Update iterators for consistency across library

This updates all the `foreach()` type functions across the library
that take callbacks from the user to have a consistent behavior.
The rules are:

* A callback terminates the loop by returning any non-zero value
* Once the callback returns non-zero, it will not be called again
  (i.e. the loop stops all iteration regardless of state)
* If the callback returns non-zero, the parent fn returns GIT_EUSER
* Although the parent returns GIT_EUSER, no error will be set in
  the library and `giterr_last()` will return NULL if called.

This commit makes those changes across the library and adds tests
for most of the iteration APIs to make sure that they follow the
above rules.

14 files changed, 149 insertions, 112 deletions

diff --git a/src/attr.c b/src/attr.c
index 6fbd005d5..c58a1f045 100644
--- a/src/attr.c
+++ b/src/attr.c
@@ -163,11 +163,14 @@ int git_attr_foreach(
 					continue;
 
 				git_strmap_insert(seen, assign->name, assign, error);
-				if (error >= 0)
-					error = callback(assign->name, assign->value, payload);
+				if (error < 0)
+					goto cleanup;
 
-				if (error != 0)
+				error = callback(assign->name, assign->value, payload);
+				if (error) {
+					error = GIT_EUSER;
 					goto cleanup;
+				}
 			}
 		}
 	}
diff --git a/src/config_file.c b/src/config_file.c
index 7ced1e5ba..80c63d2a3 100644
--- a/src/config_file.c
+++ b/src/config_file.c
@@ -218,8 +218,10 @@ static int file_foreach(
 				continue;
 
 			/* abort iterator on non-zero return value */
-			if ((result = fn(key, var->value, data)) != 0)
+			if (fn(key, var->value, data)) {
+				result = GIT_EUSER;
 				goto cleanup;
+			}
 		}
 	);
 
diff --git a/src/diff_output.c b/src/diff_output.c
index f6650b345..9f8779787 100644
--- a/src/diff_output.c
+++ b/src/diff_output.c
@@ -23,6 +23,7 @@ typedef struct {
 	unsigned int index;
 	git_diff_delta *delta;
 	git_diff_range range;
+	int error;
 } diff_output_info;
 
 static int read_next_int(const char **str, int *value)
@@ -49,25 +50,24 @@ static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 
 		/* expect something of the form "@@ -%d[,%d] +%d[,%d] @@" */
 		if (*scan != '@')
-			return -1;
-
-		if (read_next_int(&scan, &range.old_start) < 0)
-			return -1;
-		if (*scan == ',' && read_next_int(&scan, &range.old_lines) < 0)
-			return -1;
-
-		if (read_next_int(&scan, &range.new_start) < 0)
-			return -1;
-		if (*scan == ',' && read_next_int(&scan, &range.new_lines) < 0)
-			return -1;
-
-		if (range.old_start < 0 || range.new_start < 0)
-			return -1;
-
-		memcpy(&info->range, &range, sizeof(git_diff_range));
-
-		return info->hunk_cb(
-			info->cb_data, info->delta, &range, bufs[0].ptr, bufs[0].size);
+			info->error = -1;
+		else if (read_next_int(&scan, &range.old_start) < 0)
+			info->error = -1;
+		else if (*scan == ',' && read_next_int(&scan, &range.old_lines) < 0)
+			info->error = -1;
+		else if (read_next_int(&scan, &range.new_start) < 0)
+			info->error = -1;
+		else if (*scan == ',' && read_next_int(&scan, &range.new_lines) < 0)
+			info->error = -1;
+		else if (range.old_start < 0 || range.new_start < 0)
+			info->error = -1;
+		else {
+			memcpy(&info->range, &range, sizeof(git_diff_range));
+
+			if (info->hunk_cb(
+					info->cb_data, info->delta, &range, bufs[0].ptr, bufs[0].size))
+				info->error = GIT_EUSER;
+		}
 	}
 
 	if ((len == 2 || len == 3) && info->line_cb) {
@@ -80,23 +80,24 @@ static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 			GIT_DIFF_LINE_CONTEXT;
 
 		if (info->line_cb(
-			info->cb_data, info->delta, &info->range, origin, bufs[1].ptr, bufs[1].size) < 0)
-			return -1;
+				info->cb_data, info->delta, &info->range, origin, bufs[1].ptr, bufs[1].size))
+			info->error = GIT_EUSER;
 
 		/* This should only happen if we are adding a line that does not
 		 * have a newline at the end and the old code did.  In that case,
 		 * we have a ADD with a DEL_EOFNL as a pair.
 		 */
-		if (len == 3) {
+		else if (len == 3) {
 			origin = (origin == GIT_DIFF_LINE_ADDITION) ?
 				GIT_DIFF_LINE_DEL_EOFNL : GIT_DIFF_LINE_ADD_EOFNL;
 
-			return info->line_cb(
-				info->cb_data, info->delta, &info->range, origin, bufs[2].ptr, bufs[2].size);
+			if (info->line_cb(
+					info->cb_data, info->delta, &info->range, origin, bufs[2].ptr, bufs[2].size))
+				info->error = GIT_EUSER;
 		}
 	}
 
-	return 0;
+	return info->error;
 }
 
 #define BINARY_DIFF_FLAGS (GIT_DIFF_FILE_BINARY|GIT_DIFF_FILE_NOT_BINARY)
@@ -318,6 +319,7 @@ int git_diff_foreach(
 	xdemitconf_t xdiff_config;
 	xdemitcb_t   xdiff_callback;
 
+	memset(&info, 0, sizeof(info));
 	info.diff    = diff;
 	info.cb_data = data;
 	info.hunk_cb = hunk_cb;
@@ -422,11 +424,11 @@ int git_diff_foreach(
 		 * diffs to tell if a file has really been changed.
 		 */
 
-		if (file_cb != NULL) {
-			error = file_cb(
-				data, delta, (float)info.index / diff->deltas.length);
-			if (error < 0)
-				goto cleanup;
+		if (file_cb != NULL &&
+			file_cb(data, delta, (float)info.index / diff->deltas.length))
+		{
+			error = GIT_EUSER;
+			goto cleanup;
 		}
 
 		/* don't do hunk and line diffs if file is binary */
@@ -451,6 +453,7 @@ int git_diff_foreach(
 
 		xdl_diff(&old_xdiff_data, &new_xdiff_data,
 			&xdiff_params, &xdiff_config, &xdiff_callback);
+		error = info.error;
 
 cleanup:
 		release_content(&delta->old_file, &old_data, old_blob);
@@ -524,7 +527,11 @@ static int print_compact(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	return pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 int git_diff_print_compact(
@@ -586,7 +593,6 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	const char *oldpath = delta->old_file.path;
 	const char *newpfx = pi->diff->opts.new_prefix;
 	const char *newpath = delta->new_file.path;
-	int result;
 
 	GIT_UNUSED(progress);
 
@@ -619,9 +625,8 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-    result = pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
-    if (result < 0)
-        return result;
+    if (pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
 
     if (delta->binary != 1)
         return 0;
@@ -633,7 +638,11 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	return pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_BINARY, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_BINARY,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 static int print_patch_hunk(
@@ -649,7 +658,11 @@ static int print_patch_hunk(
 	if (git_buf_printf(pi->buf, "%.*s", (int)header_len, header) < 0)
 		return -1;
 
-	return pi->print_cb(pi->cb_data, d, r, GIT_DIFF_LINE_HUNK_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, d, r, GIT_DIFF_LINE_HUNK_HDR,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 static int print_patch_line(
@@ -674,7 +687,11 @@ static int print_patch_line(
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	return pi->print_cb(pi->cb_data, delta, range, line_origin, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, delta, range, line_origin,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 int git_diff_print_patch(
@@ -763,11 +780,8 @@ int git_diff_blobs(
 	if (file_is_binary_by_content(&delta, &old_map, &new_map) < 0)
 		return -1;
 
-	if (file_cb != NULL) {
-		int error = file_cb(cb_data, &delta, 1);
-		if (error < 0)
-			return error;
-	}
+	if (file_cb != NULL && file_cb(cb_data, &delta, 1))
+		return GIT_EUSER;
 
 	/* don't do hunk and line diffs if the two blobs are identical */
 	if (delta.status == GIT_DELTA_UNMODIFIED)
@@ -777,6 +791,7 @@ int git_diff_blobs(
 	if (delta.binary == 1)
 		return 0;
 
+	memset(&info, 0, sizeof(info));
 	info.diff    = NULL;
 	info.delta   = &delta;
 	info.cb_data = cb_data;
@@ -790,5 +805,5 @@ int git_diff_blobs(
 
 	xdl_diff(&old_data, &new_data, &xdiff_params, &xdiff_config, &xdiff_callback);
 
-	return 0;
+	return info.error;
 }
diff --git a/src/notes.c b/src/notes.c
index 7813e9985..212413a5a 100644
--- a/src/notes.c
+++ b/src/notes.c
@@ -522,13 +522,13 @@ static int process_entry_path(
 	int (*note_cb)(git_note_data *note_data, void *payload),
 	void *payload)
 {
-	int i = 0, j = 0, error = -1, len;
+	int i = 0, j = 0, error, len;
 	git_buf buf = GIT_BUF_INIT;
 	git_note_data note_data;
 
-	if (git_buf_puts(&buf, entry_path) < 0)
+	if ((error = git_buf_puts(&buf, entry_path)) < 0)
 		goto cleanup;
-	
+
 	len = git_buf_len(&buf);
 
 	while (i < len) {
@@ -536,10 +536,9 @@ static int process_entry_path(
 			i++;
 			continue;
 		}
-		
+
 		if (git__fromhex(buf.ptr[i]) < 0) {
 			/* This is not a note entry */
-			error = 0;
 			goto cleanup;
 		}
 
@@ -555,16 +554,17 @@ static int process_entry_path(
 
 	if (j != GIT_OID_HEXSZ) {
 		/* This is not a note entry */
-		error = 0;
 		goto cleanup;
 	}
 
-	if (git_oid_fromstr(&note_data.annotated_object_oid, buf.ptr) < 0)
-		return -1;
+	if ((error = git_oid_fromstr(
+			&note_data.annotated_object_oid, buf.ptr)) < 0)
+		goto cleanup;
 
 	git_oid_cpy(&note_data.blob_oid, note_oid);
 
-	error = note_cb(&note_data, payload);
+	if (note_cb(&note_data, payload))
+		error = GIT_EUSER;
 
 cleanup:
 	git_buf_free(&buf);
@@ -577,34 +577,27 @@ int git_note_foreach(
 	int (*note_cb)(git_note_data *note_data, void *payload),
 	void *payload)
 {
-	int error = -1;
+	int error;
 	git_iterator *iter = NULL;
 	git_tree *tree = NULL;
 	git_commit *commit = NULL;
 	const git_index_entry *item;
 
-	if ((error = retrieve_note_tree_and_commit(&tree, &commit, repo, &notes_ref)) < 0)
-		goto cleanup;
-
-	if (git_iterator_for_tree(&iter, repo, tree) < 0)
-		goto cleanup;
+	if (!(error = retrieve_note_tree_and_commit(
+			&tree, &commit, repo, &notes_ref)) &&
+		!(error = git_iterator_for_tree(&iter, repo, tree)))
+		error = git_iterator_current(iter, &item);
 
-	if (git_iterator_current(iter, &item) < 0)
-		goto cleanup;
-
-	while (item) {
-		if (process_entry_path(item->path, &item->oid, note_cb, payload) < 0)
-			goto cleanup;
+	while (!error && item) {
+		error = process_entry_path(item->path, &item->oid, note_cb, payload);
 
-		if (git_iterator_advance(iter, &item) < 0)
-			goto cleanup;
+		if (!error)
+			error = git_iterator_advance(iter, &item);
 	}
 
-	error = 0;
-
-cleanup:
 	git_iterator_free(iter);
 	git_tree_free(tree);
 	git_commit_free(commit);
+
 	return error;
 }
diff --git a/src/odb.c b/src/odb.c
index 493c8292a..db2f03c9e 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -609,9 +609,12 @@ int git_odb_foreach(git_odb *db, int (*cb)(git_oid *oid, void *data), void *data
 {
 	unsigned int i;
 	backend_internal *internal;
+
 	git_vector_foreach(&db->backends, i, internal) {
 		git_odb_backend *b = internal->backend;
-		b->foreach(b, cb, data);
+		int error = b->foreach(b, cb, data);
+		if (error < 0)
+			return error;
 	}
 
 	return 0;
diff --git a/src/odb_loose.c b/src/odb_loose.c
index 2197a4264..ccb899e8c 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -680,6 +680,7 @@ struct foreach_state {
 	size_t dir_len;
 	int (*cb)(git_oid *oid, void *data);
 	void *data;
+	int cb_error;
 };
 
 GIT_INLINE(int) filename_to_oid(git_oid *oid, const char *ptr)
@@ -718,8 +719,10 @@ static int foreach_object_dir_cb(void *_state, git_buf *path)
 	if (filename_to_oid(&oid, path->ptr + state->dir_len) < 0)
 		return 0;
 
-	if (state->cb(&oid, state->data) < 0)
+	if (state->cb(&oid, state->data)) {
+		state->cb_error = GIT_EUSER;
 		return -1;
+	}
 
 	return 0;
 }
@@ -728,10 +731,7 @@ static int foreach_cb(void *_state, git_buf *path)
 {
 	struct foreach_state *state = (struct foreach_state *) _state;
 
-	if (git_path_direach(path, foreach_object_dir_cb, state) < 0)
-		return -1;
-
-	return 0;
+	return git_path_direach(path, foreach_object_dir_cb, state);
 }
 
 static int loose_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *oid, void *data), void *data)
@@ -749,14 +749,16 @@ static int loose_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *
 	git_buf_sets(&buf, objects_dir);
 	git_path_to_dir(&buf);
 
+	memset(&state, 0, sizeof(state));
 	state.cb = cb;
 	state.data = data;
 	state.dir_len = git_buf_len(&buf);
 
 	error = git_path_direach(&buf, foreach_cb, &state);
+
 	git_buf_free(&buf);
 
-	return error;
+	return state.cb_error ? state.cb_error : error;
 }
 
 static int loose_backend__stream_fwrite(git_oid *oid, git_odb_stream *_stream)
diff --git a/src/odb_pack.c b/src/odb_pack.c
index 4b860e864..176be5f01 100644
--- a/src/odb_pack.c
+++ b/src/odb_pack.c
@@ -422,6 +422,7 @@ static int pack_backend__exists(git_odb_backend *backend, const git_oid *oid)
 
 static int pack_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *oid, void *data), void *data)
 {
+	int error;
 	struct git_pack_file *p;
 	struct pack_backend *backend;
 	unsigned int i;
@@ -430,12 +431,14 @@ static int pack_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *o
 	backend = (struct pack_backend *)_backend;
 
 	/* Make sure we know about the packfiles */
-	if (packfile_refresh_all(backend) < 0)
-		return -1;
+	if ((error = packfile_refresh_all(backend)) < 0)
+		return error;
 
 	git_vector_foreach(&backend->packs, i, p) {
-		git_pack_foreach_entry(p, cb, &data);
+		if ((error = git_pack_foreach_entry(p, cb, &data)) < 0)
+			return error;
 	}
+
 	return 0;
 }
 
diff --git a/src/pack.c b/src/pack.c
index 1d88eaa7d..acdb40d35 100644
--- a/src/pack.c
+++ b/src/pack.c
@@ -687,10 +687,9 @@ static git_off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_
 }
 
 int git_pack_foreach_entry(
-		struct git_pack_file *p,
-		int (*cb)(git_oid *oid, void *data),
-		void *data)
-
+	struct git_pack_file *p,
+	int (*cb)(git_oid *oid, void *data),
+	void *data)
 {
 	const unsigned char *index = p->index_map.data, *current;
 	unsigned stride;
@@ -722,7 +721,9 @@ int git_pack_foreach_entry(
 
 	current = index;
 	for (i = 0; i < p->num_objects; i++) {
-		cb((git_oid *)current, data);
+		if (cb((git_oid *)current, data))
+			return GIT_EUSER;
+
 		current += stride;
 	}
 
diff --git a/src/path.h b/src/path.h
index d68393b3d..d611428c1 100644
--- a/src/path.h
+++ b/src/path.h
@@ -217,6 +217,7 @@ extern int git_path_apply_relative(git_buf *target, const char *relpath);
  *		the input state and the second arg is pathbuf. The function
  *		may modify the pathbuf, but only by appending new text.
  * @param state to pass to fn as the first arg.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 extern int git_path_direach(
 	git_buf *pathbuf,
diff --git a/src/refs.c b/src/refs.c
index b3c140bec..723695cd6 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -501,6 +501,7 @@ struct dirent_list_data {
 
 	int (*callback)(const char *, void *);
 	void *callback_payload;
+	int callback_error;
 };
 
 static int _dirent_loose_listall(void *_data, git_buf *full_path)
@@ -521,7 +522,10 @@ static int _dirent_loose_listall(void *_data, git_buf *full_path)
 			return 0; /* we are filtering out this reference */
 	}
 
-	return data->callback(file_path, data->callback_payload);
+	if (data->callback(file_path, data->callback_payload))
+		data->callback_error = GIT_EUSER;
+
+	return data->callback_error;
 }
 
 static int _dirent_loose_load(void *data, git_buf *full_path)
@@ -844,15 +848,17 @@ static int reference_path_available(
 	const char *ref,
 	const char* old_ref)
 {
+	int error;
 	struct reference_available_t data;
 
 	data.new_ref = ref;
 	data.old_ref = old_ref;
 	data.available = 1;
 
-	if (git_reference_foreach(repo, GIT_REF_LISTALL,
-		_reference_available_cb, (void *)&data) < 0)
-		return -1;
+	error = git_reference_foreach(
+		repo, GIT_REF_LISTALL, _reference_available_cb, (void *)&data);
+	if (error < 0)
+		return error;
 
 	if (!data.available) {
 		giterr_set(GITERR_REFERENCE,
@@ -1487,8 +1493,8 @@ int git_reference_foreach(
 			return -1;
 
 		git_strmap_foreach(repo->references.packfile, ref_name, ref, {
-			if (callback(ref_name, payload) < 0)
-				return 0;
+			if (callback(ref_name, payload))
+				return GIT_EUSER;
 		});
 	}
 
@@ -1500,14 +1506,16 @@ int git_reference_foreach(
 	data.repo = repo;
 	data.callback = callback;
 	data.callback_payload = payload;
+	data.callback_error = 0;
 
 	if (git_buf_joinpath(&refs_path, repo->path_repository, GIT_REFS_DIR) < 0)
 		return -1;
 
 	result = git_path_direach(&refs_path, _dirent_loose_listall, &data);
+
 	git_buf_free(&refs_path);
 
-	return result;
+	return data.callback_error ? GIT_EUSER : result;
 }
 
 static int cb__reflist_add(const char *ref, void *data)
diff --git a/src/status.c b/src/status.c
index d78237689..618f60fd0 100644
--- a/src/status.c
+++ b/src/status.c
@@ -114,7 +114,8 @@ int git_status_foreach_ext(
 	if (show == GIT_STATUS_SHOW_INDEX_THEN_WORKDIR) {
 		for (i = 0; !err && i < idx2head->deltas.length; i++) {
 			i2h = GIT_VECTOR_GET(&idx2head->deltas, i);
-			err = cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata);
+			if (cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata))
+				err = GIT_EUSER;
 		}
 		git_diff_list_free(idx2head);
 		idx2head = NULL;
@@ -130,14 +131,17 @@ int git_status_foreach_ext(
 		cmp = !w2i ? -1 : !i2h ? 1 : strcmp(i2h->old_file.path, w2i->old_file.path);
 
 		if (cmp < 0) {
-			err = cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata);
+			if (cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata))
+				err = GIT_EUSER;
 			i++;
 		} else if (cmp > 0) {
-			err = cb(w2i->old_file.path, workdir_delta2status(w2i->status), cbdata);
+			if (cb(w2i->old_file.path, workdir_delta2status(w2i->status), cbdata))
+				err = GIT_EUSER;
 			j++;
 		} else {
-			err = cb(i2h->old_file.path, index_delta2status(i2h->status) |
-					 workdir_delta2status(w2i->status), cbdata);
+			if (cb(i2h->old_file.path, index_delta2status(i2h->status) |
+				   workdir_delta2status(w2i->status), cbdata))
+				err = GIT_EUSER;
 			i++; j++;
 		}
 	}
@@ -146,6 +150,7 @@ cleanup:
 	git_tree_free(head);
 	git_diff_list_free(idx2head);
 	git_diff_list_free(wd2idx);
+
 	return err;
 }
 
@@ -166,9 +171,10 @@ int git_status_foreach(
 }
 
 struct status_file_info {
+	char *expected;
 	unsigned int count;
 	unsigned int status;
-	char *expected;
+	int ambiguous;
 };
 
 static int get_one_status(const char *path, unsigned int status, void *data)
@@ -183,6 +189,7 @@ static int get_one_status(const char *path, unsigned int status, void *data)
 		p_fnmatch(sfi->expected, path, 0) != 0)) {
 		giterr_set(GITERR_INVALID,
 			"Ambiguous path '%s' given to git_status_file", sfi->expected);
+		sfi->ambiguous = true;
 		return GIT_EAMBIGUOUS;
 	}
 
@@ -215,6 +222,9 @@ int git_status_file(
 
 	error = git_status_foreach_ext(repo, &opts, get_one_status, &sfi);
 
+	if (error < 0 && sfi.ambiguous)
+		error = GIT_EAMBIGUOUS;
+
 	if (!error && !sfi.count) {
 		giterr_set(GITERR_INVALID,
 			"Attempt to get status of nonexistent file '%s'", path);
diff --git a/src/transports/git.c b/src/transports/git.c
index 45f571f20..0d0ec7821 100644
--- a/src/transports/git.c
+++ b/src/transports/git.c
@@ -239,10 +239,8 @@ static int git_ls(git_transport *transport, git_headlist_cb list_cb, void *opaqu
 
 		pkt = (git_pkt_ref *)p;
 
-		if (list_cb(&pkt->head, opaque) < 0) {
-			giterr_set(GITERR_NET, "User callback returned error");
-			return -1;
-		}
+		if (list_cb(&pkt->head, opaque))
+			return GIT_EUSER;
 	}
 
 	return 0;
diff --git a/src/transports/http.c b/src/transports/http.c
index f25d639f3..993070aac 100644
--- a/src/transports/http.c
+++ b/src/transports/http.c
@@ -324,10 +324,8 @@ static int http_ls(git_transport *transport, git_headlist_cb list_cb, void *opaq
 		if (p->type != GIT_PKT_REF)
 			continue;
 
-		if (list_cb(&p->head, opaque) < 0) {
-			giterr_set(GITERR_NET, "The user callback returned error");
-			return -1;
-		}
+		if (list_cb(&p->head, opaque))
+			return GIT_EUSER;
 	}
 
 	return 0;
diff --git a/src/transports/local.c b/src/transports/local.c
index 0e1ae3752..ccbfb0492 100644
--- a/src/transports/local.c
+++ b/src/transports/local.c
@@ -126,8 +126,8 @@ static int local_ls(git_transport *transport, git_headlist_cb list_cb, void *pay
 	assert(transport && transport->connected);
 
 	git_vector_foreach(refs, i, h) {
-		if (list_cb(h, payload) < 0)
-			return -1;
+		if (list_cb(h, payload))
+			return GIT_EUSER;
 	}
 
 	return 0;