Merge branch 'jc/ignore-epipe-in-filter'

Filter scripts were run with SIGPIPE disabled on the Git side,
expecting that they may not read what Git feeds them to filter.
We however treated a filter that does not read its input fully
before exiting as an error.

This changes semantics, but arguably in a good way.  If a filter
can produce its output without consuming its input using whatever
magic, we now let it do so, instead of diagnosing it as a
programming error.

* jc/ignore-epipe-in-filter:
  filter_buffer_or_fd(): ignore EPIPE
  copy.c: make copy_fd() report its status silently

cache.h

@@ -1541,9 +1541,13 @@ extern const char *git_mailmap_blob;
 extern void maybe_flush_or_die(FILE *, const char *);
 __attribute__((format (printf, 2, 3)))
 extern void fprintf_or_die(FILE *, const char *fmt, ...);
+
+#define COPY_READ_ERROR (-2)
+#define COPY_WRITE_ERROR (-3)
 extern int copy_fd(int ifd, int ofd);
 extern int copy_file(const char *dst, const char *src, int mode);
 extern int copy_file_with_time(const char *dst, const char *src, int mode);
+
 extern void write_or_die(int fd, const void *buf, size_t count);
 extern int write_or_whine(int fd, const void *buf, size_t count, const char *msg);
 extern int write_or_whine_pipe(int fd, const void *buf, size_t count, const char *msg);

convert.c

@@ -356,9 +356,14 @@ static int filter_buffer_or_fd(int in, int out, void *data)
 	sigchain_push(SIGPIPE, SIG_IGN);
 
 	if (params->src) {
-		write_err = (write_in_full(child_process.in, params->src, params->size) < 0);
+		write_err = (write_in_full(child_process.in,
+					   params->src, params->size) < 0);
+		if (errno == EPIPE)
+			write_err = 0;
 	} else {
 		write_err = copy_fd(params->fd, child_process.in);
+		if (write_err == COPY_WRITE_ERROR && errno == EPIPE)
+			write_err = 0;
 	}
 
 	if (close(child_process.in))

copy.c

@@ -7,13 +7,10 @@ int copy_fd(int ifd, int ofd)
 		ssize_t len = xread(ifd, buffer, sizeof(buffer));
 		if (!len)
 			break;
-		if (len < 0) {
-			return error("copy-fd: read returned %s",
-				     strerror(errno));
-		}
+		if (len < 0)
+			return COPY_READ_ERROR;
 		if (write_in_full(ofd, buffer, len) < 0)
-			return error("copy-fd: write returned %s",
-				     strerror(errno));
+			return COPY_WRITE_ERROR;
 	}
 	return 0;
 }
@@ -43,6 +40,14 @@ int copy_file(const char *dst, const char *src, int mode)
 		return fdo;
 	}
 	status = copy_fd(fdi, fdo);
+	switch (status) {
+	case COPY_READ_ERROR:
+		error("copy-fd: read returned %s", strerror(errno));
+		break;
+	case COPY_WRITE_ERROR:
+		error("copy-fd: write returned %s", strerror(errno));
+		break;
+	}
 	close(fdi);
 	if (close(fdo) != 0)
 		return error("%s: close error: %s", dst, strerror(errno));

lockfile.c

@@ -289,7 +289,7 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
 		int save_errno = errno;
 
 		if (flags & LOCK_DIE_ON_ERROR)
-			exit(128);
+			die("failed to prepare '%s' for appending", path);
 		close(orig_fd);
 		rollback_lock_file(lk);
 		errno = save_errno;

t/t0021-conversion.sh

@@ -204,6 +204,16 @@ test_expect_success 'filtering large input to small output should use little mem
 	GIT_MMAP_LIMIT=1m GIT_ALLOC_LIMIT=1m git add 30MB
 '
 
+test_expect_success 'filter that does not read is fine' '
+	test-genrandom foo $((128 * 1024 + 1)) >big &&
+	echo "big filter=epipe" >.gitattributes &&
+	git config filter.epipe.clean "echo xyzzy" &&
+	git add big &&
+	git cat-file blob :big >actual &&
+	echo xyzzy >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success EXPENSIVE 'filter large file' '
 	git config filter.largefile.smudge cat &&
 	git config filter.largefile.clean cat &&