[PATCH] Operations on refs

This patch adds code to read a hash out of a specified file under
{GIT_DIR}/refs/, and to write such files atomically and optionally with an
compare and lock.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 173 insertions, 0 deletions

diff --git a/refs.c b/refs.c
new file mode 100644
index 000000000..9973d1fc2
--- /dev/null
+++ b/refs.c
@@ -0,0 +1,173 @@
+#include "refs.h"
+#include "cache.h"
+
+#include <errno.h>
+
+static char *ref_file_name(const char *ref)
+{
+	char *base = get_refs_directory();
+	int baselen = strlen(base);
+	int reflen = strlen(ref);
+	char *ret = xmalloc(baselen + 2 + reflen);
+	sprintf(ret, "%s/%s", base, ref);
+	return ret;
+}
+
+static char *ref_lock_file_name(const char *ref)
+{
+	char *base = get_refs_directory();
+	int baselen = strlen(base);
+	int reflen = strlen(ref);
+	char *ret = xmalloc(baselen + 7 + reflen);
+	sprintf(ret, "%s/%s.lock", base, ref);
+	return ret;
+}
+
+static int read_ref_file(const char *filename, unsigned char *sha1) {
+	int fd = open(filename, O_RDONLY);
+	char hex[41];
+	if (fd < 0) {
+		return error("Couldn't open %s\n", filename);
+	}
+	if ((read(fd, hex, 41) < 41) ||
+	    (hex[40] != '\n') ||
+	    get_sha1_hex(hex, sha1)) {
+		error("Couldn't read a hash from %s\n", filename);
+		close(fd);
+		return -1;
+	}
+	close(fd);
+	return 0;
+}
+
+int get_ref_sha1(const char *ref, unsigned char *sha1)
+{
+	char *filename;
+	int retval;
+	if (check_ref_format(ref))
+		return -1;
+	filename = ref_file_name(ref);
+	retval = read_ref_file(filename, sha1);
+	free(filename);
+	return retval;
+}
+
+static int lock_ref_file(const char *filename, const char *lock_filename,
+			 const unsigned char *old_sha1)
+{
+	int fd = open(lock_filename, O_WRONLY | O_CREAT | O_EXCL, 0666);
+	unsigned char current_sha1[20];
+	int retval;
+	if (fd < 0) {
+		return error("Couldn't open lock file for %s: %s",
+			     filename, strerror(errno));
+	}
+	retval = read_ref_file(filename, current_sha1);
+	if (old_sha1) {
+		if (retval) {
+			close(fd);
+			unlink(lock_filename);
+			return error("Could not read the current value of %s",
+				     filename);
+		}
+		if (memcmp(current_sha1, old_sha1, 20)) {
+			close(fd);
+			unlink(lock_filename);
+			error("The current value of %s is %s",
+			      filename, sha1_to_hex(current_sha1));
+			return error("Expected %s",
+				     sha1_to_hex(old_sha1));
+		}
+	} else {
+		if (!retval) {
+			close(fd);
+			unlink(lock_filename);
+			return error("Unexpectedly found a value of %s for %s",
+				     sha1_to_hex(current_sha1), filename);
+		}
+	}
+	return fd;
+}
+
+int lock_ref_sha1(const char *ref, const unsigned char *old_sha1)
+{
+	char *filename;
+	char *lock_filename;
+	int retval;
+	if (check_ref_format(ref))
+		return -1;
+	filename = ref_file_name(ref);
+	lock_filename = ref_lock_file_name(ref);
+	retval = lock_ref_file(filename, lock_filename, old_sha1);
+	free(filename);
+	free(lock_filename);
+	return retval;
+}
+
+static int write_ref_file(const char *filename,
+			  const char *lock_filename, int fd,
+			  const unsigned char *sha1)
+{
+	char *hex = sha1_to_hex(sha1);
+	char term = '\n';
+	if (write(fd, hex, 40) < 40 ||
+	    write(fd, &term, 1) < 1) {
+		error("Couldn't write %s\n", filename);
+		close(fd);
+		return -1;
+	}
+	close(fd);
+	rename(lock_filename, filename);
+	return 0;
+}
+
+int write_ref_sha1(const char *ref, int fd, const unsigned char *sha1)
+{
+	char *filename;
+	char *lock_filename;
+	int retval;
+	if (fd < 0)
+		return -1;
+	if (check_ref_format(ref))
+		return -1;
+	filename = ref_file_name(ref);
+	lock_filename = ref_lock_file_name(ref);
+	retval = write_ref_file(filename, lock_filename, fd, sha1);
+	free(filename);
+	free(lock_filename);
+	return retval;
+}
+
+int check_ref_format(const char *ref)
+{
+	char *middle;
+	if (ref[0] == '.' || ref[0] == '/')
+		return -1;
+	middle = strchr(ref, '/');
+	if (!middle || !middle[1])
+		return -1;
+	if (strchr(middle + 1, '/'))
+		return -1;
+	return 0;
+}
+
+int write_ref_sha1_unlocked(const char *ref, const unsigned char *sha1)
+{
+	char *filename;
+	char *lock_filename;
+	int fd;
+	int retval;
+	if (check_ref_format(ref))
+		return -1;
+	filename = ref_file_name(ref);
+	lock_filename = ref_lock_file_name(ref);
+	fd = open(lock_filename, O_WRONLY | O_CREAT | O_EXCL, 0666);
+	if (fd < 0) {
+		error("Writing %s", lock_filename);
+		perror("Open");
+	}
+	retval = write_ref_file(filename, lock_filename, fd, sha1);
+	free(filename);
+	free(lock_filename);
+	return retval;
+}