From 48b5dd5e7b319637968db35184bd46886e7355f0 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Fri, 5 May 2017 16:36:04 -0400
Subject: [PATCH] tests: Fix race condition in tmp webserver

I was seeing this when trying to run flatpak's tests in ostree's CI:
https://github.com/ostreedev/ostree/pull/824

The race here is that the python process can still be writing to the output
while sed is reading it, and hence we'll find a difference on the next line.
Fix this by making a tmp copy of the file, which then both sed and cmp will
read consistently.

I'm not *entirely* sure this will fix the problem as I couldn't easily reproduce
the race locally, but I believe it at least fixes *a* race.
---
 tests/test-webserver.sh | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/tests/test-webserver.sh b/tests/test-webserver.sh
index 3291b061..2964ce96 100755
--- a/tests/test-webserver.sh
+++ b/tests/test-webserver.sh
@@ -10,9 +10,15 @@ env PYTHONUNBUFFERED=1 setsid python -m SimpleHTTPServer 0 >${test_tmpdir}/httpd
 child_pid=$!
 
 for x in $(seq 50); do
-    sed -e 's,Serving HTTP on 0.0.0.0 port \([0-9]*\) \.\.\.,\1,' < ${test_tmpdir}/httpd-output > ${test_tmpdir}/httpd-port
-    if ! cmp ${test_tmpdir}/httpd-output ${test_tmpdir}/httpd-port 1>/dev/null; then
-        break
+    # Snapshot the output
+    cp ${test_tmpdir}/httpd-output{,.tmp}
+    # If it's non-empty, see whether it matches our regexp
+    if test -s ${test_tmpdir}/httpd-output.tmp; then
+        sed -e 's,Serving HTTP on 0.0.0.0 port \([0-9]*\) \.\.\.,\1,' < ${test_tmpdir}/httpd-output.tmp > ${test_tmpdir}/httpd-port
+        if ! cmp ${test_tmpdir}/httpd-output.tmp ${test_tmpdir}/httpd-port 1>/dev/null; then
+            # If so, we've successfully extracted the port
+            break
+        fi
     fi
     sleep 0.1
 done