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:

控制文件使用二进制格式来存储下载的进度信息。下面是每个字段的图：

 0                   1                   2                   30 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.

应为版本0（0x0000）或版本1（0x0001）。在版本1中，所有多字节整数以网络字节顺序（大字节序）保存。在版本0中，所有多字节整数以主机字节顺序保存。aria2 1.4.1可以读取这两个版本，并且只写入版本1格式的控制文件。版本0支持将在以后的版本中消失。

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.

如果LSB为1（即），aria2将检查保存的！InfoHash和当前下载的信息是否相同。如果它们不相同，则抛出异常。这被称为“infoHashCheck”扩展。EXT[3]&1 == 1

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.

位于此字段后面的InfoHash的长度。如果启用了“infoHashCheck”扩展，如果此值为0，则抛出异常。对于http / ftp下载，此值应为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.