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- Technical Notes
- ===============
- This document describes additional technical information of aria2. The
- expected audience is developers.
- Control File (\*.aria2) Format
- ------------------------------
- The control file uses a binary format to store progress information of
- a download. Here is the diagram for each field:
- .. code-block:: text
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +---+-------+-------+-------------------------------------------+
- |VER| EXT |INFO |INFO HASH ... |
- |(2)| (4) |HASH | (INFO HASH LENGTH) |
- | | |LENGTH | |
- | | | (4) | |
- +---+---+---+-------+---+---------------+-------+---------------+
- |PIECE |TOTAL LENGTH |UPLOAD LENGTH |BIT- |BITFIELD ... |
- |LENGTH | (8) | (8) |FIELD | (BITFIELD |
- | (4) | | |LENGTH | LENGTH) |
- | | | | (4) | |
- +-------+-------+-------+-------+-------+-------+---------------+
- |NUM |INDEX |LENGTH |PIECE |PIECE BITFIELD ... |
- |IN- | (4) | (4) |BIT- | (PIECE BITFIELD LENGTH) |
- |FLIGHT | | |FIELD | |
- |PIECE | | |LENGTH | |
- | (4) | | | (4) | |
- +-------+-------+-------+-------+-------------------------------+
- ^ ^
- | |
- +-------------------------------------------------------+
- Repeated in (NUM IN-FLIGHT) PIECE times
- ``VER`` (VERSION): 2 bytes
- Should be either version 0(0x0000) or version 1(0x0001). In
- version 1, all multi-byte integers are saved in network byte
- order(big endian). In version 0, all multi-byte integers are saved
- in host byte order. aria2 1.4.1 can read both versions and only
- writes a control file in version 1 format. version 0 support will
- be disappear in the future version.
- ``EXT`` (EXTENSION): 4 bytes
- If LSB is 1(i.e. ``EXT[3]&1 == 1``), aria2 checks whether the saved
- InfoHash and current downloading one are the same. If they are not
- the same, an exception is thrown. This is called "infoHashCheck"
- extension.
- ``INFO HASH LENGTH``: 4 bytes
- The length of InfoHash that is located after this field. If
- "infoHashCheck" extension is enabled, if this value is 0, then an
- exception is thrown. For http/ftp downloads, this value should be
- 0.
- ``INFO HASH``: ``(INFO HASH LENGTH)`` bytes
- BitTorrent InfoHash.
- ``PIECE LENGTH``: 4 bytes
- The length of the piece.
- ``TOTAL LENGTH``: 8 bytes
- The total length of the download.
- ``UPLOAD LENGTH``: 8 bytes
- The uploaded length in this download.
- ``BITFIELD LENGTH``: 4 bytes
- The length of bitfield.
- ``BITFIELD``: ``(BITFIELD LENGTH)`` bytes
- This is the bitfield which represents current download progress.
- ``NUM IN-FLIGHT PIECE``: 4 bytes
- The number of in-flight pieces. These piece is not marked
- 'downloaded' in the bitfield, but it has at least one downloaded
- chunk.
- The following 4 fields are repeated in ``(NUM IN-FLIGHT PIECE)``
- times.
- ``INDEX``: 4 bytes
- The index of the piece.
- ``LENGTH``: 4 bytes
- The length of the piece.
- ``PIECE BITFIELD LENGTH``: 4 bytes
- The length of bitfield of this piece.
- ``PIECE BITFIELD``: ``(PIECE BITFIELD LENGTH)`` bytes
- The bitfield of this piece. The each bit represents 16KiB chunk.
- DHT routing table file format
- -----------------------------
- aria2 saves IPv4 DHT routing table in
- ``${XDG_CACHE_HOME}/aria2/dht.dat`` and IPv6 DHT routing table in
- ``${XDG_CACHE_HOME}/aria2/dht6.dat`` by default unless
- ``${HOME}/.aria2/dht.dat`` and ``${HOME}/.aria2/dht.dat`` are present.
- ``dht.dat`` and ``dht6.dat`` files use same binary encoding and have
- following fields. All multi byte integers are in network byte
- order. ``RSV`` (RESERVED) fields are reserved for future use. For now
- they should be all zeros:
- .. code-block:: text
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- +---+-+---+-----+---------------+---------------+---------------+
- |MGC|F|VER| RSV | MTIME | RSV |LOCAL NODE ID :
- |(2)|M|(2)| (3) | (8) | (8) | (20) :
- | |T| | | | | :
- +---+-+---+-----+-------+-------+-------+-------+---------------+
- :LOCAL NODE ID | RSV | NUM | RSV |
- : (continued) | (4) | NODE | (4) |
- : | | (4) | |
- +-+-------------+-------+-------+-+-----+-------+---------------+
- |P| RSV |COMPACT PEER INFO| RSV | <-+
- |L| (7) | (PLEN) | (24 - PLEN) | |
- |E| | | | |
- |N| | | | |
- +-+-------------+-----------------+-----+-------+---------------+ |
- | NODE ID | RSV | |
- | (20) | (4) | <-----------------+
- +---------------------------------------+-------+ Repeated in
- (NUM NODE) times.
- ``MGC`` (MAGIC): 2 bytes
- It must be ``0xa1 0xa2``.
- ``FMT`` (FORMAT ID): 1 byte
- The format ID should be ``0x02``.
- ``VER`` (VERSION): 2 bytes
- The version number should be ``0x00 0x03``.
- ``MTIME``: 8 bytes
- This is the time when aria2 saved the file. The value is the time
- since the Epoch(1970/1/1 00:00:00) in 64 bits integer.
- ``LOCALNODE ID``: 20 bytes
- Node ID of the client.
- ``NUM NODE``: 4 bytes
- The number of nodes the routing table has. ``NUM NODE`` node
- information follows.
- The data of ``NUM NODE`` node will follow. The node information are
- stored in the following fields. They are repeated in ``NUM NODE``
- times.
- ``PLEN`` (COMPACT PEER INFO LENGTH): 1 byte
- The length of compact peer info. For IPv4 DHT, it must be 6. For
- IPv6 DHT, it must be 18.
- ``COMPACT PEER INFO``: ``(PLEN)`` bytes
- The address and port of peer in compact peer format.
- ``NODE ID``: 20 bytes
- The node ID of this node.
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