phacility/phabricator · error · Exception

Client transmitted more than 1MB of data without transmittin

Error message

Client transmitted more than 1MB of data without transmitting a recognizable protocol frame.

What it means

While peeking at the first ra_svn frame, the workflow accumulates raw client bytes in peekBuffer; if it exceeds 1MiB without DiffusionSubversionWireProtocol yielding a parseable frame, the connection is cut. The guard bounds memory against garbage input and doubles as a compatibility check - a client speaking something the parser does not recognize trips it.

Source

Thrown at src/applications/diffusion/ssh/DiffusionSubversionServeSSHWorkflow.php:100

      if (!$exec_channel->isOpenForReading()) {
        throw new Exception(
          pht(
            '%s subprocess exited before emitting a protocol frame.',
            'svnserve'));
      }
    }

    $io_protocol = new DiffusionSubversionWireProtocol();
    while (true) {
      PhutilChannel::waitForAny(array($io_channel));
      $io_channel->update();

      $in_message = $io_channel->read();
      if ($in_message !== null) {
        $this->peekBuffer .= $in_message;
        if (strlen($this->peekBuffer) > (1024 * 1024)) {
          throw new Exception(
            pht(
              'Client transmitted more than 1MB of data without transmitting '.
              'a recognizable protocol frame.'));
        }

        $messages = $io_protocol->writeData($in_message);
        if ($messages) {
          $message = head($messages);
          $struct = $message['structure'];

          // This is the:
          //
          //   ( version ( cap1 ... ) url ... )
          //
          // The `url` allows us to identify the repository.

          $uri = $struct[2]['value'];
          $path = $this->getPathFromSubversionURI($uri);

View on GitHub (pinned to 5720a38cfe)

Solutions

Connect with a compatible svn client over svn+ssh:// with no extra tunnel rewriting
Reproduce with 'svn ls svn+ssh://user@host/REPO' from the same machine to isolate client configuration
Remove custom tunnel definitions in ~/.subversion/config that alter the command or the stream

Defensive patterns

Strategy: try-catch

Try / catch

try {
  $workflow->executeRepositoryOperations();
} catch (Exception $ex) {
  // The 1MB guard is terminal for the session: log, close the channel,
  // and report to the client - do not retry with the same stream.
  phlog($ex);
  $io_channel->closeForRead();
  $io_channel->closeForWrite();
}

Prevention

Treat this error as terminal for the session - retrying with the same client config reproduces it
When building custom SVN tooling, parse frames incrementally client-side instead of streaming raw blobs

When it happens

Trigger: A non-SVN or incompatible SVN client opens svn+ssh to the Phabricator SSH endpoint; a tunnel wrapper corrupts stdin so the byte stream never parses; deliberately oversized junk streamed at the endpoint.

Common situations: Users pointing tools other than svn at the Phabricator SSH user; SVN client versions far newer than the supported ra_svn dialect; ssh ProxyCommand setups that mangle the channel.

Related errors

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/c6bd6388c09ab33d. Report an issue: GitHub.