text: #include "cache.h"
  #include "walker.h"
  #include "commit.h"
  #include "tree.h"
  #include "tree-walk.h"
  #include "tag.h"
  #include "blob.h"
  #include "refs.h"
  
  static unsigned char current_commit_sha1[20];
  
  void walker_say(struct walker *walker, const char *fmt, const char *hex)
  {
  	if (walker->get_verbosely)
  		fprintf(stderr, fmt, hex);
  }
  
  static void report_missing(const struct object *obj)
  {
  	char missing_hex[41];
  	strcpy(missing_hex, sha1_to_hex(obj->sha1));
  	fprintf(stderr, "Cannot obtain needed %s %s\n",
  		obj->type ? typename(obj->type): "object", missing_hex);
  	if (!is_null_sha1(current_commit_sha1))
  		fprintf(stderr, "while processing commit %s.\n",
  			sha1_to_hex(current_commit_sha1));
  }
  
  static int process(struct walker *walker, struct object *obj);
  
  static int process_tree(struct walker *walker, struct tree *tree)
  {
  	struct tree_desc desc;
  	struct name_entry entry;
  
  	if (parse_tree(tree))
  		return -1;
  
  	init_tree_desc(&desc, tree->buffer, tree->size);
  	while (tree_entry(&desc, &entry)) {
  		struct object *obj = NULL;
  
  		/* submodule commits are not stored in the superproject */
  		if (S_ISGITLINK(entry.mode))
  			continue;
  		if (S_ISDIR(entry.mode)) {
  			struct tree *tree = lookup_tree(entry.sha1);
  			if (tree)
  				obj = &tree->object;
  		}
  		else {
  			struct blob *blob = lookup_blob(entry.sha1);
  			if (blob)
  				obj = &blob->object;
  		}
  		if (!obj || process(walker, obj))
  			return -1;
  	}
  	free_tree_buffer(tree);
  	return 0;
  }
  
  /* Remember to update object flag allocation in object.h */
  #define COMPLETE	(1U << 0)
  #define SEEN		(1U << 1)
  #define TO_SCAN		(1U << 2)
  
  static struct commit_list *complete = NULL;
  
  static int process_commit(struct walker *walker, struct commit *commit)
  {
  	if (parse_commit(commit))
  		return -1;
  
  	while (complete && complete->item->date >= commit->date) {
  		pop_most_recent_commit(&complete, COMPLETE);
  	}
  
  	if (commit->object.flags & COMPLETE)
  		return 0;
  
  	hashcpy(current_commit_sha1, commit->object.sha1);
  
  	walker_say(walker, "walk %s\n", sha1_to_hex(commit->object.sha1));
  
  	if (walker->get_tree) {
  		if (process(walker, &commit->tree->object))
  			return -1;
  		if (!walker->get_all)
  			walker->get_tree = 0;
  	}
  	if (walker->get_history) {
  		struct commit_list *parents = commit->parents;
  		for (; parents; parents = parents->next) {
  			if (process(walker, &parents->item->object))
  				return -1;
  		}
  	}
  	return 0;
  }
  
  static int process_tag(struct walker *walker, struct tag *tag)
  {
  	if (parse_tag(tag))
  		return -1;
  	return process(walker, tag->tagged);
  }
  
  static struct object_list *process_queue = NULL;
  static struct object_list **process_queue_end = &process_queue;
  
  static int process_object(struct walker *walker, struct object *obj)
  {
  	if (obj->type == OBJ_COMMIT) {
  		if (process_commit(walker, (struct commit *)obj))
  			return -1;
  		return 0;
  	}
  	if (obj->type == OBJ_TREE) {
  		if (process_tree(walker, (struct tree *)obj))
  			return -1;
  		return 0;
  	}
  	if (obj->type == OBJ_BLOB) {
  		return 0;
  	}
  	if (obj->type == OBJ_TAG) {
  		if (process_tag(walker, (struct tag *)obj))
  			return -1;
  		return 0;
  	}
  	return error("Unable to determine requirements "
  		     "of type %s for %s",
  		     typename(obj->type), sha1_to_hex(obj->sha1));
  }
  
  static int process(struct walker *walker, struct object *obj)
  {
  	if (obj->flags & SEEN)
  		return 0;
  	obj->flags |= SEEN;
  
  	if (has_sha1_file(obj->sha1)) {
  		/* We already have it, so we should scan it now. */
  		obj->flags |= TO_SCAN;
  	}
  	else {
  		if (obj->flags & COMPLETE)
  			return 0;
  		walker->prefetch(walker, obj->sha1);
  	}
  
  	object_list_insert(obj, process_queue_end);
  	process_queue_end = &(*process_queue_end)->next;
  	return 0;
  }
  
  static int loop(struct walker *walker)
  {
  	struct object_list *elem;
  
  	while (process_queue) {
  		struct object *obj = process_queue->item;
  		elem = process_queue;
  		process_queue = elem->next;
  		free(elem);
  		if (!process_queue)
  			process_queue_end = &process_queue;
  
  		/* If we are not scanning this object, we placed it in
  		 * the queue because we needed to fetch it first.
  		 */
  		if (! (obj->flags & TO_SCAN)) {
  			if (walker->fetch(walker, obj->sha1)) {
  				report_missing(obj);
  				return -1;
  			}
  		}
  		if (!obj->type)
  			parse_object(obj->sha1);
  		if (process_object(walker, obj))
  			return -1;
  	}
  	return 0;
  }
  
  static int interpret_target(struct walker *walker, char *target, unsigned char *sha1)
  {
  	if (!get_sha1_hex(target, sha1))
  		return 0;
  	if (!check_refname_format(target, 0)) {
  		struct ref *ref = alloc_ref(target);
  		if (!walker->fetch_ref(walker, ref)) {
  			hashcpy(sha1, ref->old_sha1);
  			free(ref);
  			return 0;
  		}
  		free(ref);
  	}
  	return -1;
  }
  
  static int mark_complete(const char *path, const struct object_id *oid,
  			 int flag, void *cb_data)
  {
  	struct commit *commit = lookup_commit_reference_gently(oid->hash, 1);
  
  	if (commit) {
  		commit->object.flags |= COMPLETE;
  		commit_list_insert(commit, &complete);
  	}
  	return 0;
  }
  
  int walker_targets_stdin(char ***target, const char ***write_ref)
  {
  	int targets = 0, targets_alloc = 0;
  	struct strbuf buf = STRBUF_INIT;
  	*target = NULL; *write_ref = NULL;
  	while (1) {
  		char *rf_one = NULL;
  		char *tg_one;
  
  		if (strbuf_getline(&buf, stdin, '\n') == EOF)
  			break;
  		tg_one = buf.buf;
  		rf_one = strchr(tg_one, '\t');
  		if (rf_one)
  			*rf_one++ = 0;
  
  		if (targets >= targets_alloc) {
  			targets_alloc = targets_alloc ? targets_alloc * 2 : 64;
  			REALLOC_ARRAY(*target, targets_alloc);
  			REALLOC_ARRAY(*write_ref, targets_alloc);
  		}
  		(*target)[targets] = xstrdup(tg_one);
  		(*write_ref)[targets] = xstrdup_or_null(rf_one);
  		targets++;
  	}
  	strbuf_release(&buf);
  	return targets;
  }
  
  void walker_targets_free(int targets, char **target, const char **write_ref)
  {
  	while (targets--) {
  		free(target[targets]);
  		if (write_ref)
  			free((char *) write_ref[targets]);
  	}
  }
  
  int walker_fetch(struct walker *walker, int targets, char **target,
  		 const char **write_ref, const char *write_ref_log_details)
  {
  	struct strbuf refname = STRBUF_INIT;
  	struct strbuf err = STRBUF_INIT;
  	struct ref_transaction *transaction = NULL;
  	unsigned char *sha1 = xmalloc(targets * 20);
  	char *msg = NULL;
  	int i, ret = -1;
  
  	save_commit_buffer = 0;
  
  	if (write_ref) {
  		transaction = ref_transaction_begin(&err);
  		if (!transaction) {
  			error("%s", err.buf);
  			goto done;
  		}
  	}
  
  	if (!walker->get_recover) {
  		for_each_ref(mark_complete, NULL);
  		commit_list_sort_by_date(&complete);
  	}
  
  	for (i = 0; i < targets; i++) {
  		if (interpret_target(walker, target[i], &sha1[20 * i])) {
  			error("Could not interpret response from server '%s' as something to pull", target[i]);
  			goto done;
  		}
  		if (process(walker, lookup_unknown_object(&sha1[20 * i])))
  			goto done;
  	}
  
  	if (loop(walker))
  		goto done;
  	if (!write_ref) {
  		ret = 0;
  		goto done;
  	}
  	if (write_ref_log_details) {
  		msg = xstrfmt("fetch from %s", write_ref_log_details);
  	} else {
  		msg = NULL;
  	}
  	for (i = 0; i < targets; i++) {
  		if (!write_ref[i])
  			continue;
  		strbuf_reset(&refname);
  		strbuf_addf(&refname, "refs/%s", write_ref[i]);
  		if (ref_transaction_update(transaction, refname.buf,
  					   &sha1[20 * i], NULL, 0,
  					   msg ? msg : "fetch (unknown)",
  					   &err)) {
  			error("%s", err.buf);
  			goto done;
  		}
  	}
  	if (ref_transaction_commit(transaction, &err)) {
  		error("%s", err.buf);
  		goto done;
  	}
  
  	ret = 0;
  
  done:
  	ref_transaction_free(transaction);
  	free(msg);
  	free(sha1);
  	strbuf_release(&err);
  	strbuf_release(&refname);
  	return ret;
  }
  
  void walker_free(struct walker *walker)
  {
  	walker->cleanup(walker);
  	free(walker);
  }
  