Update get_sha1() to grok extended format.

Everybody envies rev-parse, who is the only one that can grok
the extended sha1 format.  Move the get_extended_sha1() out of
rev-parse, rename it to get_sha1() and make it available to
everybody else.

The one I posted earlier to the list had one bug where it did
not handle a name that ends with a digit correctly (it
incorrectly tried the "Nth parent" path).  This commit fixes it.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 228 insertions, 0 deletions

diff --git a/sha1_name.c b/sha1_name.c
new file mode 100644
index 0000000000..df3ba2d43f
--- /dev/null
+++ b/sha1_name.c
@@ -0,0 +1,228 @@
+#include "cache.h"
+#include "commit.h"
+
+static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
+{
+	static char dirname[PATH_MAX];
+	char hex[40];
+	DIR *dir;
+	int found;
+
+	snprintf(dirname, sizeof(dirname), "%s/%.2s", get_object_directory(), name);
+	dir = opendir(dirname);
+	sprintf(hex, "%.2s", name);
+	found = 0;
+	if (dir) {
+		struct dirent *de;
+		while ((de = readdir(dir)) != NULL) {
+			if (strlen(de->d_name) != 38)
+				continue;
+			if (memcmp(de->d_name, name + 2, len-2))
+				continue;
+			memcpy(hex + 2, de->d_name, 38);
+			if (++found > 1)
+				break;
+		}
+		closedir(dir);
+	}
+	if (found == 1)
+		return get_sha1_hex(hex, sha1) == 0;
+	return 0;
+}
+
+static int match_sha(unsigned len, const unsigned char *a, const unsigned char *b)
+{
+	do {
+		if (*a != *b)
+			return 0;
+		a++;
+		b++;
+		len -= 2;
+	} while (len > 1);
+	if (len)
+		if ((*a ^ *b) & 0xf0)
+			return 0;
+	return 1;
+}
+
+static int find_short_packed_object(int len, const unsigned char *match, unsigned char *sha1)
+{
+	struct packed_git *p;
+
+	prepare_packed_git();
+	for (p = packed_git; p; p = p->next) {
+		unsigned num = num_packed_objects(p);
+		unsigned first = 0, last = num;
+		while (first < last) {
+			unsigned mid = (first + last) / 2;
+			unsigned char now[20];
+			int cmp;
+
+			nth_packed_object_sha1(p, mid, now);
+			cmp = memcmp(match, now, 20);
+			if (!cmp) {
+				first = mid;
+				break;
+			}
+			if (cmp > 0) {
+				first = mid+1;
+				continue;
+			}
+			last = mid;
+		}
+		if (first < num) {
+			unsigned char now[20], next[20];
+			nth_packed_object_sha1(p, first, now);
+			if (match_sha(len, match, now)) {
+				if (nth_packed_object_sha1(p, first+1, next) || !match_sha(len, match, next)) {
+					memcpy(sha1, now, 20);
+					return 1;
+				}
+			}
+		}
+	}
+	return 0;
+}
+
+static int get_short_sha1(const char *name, unsigned char *sha1)
+{
+	int i;
+	char canonical[40];
+	unsigned char res[20];
+
+	memset(res, 0, 20);
+	memset(canonical, 'x', 40);
+	for (i = 0;;i++) {
+		unsigned char c = name[i];
+		unsigned char val;
+		if (!c || i > 40)
+			break;
+		if (c >= '0' && c <= '9')
+			val = c - '0';
+		else if (c >= 'a' && c <= 'f')
+			val = c - 'a' + 10;
+		else if (c >= 'A' && c <='F') {
+			val = c - 'A' + 10;
+			c -= 'A' - 'a';
+		}
+		else
+			return -1;
+		canonical[i] = c;
+		if (!(i & 1))
+			val <<= 4;
+		res[i >> 1] |= val;
+	}
+	if (i < 4)
+		return -1;
+	if (find_short_object_filename(i, canonical, sha1))
+		return 0;
+	if (find_short_packed_object(i, res, sha1))
+		return 0;
+	return -1;
+}
+
+static int get_sha1_file(const char *path, unsigned char *result)
+{
+	char buffer[60];
+	int fd = open(path, O_RDONLY);
+	int len;
+
+	if (fd < 0)
+		return -1;
+	len = read(fd, buffer, sizeof(buffer));
+	close(fd);
+	if (len < 40)
+		return -1;
+	return get_sha1_hex(buffer, result);
+}
+
+static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
+{
+	static const char *prefix[] = {
+		"",
+		"refs",
+		"refs/tags",
+		"refs/heads",
+		"refs/snap",
+		NULL
+	};
+	const char **p;
+
+	if (!get_sha1_hex(str, sha1))
+		return 0;
+
+	for (p = prefix; *p; p++) {
+		char *pathname = git_path("%s/%.*s", *p, len, str);
+		if (!get_sha1_file(pathname, sha1))
+			return 0;
+	}
+
+	return -1;
+}
+
+static int get_sha1_1(const char *name, int len, unsigned char *sha1);
+
+static int get_parent(const char *name, int len,
+		      unsigned char *result, int idx)
+{
+	unsigned char sha1[20];
+	int ret = get_sha1_1(name, len, sha1);
+	struct commit *commit;
+	struct commit_list *p;
+
+	if (ret)
+		return ret;
+	commit = lookup_commit_reference(sha1);
+	if (!commit)
+		return -1;
+	if (parse_commit(commit))
+		return -1;
+	if (!idx) {
+		memcpy(result, commit->object.sha1, 20);
+		return 0;
+	}
+	p = commit->parents;
+	while (p) {
+		if (!--idx) {
+			memcpy(result, p->item->object.sha1, 20);
+			return 0;
+		}
+		p = p->next;
+	}
+	return -1;
+}
+
+static int get_sha1_1(const char *name, int len, unsigned char *sha1)
+{
+	int parent, ret;
+
+	/* foo^[0-9] or foo^ (== foo^1); we do not do more than 9 parents. */
+	if (len > 2 && name[len-2] == '^' &&
+	    name[len-1] >= '0' && name[len-1] <= '9') {
+		parent = name[len-1] - '0';
+		len -= 2;
+	}
+	else if (len > 1 && name[len-1] == '^')
+		parent = 1;
+	else
+		parent = -1;
+
+	if (0 <= parent) {
+		ret = get_parent(name, len-1, sha1, parent);
+		if (!ret)
+			return 0;
+	}
+	ret = get_sha1_basic(name, len, sha1);
+	if (!ret)
+		return 0;
+	return get_short_sha1(name, sha1);
+}
+
+/*
+ * This is like "get_sha1_basic()", except it allows "sha1 expressions",
+ * notably "xyz^" for "parent of xyz"
+ */
+int get_sha1(const char *name, unsigned char *sha1)
+{
+	return get_sha1_1(name, strlen(name), sha1);
+}