From b1df1d557eb8e3c40778a01af9cd972c80a19d95 Mon Sep 17 00:00:00 2001
From: =?utf8?q?P=C3=A1draig=20Brady?= <P@draigBrady.com>
Date: Sat, 15 Jul 2023 21:43:07 +0100
Subject: [PATCH] comm: promptly diagnose write errors

* src/comm.c (writeline): Simplify by removing the unneeded STREAM
parameter.  Call write_error() upon ferror().
(compare_files): Adjust to simplified writeline().
* tests/misc/write-errors.sh: Enable comm test.
* NEWS: Mention the improvement.
---
 NEWS                       |  4 ++--
 src/comm.c                 | 21 ++++++++++++---------
 tests/misc/write-errors.sh |  2 +-
 3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/NEWS b/NEWS
index 8d15f27382..24c018374e 100644
--- a/NEWS
+++ b/NEWS
@@ -62,8 +62,8 @@ GNU coreutils NEWS                                    -*- outline -*-
   irrespective of which kernel version coreutils is built against,
   reinstating that behaviour from coreutils-9.0.
 
-  cut, od, and uniq will now exit immediately upon receiving a write error,
-  which is significant when reading large / unbounded inputs.
+  comm, cut, od, and uniq will now exit immediately upon receiving a
+  write error, which is significant when reading large / unbounded inputs.
 
   split now uses more tuned access patterns for its potentially large input.
   This was seen to improve throughput by 5% when reading from SSD.
diff --git a/src/comm.c b/src/comm.c
index 12fa9c9eaa..5cb2410e58 100644
--- a/src/comm.c
+++ b/src/comm.c
@@ -163,13 +163,13 @@ Examples:\n\
   exit (status);
 }
 
-/* Output the line in linebuffer LINE to stream STREAM
+/* Output the line in linebuffer LINE to stdout
    provided the switches say it should be output.
    CLASS is 1 for a line found only in file 1,
    2 for a line only in file 2, 3 for a line in both. */
 
 static void
-writeline (struct linebuffer const *line, FILE *stream, int class)
+writeline (struct linebuffer const *line, int class)
 {
   switch (class)
     {
@@ -182,20 +182,23 @@ writeline (struct linebuffer const *line, FILE *stream, int class)
       if (!only_file_2)
         return;
       if (only_file_1)
-        fwrite (col_sep, 1, col_sep_len, stream);
+        fwrite (col_sep, 1, col_sep_len, stdout);
       break;
 
     case 3:
       if (!both)
         return;
       if (only_file_1)
-        fwrite (col_sep, 1, col_sep_len, stream);
+        fwrite (col_sep, 1, col_sep_len, stdout);
       if (only_file_2)
-        fwrite (col_sep, 1, col_sep_len, stream);
+        fwrite (col_sep, 1, col_sep_len, stdout);
       break;
     }
 
-  fwrite (line->buffer, sizeof (char), line->length, stream);
+  fwrite (line->buffer, sizeof (char), line->length, stdout);
+
+  if (ferror (stdout))
+    write_error ();
 }
 
 /* Check that successive input lines PREV and CURRENT from input file
@@ -329,7 +332,7 @@ compare_files (char **infiles)
         {
           /* Line is seen in both files.  */
           total[2]++;
-          writeline (thisline[1], stdout, 3);
+          writeline (thisline[1], 3);
         }
       else
         {
@@ -338,13 +341,13 @@ compare_files (char **infiles)
             {
               /* Line is seen in file 1 only.  */
               total[0]++;
-              writeline (thisline[0], stdout, 1);
+              writeline (thisline[0], 1);
             }
           else
             {
               /* Line is seen in file 2 only.  */
               total[1]++;
-              writeline (thisline[1], stdout, 2);
+              writeline (thisline[1], 2);
             }
         }
 
diff --git a/tests/misc/write-errors.sh b/tests/misc/write-errors.sh
index e217c5512b..a9e112c3a8 100755
--- a/tests/misc/write-errors.sh
+++ b/tests/misc/write-errors.sh
@@ -27,7 +27,7 @@ fi
 # First word in command line is checked against built programs
 echo "\
 cat /dev/zero
-# TODO: comm -z /dev/zero /dev/zero
+comm -z /dev/zero /dev/zero
 cut -z -c1- /dev/zero
 cut -z -f1- /dev/zero
 dd if=/dev/zero
-- 
2.47.2