From 108fe574a0043e1bccfb13e76cce6e89197905cd Mon Sep 17 00:00:00 2001
From: ridiculousfish <rf@fishshell.com>
Date: Sat, 2 Apr 2022 11:31:55 -0700
Subject: [PATCH] Finally track down that cursed read test failure

The read.fish check has a test where it limits the amount of data passed to
`read` to 8192 bytes, and verifies that fish reads exactly that amount.
This check occasionally fails on the OBS builds; it's very hard to repro a
failure locally, but I finally did it.

The amount of data written is limited via `yes` and `dd`:

    yes $line | dd bs=1024 count=(math "$fish_read_limit / 1024")

The bug is that `dd` outputs a fixed number of "blocks" where a block
corresponds to a single read. As `yes` and `dd` are running concurrently,
it may happen that `dd` performs a short read; this then counts as a single
block. So `dd` may output less than the desired amount of data.

This can be verified by removing the 2>/dev/null redirection; on a
successful run dd reports `8+0 records out`, on a failed run it reports
`7+1 records out` because one of the records was short.

Fix this by using `fullblock` so that dd will no longer count a short read
as a single block. `head` would probably be a simpler tool to use but we'll
do this for now.

Happily it's not a fish bug. No need to relnote it.
---
 tests/checks/read.fish | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/checks/read.fish b/tests/checks/read.fish
index b0bfa37ad..bf45320e3 100644
--- a/tests/checks/read.fish
+++ b/tests/checks/read.fish
@@ -192,7 +192,7 @@ set line abcdefghijklmnopqrstuvwxyz
 # Ensure the `read` command terminates if asked to read too much data. The var
 # should be empty. We throw away any data we read if it exceeds the limit on
 # what we consider reasonable.
-yes $line | dd bs=1024 count=(math "1 + $fish_read_limit / 1024") 2>/dev/null | read --null x
+yes $line | dd iflag=fullblock bs=1024 count=(math "1 + $fish_read_limit / 1024") 2>/dev/null | read --null x
 if test $status -ne 122
     echo reading too much data did not terminate with failure status
 end
@@ -239,13 +239,13 @@ end
 
 # Same as previous test but limit the amount of data fed to `read` rather than
 # using the `--nchars` flag.
-yes $line | dd bs=1024 count=(math "$fish_read_limit / 1024") 2>/dev/null | read --null x
+yes $line | dd iflag=fullblock bs=1024 count=(math "$fish_read_limit / 1024") 2>/dev/null | read --null x
 if test $status -ne 0
     echo the read of the max amount of data failed unexpectedly
 end
 if test (string length "$x") -ne $fish_read_limit
     # See how much data 'yes' produced.
-    set yeslen (yes $line | dd bs=1024 count=(math "$fish_read_limit / 1024") 2>/dev/null | wc -c | tr -d " \t\n\r")
+    set yeslen (yes $line | dd iflag=fullblock bs=1024 count=(math "$fish_read_limit / 1024") 2>/dev/null | wc -c | tr -d " \t\n\r")
     echo reading the max amount of data with --nchars failed the length test. read: (string length "$x"), limit: $fish_read_limit, yes produced: $yeslen
 end