# Alerts
Author: Arvid Norberg, arvid@rasterbar.com

Author: | Arvid Norberg, arvid@rasterbar.com
Version: | 1.0.0

Table of contents

- alert
- torrent_alert
- peer_alert
- tracker_alert
- torrent_added_alert
- torrent_removed_alert
- read_piece_alert
- file_completed_alert
- file_renamed_alert
- file_rename_failed_alert
- performance_alert
- state_changed_alert
- tracker_error_alert
- tracker_warning_alert
- scrape_reply_alert
- scrape_failed_alert
- tracker_reply_alert
- dht_reply_alert
- tracker_announce_alert
- hash_failed_alert
- peer_ban_alert
- peer_unsnubbed_alert
- peer_snubbed_alert
- peer_error_alert
- peer_connect_alert
- peer_disconnected_alert
- invalid_request_alert
- torrent_finished_alert
- piece_finished_alert
- request_dropped_alert
- block_timeout_alert
- block_finished_alert
- block_downloading_alert
- unwanted_block_alert
- storage_moved_alert
- storage_moved_failed_alert
- torrent_deleted_alert
- torrent_delete_failed_alert
- save_resume_data_alert
- save_resume_data_failed_alert
- torrent_paused_alert
- torrent_resumed_alert
- torrent_checked_alert
- url_seed_alert
- file_error_alert
- metadata_failed_alert
- metadata_received_alert
- udp_error_alert
- external_ip_alert
- listen_failed_alert
- listen_succeeded_alert
- portmap_error_alert
- portmap_alert
- portmap_log_alert
- fastresume_rejected_alert
- peer_blocked_alert
- dht_announce_alert
- dht_get_peers_alert
- stats_alert
- cache_flushed_alert
- anonymous_mode_alert
- lsd_peer_alert
- trackerid_alert
- dht_bootstrap_alert
- rss_alert
- torrent_error_alert
- torrent_need_cert_alert
- incoming_connection_alert
- add_torrent_alert
- state_update_alert
- torrent_update_alert
- rss_item_alert
- dht_error_alert
- dht_immutable_item_alert
- dht_mutable_item_alert
- dht_put_alert
- i2p_alert

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_alert() will return an empty list.

By default, only errors are reported. set_alert_mask() can be used to specify which kinds of events should be reported. The alert mask is comprised by bits from the category_t enum.

Every alert belongs to one or more category. There is a small cost involved in 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).

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.

# alert

Declared in "libtorrent/alert.hpp"

The `alert` class is the base class that specific messages are derived from.

    class alert
    {
       ptime timestamp () const;
       virtual int type () const = 0;
       virtual char const* what () const = 0;
       virtual std::string message () const = 0;
       virtual int category () const = 0;
       virtual bool discardable () const;
       virtual std::auto_ptr<alert> clone () const = 0;

       enum category_t
       {
          error_notification,
          peer_notification,
          port_mapping_notification,
          storage_notification,
          tracker_notification,
          debug_notification,
          status_notification,
          progress_notification,
          ip_block_notification,
          performance_warning,
          dht_notification,
          stats_notification,
          rss_notification,
          all_categories,
       };
    };

## timestamp()

    ptime timestamp () const;

a timestamp is automatically created in the constructor

## type()

    virtual int type () const = 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::auto_ptr<alert> a = ses.pop_alert();
    switch (a->type())
    {
            case read_piece_alert::alert_type:
            {
                    read_piece_alert* p = (read_piece_alert*)a.get();
                    if (p->ec) {
                            // read_piece failed
                            break;
                    }
                    // use p
                    break;
            }
            case file_renamed_alert::alert_type:
            {
                    // etc...
            }
    }

## what()

    virtual char const* what () const = 0;

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

## 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.

## category()

    virtual int category () const = 0;

returns a bitmask specifying which categories this alert belong to.

## discardable()

    virtual bool discardable () const;

determines whether or not an alert is allowed to be discarded when the alert queue is full. There are a few alerts which may not be discared, since they would break the user contract, such as save_resume_data_alert.

## clone()

    virtual std::auto_ptr<alert> clone () const = 0;

returns a pointer to a copy of the alert.

## enum category_t

Declared in "libtorrent/alert.hpp"

name | value | description
--- | --- | ---

error_notification

1

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_notification | 2 | Enables alerts when peers send invalid requests, get banned or snubbed.
port_mapping_notification | 4 | Enables alerts for port mapping events. For NAT-PMP and UPnP.
storage_notification | 8 | Enables alerts for events related to the storage. File errors and synchronization events for moving the storage, renaming files etc.
tracker_notification | 16 | Enables all tracker events. Includes announcing to trackers, receiving responses, warnings and errors.
debug_notification | 32 | Low level alerts for when peers are connected and disconnected.
status_notification | 64 | Enables alerts for when a torrent or the session changes state.
progress_notification | 128 | Alerts for when blocks are requested and completed. Also when pieces are completed.
ip_block_notification | 256 | Alerts when a peer is blocked by the ip blocker or port blocker.
performance_warning | 512 | Alerts when some limit is reached that might limit the download or upload rate.
dht_notification | 1024 | Alerts on events in the DHT node. For incoming searches or bootstrapping being done etc.
stats_notification | 2048 | 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.
rss_notification | 4096 | Alerts on RSS related events, like feeds being updated, feed error conditions and successful RSS feed updates. Enabling this categoty will make you receive rss_alert alerts.
all_categories | 2147483647 | 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.

# 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
    {
       torrent_handle handle;
    };

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

# 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
    {
       virtual int category () const;
       virtual std::string message () const;

       const static int alert_type = 2;
       const static int static_category = alert::peer_notification;
       tcp::endpoint ip;
       peer_id pid;
    };

ip
  The peer's IP address and port.

pid
  the peer ID, if known.

# 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
    {
       virtual int category () const;
       virtual std::string message () const;

       const static int alert_type = 3;
       const static int static_category = alert::tracker_notification;
       std::string url;
    };

url
  The tracker URL

# torrent_added_alert

Declared in "libtorrent/alert_types.hpp"

The `torrent_added_alert` is posted once every time a torrent is successfully added. It doesn't contain any members of its own, but inherits the torrent handle from its base class. It's posted when the `status_notification` bit is set in the alert_mask.

    struct torrent_added_alert: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
    };

# 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 baseclass 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 `status_notification` 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       sha1_hash info_hash;
    };

# 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, ec will indicat what went wrong.

    struct read_piece_alert: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       error_code ec;
       boost::shared_array<char> buffer;
       int piece;
       int size;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::progress_notification;
       int index;
    };

index
  refers to the index of the file that completed.

# 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: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       std::string name;
       int index;
    };

index
  refers to the index of the file that was renamed, `name` is the new name of the file.

# 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: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       int index;
       error_code error;
    };

index error
  refers to the index of the file that was supposed to be renamed, `error` is the error code returned from the filesystem.

# 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: torrent_alert
    {
       virtual std::string message () const;

       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,
          bittyrant_with_no_uplimit,
          too_few_outgoing_ports,
          too_few_file_descriptors,
          num_warnings,
       };

       const static int static_category = alert::performance_warning;
       performance_warning_t warning_code;
    };

## 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 (`session_settings::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 `session_settings::max_out_request_queue`. The queue length libtorrent is trying to achieve is determined by the download rate and the assumed round-trip-time (`session_settings::request_queue_time`). The assumed rount-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 mcuh 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 migth 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`.

bittyrant_with_no_uplimit | 7 |
too_few_outgoing_ports | 8 | This is generated if outgoing peer connections are failing because of address in use errors, indicating that `session_settings::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 | 9 |
num_warnings | 10 |

# state_changed_alert

Declared in "libtorrent/alert_types.hpp"

Generated whenever a torrent changes its state.

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

       const static int static_category = alert::status_notification;
       torrent_status::state_t state;
       torrent_status::state_t prev_state;
    };

state
  the new state of the torrent.

prev_state
  the previous state.

# 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.

The `times_in_row` member says how many times in a row this tracker has failed. `status_code` is the code returned from the HTTP server. 401 means the tracker needs authentication, 404 means not found etc. If the tracker timed out, the code will be set to 0.

    struct tracker_error_alert: tracker_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::tracker_notification | alert::error_notification;
       int times_in_row;
       int status_code;
       error_code error;
       std::string msg;
    };

# 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: tracker_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::tracker_notification | alert::error_notification;
       std::string msg;
    };

msg
  contains the warning message from the tracker.

# scrape_reply_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a scrape request succeeds.

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

       int incomplete;
       int complete;
    };

incomplete complete
  the data returned in the scrape response. These numbers may be -1 if the reponse was malformed.

# 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: tracker_alert
    {
       scrape_failed_alert (torrent_handle const& h
          , std::string const& u
          , std::string const& m);
       virtual std::string message () const;

       const static int static_category = alert::tracker_notification | alert::error_notification;
       std::string msg;
    };

msg
  contains a message describing the error.

# 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: tracker_alert
    {
       virtual std::string message () const;

       int num_peers;
    };

num_peers
  tells how many peers the tracker returned in this response. This is not expected to be more thant the `num_want` settings. These are not necessarily all new peers, some of them may already be connected.

# 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: tracker_alert
    {
       virtual std::string message () const;

       int num_peers;
    };

# 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: tracker_alert
    {
       virtual std::string message () const;

       int event;
    };

event

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

  0. None
  1. Completed
  2. Started
  3. Stopped

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       int piece_index;
    };

# 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: peer_alert
    {
       virtual std::string message () const;
    };

# peer_unsnubbed_alert

Declared in "libtorrent/alert_types.hpp"

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

    struct peer_unsnubbed_alert: peer_alert
    {
       virtual std::string message () const;
    };

# 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: peer_alert
    {
       virtual std::string message () const;
    };

# 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: peer_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::peer_notification;
       error_code error;
    };

error
  tells you what error caused this alert.

# peer_connect_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted every time an outgoing peer connect attempts succeeds.

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

       const static int static_category = alert::debug_notification;
       int socket_type;
    };

# 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: peer_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::debug_notification;
       error_code error;
    };

error
  tells you what error caused peer to disconnect.

# 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: peer_alert
    {
       virtual std::string message () const;

       peer_request request;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
    };

# 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.

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

       const static int static_category = alert::progress_notification;
       int piece_index;
    };

piece_index
  the index of the piece that finished

# 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: peer_alert
    {
       virtual std::string message () const;

       | alert::peer_notification;
       int block_index;
       int piece_index;
    };

# block_timeout_alert

Declared in "libtorrent/alert_types.hpp"

This alert is generated when a block request times out.

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

       | alert::peer_notification;
       int block_index;
       int piece_index;
    };

# block_finished_alert

Declared in "libtorrent/alert_types.hpp"

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

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

       const static int static_category = alert::progress_notification;
       int block_index;
       int piece_index;
    };

# 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: peer_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::progress_notification;
       char const* peer_speedmsg;
       int block_index;
       int piece_index;
    };

# 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: peer_alert
    {
       virtual std::string message () const;

       int block_index;
       int piece_index;
    };

# 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 `path` member is the new path of the storage.

    struct storage_moved_alert: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       std::string path;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       error_code error;
    };

# torrent_deleted_alert

Declared in "libtorrent/alert_types.hpp"

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

The `info_hash` is 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_hash` member is hence the main way of identifying which torrent just completed the delete.

This alert is posted in the `storage_notification` category, and that bit needs to be set in the alert_mask.

    struct torrent_deleted_alert: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       sha1_hash info_hash;
    };

# 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: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       | alert::error_notification;
       error_code error;
       sha1_hash info_hash;
    };

error
  tells you why it failed.

info_hash
  the info hash of the torrent whose files failed to be deleted

# 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: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::storage_notification;
       boost::shared_ptr<entry> resume_data;
    };

resume_data
  points to the resume data.

# 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: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       | alert::error_notification;
       error_code error;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
    };

# url_seed_alert

Declared in "libtorrent/alert_types.hpp"

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

    struct url_seed_alert: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::peer_notification | alert::error_notification;
       std::string url;
       std::string msg;
    };

url
  the HTTP seed that failed

msg
  the error message, potentially from the server

# 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: torrent_alert
    {
       virtual std::string message () const;

       | alert::storage_notification;
       std::string file;
       error_code error;
    };

file
  the path to the file that was accessed when the error occurred.

error
  the error code describing the error.

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::error_notification;
       error_code error;
    };

error
  the error that occurred

# 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()) {
            boost::intrusive_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_hash().to_string()) + ".torrent").c_str(), "wb+");
            if (f) {
                    fwrite(&buffer[0], 1, buffer.size(), f);
                    fclose(f);
            }
    }

    struct metadata_received_alert: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
    };

# udp_error_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when there is an error on the UDP socket. The UDP socket is used for all uTP, DHT and UDP tracker traffic. It's global to the session.

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

       const static int static_category = alert::error_notification;
       udp::endpoint endpoint;
       error_code error;
    };

endpoint
  the source address associated with the error (if any)

error
  the error code describing the error

# 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: alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       address external_address;
    };

external_address
  the IP address that is believed to be our external IP

# 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 `endpoint` member is the interface and port that failed, `error` is the error code describing the failure.

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: alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       enum socket_type_t
       {
          tcp,
          tcp_ssl,
          udp,
          i2p,
          socks5,
       };

       enum op_t
       {
          parse_addr,
          open,
          bind,
          listen,
          get_peer_name,
          accept,
       };

       const static int static_category = alert::status_notification | alert::error_notification;
       tcp::endpoint endpoint;
       error_code error;
       int operation;
       socket_type_t sock_type;
    };

## enum socket_type_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
tcp | 0 |
tcp_ssl | 1 |
udp | 2 |
i2p | 3 |
socks5 | 4 |

## enum op_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
parse_addr | 0 |
open | 1 |
bind | 2 |
listen | 3 |
get_peer_name | 4 |
accept | 5 |

endpoint
  the endpoint libtorrent attempted to listen on

error
  the error the system returned

operation
  the specific low level operation that failed. See op_t.

sock_type
  the type of listen socket this alert refers to.

# 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. `endpoint` is the endpoint that successfully was opened for listening.

    struct listen_succeeded_alert: alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       enum socket_type_t
       {
          tcp,
          tcp_ssl,
          udp,
       };

       const static int static_category = alert::status_notification;
       tcp::endpoint endpoint;
       socket_type_t sock_type;
    };

## enum socket_type_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
tcp | 0 |
tcp_ssl | 1 |
udp | 2 |

endpoint
  the endpoint libtorrent ended up listening on. The address refers to the local interface and the port is the listen port.

sock_type
  the type of listen socket this alert refers to.

# 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: alert
    {
       virtual std::string message () const;

       | alert::error_notification;
       int mapping;
       int map_type;
       error_code error;
    };

mapping
  refers to the mapping index of the port map that failed, i.e. the index returned from add_mapping().

map_type
  is 0 for NAT-PMP and 1 for UPnP.

error
  tells you what failed.

# 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: alert
    {
       virtual std::string message () const;

       const static int static_category = alert::port_mapping_notification;
       int mapping;
       int external_port;
       int map_type;
    };

mapping
  refers to the mapping index of the port map that failed, i.e. the index returned from add_mapping().

external_port
  the external port allocated for the mapping.

map_type
  0 for NAT-PMP and 1 for UPnP.

# 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.

    struct portmap_log_alert: alert
    {
       virtual std::string message () const;

       const static int static_category = alert::port_mapping_notification;
       int map_type;
       std::string msg;
    };

# fastresume_rejected_alert

Declared in "libtorrent/alert_types.hpp"

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

    struct fastresume_rejected_alert: torrent_alert
    {
       virtual std::string message () const;

       | alert::error_notification;
       error_code error;
    };

# 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: torrent_alert
    {
       virtual std::string message () const;

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

       const static int static_category = alert::ip_block_notification;
       address ip;
       int reason;
    };

## 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 |

ip
  the address that was blocked.

# 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 `dht_notification` category.

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

       const static int static_category = alert::dht_notification;
       address ip;
       int port;
       sha1_hash info_hash;
    };

# 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 `dht_notification` category.

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

       const static int static_category = alert::dht_notification;
       sha1_hash info_hash;
    };

# stats_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted approximately once every second, and it contains byte counters of most statistics that's tracked for torrents. Each active torrent posts these alerts regularly.

    struct stats_alert: torrent_alert
    {
       virtual std::string message () const;

       enum stats_channel
       {
          upload_payload,
          upload_protocol,
          download_payload,
          download_protocol,
          upload_ip_protocol,
          upload_dht_protocol,
          upload_tracker_protocol,
          download_ip_protocol,
          download_dht_protocol,
          download_tracker_protocol,
          num_channels,
       };

       const static int static_category = alert::stats_notification;
       int transferred[num_channels];
       int interval;
    };

## enum stats_channel

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
upload_payload | 0 |
upload_protocol | 1 |
download_payload | 2 |
download_protocol | 3 |
upload_ip_protocol | 4 |
upload_dht_protocol | 5 |
upload_tracker_protocol | 6 |
download_ip_protocol | 7 |
download_dht_protocol | 8 |
download_tracker_protocol | 9 |
num_channels | 10 |

transferred[num_channels]
  an array of samples. The enum describes what each sample is a measurement of. All of these are raw, and not smoothing is performed.

interval
  the number of milliseconds during which these stats were collected. This is typically just above 1000, but if CPU is limited, it may be higher than that.

# 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 `storage_notification` 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: torrent_alert
    {
       const static int static_category = alert::storage_notification;
    };

# anonymous_mode_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted when a bittorrent feature is blocked because of the anonymous mode. For instance, if the tracker proxy is not set up, no trackers will be used, because trackers can only be used through proxies when in anonymous mode.

    struct anonymous_mode_alert: torrent_alert
    {
       virtual std::string message () const;

       enum kind_t
       {
          tracker_not_anonymous,
       };

       const static int static_category = alert::error_notification;
       int kind;
       std::string str;
    };

## enum kind_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
tracker_not_anonymous | 0 | means that there's no proxy set up for tracker communication and the tracker will not be contacted. The tracker which this failed for is specified in the `str` member.

kind str
  specifies what error this is, see kind_t.

# 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: peer_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::peer_notification;
    };

# 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. The libtorrent will store the tracker ID for this tracker and repeat it in subsequent announces.

    struct trackerid_alert: tracker_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       std::string trackerid;
    };

trackerid
  The tracker ID returned by the tracker

# dht_bootstrap_alert

Declared in "libtorrent/alert_types.hpp"

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

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

       const static int static_category = alert::dht_notification;
    };

# rss_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted on RSS feed events such as start of RSS feed updates, successful completed updates and errors during updates.

This alert is only posted if the `rss_notifications` category is enabled in the alert_mask.

    struct rss_alert: alert
    {
       virtual std::string message () const;

       enum state_t
       {
          state_updating,
          state_updated,
          state_error,
       };

       const static int static_category = alert::rss_notification;
       feed_handle handle;
       std::string url;
       int state;
       error_code error;
    };

## enum state_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
state_updating | 0 | An update of this feed was just initiated, it will either succeed or fail soon.
state_updated | 1 | The feed just completed a successful update, there may be new items in it. If you're adding torrents manually, you may want to request the feed status of the feed and look through the `items` vector.
state_error | 2 | An error just occurred. See the `error` field for information on what went wrong.

handle
  the handle to the feed which generated this alert.

url
  a short cut to access the url of the feed, without having to call feed_handle::get_settings().

state
  one of the values from rss_alert::state_t.

error
  an error code used for when an error occurs on the feed.

# 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: torrent_alert
    {
       virtual std::string message () const;

       const static int static_category = alert::error_notification | alert::status_notification;
       error_code error;
    };

error
  specifies which error the torrent encountered.

# 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: torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       error_code error;
    };

# 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 straigh-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 ofer a Socks5 or i2p listen socket, or via a torrent specific listen socket for SSL torrents.

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

       const static int static_category = alert::peer_notification;
       int socket_type;
       tcp::endpoint ip;
    };

socket_type

  tells you what kind of socket the connection was accepted as:

  0. none (no socket instantiated)
  1. TCP
  2. Socks5
  3. HTTP
  4. uTP
  5. i2p
  6. SSL/TCP
  7. SSL/Socks5
  8. HTTPS (SSL/HTTP)
  9. SSL/uTP

ip
  is the IP address and port the connection came from.

# 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 in the base class' `handle` member. If adding the torrent failed, `error` contains the error code.

    struct add_torrent_alert : torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       add_torrent_params params;
       error_code error;
    };

params
  a copy of the parameters used when adding the torrent, it can be used to identify which invocation to `async_add_torrent()` caused this alert.

error
  set to the error, if one occurred while adding the torrent.

# 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 `status_notification`, but it's not subject to filtering, since it's only manually posted anyway.

    struct state_update_alert : alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       std::vector<torrent_status> status;
    };

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.

# torrent_update_alert

Declared in "libtorrent/alert_types.hpp"

When a torrent changes its info-hash, this alert is posted. This only happens in very specific cases. For instance, when a torrent is downloaded from a URL, the true info hash is not known immediately. First the .torrent file must be downloaded and parsed.

Once this download completes, the `torrent_update_alert` is posted to notify the client of the info-hash changing.

    struct torrent_update_alert : torrent_alert
    {
       virtual bool discardable () const;
       virtual std::string message () const;

       const static int static_category = alert::status_notification;
       sha1_hash old_ih;
       sha1_hash new_ih;
    };

old_ih new_ih
  `old_ih` and `new_ih` are the previous and new info-hash for the torrent, respectively.

# rss_item_alert

Declared in "libtorrent/alert_types.hpp"

This alert is posted every time a new RSS item (i.e. torrent) is received from an RSS feed.

It is only posted if the `rss_notifications` category is enabled in the alert_mask.

    struct rss_item_alert : alert
    {
       virtual std::string message () const;

       const static int static_category = alert::rss_notification;
       feed_handle handle;
       feed_item item;
    };

# 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: alert
    {
       virtual std::string message () const;

       enum op_t
       {
          unknown,
          hostname_lookup,
       };

       | alert::dht_notification;
       error_code error;
       op_t operation;
    };

## enum op_t

Declared in "libtorrent/alert_types.hpp"

name | value | description
--- | --- | ---
unknown | 0 |
hostname_lookup | 1 |

error
  the error code

operation
  the operation that failed

# 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: alert
    {
       virtual bool discardable () const;
       dht_immutable_item_alert (sha1_hash const& t, entry const& i);
       virtual std::string message () const;

       | alert::dht_notification;
       sha1_hash target;
       entry item;
    };

target
  the target hash of the immutable item. This must match the sha-1 hash of the bencoded form of `item`.

item
  the data for this item

# 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: alert
    {
       dht_mutable_item_alert (boost::array<char, 32> k
          , boost::array<char, 64> sig
          , boost::uint64_t sequence
          , std::string const& s
          , entry const& i);
       virtual bool discardable () const;
       virtual std::string message () const;

       | alert::dht_notification;
       boost::array<char, 32> key;
       boost::array<char, 64> signature;
       boost::uint64_t seq;
       std::string salt;
       entry item;
    };

key
  the public key that was looked up

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.

seq
  the sequence number of this item

salt
  the salf, if any, used to lookup and store this item. If no salt was used, this is an empty string

item
  the data for this item

# 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: alert
    {
       virtual std::string message () const;

       const static int static_category = alert::dht_notification;
       sha1_hash target;
       boost::array<char, 32> public_key;
       boost::array<char, 64> signature;
       std::string salt;
       boost::uint64_t seq;
    };

target
  the target hash the item was stored under if this was an immutable item.

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.

# i2p_alert

Declared in "libtorrent/alert_types.hpp"

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

    struct i2p_alert : alert
    {
       i2p_alert (error_code const& ec);
       virtual std::string message () const;

       const static int static_category = alert::error_notification;
       error_code error;
    };

error
  the error that occurred in the i2p SAM connection