Do SHA1 hash _before_ compression.

And add a "convert-cache" program to convert from old-style
to new-style.

convert-cache.c

@@ -0,0 +1,138 @@
+#include "cache.h"
+
+struct entry {
+	unsigned char old_sha1[20];
+	unsigned char new_sha1[20];
+	int converted;
+};
+
+#define MAXOBJECTS (1000000)
+
+static struct entry *convert[MAXOBJECTS];
+static int nr_convert;
+
+static struct entry * convert_entry(unsigned char *sha1);
+
+static struct entry *insert_new(unsigned char *sha1, int pos)
+{
+	struct entry *new = malloc(sizeof(struct entry));
+
+	memset(new, 0, sizeof(*new));
+	memcpy(new->old_sha1, sha1, 20);
+	memmove(convert + pos + 1, convert + pos, (nr_convert - pos) * sizeof(struct entry *));
+	convert[pos] = new;
+	nr_convert++;
+	if (nr_convert == MAXOBJECTS)
+		die("you're kidding me - hit maximum object limit");
+	return new;
+}
+
+static struct entry *lookup_entry(unsigned char *sha1)
+{
+	int low = 0, high = nr_convert;
+
+	while (low < high) {
+		int next = (low + high) / 2;
+		struct entry *n = convert[next];
+		int cmp = memcmp(sha1, n->old_sha1, 20);
+		if (!cmp)
+			return n;
+		if (cmp < 0) {
+			high = next;
+			continue;
+		}
+		low = next+1;
+	}
+	return insert_new(sha1, low);
+}
+
+static void convert_blob(void *buffer, unsigned long size)
+{
+	/* Nothing to do */
+}
+
+static void convert_binary_sha1(void *buffer)
+{
+	struct entry *entry = convert_entry(buffer);
+	memcpy(buffer, entry->new_sha1, 20);
+}
+
+static void convert_ascii_sha1(void *buffer)
+{
+	unsigned char sha1[20];
+	struct entry *entry;
+
+	if (get_sha1_hex(buffer, sha1))
+		die("bad sha1");
+	entry = convert_entry(sha1);
+	memcpy(buffer, sha1_to_hex(entry->new_sha1), 40);
+}
+
+static void convert_tree(void *buffer, unsigned long size)
+{
+	while (size) {
+		int len = 1+strlen(buffer);
+
+		convert_binary_sha1(buffer + len);
+
+		len += 20;
+		if (len > size)
+			die("corrupt tree object");
+		size -= len;
+		buffer += len;
+	}
+}
+
+static void convert_commit(void *buffer, unsigned long size)
+{
+	convert_ascii_sha1(buffer+5);
+	buffer += 46;    /* "tree " + "hex sha1" + "\n" */
+	while (!memcmp(buffer, "parent ", 7)) {
+		convert_ascii_sha1(buffer+7);
+		buffer += 48;
+	}
+}
+
+static struct entry * convert_entry(unsigned char *sha1)
+{
+	struct entry *entry = lookup_entry(sha1);
+	char type[20];
+	void *buffer, *data;
+	unsigned long size, offset;
+
+	if (entry->converted)
+		return entry;
+	data = read_sha1_file(sha1, type, &size);
+	if (!data)
+		die("unable to read object %s", sha1_to_hex(sha1));
+
+	buffer = malloc(size + 100);
+	offset = sprintf(buffer, "%s %lu", type, size)+1;
+	memcpy(buffer + offset, data, size);
+	
+	if (!strcmp(type, "blob"))
+		convert_blob(buffer + offset, size);
+	else if (!strcmp(type, "tree"))
+		convert_tree(buffer + offset, size);
+	else if (!strcmp(type, "commit"))
+		convert_commit(buffer + offset, size);
+	else
+		die("unknown object type '%s' in %s", type, sha1_to_hex(sha1));
+	write_sha1_file(buffer, size + offset, entry->new_sha1);
+	entry->converted = 1;
+	free(buffer);
+	return entry;
+}
+
+int main(int argc, char **argv)
+{
+	unsigned char sha1[20];
+	struct entry *entry;
+
+	if (argc != 2 || get_sha1_hex(argv[1], sha1))
+		usage("convert-cache <sha1>");
+
+	entry = convert_entry(sha1);
+	printf("new sha1: %s\n", sha1_to_hex(entry->new_sha1));
+	return 0;
+}