streaming: make streaming-write-entry to be more reusable

The static function in entry.c takes a cache entry and streams its blob
contents to a file in the working tree.  Refactor the logic to a new API
function stream_blob_to_fd() that takes an object name and an open file
descriptor, so that it can be reused by other callers.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

entry.c

@@ -120,58 +120,15 @@ static int streaming_write_entry(struct cache_entry *ce, char *path,
 				 const struct checkout *state, int to_tempfile,
 				 int *fstat_done, struct stat *statbuf)
 {
-	struct git_istream *st;
-	enum object_type type;
-	unsigned long sz;
 	int result = -1;
-	ssize_t kept = 0;
+	int fd;
-	int fd = -1;
-
-	st = open_istream(ce->sha1, &type, &sz, filter);
-	if (!st)
-		return -1;
-	if (type != OBJ_BLOB)
-		goto close_and_exit;
 
 	fd = open_output_fd(path, ce, to_tempfile);
-	if (fd < 0)
+	if (0 <= fd) {
-		goto close_and_exit;
+		result = stream_blob_to_fd(fd, ce->sha1, filter, 1);
-
+		*fstat_done = fstat_output(fd, state, statbuf);
-	for (;;) {
-		char buf[1024 * 16];
-		ssize_t wrote, holeto;
-		ssize_t readlen = read_istream(st, buf, sizeof(buf));
-
-		if (!readlen)
-			break;
-		if (sizeof(buf) == readlen) {
-			for (holeto = 0; holeto < readlen; holeto++)
-				if (buf[holeto])
-					break;
-			if (readlen == holeto) {
-				kept += holeto;
-				continue;
-			}
-		}
-
-		if (kept && lseek(fd, kept, SEEK_CUR) == (off_t) -1)
-			goto close_and_exit;
-		else
-			kept = 0;
-		wrote = write_in_full(fd, buf, readlen);
-
-		if (wrote != readlen)
-			goto close_and_exit;
-	}
-	if (kept && (lseek(fd, kept - 1, SEEK_CUR) == (off_t) -1 ||
-		     write(fd, "", 1) != 1))
-		goto close_and_exit;
-	*fstat_done = fstat_output(fd, state, statbuf);
-
-close_and_exit:
-	close_istream(st);
-	if (0 <= fd)
 		result = close(fd);
+	}
 	if (result && 0 <= fd)
 		unlink(path);
 	return result;

streaming.c

@@ -489,3 +489,58 @@ static open_method_decl(incore)
 
 	return st->u.incore.buf ? 0 : -1;
 }
+
+
+/****************************************************************
+ * Users of streaming interface
+ ****************************************************************/
+
+int stream_blob_to_fd(int fd, unsigned const char *sha1, struct stream_filter *filter,
+		      int can_seek)
+{
+	struct git_istream *st;
+	enum object_type type;
+	unsigned long sz;
+	ssize_t kept = 0;
+	int result = -1;
+
+	st = open_istream(sha1, &type, &sz, filter);
+	if (!st)
+		return result;
+	if (type != OBJ_BLOB)
+		goto close_and_exit;
+	for (;;) {
+		char buf[1024 * 16];
+		ssize_t wrote, holeto;
+		ssize_t readlen = read_istream(st, buf, sizeof(buf));
+
+		if (!readlen)
+			break;
+		if (can_seek && sizeof(buf) == readlen) {
+			for (holeto = 0; holeto < readlen; holeto++)
+				if (buf[holeto])
+					break;
+			if (readlen == holeto) {
+				kept += holeto;
+				continue;
+			}
+		}
+
+		if (kept && lseek(fd, kept, SEEK_CUR) == (off_t) -1)
+			goto close_and_exit;
+		else
+			kept = 0;
+		wrote = write_in_full(fd, buf, readlen);
+
+		if (wrote != readlen)
+			goto close_and_exit;
+	}
+	if (kept && (lseek(fd, kept - 1, SEEK_CUR) == (off_t) -1 ||
+		     write(fd, "", 1) != 1))
+		goto close_and_exit;
+	result = 0;
+
+ close_and_exit:
+	close_istream(st);
+	return result;
+}

streaming.h

@@ -12,4 +12,6 @@ extern struct git_istream *open_istream(const unsigned char *, enum object_type
 extern int close_istream(struct git_istream *);
 extern ssize_t read_istream(struct git_istream *, char *, size_t);
 
+extern int stream_blob_to_fd(int fd, const unsigned char *, struct stream_filter *, int can_seek);
+
 #endif /* STREAMING_H */