Make read-tree actually unpack the whole tree.

I needed this to make a "sparse" archive conversion from my old
BitKeeper tree data. The scripts to do the conversion are just
incredibly ugly, but they seem to validate the notion that you
can actually use this silly 'git' thing to save your history in.

read-tree.c

@@ -5,6 +5,32 @@
  */
 #include "cache.h"
 
+static void create_directories(const char *path)
+{
+	int len = strlen(path);
+	char *buf = malloc(len + 1);
+	const char *slash = path;
+
+	while ((slash = strchr(slash+1, '/')) != NULL) {
+		len = slash - path;
+		memcpy(buf, path, len);
+		buf[len] = 0;
+		mkdir(buf, 0700);
+	}
+}
+
+static int create_file(const char *path)
+{
+	int fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, 0600);
+	if (fd < 0) {
+		if (errno == ENOENT) {
+			create_directories(path);
+			fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, 0600);
+		}
+	}
+	return fd;
+}
+
 static int unpack(unsigned char *sha1)
 {
 	void *buffer;
@@ -20,12 +46,26 @@ static int unpack(unsigned char *sha1)
 		int len = strlen(buffer)+1;
 		unsigned char *sha1 = buffer + len;
 		char *path = strchr(buffer, ' ')+1;
+		char *data;
+		unsigned long filesize;
 		unsigned int mode;
+		int fd;
+
 		if (size < len + 20 || sscanf(buffer, "%o", &mode) != 1)
 			usage("corrupt 'tree' file");
 		buffer = sha1 + 20;
 		size -= len + 20;
-		printf("%o %s (%s)\n", mode, path, sha1_to_hex(sha1));
+		data = read_sha1_file(sha1, type, &filesize);
+		if (!data || strcmp(type, "blob"))
+			usage("tree file refers to bad file data");
+		fd = create_file(path);
+		if (fd < 0)
+			usage("unable to create file");
+		if (write(fd, data, filesize) != filesize)
+			usage("unable to write file");
+		fchmod(fd, mode);
+		close(fd);
+		free(data);
 	}
 	return 0;
 }