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PhabricatorSSHPassthruCommand.php
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Thu, Sep 26, 04:29

PhabricatorSSHPassthruCommand.php
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<?php
/**
* Proxy an IO channel to an underlying command, with optional callbacks. This
* is a mostly a more general version of @{class:PhutilExecPassthru}. This
* class is used to proxy Git, SVN and Mercurial traffic to the commands which
* can actually serve it.
*
* Largely, this just reads an IO channel (like stdin from SSH) and writes
* the results into a command channel (like a command's stdin). Then it reads
* the command channel (like the command's stdout) and writes it into the IO
* channel (like stdout from SSH):
*
* IO Channel Command Channel
* stdin -> stdin
* stdout <- stdout
* stderr <- stderr
*
* You can provide **read and write callbacks** which are invoked as data
* is passed through this class. They allow you to inspect and modify traffic.
*
* IO Channel Passthru Command Channel
* stdout -> willWrite -> stdin
* stdin <- willRead <- stdout
* stderr <- (identity) <- stderr
*
* Primarily, this means:
*
* - the **IO Channel** can be a @{class:PhutilProtocolChannel} if the
* **write callback** can convert protocol messages into strings; and
* - the **write callback** can inspect and reject requests over the channel,
* e.g. to enforce policies.
*
* In practice, this is used when serving repositories to check each command
* issued over SSH and determine if it is a read command or a write command.
* Writes can then be checked for appropriate permissions.
*/
final class PhabricatorSSHPassthruCommand extends Phobject {
private $commandChannel;
private $ioChannel;
private $errorChannel;
private $execFuture;
private $willWriteCallback;
private $willReadCallback;
private $pauseIOReads;
public function setCommandChannelFromExecFuture(ExecFuture $exec_future) {
$exec_channel = new PhutilExecChannel($exec_future);
$exec_channel->setStderrHandler(array($this, 'writeErrorIOCallback'));
$this->execFuture = $exec_future;
$this->commandChannel = $exec_channel;
return $this;
}
public function setIOChannel(PhutilChannel $io_channel) {
$this->ioChannel = $io_channel;
return $this;
}
public function setErrorChannel(PhutilChannel $error_channel) {
$this->errorChannel = $error_channel;
return $this;
}
public function setWillReadCallback($will_read_callback) {
$this->willReadCallback = $will_read_callback;
return $this;
}
public function setWillWriteCallback($will_write_callback) {
$this->willWriteCallback = $will_write_callback;
return $this;
}
public function writeErrorIOCallback(PhutilChannel $channel, $data) {
$this->errorChannel->write($data);
}
public function setPauseIOReads($pause) {
$this->pauseIOReads = $pause;
return $this;
}
public function execute() {
$command_channel = $this->commandChannel;
$io_channel = $this->ioChannel;
$error_channel = $this->errorChannel;
if (!$command_channel) {
throw new Exception(
pht(
'Set a command channel before calling %s!',
__FUNCTION__.'()'));
}
if (!$io_channel) {
throw new Exception(
pht(
'Set an IO channel before calling %s!',
__FUNCTION__.'()'));
}
if (!$error_channel) {
throw new Exception(
pht(
'Set an error channel before calling %s!',
__FUNCTION__.'()'));
}
$channels = array($command_channel, $io_channel, $error_channel);
// We want to limit the amount of data we'll hold in memory for this
// process. See T4241 for a discussion of this issue in general.
$buffer_size = (1024 * 1024); // 1MB
$io_channel->setReadBufferSize($buffer_size);
$command_channel->setReadBufferSize($buffer_size);
// TODO: This just makes us throw away stderr after the first 1MB, but we
// don't currently have the support infrastructure to buffer it correctly.
// It's difficult to imagine this causing problems in practice, though.
$this->execFuture->getStderrSizeLimit($buffer_size);
while (true) {
PhutilChannel::waitForAny($channels);
$io_channel->update();
$command_channel->update();
$error_channel->update();
// If any channel is blocked on the other end, wait for it to flush before
// we continue reading. For example, if a user is running `git clone` on
// a 1GB repository, the underlying `git-upload-pack` may
// be able to produce data much more quickly than we can send it over
// the network. If we don't throttle the reads, we may only send a few
// MB over the I/O channel in the time it takes to read the entire 1GB off
// the command channel. That leaves us with 1GB of data in memory.
while ($command_channel->isOpen() &&
$io_channel->isOpenForWriting() &&
($command_channel->getWriteBufferSize() >= $buffer_size ||
$io_channel->getWriteBufferSize() >= $buffer_size ||
$error_channel->getWriteBufferSize() >= $buffer_size)) {
PhutilChannel::waitForActivity(array(), $channels);
$io_channel->update();
$command_channel->update();
$error_channel->update();
}
// If the subprocess has exited and we've read everything from it,
// we're all done.
$done = !$command_channel->isOpenForReading() &&
$command_channel->isReadBufferEmpty();
if (!$this->pauseIOReads) {
$in_message = $io_channel->read();
if ($in_message !== null) {
$this->writeIORead($in_message);
}
}
$out_message = $command_channel->read();
if (strlen($out_message)) {
$out_message = $this->willReadData($out_message);
if ($out_message !== null) {
$io_channel->write($out_message);
}
}
// If we have nothing left on stdin, close stdin on the subprocess.
if (!$io_channel->isOpenForReading()) {
$command_channel->closeWriteChannel();
}
if ($done) {
break;
}
// If the client has disconnected, kill the subprocess and bail.
if (!$io_channel->isOpenForWriting()) {
$this->execFuture
->setStdoutSizeLimit(0)
->setStderrSizeLimit(0)
->setReadBufferSize(null)
->resolveKill();
break;
}
}
list($err) = $this->execFuture
->setStdoutSizeLimit(0)
->setStderrSizeLimit(0)
->setReadBufferSize(null)
->resolve();
return $err;
}
public function writeIORead($in_message) {
$in_message = $this->willWriteData($in_message);
if (strlen($in_message)) {
$this->commandChannel->write($in_message);
}
}
public function willWriteData($message) {
if ($this->willWriteCallback) {
return call_user_func($this->willWriteCallback, $this, $message);
} else {
if (strlen($message)) {
return $message;
} else {
return null;
}
}
}
public function willReadData($message) {
if ($this->willReadCallback) {
return call_user_func($this->willReadCallback, $this, $message);
} else {
if (strlen($message)) {
return $message;
} else {
return null;
}
}
}
}

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