ArcanistHgClientChannel.php
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	<?php

	/**
	* Channel to a Mercurial "cmdserver" client. For a detailed description of the
	* "cmdserver" protocol, see @{class:ArcanistHgServerChannel}. This channel
	* implements the other half of the protocol: it decodes messages from the
	* client and encodes messages from the server.
	*
	* Because the proxy server speaks the exact same protocol that Mercurial
	* does and fully decodes both sides of the protocol, we need this half of the
	* decode/encode to talk to clients. Without it, we wouldn't be able to
	* determine when a client request had completed and was ready for transmission
	* to the Mercurial server.
	*
	* (Technically, we could get away without re-encoding messages from the
	* server, but the serialization is not complicated and having a general
	* implementation of encoded/decode for both the client and server dialects
	* seemed useful.)
	*
	* @task protocol Protocol Implementation
	*/
	final class ArcanistHgClientChannel extends PhutilProtocolChannel {

	const MODE_COMMAND = 'command';
	const MODE_LENGTH = 'length';
	const MODE_ARGUMENTS = 'arguments';

	private $command;
	private $byteLengthOfNextChunk;

	private $buf = '';
	private $mode = self::MODE_COMMAND;


	/* -( Protocol Implementation )-------------------------------------------- */


	/**
	* Encode a message for transmission to the client. The message should be
	* a pair with the channel name and the a block of data, like this:
	*
	* array('o', '<some data...>');
	*
	* We encode it like this:
	*
	* o
	* 1234 # Length, as a 4-byte unsigned long.
	* <data: 1234 bytes>
	*
	* For a detailed description of the cmdserver protocol, see
	* @{class:ArcanistHgServerChannel}.
	*
	* @param pair<string,string> $argv The <channel, data> pair to encode.
	* @return string Encoded string for transmission to the client.
	*
	* @task protocol
	*/
	protected function encodeMessage($argv) {
	if (!is_array($argv) \|\| count($argv) !== 2) {
	throw new Exception(pht('Message should be %s.', '<channel, data>'));
	}

	$channel = head($argv);
	$data = last($argv);

	$len = strlen($data);
	$len = pack('N', $len);

	return "{$channel}{$len}{$data}";
	}


	/**
	* Decode a message received from the client. The message looks like this:
	*
	* runcommand\n
	* 8 # Length, as a 4-byte unsigned long.
	* log\0
	* -l\0
	* 5
	*
	* We decode it into a list in PHP, which looks like this:
	*
	* array(
	* 'runcommand',
	* 'log',
	* '-l',
	* '5',
	* );
	*
	* @param string $data Bytes from the server.
	* @return list<list<string>> Zero or more complete commands.
	*
	* @task protocol
	*/
	protected function decodeStream($data) {
	$this->buf .= $data;

	// The first part is terminated by "\n", so we don't always know how many
	// bytes we need to look for. This makes parsing a bit of a pain.

	$messages = array();

	do {
	$continue_parsing = false;

	switch ($this->mode) {
	case self::MODE_COMMAND:
	// We're looking for "\n", which indicates the end of the command
	// name, like "runcommand". Next, we'll expect a length.

	$pos = strpos($this->buf, "\n");
	if ($pos === false) {
	break;
	}

	$this->command = substr($this->buf, 0, $pos);
	$this->buf = substr($this->buf, $pos + 1);
	$this->mode = self::MODE_LENGTH;

	$continue_parsing = true;
	break;
	case self::MODE_LENGTH:
	// We're looking for a byte length, as a 4-byte big-endian unsigned
	// integer. Next, we'll expect that many bytes of data.

	if (strlen($this->buf) < 4) {
	break;
	}

	$len = substr($this->buf, 0, 4);
	$len = unpack('N', $len);
	$len = head($len);

	$this->buf = substr($this->buf, 4);

	$this->mode = self::MODE_ARGUMENTS;
	$this->byteLengthOfNextChunk = $len;

	$continue_parsing = true;
	break;
	case self::MODE_ARGUMENTS:
	// We're looking for the data itself, which is a block of bytes
	// of the given length. These are arguments delimited by "\0". Next
	// we'll expect another command.

	if (strlen($this->buf) < $this->byteLengthOfNextChunk) {
	break;
	}

	$data = substr($this->buf, 0, $this->byteLengthOfNextChunk);
	$this->buf = substr($this->buf, $this->byteLengthOfNextChunk);

	$message = array_merge(array($this->command), explode("\0", $data));

	$this->mode = self::MODE_COMMAND;
	$this->command = null;
	$this->byteLengthOfNextChunk = null;

	$messages[] = $message;

	$continue_parsing = true;
	break;
	}
	} while ($continue_parsing);

	return $messages;
	}

	}

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