reftable/stack: stop using read_in_full()

There is a single callsite of `read_in_full()` in the reftable library.
Open-code the function to reduce our dependency on the Git library.

Note that we only partially port over the logic from `read_in_full()`
and its underlying `xread()` helper. Most importantly, the latter also
knows to handle `EWOULDBLOCK` via `handle_nonblock()`. This logic is
irrelevant for us though because the reftable library never sets the
`O_NONBLOCK` option in the first place.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/stack.c

@@ -115,13 +115,16 @@ int reftable_new_stack(struct reftable_stack **dest, const char *dir,
 
 static int fd_read_lines(int fd, char ***namesp)
 {
-	off_t size = lseek(fd, 0, SEEK_END);
 	char *buf = NULL;
 	int err = 0;
+	off_t size;
+
+	size = lseek(fd, 0, SEEK_END);
 	if (size < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
 	}
+
 	err = lseek(fd, 0, SEEK_SET);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
@@ -134,9 +137,16 @@ static int fd_read_lines(int fd, char ***namesp)
 		goto done;
 	}
 
-	if (read_in_full(fd, buf, size) != size) {
-		err = REFTABLE_IO_ERROR;
-		goto done;
+	for (off_t total_read = 0; total_read < size; ) {
+		ssize_t bytes_read = read(fd, buf + total_read, size - total_read);
+		if (bytes_read < 0 && (errno == EAGAIN || errno == EINTR))
+			continue;
+		if (bytes_read < 0 || !bytes_read) {
+			err = REFTABLE_IO_ERROR;
+			goto done;
+		}
+
+		total_read += bytes_read;
 	}
 	buf[size] = 0;