From 6f8775499f6b0f70472c9449bf4f4da483e4cadb Mon Sep 17 00:00:00 2001
From: Kurtis Rader <krader@skepticism.us>
Date: Fri, 6 Jan 2017 23:51:49 -0800
Subject: [PATCH] don't warn about EPIPE errors

Emitting warnings about EPIPE errors when writing to stdout or stderr is
more annoying than helpful. So suppress that specific warning message.

Fixes #2516
---
 src/common.cpp   |  2 ++
 src/postfork.cpp | 18 +++++++++++++-----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/common.cpp b/src/common.cpp
index bdc476ec2..6e9604227 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -511,6 +511,8 @@ long read_blocked(int fd, void *buf, size_t count) {
     return res;
 }
 
+/// Loop a write request while failure is non-critical. Return -1 and set errno in case of critical
+/// error.
 ssize_t write_loop(int fd, const char *buff, size_t count) {
     size_t out_cum = 0;
     while (out_cum < count) {
diff --git a/src/postfork.cpp b/src/postfork.cpp
index 41fe0e30b..06bb81d02 100644
--- a/src/postfork.cpp
+++ b/src/postfork.cpp
@@ -499,15 +499,23 @@ void safe_report_exec_error(int err, const char *actual_cmd, const char *const *
 /// Perform output from builtins. May be called from a forked child, so don't do anything that may
 /// allocate memory, etc.
 bool do_builtin_io(const char *out, size_t outlen, const char *err, size_t errlen) {
+    int saved_errno = 0;
     bool success = true;
     if (out && outlen && write_loop(STDOUT_FILENO, out, outlen) < 0) {
-        int e = errno;
-        debug_safe(0, "Error while writing to stdout");
-        safe_perror("write_loop");
+        saved_errno = errno;
+        if (errno != EPIPE) {
+            debug_safe(0, "Error while writing to stdout");
+            errno = saved_errno;
+            safe_perror("write_loop");
+        }
         success = false;
-        errno = e;
     }
 
-    if (err && errlen && write_loop(STDERR_FILENO, err, errlen) < 0) success = false;
+    if (err && errlen && write_loop(STDERR_FILENO, err, errlen) < 0) {
+        saved_errno = errno;
+        success = false;
+    }
+
+    errno = saved_errno;
     return success;
 }