Command Server

A server that allows communication with Mercurial's API over a pipe.

Contents

1. Protocol

All communication with the server is done on stdin/stdout. The byte order used by the server is big-endian.

Data sent from the server is channel based, meaning a (channel [character], length [unsigned int]) pair is sent before the actual data. For example:

o
1234
<data: 1234 bytes>

that is 1234 bytes sent on channel 'o', with the data following.

When starting the server, it will send a new-line separated list of capabilities (on the 'o' channel), in this format:

capabilities:\n
capability1\n
capability2\n
...

At the most basic level, the server will support the 'runcommand' capability.

Strings are encoded in the local encoding.

There are currently 5 channels:

o - Output channel. Most of the communication happens on this channel. When running commands, output Mercurial writes to stdout is written to this channel.
e - Error channel. When running commands, this correlates to stderr.
i - Input channel. The length field here can either be 0, telling the client to send all input, or some positive number telling the client to send at most <length> bytes.
l - Line based input channel. The client should send a single line of input (trimmed if length is not 0). This channel is used when Mercurial interacts with the user or when iterating over stdin.

Input should be sent on stdin in the following format:

length
data

length = 0 sent by the client is interpreted as EOF by the server.

The server is running on an endless loop (until stdin is closed) waiting for commands. A command request looks like this:

commandname\n
<command specific request>

runcommand - Run the command specified by a list of \0-terminated strings. An unsigned int indicating the length of the arguments should be sent before the list. Example:

runcommand\n
8
log\0
-l\0
5

Which corresponds to running 'hg log -l 5'.