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Add a couple of clarifying comments to the Mercurial protocol parser

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Summary: See D18857. Ref T13036. See PHI275. Explain what's going on here a little better since it isn't entirely obvious and debugging these stream parsers is a gigantic pain.

Test Plan: Read text.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13036

Differential Revision: https://secure.phabricator.com/D18859
This commit is contained in:
epriestley 2018-01-04 14:11:54 -08:00
parent 94db95a165
commit 5543592034
1 changed files with 19 additions and 0 deletions
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19
src/applications/diffusion/ssh/DiffusionMercurialWireClientSSHProtocolChannel.php
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@ -180,6 +180,15 @@ final class DiffusionMercurialWireClientSSHProtocolChannel
$this->state = 'arguments';
}
} else if ($this->state == 'data-length') {
// We're reading the length of a chunk of raw data. It looks like
// this:
//
// <length-in-bytes>\n
//
// The length is human-readable text (for example, "4096"), and
// may be 0.
$line = $this->readProtocolLine();
if ($line === null) {
break;
@ -192,6 +201,9 @@ final class DiffusionMercurialWireClientSSHProtocolChannel
$this->state = 'data-bytes';
}
} else if ($this->state == 'data-bytes') {
// We're reading some known, nonzero number of raw bytes of data.
// If we don't have any more bytes on the buffer yet, just bail:
// otherwise, we'll emit a pointless and possibly harmful 0-byte data
// frame. See T13036 for discussion.
@ -203,6 +215,13 @@ final class DiffusionMercurialWireClientSSHProtocolChannel
$this->buffer = substr($this->buffer, strlen($bytes));
$this->expectBytes -= strlen($bytes);
// NOTE: We emit a data frame as soon as we read some data. This can
// cause us to repackage frames: for example, if we receive one large
// frame slowly, we may emit it as several smaller frames. In theory
// this is good; in practice, Mercurial never seems to select a frame
// size larger than 4096 bytes naturally and this may be more
// complexity and trouble than it is worth. See T13036.
$messages[] = $this->newDataMessage($bytes);
if (!$this->expectBytes) {