[report issue]

trackerid_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted whenever a tracker responds with a trackerid. The tracker ID is like a cookie. libtorrent will store the tracker ID for this tracker and repeat it in subsequent announces.

struct trackerid_alert final : tracker_alert
{
   std::string message () const override;
   char const* tracker_id () const;

   static constexpr alert_category_t static_category  = alert_category::status;
};
[report issue]

tracker_id()

char const* tracker_id () const;

The tracker ID returned by the tracker

[report issue]

dht_bootstrap_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when the initial DHT bootstrap is done.

struct dht_bootstrap_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
};
[report issue]

torrent_error_alert

Declared in "libtorrent/alert_types.hpp"

This is posted whenever a torrent is transitioned into the error state.

struct torrent_error_alert final : torrent_alert
{
   std::string message () const override;
   char const* filename () const;

   static constexpr alert_category_t static_category  = alert_category::error | alert_category::status;
   error_code const error;
};
[report issue]

filename()

char const* filename () const;

the filename (or object) the error occurred on.

[report issue]
error
specifies which error the torrent encountered.
[report issue]

torrent_need_cert_alert

Declared in "libtorrent/alert_types.hpp"

This is always posted for SSL torrents. This is a reminder to the client that the torrent won't work unless torrent_handle::set_ssl_certificate() is called with a valid certificate. Valid certificates MUST be signed by the SSL certificate in the .torrent file.

struct torrent_need_cert_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
};
[report issue]

incoming_connection_alert

Declared in "libtorrent/alert_types.hpp"

The incoming connection alert is posted every time we successfully accept an incoming connection, through any mean. The most straight-forward ways of accepting incoming connections are through the TCP listen socket and the UDP listen socket for uTP sockets. However, connections may also be accepted through a Socks5 or i2p listen socket, or via an SSL listen socket.

struct incoming_connection_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::peer;
   socket_type_t socket_type;
   aux::noexcept_movable<tcp::endpoint> endpoint;
};
[report issue]
socket_type
tells you what kind of socket the connection was accepted
[report issue]
endpoint
is the IP address and port the connection came from.
[report issue]

add_torrent_alert

Declared in "libtorrent/alert_types.hpp"

This alert is always posted when a torrent was attempted to be added and contains the return status of the add operation. The torrent handle of the new torrent can be found as the handle member in the base class. If adding the torrent failed, error contains the error code.

struct add_torrent_alert final : torrent_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   add_torrent_params params;
   error_code error;
};
[report issue]
params

This contains copies of the most important fields from the original add_torrent_params object, passed to add_torrent() or async_add_torrent(). Specifically, these fields are copied:

  • version
  • ti
  • name
  • save_path
  • userdata
  • tracker_id
  • flags
  • info_hash

the info_hash field will be updated with the info-hash of the torrent specified by ti.

[report issue]
error
set to the error, if one occurred while adding the torrent.
[report issue]

state_update_alert

Declared in "libtorrent/alert_types.hpp"

This alert is only posted when requested by the user, by calling session::post_torrent_updates() on the session. It contains the torrent status of all torrents that changed since last time this message was posted. Its category is alert_category::status, but it's not subject to filtering, since it's only manually posted anyway.

struct state_update_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::status;
   std::vector<torrent_status> status;
};
[report issue]
status
contains the torrent status of all torrents that changed since last time this message was posted. Note that you can map a torrent status to a specific torrent via its handle member. The receiving end is suggested to have all torrents sorted by the torrent_handle or hashed by it, for efficient updates.
[report issue]

session_stats_alert

Declared in "libtorrent/alert_types.hpp"

The session_stats_alert is posted when the user requests session statistics by calling post_session_stats() on the session object. This alert does not have a category, since it's only posted in response to an API call. It is not subject to the alert_mask filter.

the message() member function returns a string representation of the values that properly match the line returned in session_stats_header_alert::message().

this specific output is parsed by tools/parse_session_stats.py if this is changed, that parser should also be changed

struct session_stats_alert final : alert
{
   std::string message () const override;
   span<std::int64_t const> counters () const;

   static constexpr alert_category_t static_category  = {};
};
[report issue]

counters()

span<std::int64_t const> counters () const;

An array are a mix of counters and gauges, which meanings can be queries via the session_stats_metrics() function on the session. The mapping from a specific metric to an index into this array is constant for a specific version of libtorrent, but may differ for other versions. The intended usage is to request the mapping, i.e. call session_stats_metrics(), once on startup, and then use that mapping to interpret these values throughout the process' runtime.

For more information, see the session statistics section.

[report issue]

dht_error_alert

Declared in "libtorrent/alert_types.hpp"

posted when something fails in the DHT. This is not necessarily a fatal error, but it could prevent proper operation

struct dht_error_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error | alert_category::dht;
   error_code error;
   operation_t op;
};
[report issue]
error
the error code
[report issue]
op
the operation that failed
[report issue]

dht_immutable_item_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted as a response to a call to session::get_item(), specifically the overload for looking up immutable items in the DHT.

struct dht_immutable_item_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
   sha1_hash target;
   entry item;
};
[report issue]
target
the target hash of the immutable item. This must match the SHA-1 hash of the bencoded form of item.
[report issue]
item
the data for this item
[report issue]

dht_mutable_item_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted as a response to a call to session::get_item(), specifically the overload for looking up mutable items in the DHT.

struct dht_mutable_item_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
   std::array<char, 32> key;
   std::array<char, 64> signature;
   std::int64_t seq;
   std::string salt;
   entry item;
   bool authoritative;
};
[report issue]
key
the public key that was looked up
[report issue]
signature
the signature of the data. This is not the signature of the plain encoded form of the item, but it includes the sequence number and possibly the hash as well. See the dht_store document for more information. This is primarily useful for echoing back in a store request.
[report issue]
seq
the sequence number of this item
[report issue]
salt
the salt, if any, used to lookup and store this item. If no salt was used, this is an empty string
[report issue]
item
the data for this item
[report issue]
authoritative
the last response for mutable data is authoritative.
[report issue]

dht_put_alert

Declared in "libtorrent/alert_types.hpp"

this is posted when a DHT put operation completes. This is useful if the client is waiting for a put to complete before shutting down for instance.

struct dht_put_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
   sha1_hash target;
   std::array<char, 32> public_key;
   std::array<char, 64> signature;
   std::string salt;
   std::int64_t seq;
   int num_success;
};
[report issue]
target
the target hash the item was stored under if this was an immutable item.
[report issue]
public_key signature salt seq
if a mutable item was stored, these are the public key, signature, salt and sequence number the item was stored under.
[report issue]
num_success
DHT put operation usually writes item to k nodes, maybe the node is stale so no response, or the node doesn't support 'put', or the token for write is out of date, etc. num_success is the number of successful responses we got from the puts.
[report issue]

i2p_alert

Declared in "libtorrent/alert_types.hpp"

this alert is used to report errors in the i2p SAM connection

struct i2p_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   error_code error;
};
[report issue]
error
the error that occurred in the i2p SAM connection
[report issue]

dht_outgoing_get_peers_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when we send a get_peers request It belongs to the alert_category::dht category.

struct dht_outgoing_get_peers_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::dht;
   sha1_hash info_hash;
   sha1_hash obfuscated_info_hash;
   aux::noexcept_movable<udp::endpoint> endpoint;
};
[report issue]
info_hash
the info_hash of the torrent we're looking for peers for.
[report issue]
obfuscated_info_hash
if this was an obfuscated lookup, this is the info-hash target actually sent to the node.
[report issue]
endpoint
the endpoint we're sending this query to
[report issue]

log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted by some session wide event. Its main purpose is trouble shooting and debugging. It's not enabled by the default alert mask and is enabled by the alert_category::session_log bit. Furthermore, it's by default disabled as a build configuration.

struct log_alert final : alert
{
   std::string message () const override;
   char const* log_message () const;

   static constexpr alert_category_t static_category  = alert_category::session_log;
};
[report issue]

log_message()

char const* log_message () const;

returns the log message

[report issue]

torrent_log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted by torrent wide events. It's meant to be used for trouble shooting and debugging. It's not enabled by the default alert mask and is enabled by the alert_category::torrent_log bit. By default it is disabled as a build configuration.

struct torrent_log_alert final : torrent_alert
{
   std::string message () const override;
   char const* log_message () const;

   static constexpr alert_category_t static_category  = alert_category::torrent_log;
};
[report issue]

log_message()

char const* log_message () const;

returns the log message

[report issue]

peer_log_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted by events specific to a peer. It's meant to be used for trouble shooting and debugging. It's not enabled by the default alert mask and is enabled by the alert_category::peer_log bit. By default it is disabled as a build configuration.

struct peer_log_alert final : peer_alert
{
   std::string message () const override;
   char const* log_message () const;

   enum direction_t
   {
      incoming_message,
      outgoing_message,
      incoming,
      outgoing,
      info,
   };

   static constexpr alert_category_t static_category  = alert_category::peer_log;
   char const* event_type;
   direction_t direction;
};
[report issue]

log_message()

char const* log_message () const;

returns the log message

[report issue]

enum direction_t

Declared in "libtorrent/alert_types.hpp"

name value description
incoming_message 0  
outgoing_message 1  
incoming 2  
outgoing 3  
info 4  
[report issue]
event_type
string literal indicating the kind of event. For messages, this is the message name.
[report issue]

lsd_error_alert

Declared in "libtorrent/alert_types.hpp"

posted if the local service discovery socket fails to start properly. it's categorized as alert_category::error.

struct lsd_error_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   aux::noexcept_movable<address> local_address;
   error_code error;
};
[report issue]
local_address
the local network the corresponding local service discovery is running on
[report issue]
error
The error code
[report issue]

dht_lookup

Declared in "libtorrent/alert_types.hpp"

holds statistics about a current dht_lookup operation. a DHT lookup is the traversal of nodes, looking up a set of target nodes in the DHT for retrieving and possibly storing information in the DHT

struct dht_lookup
{
   char const* type;
   int outstanding_requests;
   int timeouts;
   int responses;
   int branch_factor;
   int nodes_left;
   int last_sent;
   int first_timeout;
   sha1_hash target;
};
[report issue]
type
string literal indicating which kind of lookup this is
[report issue]
outstanding_requests
the number of outstanding request to individual nodes this lookup has right now
[report issue]
timeouts
the total number of requests that have timed out so far for this lookup
[report issue]
responses
the total number of responses we have received for this lookup so far for this lookup
[report issue]
branch_factor
the branch factor for this lookup. This is the number of nodes we keep outstanding requests to in parallel by default. when nodes time out we may increase this.
[report issue]
nodes_left
the number of nodes left that could be queries for this lookup. Many of these are likely to be part of the trail while performing the lookup and would never end up actually being queried.
[report issue]
last_sent
the number of seconds ago the last message was sent that's still outstanding
[report issue]
first_timeout
the number of outstanding requests that have exceeded the short timeout and are considered timed out in the sense that they increased the branch factor
[report issue]
target
the node-id or info-hash target for this lookup
[report issue]

dht_stats_alert

Declared in "libtorrent/alert_types.hpp"

contains current DHT state. Posted in response to session::post_dht_stats().

struct dht_stats_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = {};
   std::vector<dht_lookup> active_requests;
   std::vector<dht_routing_bucket> routing_table;
   sha1_hash nid;
   aux::noexcept_movable<udp::endpoint> local_endpoint;
};
[report issue]
active_requests
a vector of the currently running DHT lookups.
[report issue]
routing_table
contains information about every bucket in the DHT routing table.
[report issue]
nid
the node ID of the DHT node instance
[report issue]
local_endpoint
the local socket this DHT node is running on
[report issue]

incoming_request_alert

Declared in "libtorrent/alert_types.hpp"

posted every time an incoming request from a peer is accepted and queued up for being serviced. This alert is only posted if the alert_category::incoming_request flag is enabled in the alert mask.

struct incoming_request_alert final : peer_alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::incoming_request;
   peer_request req;
};
[report issue]
req
the request this peer sent to us
[report issue]

dht_log_alert

Declared in "libtorrent/alert_types.hpp"

debug logging of the DHT when alert_category::dht_log is set in the alert mask.

struct dht_log_alert final : alert
{
   std::string message () const override;
   char const* log_message () const;

   enum dht_module_t
   {
      tracker,
      node,
      routing_table,
      rpc_manager,
      traversal,
   };

   static constexpr alert_category_t static_category  = alert_category::dht_log;
   dht_module_t module;
};
[report issue]

log_message()

char const* log_message () const;

the log message

[report issue]

enum dht_module_t

Declared in "libtorrent/alert_types.hpp"

name value description
tracker 0  
node 1  
routing_table 2  
rpc_manager 3  
traversal 4  
[report issue]
module
the module, or part, of the DHT that produced this log message.
[report issue]

dht_pkt_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted every time a DHT message is sent or received. It is only posted if the alert_category::dht_log alert category is enabled. It contains a verbatim copy of the message.

struct dht_pkt_alert final : alert
{
   std::string message () const override;
   span<char const> pkt_buf () const;

   enum direction_t
   {
      incoming,
      outgoing,
   };

   static constexpr alert_category_t static_category  = alert_category::dht_log;
   direction_t direction;
   aux::noexcept_movable<udp::endpoint> node;
};
[report issue]

pkt_buf()

span<char const> pkt_buf () const;

returns a pointer to the packet buffer and size of the packet, respectively. This buffer is only valid for as long as the alert itself is valid, which is owned by libtorrent and reclaimed whenever pop_alerts() is called on the session.

[report issue]

enum direction_t

Declared in "libtorrent/alert_types.hpp"

name value description
incoming 0  
outgoing 1  
[report issue]
direction
whether this is an incoming or outgoing packet.
[report issue]
node
the DHT node we received this packet from, or sent this packet to (depending on direction).
[report issue]

dht_get_peers_reply_alert

Declared in "libtorrent/alert_types.hpp"

Posted when we receive a response to a DHT get_peers request.

struct dht_get_peers_reply_alert final : alert
{
   std::string message () const override;
   int num_peers () const;
   std::vector<tcp::endpoint> peers () const;

   static constexpr alert_category_t static_category  = alert_category::dht_operation;
   sha1_hash info_hash;
};
[report issue]

dht_direct_response_alert

Declared in "libtorrent/alert_types.hpp"

This is posted exactly once for every call to session_handle::dht_direct_request. If the request failed, response() will return a default constructed bdecode_node.

struct dht_direct_response_alert final : alert
{
   std::string message () const override;
   bdecode_node response () const;

   static constexpr alert_category_t static_category  = alert_category::dht;
   client_data_t userdata;
   aux::noexcept_movable<udp::endpoint> endpoint;
};
[report issue]

picker_log_alert

Declared in "libtorrent/alert_types.hpp"

this is posted when one or more blocks are picked by the piece picker, assuming the verbose piece picker logging is enabled (see alert_category::picker_log).

struct picker_log_alert final : peer_alert
{
   std::string message () const override;
   std::vector<piece_block> blocks () const;

   static constexpr alert_category_t static_category  = alert_category::picker_log;
   static constexpr picker_flags_t partial_ratio  = 0_bit;
   static constexpr picker_flags_t prioritize_partials  = 1_bit;
   static constexpr picker_flags_t rarest_first_partials  = 2_bit;
   static constexpr picker_flags_t rarest_first  = 3_bit;
   static constexpr picker_flags_t reverse_rarest_first  = 4_bit;
   static constexpr picker_flags_t suggested_pieces  = 5_bit;
   static constexpr picker_flags_t prio_sequential_pieces  = 6_bit;
   static constexpr picker_flags_t sequential_pieces  = 7_bit;
   static constexpr picker_flags_t reverse_pieces  = 8_bit;
   static constexpr picker_flags_t time_critical  = 9_bit;
   static constexpr picker_flags_t random_pieces  = 10_bit;
   static constexpr picker_flags_t prefer_contiguous  = 11_bit;
   static constexpr picker_flags_t reverse_sequential  = 12_bit;
   static constexpr picker_flags_t backup1  = 13_bit;
   static constexpr picker_flags_t backup2  = 14_bit;
   static constexpr picker_flags_t end_game  = 15_bit;
   static constexpr picker_flags_t extent_affinity  = 16_bit;
   picker_flags_t const picker_flags;
};
[report issue]
picker_flags
this is a bitmask of which features were enabled for this particular pick. The bits are defined in the picker_flags_t enum.
[report issue]

session_error_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted when the session encounters a serious error, potentially fatal

struct session_error_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   error_code const error;
};
[report issue]
error
The error code, if one is associated with this error
[report issue]

dht_live_nodes_alert

Declared in "libtorrent/alert_types.hpp"

posted in response to a call to session::dht_live_nodes(). It contains the live nodes from the DHT routing table of one of the DHT nodes running locally.

struct dht_live_nodes_alert final : alert
{
   std::string message () const override;
   std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;
   int num_nodes () const;

   static constexpr alert_category_t static_category  = alert_category::dht;
   sha1_hash node_id;
};
[report issue]

num_nodes() nodes()

std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;
int num_nodes () const;

the number of nodes in the routing table and the actual nodes.

[report issue]
node_id
the local DHT node's node-ID this routing table belongs to
[report issue]

session_stats_header_alert

Declared in "libtorrent/alert_types.hpp"

The session_stats_header alert is posted the first time post_session_stats() is called

the message() member function returns a string representation of the header that properly match the stats values string returned in session_stats_alert::message().

this specific output is parsed by tools/parse_session_stats.py if this is changed, that parser should also be changed

struct session_stats_header_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = {};
};
[report issue]

dht_sample_infohashes_alert

Declared in "libtorrent/alert_types.hpp"

posted as a response to a call to session::dht_sample_infohashes() with the information from the DHT response message.

struct dht_sample_infohashes_alert final : alert
{
   std::string message () const override;
   int num_samples () const;
   std::vector<sha1_hash> samples () const;
   int num_nodes () const;
   std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;

   static constexpr alert_category_t static_category  = alert_category::dht_operation;
   sha1_hash node_id;
   aux::noexcept_movable<udp::endpoint> endpoint;
   time_duration const interval;
   int const num_infohashes;
};
[report issue]

samples() num_samples()

int num_samples () const;
std::vector<sha1_hash> samples () const;

returns the number of info-hashes returned by the node, as well as the actual info-hashes. num_samples() is more efficient than samples().size().

[report issue]

num_nodes()

int num_nodes () const;

The total number of nodes returned by nodes().

[report issue]

nodes()

std::vector<std::pair<sha1_hash, udp::endpoint>> nodes () const;

This is the set of more DHT nodes returned by the request.

The information is included so that indexing nodes can perform a key space traversal with a single RPC per node by adjusting the target value for each RPC.

[report issue]
node_id
id of the node the request was sent to (and this response was received from)
[report issue]
endpoint
the node the request was sent to (and this response was received from)
[report issue]
interval
the interval to wait before making another request to this node
[report issue]
num_infohashes
This field indicates how many info-hash keys are currently in the node's storage. If the value is larger than the number of returned samples it indicates that the indexer may obtain additional samples after waiting out the interval.
[report issue]

block_uploaded_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when a block intended to be sent to a peer is placed in the send buffer. Note that if the connection is closed before the send buffer is sent, the alert may be posted without the bytes having been sent to the peer. It belongs to the alert_category::upload category.

struct block_uploaded_alert final : peer_alert
{
   std::string message () const override;

   int const block_index;
   piece_index_t const piece_index;
};
[report issue]

alerts_dropped_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted to indicate to the client that some alerts were dropped. Dropped meaning that the alert failed to be delivered to the client. The most common cause of such failure is that the internal alert queue grew too big (controlled by alert_queue_size).

struct alerts_dropped_alert final : alert
{
   static_assert (num_alert_types <= abi_alert_count, "need to increase bitset. This is an ABI break");
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   std::bitset<abi_alert_count> dropped_alerts;
};
[report issue]
dropped_alerts
a bitmask indicating which alerts were dropped. Each bit represents the alert type ID, where bit 0 represents whether any alert of type 0 has been dropped, and so on.
[report issue]

socks5_alert

Declared in "libtorrent/alert_types.hpp"

this alert is posted with SOCKS5 related errors, when a SOCKS5 proxy is configured. It's enabled with the alert_category::error alert category.

struct socks5_alert final : alert
{
   std::string message () const override;

   static constexpr alert_category_t static_category  = alert_category::error;
   error_code error;
   operation_t op;
   aux::noexcept_movable<tcp::endpoint> ip;
};
[report issue]
error
the error
[report issue]
op
the operation that failed
[report issue]
ip
the endpoint configured as the proxy
[report issue]

alert_cast()

Declared in "libtorrent/alert.hpp"

template <typename T> T const* alert_cast (alert const* a);
template <typename T> T* alert_cast (alert* a);

When you get an alert, you can use alert_cast<> to attempt to cast the pointer to a specific alert type, in order to query it for more information.

Note

alert_cast<> can only cast to an exact alert type, not a base class

[report issue]

operation_name()

Declared in "libtorrent/operations.hpp"

char const* operation_name (operation_t op);

maps an operation id (from peer_error_alert and peer_disconnected_alert) to its name. See operation_t for the constants

[report issue]

enum operation_t

Declared in "libtorrent/operations.hpp"

name value description
unknown 0 the error was unexpected and it is unknown which operation caused it
bittorrent 1 this is used when the bittorrent logic determines to disconnect
iocontrol 2 a call to iocontrol failed
getpeername 3 a call to getpeername() failed (querying the remote IP of a connection)
getname 4 a call to getname failed (querying the local IP of a connection)
alloc_recvbuf 5 an attempt to allocate a receive buffer failed
alloc_sndbuf 6 an attempt to allocate a send buffer failed
file_write 7 writing to a file failed
file_read 8 reading from a file failed
file 9 a non-read and non-write file operation failed
sock_write 10 a socket write operation failed
sock_read 11 a socket read operation failed
sock_open 12 a call to open(), to create a socket socket failed
sock_bind 13 a call to bind() on a socket failed
available 14 an attempt to query the number of bytes available to read from a socket failed
encryption 15 a call related to bittorrent protocol encryption failed
connect 16 an attempt to connect a socket failed
ssl_handshake 17 establishing an SSL connection failed
get_interface 18 a connection failed to satisfy the bind interface setting
sock_listen 19 a call to listen() on a socket
sock_bind_to_device 20 a call to the ioctl to bind a socket to a specific network device or adapter
sock_accept 21 a call to accept() on a socket
parse_address 22 convert a string into a valid network address
enum_if 23 enumeration network devices or adapters
file_stat 24 invoking stat() on a file
file_copy 25 copying a file
file_fallocate 26 allocating storage for a file
file_hard_link 27 creating a hard link
file_remove 28 removing a file
file_rename 29 renaming a file
file_open 30 opening a file
mkdir 31 creating a directory
check_resume 32 check fast resume data against files on disk
exception 33 an unknown exception
alloc_cache_piece 34 allocate space for a piece in the cache
partfile_move 35 move a part-file
partfile_read 36 read from a part file
partfile_write 37 write to a part-file
hostname_lookup 38 a hostname lookup
symlink 39 create or read a symlink
handshake 40 handshake with a peer or server
sock_option 41 set socket option
enum_route 42 enumeration of network routes
file_seek 43 moving read/write position in a file, operation_t::hostname_lookup
timer 44 an async wait operation on a timer
[report issue]

alert_category_t

Declared in "libtorrent/alert.hpp"

error

Enables alerts that report an error. This includes:

  • tracker errors
  • tracker warnings
  • file errors
  • resume data failures
  • web seed errors
  • .torrent files errors
  • listen socket errors
  • port mapping errors
peer
Enables alerts when peers send invalid requests, get banned or snubbed.
port_mapping
Enables alerts for port mapping events. For NAT-PMP and UPnP.
storage
Enables alerts for events related to the storage. File errors and synchronization events for moving the storage, renaming files etc.
tracker
Enables all tracker events. Includes announcing to trackers, receiving responses, warnings and errors.
connect
Low level alerts for when peers are connected and disconnected.
status
Enables alerts for when a torrent or the session changes state.
ip_block
Alerts when a peer is blocked by the ip blocker or port blocker.
performance_warning
Alerts when some limit is reached that might limit the download or upload rate.
dht
Alerts on events in the DHT node. For incoming searches or bootstrapping being done etc.
stats
If you enable these alerts, you will receive a stats_alert approximately once every second, for every active torrent. These alerts contain all statistics counters for the interval since the lasts stats alert.
session_log
Enables debug logging alerts. These are available unless libtorrent was built with logging disabled (TORRENT_DISABLE_LOGGING). The alerts being posted are log_alert and are session wide.
torrent_log
Enables debug logging alerts for torrents. These are available unless libtorrent was built with logging disabled (TORRENT_DISABLE_LOGGING). The alerts being posted are torrent_log_alert and are torrent wide debug events.
peer_log
Enables debug logging alerts for peers. These are available unless libtorrent was built with logging disabled (TORRENT_DISABLE_LOGGING). The alerts being posted are peer_log_alert and low-level peer events and messages.
incoming_request
enables the incoming_request_alert.
dht_log
enables dht_log_alert, debug logging for the DHT
dht_operation
enable events from pure dht operations not related to torrents
port_mapping_log
enables port mapping log events. This log is useful for debugging the UPnP or NAT-PMP implementation
picker_log
enables verbose logging from the piece picker.
file_progress
alerts when files complete downloading
piece_progress
alerts when pieces complete downloading or fail hash check
upload
alerts when we upload blocks to other peers
block_progress
alerts on individual blocks being requested, downloading, finished, rejected, time-out and cancelled. This is likely to post alerts at a high rate.
all

The full bitmask, representing all available categories.

since the enum is signed, make sure this isn't interpreted as -1. For instance, boost.python does that and fails when assigning it to an unsigned parameter.

[report issue]

int

Declared in "libtorrent/alert_types.hpp"

user_alert_id
user defined alerts should use IDs greater than this
num_alert_types
this constant represents "max_alert_index" + 1