transmission-rpc

A Crystal client for the Transmission BitTorrent daemon's RPC API.

It speaks both Transmission RPC dialects:

• the JSON-RPC 2.0 ("modern") protocol introduced in Transmission 4.1.0, where method names and fields use snake_case, and
• the original ("classic") protocol — {"method":"torrent-get","arguments":{…},"tag":n} with hyphenated/camelCase keys and camelCase responses — understood by every version, and the only one Transmission 4.0.x speaks.

By default the client auto-detects which dialect the daemon speaks on its first call and caches the result; pass protocol: to force one. The public API is snake_case regardless of dialect.

It is built on json-rpc: a custom transport handles Transmission's X-Transmission-Session-Id CSRF dance (shared by both dialects), and the JSON-RPC client handles the modern envelope.

Installation

Add to your shard.yml:

dependencies:
  transmission-rpc:
    github: plambert/transmission-rpc.cr

Then run shards install.

Usage

require "transmission-rpc"

client = Transmission::RPC::Client.new(
  "http://nas.local:9091/transmission/rpc",
  username: "admin", password: "secret")

# List torrents (parsed into Transmission::RPC::Torrent structs).
client.torrent_get.each do |torrent|
  puts "#{torrent.name} — #{torrent.state} — #{torrent.percent_done.try { |done| (done * 100).round(1) }}%"
end

# Add a torrent by magnet link, then start it.
added = client.torrent_add(filename: "magnet:?xt=urn:btih:...")
client.torrent_start([added.id])

# Throttle and label a torrent.
client.torrent_set([added.id], upload_limited: true, upload_limit: 50, labels: ["linux"])

# Session-wide stats and settings.
stats = client.session_stats
puts "#{stats.torrent_count} torrents, #{stats.download_speed} B/s down"
client.session_set(speed_limit_down: 1000, speed_limit_down_enabled: true)

The default endpoint is http://localhost:9091/transmission/rpc, so Transmission::RPC::Client.new with no arguments talks to a local daemon.

Protocol selection

The dialect is auto-detected by default. To force one (skipping the probe):

client = Transmission::RPC::Client.new(url, protocol: Transmission::RPC::Protocol::Classic)
client = Transmission::RPC::Client.new(url, protocol: Transmission::RPC::Protocol::Modern)
# client.resolved_protocol reports which dialect is in use (nil until the first
# call under the default Protocol::Auto).

Selecting torrents

Methods that act on torrents accept an ids argument that may be:

• a single id (Int) or info hash (String) — wrapped into an array automatically,
• an array of ids/hashes,
• nil — meaning all torrents,
• or, for torrent_get, recently_active: true to fetch only recently active torrents.

Implemented methods

Category	Methods
Torrent actions	torrent_start (with now:), torrent_stop, torrent_verify, torrent_reannounce
Torrent data	torrent_get, torrent_get_raw, torrent_set, torrent_add, torrent_remove, torrent_set_location, torrent_rename_path
Queue	queue_move_top, queue_move_up, queue_move_down, queue_move_bottom
Session	session_get, session_set, session_stats, session_close
Server	blocklist_update, port_test, free_space
Bandwidth groups	group_get, group_set

torrent_get returns Array(Torrent) for the common fields; use torrent_get_raw (returning JSON::Any) for any field not on the struct. session_get and group_get return JSON::Any because their field sets are large and version-dependent.

Errors

• A JSON-RPC error from the daemon raises JSON::RPC::Error (#code, #message, #data).
• A transport failure (auth, connectivity, unexpected HTTP status) raises JSON::RPC::TransportError.

Development

shards install
crystal spec -v --error-trace
crystal tool format
ameba

The specs use a recording transport for the client and a throwaway local HTTP server to exercise the CSRF session-id negotiation — no live Transmission daemon required.

License

MIT