Improve error checking on output.

4 files changed, 27 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index cf5dd1aa..7da12705 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2022-07-29         Arnold D. Robbins     <arnold@skeeve.com>
+
+	* builtin.c (efwrite): Check ferror() also, fixes some weird
+	cases. Reported by Nikita Zlobin <cook60020tmp@mail.ru>.
+	* io.c (gawk_fwrite): Remove static from definition.
+	* awk.h (gawk_fwrite): Add declaration.
+
 2022-07-22         Arnold D. Robbins     <arnold@skeeve.com>
 
 	* NEWS: Updated.
diff --git a/awk.h b/awk.h
index dacf6f32..84fd714c 100644
--- a/awk.h
+++ b/awk.h
@@ -1665,6 +1665,7 @@ extern bool is_non_fatal_redirect(const char *str, size_t len);
 extern void ignore_sigpipe(void);
 extern void set_sigpipe_to_default(void);
 extern bool non_fatal_flush_std_file(FILE *fp);
+extern size_t gawk_fwrite(const void *buf, size_t size, size_t count, FILE *fp, void *opaque);
 
 /* main.c */
 extern int arg_assign(char *arg, bool initing);
diff --git a/builtin.c b/builtin.c
index 30795406..21125453 100644
--- a/builtin.c
+++ b/builtin.c
@@ -167,11 +167,27 @@ efwrite(const void *ptr,
 {
 	errno = 0;
 	if (rp != NULL) {
-		if (rp->output.gawk_fwrite(ptr, size, count, fp, rp->output.opaque) != count) {
+		/*
+		 * 7/2022: We need to also check ferror(); there can be times when write(2) fails but
+		 * fwrite succeeds!  To do that, we make sure that rp->output.gawk_fwrite is not
+		 * taken over by an extension before checking ferror().  From the bug report
+		 * (https://lists.gnu.org/archive/html/bug-gawk/2022-07/msg00000.html):
+		 *
+		 * Minimal working example:
+		 * yes | stdbuf -oL gawk '{print}' | head -n1 # Prints but hangs
+		 * yes | stdbuf -o0 gawk '{print}' | head -n1 # OK
+		 * yes | gawk '{print; fflush()}'  | head -n1 # OK
+		 *
+		 * After this change, all three work.
+		 */
+		bool err_on_write = (rp->output.gawk_fwrite(ptr, size, count, fp, rp->output.opaque) != count);
+		bool err_on_fp = (rp->output.gawk_fwrite == gawk_fwrite && ferror(fp));
+
+		if (err_on_write || err_on_fp) {
 			wrerror(fp, from, rp);
 			return;
 		}
-	} else if (fwrite(ptr, size, count, fp) != count) {
+	} else if (fwrite(ptr, size, count, fp) != count || ferror(fp)) {
 		wrerror(fp, from, rp);
 		return;
 	}
diff --git a/io.c b/io.c
index 91fa2225..d7372b6f 100644
--- a/io.c
+++ b/io.c
@@ -4413,7 +4413,7 @@ read_with_timeout(int fd, void *buf, size_t size)
 
 /* gawk_fwrite --- like fwrite */
 
-static size_t
+size_t
 gawk_fwrite(const void *buf, size_t size, size_t count, FILE *fp, void *opaque)
 {
 	(void) opaque;