From 5448fe2165df0d37c1042779a16346050dd09f8d Mon Sep 17 00:00:00 2001
From: epriestley <git@epriestley.com>
Date: Fri, 1 May 2020 06:59:05 -0700
Subject: [PATCH] When recent PHP raises a "broken pipe" error in ExecFuture,
 treat it as a blocked stdin

Summary:
Ref T13528. If we start a subprocess that immediately exits and then write to it, we can get a broken pipe error.

Recent versions of PHP appear to raise this as an actual warning, and recent changes upgrade the warning to a runtime exception.

I can't find any way to tell if the RuntimeException is a broken pipe or something else, except by examining the text of the error string.

At least for now, treat this like a "blocked pipe" condition. Since the subprocess has exited and the bytes didn't write, this should generally be reasonable.

Test Plan:
  - Viewed a file in Paste with an extension that Pygments does not have a lexer for.
  - This causes Pygments to exit immediately with an "unrecognized lexer" error. This closes the pipe, and the next write will fail with a broken pipe error.
  - Before patch: fatal on broken pipe.
  - After patch: clean resolution of the future and error condition.

Maniphest Tasks: T13528

Differential Revision: https://secure.phabricator.com/D21199
---
 src/future/exec/ExecFuture.php | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/future/exec/ExecFuture.php b/src/future/exec/ExecFuture.php
index 48911930..0264d4d3 100644
--- a/src/future/exec/ExecFuture.php
+++ b/src/future/exec/ExecFuture.php
@@ -713,7 +713,17 @@ final class ExecFuture extends PhutilExecutableFuture {
     while (isset($this->stdin) && $this->stdin->getByteLength()) {
       $write_segment = $this->stdin->getAnyPrefix();
 
-      $bytes = fwrite($stdin, $write_segment);
+      try {
+        $bytes = fwrite($stdin, $write_segment);
+      } catch (RuntimeException $ex) {
+        // If the subprocess has exited, we may get a broken pipe error here
+        // in recent versions of PHP. There does not seem to be any way to
+        // get the actual error code other than reading the exception string.
+
+        // For now, treat this as if writes are blocked.
+        break;
+      }
+
       if ($bytes === false) {
         throw new Exception(pht('Unable to write to stdin!'));
       } else if ($bytes) {