Merge pull request #590 from arrbee/new-error-handling

Migrating diff to new error handling

14 files changed, 369 insertions, 426 deletions

diff --git a/src/attr_file.c b/src/attr_file.c
index 48424123a..029934317 100644
--- a/src/attr_file.c
+++ b/src/attr_file.c
@@ -11,24 +11,19 @@ static void git_attr_rule__clear(git_attr_rule *rule);
 
 int git_attr_file__new(git_attr_file **attrs_ptr)
 {
-	int error;
 	git_attr_file *attrs = NULL;
 
 	attrs = git__calloc(1, sizeof(git_attr_file));
-	if (attrs == NULL)
-		error = GIT_ENOMEM;
-	else
-		error = git_vector_init(&attrs->rules, 4, NULL);
+	GITERR_CHECK_ALLOC(attrs);
 
-	if (error != GIT_SUCCESS) {
-		git__rethrow(error, "Could not allocate attribute storage");
+	if (git_vector_init(&attrs->rules, 4, NULL) < 0) {
 		git__free(attrs);
 		attrs = NULL;
 	}
 
 	*attrs_ptr = attrs;
 
-	return error;
+	return attrs ? 0 : -1;
 }
 
 int git_attr_file__set_path(
@@ -50,13 +45,15 @@ int git_attr_file__set_path(
 			file->path = git__strdup(path);
 	}
 
-	return (file->path == NULL) ? GIT_ENOMEM : GIT_SUCCESS;
+	GITERR_CHECK_ALLOC(file->path);
+
+	return 0;
 }
 
 int git_attr_file__from_buffer(
 	git_repository *repo, const char *buffer, git_attr_file *attrs)
 {
-	int error = GIT_SUCCESS;
+	int error = 0;
 	const char *scan = NULL;
 	char *context = NULL;
 	git_attr_rule *rule = NULL;
@@ -68,13 +65,13 @@ int git_attr_file__from_buffer(
 	if (attrs->path && git__suffixcmp(attrs->path, GIT_ATTR_FILE) == 0) {
 		context = git__strndup(attrs->path,
 			strlen(attrs->path) - strlen(GIT_ATTR_FILE));
-		if (!context) error = GIT_ENOMEM;
+		GITERR_CHECK_ALLOC(context);
 	}
 
-	while (error == GIT_SUCCESS && *scan) {
+	while (!error && *scan) {
 		/* allocate rule if needed */
 		if (!rule && !(rule = git__calloc(1, sizeof(git_attr_rule)))) {
-			error = GIT_ENOMEM;
+			error = -1;
 			break;
 		}
 
@@ -92,10 +89,10 @@ int git_attr_file__from_buffer(
 		}
 
 		/* if the rule wasn't a pattern, on to the next */
-		if (error != GIT_SUCCESS) {
+		if (error < 0) {
 			git_attr_rule__clear(rule); /* reset rule contents */
 			if (error == GIT_ENOTFOUND)
-				error = GIT_SUCCESS;
+				error = 0;
 		} else {
 			rule = NULL; /* vector now "owns" the rule */
 		}
@@ -110,21 +107,20 @@ int git_attr_file__from_buffer(
 int git_attr_file__from_file(
 	git_repository *repo, const char *path, git_attr_file *file)
 {
-	int error = GIT_SUCCESS;
+	int error;
 	git_buf fbuf = GIT_BUF_INIT;
 
 	assert(path && file);
 
-	if (file->path == NULL)
-		error = git_attr_file__set_path(repo, path, file);
+	if (file->path == NULL && git_attr_file__set_path(repo, path, file) < 0)
+		return -1;
 
-	if (error == GIT_SUCCESS &&
-		(error = git_futils_readbuffer(&fbuf, path)) == GIT_SUCCESS)
-		error = git_attr_file__from_buffer(repo, fbuf.ptr, file);
+	if (git_futils_readbuffer(&fbuf, path) < 0)
+		return -1;
+
+	error = git_attr_file__from_buffer(repo, fbuf.ptr, file);
 
 	git_buf_free(&fbuf);
-	if (error != GIT_SUCCESS)
-		git__rethrow(error, "Could not open attribute file '%s'", path);
 
 	return error;
 }
@@ -176,7 +172,6 @@ int git_attr_file__lookup_one(
 
 	git_attr_file__foreach_matching_rule(file, path, i, rule) {
 		int pos = git_vector_bsearch(&rule->assigns, &name);
-		git_clearerror(); /* okay if search failed */
 
 		if (pos >= 0) {
 			*value = ((git_attr_assignment *)
@@ -230,7 +225,6 @@ git_attr_assignment *git_attr_rule__lookup_assignment(
 	key.name_hash = git_attr_file__name_hash(name);
 
 	pos = git_vector_bsearch(&rule->assigns, &key);
-	git_clearerror(); /* okay if search failed */
 
 	return (pos >= 0) ? git_vector_get(&rule->assigns, pos) : NULL;
 }
@@ -248,16 +242,15 @@ int git_attr_path__init(
 
 	if (base != NULL && git_path_root(path) < 0) {
 		git_buf full_path = GIT_BUF_INIT;
-		int error = git_buf_joinpath(&full_path, base, path);
-		if (error == GIT_SUCCESS)
-			info->is_dir = (int)git_path_isdir(full_path.ptr);
-
+		if (git_buf_joinpath(&full_path, base, path) < 0)
+			return -1;
+		info->is_dir = (int)git_path_isdir(full_path.ptr);
 		git_buf_free(&full_path);
-		return error;
+		return 0;
 	}
 	info->is_dir = (int)git_path_isdir(path);
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 
@@ -374,7 +367,7 @@ int git_attr_fnmatch__parse(
 
 	if (!spec->pattern) {
 		*base = git__next_line(pattern);
-		return GIT_ENOMEM;
+		return -1;
 	} else {
 		/* strip '\' that might have be used for internal whitespace */
 		char *to = spec->pattern;
@@ -390,7 +383,7 @@ int git_attr_fnmatch__parse(
 		}
 	}
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int sort_by_hash_and_name(const void *a_raw, const void *b_raw)
@@ -434,7 +427,7 @@ int git_attr_assignment__parse(
 	git_vector *assigns,
 	const char **base)
 {
-	int error = GIT_SUCCESS;
+	int error;
 	const char *scan = *base;
 	git_attr_assignment *assign = NULL;
 
@@ -442,7 +435,7 @@ int git_attr_assignment__parse(
 
 	assigns->_cmp = sort_by_hash_and_name;
 
-	while (*scan && *scan != '\n' && error == GIT_SUCCESS) {
+	while (*scan && *scan != '\n') {
 		const char *name_start, *value_start;
 
 		/* skip leading blanks */
@@ -451,10 +444,7 @@ int git_attr_assignment__parse(
 		/* allocate assign if needed */
 		if (!assign) {
 			assign = git__calloc(1, sizeof(git_attr_assignment));
-			if (!assign) {
-				error = GIT_ENOMEM;
-				break;
-			}
+			GITERR_CHECK_ALLOC(assign);
 			GIT_REFCOUNT_INC(assign);
 		}
 
@@ -489,10 +479,7 @@ int git_attr_assignment__parse(
 
 		/* allocate permanent storage for name */
 		assign->name = git__strndup(name_start, scan - name_start);
-		if (!assign->name) {
-			error = GIT_ENOMEM;
-			break;
-		}
+		GITERR_CHECK_ALLOC(assign->name);
 
 		/* if there is an equals sign, find the value */
 		if (*scan == '=') {
@@ -501,12 +488,8 @@ int git_attr_assignment__parse(
 			/* if we found a value, allocate permanent storage for it */
 			if (scan > value_start) {
 				assign->value = git__strndup(value_start, scan - value_start);
-				if (!assign->value) {
-					error = GIT_ENOMEM;
-					break;
-				} else {
-					assign->is_allocated = 1;
-				}
+				GITERR_CHECK_ALLOC(assign->value);
+				assign->is_allocated = 1;
 			}
 		}
 
@@ -524,35 +507,27 @@ int git_attr_assignment__parse(
 
 					error = git_vector_insert_sorted(
 						assigns, massign, &merge_assignments);
-
-					if (error == GIT_EEXISTS)
-						error = GIT_SUCCESS;
-					else if (error != GIT_SUCCESS)
-						break;
+					if (error < 0 && error != GIT_EEXISTS)
+						return error;
 				}
 			}
 		}
 
 		/* insert allocated assign into vector */
 		error = git_vector_insert_sorted(assigns, assign, &merge_assignments);
-		if (error == GIT_EEXISTS)
-			error = GIT_SUCCESS;
-		else if (error < GIT_SUCCESS)
-			break;
+		if (error < 0 && error != GIT_EEXISTS)
+			return error;
 
 		/* clear assign since it is now "owned" by the vector */
 		assign = NULL;
 	}
 
-	if (!assigns->length)
-		error = git__throw(GIT_ENOTFOUND, "No attribute assignments found for rule");
-
 	if (assign != NULL)
 		git_attr_assignment__free(assign);
 
 	*base = git__next_line(scan);
 
-	return error;
+	return (assigns->length == 0) ? GIT_ENOTFOUND : 0;
 }
 
 static void git_attr_rule__clear(git_attr_rule *rule)
diff --git a/src/diff.c b/src/diff.c
index a0fd5fdf1..06c61122a 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -132,10 +132,8 @@ static int diff_delta__from_one(
 	git_delta_t   status,
 	const git_index_entry *entry)
 {
-	int error;
 	git_diff_delta *delta = diff_delta__alloc(diff, status, entry->path);
-	if (!delta)
-		return git__rethrow(GIT_ENOMEM, "Could not allocate diff record");
+	GITERR_CHECK_ALLOC(delta);
 
 	/* This fn is just for single-sided diffs */
 	assert(status != GIT_DELTA_MODIFIED);
@@ -153,10 +151,12 @@ static int diff_delta__from_one(
 	delta->old.flags |= GIT_DIFF_FILE_VALID_OID;
 	delta->new.flags |= GIT_DIFF_FILE_VALID_OID;
 
-	if ((error = git_vector_insert(&diff->deltas, delta)) < GIT_SUCCESS)
+	if (git_vector_insert(&diff->deltas, delta) < 0) {
 		diff_delta__free(delta);
+		return -1;
+	}
 
-	return error;
+	return 0;
 }
 
 static int diff_delta__from_two(
@@ -166,7 +166,6 @@ static int diff_delta__from_two(
 	const git_index_entry *new,
 	git_oid *new_oid)
 {
-	int error;
 	git_diff_delta *delta;
 
 	if ((diff->opts.flags & GIT_DIFF_REVERSE) != 0) {
@@ -176,8 +175,7 @@ static int diff_delta__from_two(
 	}
 
 	delta = diff_delta__alloc(diff, status, old->path);
-	if (!delta)
-		return git__rethrow(GIT_ENOMEM, "Could not allocate diff record");
+	GITERR_CHECK_ALLOC(delta);
 
 	delta->old.mode = old->mode;
 	git_oid_cpy(&delta->old.oid, &old->oid);
@@ -188,10 +186,12 @@ static int diff_delta__from_two(
 	if (new_oid || !git_oid_iszero(&new->oid))
 		delta->new.flags |= GIT_DIFF_FILE_VALID_OID;
 
-	if ((error = git_vector_insert(&diff->deltas, delta)) < GIT_SUCCESS)
+	if (git_vector_insert(&diff->deltas, delta) < 0) {
 		diff_delta__free(delta);
+		return -1;
+	}
 
-	return error;
+	return 0;
 }
 
 #define DIFF_SRC_PREFIX_DEFAULT "a/"
@@ -284,27 +284,24 @@ static int oid_for_workdir_item(
 	const git_index_entry *item,
 	git_oid *oid)
 {
-	int error = GIT_SUCCESS;
+	int result;
 	git_buf full_path = GIT_BUF_INIT;
 
-	error = git_buf_joinpath(
-		&full_path, git_repository_workdir(repo), item->path);
-	if (error != GIT_SUCCESS)
-		return error;
+	if (git_buf_joinpath(&full_path, git_repository_workdir(repo), item->path) < 0)
+		return -1;
 
-	/* otherwise calculate OID for file */
+	/* calculate OID for file if possible*/
 	if (S_ISLNK(item->mode))
-		error = git_odb__hashlink(oid, full_path.ptr);
-	else if (!git__is_sizet(item->file_size))
-		error = git__throw(GIT_ERROR, "File size overflow for 32-bit systems");
-	else {
-		int fd;
-
-		if ((fd = p_open(full_path.ptr, O_RDONLY)) < 0)
-			error = git__throw(
-				GIT_EOSERR, "Could not open '%s'", item->path);
+		result = git_odb__hashlink(oid, full_path.ptr);
+	else if (!git__is_sizet(item->file_size)) {
+		giterr_set(GITERR_OS, "File size overflow for 32-bit systems");
+		result = -1;
+	} else {
+		int fd = git_futils_open_ro(full_path.ptr);
+		if (fd < 0)
+			result = fd;
 		else {
-			error = git_odb__hashfd(
+			result = git_odb__hashfd(
 				oid, fd, (size_t)item->file_size, GIT_OBJ_BLOB);
 			p_close(fd);
 		}
@@ -312,7 +309,7 @@ static int oid_for_workdir_item(
 
 	git_buf_free(&full_path);
 
-	return error;
+	return result;
 }
 
 static int maybe_modified(
@@ -322,7 +319,6 @@ static int maybe_modified(
 	const git_index_entry *nitem,
 	git_diff_list *diff)
 {
-	int error = GIT_SUCCESS;
 	git_oid noid, *use_noid = NULL;
 
 	GIT_UNUSED(old);
@@ -330,18 +326,18 @@ static int maybe_modified(
 	/* support "assume unchanged" & "skip worktree" bits */
 	if ((oitem->flags_extended & GIT_IDXENTRY_INTENT_TO_ADD) != 0 ||
 		(oitem->flags_extended & GIT_IDXENTRY_SKIP_WORKTREE) != 0)
-		return GIT_SUCCESS;
+		return 0;
 
 	if (GIT_MODE_TYPE(oitem->mode) != GIT_MODE_TYPE(nitem->mode)) {
-		error = diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem);
-		if (error == GIT_SUCCESS)
-			error = diff_delta__from_one(diff, GIT_DELTA_ADDED, nitem);
-		return error;
+		if (diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem) < 0 ||
+			diff_delta__from_one(diff, GIT_DELTA_ADDED, nitem) < 0)
+			return -1;
+		return 0;
 	}
 
 	if (git_oid_cmp(&oitem->oid, &nitem->oid) == 0 &&
 		oitem->mode == nitem->mode)
-		return GIT_SUCCESS;
+		return 0;
 
 	if (git_oid_iszero(&nitem->oid) && new->type == GIT_ITERATOR_WORKDIR) {
 		/* if they files look exactly alike, then we'll assume the same */
@@ -352,18 +348,18 @@ static int maybe_modified(
 			oitem->ino == nitem->ino &&
 			oitem->uid == nitem->uid &&
 			oitem->gid == nitem->gid)
-			return GIT_SUCCESS;
+			return 0;
 
 		/* TODO: check git attributes so we will not have to read the file
 		 * in if it is marked binary.
 		 */
-		error = oid_for_workdir_item(diff->repo, nitem, &noid);
-		if (error != GIT_SUCCESS)
-			return error;
+
+		if (oid_for_workdir_item(diff->repo, nitem, &noid) < 0)
+			return -1;
 
 		if (git_oid_cmp(&oitem->oid, &noid) == 0 &&
 			oitem->mode == nitem->mode)
-			return GIT_SUCCESS;
+			return 0;
 
 		/* store calculated oid so we don't have to recalc later */
 		use_noid = &noid;
@@ -380,37 +376,33 @@ static int diff_from_iterators(
 	git_iterator *new,
 	git_diff_list **diff_ptr)
 {
-	int error;
 	const git_index_entry *oitem, *nitem;
 	char *ignore_prefix = NULL;
 	git_diff_list *diff = git_diff_list_alloc(repo, opts);
-	if (!diff) {
-		error = GIT_ENOMEM;
-		goto cleanup;
-	}
+	if (!diff)
+		goto fail;
 
 	diff->old_src = old->type;
 	diff->new_src = new->type;
 
-	if ((error = git_iterator_current(old, &oitem)) < GIT_SUCCESS ||
-		(error = git_iterator_current(new, &nitem)) < GIT_SUCCESS)
-		goto cleanup;
+	if (git_iterator_current(old, &oitem) < 0 ||
+		git_iterator_current(new, &nitem) < 0)
+		goto fail;
 
 	/* run iterators building diffs */
-	while (!error && (oitem || nitem)) {
+	while (oitem || nitem) {
 
 		/* create DELETED records for old items not matched in new */
 		if (oitem && (!nitem || strcmp(oitem->path, nitem->path) < 0)) {
-			error = diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem);
-			if (error == GIT_SUCCESS)
-				error = git_iterator_advance(old, &oitem);
-			continue;
+			if (diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem) < 0 ||
+				git_iterator_advance(old, &oitem) < 0)
+				goto fail;
 		}
 
 		/* create ADDED, TRACKED, or IGNORED records for new items not
 		 * matched in old (and/or descend into directories as needed)
 		 */
-		if (nitem && (!oitem || strcmp(oitem->path, nitem->path) > 0)) {
+		else if (nitem && (!oitem || strcmp(oitem->path, nitem->path) > 0)) {
 			int is_ignored;
 			git_delta_t delta_type = GIT_DELTA_ADDED;
 
@@ -418,7 +410,8 @@ static int diff_from_iterators(
 			if (ignore_prefix != NULL &&
 				git__prefixcmp(nitem->path, ignore_prefix) == 0)
 			{
-				error = git_iterator_advance(new, &nitem);
+				if (git_iterator_advance(new, &nitem) < 0)
+					goto fail;
 				continue;
 			}
 
@@ -428,7 +421,8 @@ static int diff_from_iterators(
 				if (git__prefixcmp(oitem->path, nitem->path) == 0) {
 					if (is_ignored)
 						ignore_prefix = nitem->path;
-					error = git_iterator_advance_into_directory(new, &nitem);
+					if (git_iterator_advance_into_directory(new, &nitem) < 0)
+						goto fail;
 					continue;
 				}
 				delta_type = GIT_DELTA_UNTRACKED;
@@ -438,36 +432,35 @@ static int diff_from_iterators(
 			else if (new->type == GIT_ITERATOR_WORKDIR)
 				delta_type = GIT_DELTA_UNTRACKED;
 
-			error = diff_delta__from_one(diff, delta_type, nitem);
-			if (error == GIT_SUCCESS)
-				error = git_iterator_advance(new, &nitem);
-			continue;
+			if (diff_delta__from_one(diff, delta_type, nitem) < 0 ||
+				git_iterator_advance(new, &nitem) < 0)
+				goto fail;
 		}
 
 		/* otherwise item paths match, so create MODIFIED record
 		 * (or ADDED and DELETED pair if type changed)
 		 */
-		assert(oitem && nitem && strcmp(oitem->path, nitem->path) == 0);
+		else {
+			assert(oitem && nitem && strcmp(oitem->path, nitem->path) == 0);
 
-		error = maybe_modified(old, oitem, new, nitem, diff);
-		if (error == GIT_SUCCESS)
-			error = git_iterator_advance(old, &oitem);
-		if (error == GIT_SUCCESS)
-			error = git_iterator_advance(new, &nitem);
+			if (maybe_modified(old, oitem, new, nitem, diff) < 0 ||
+				git_iterator_advance(old, &oitem) < 0 ||
+				git_iterator_advance(new, &nitem) < 0)
+				goto fail;
+		}
 	}
 
-cleanup:
 	git_iterator_free(old);
 	git_iterator_free(new);
-
-	if (error != GIT_SUCCESS) {
-		git_diff_list_free(diff);
-		diff = NULL;
-	}
-
 	*diff_ptr = diff;
+	return 0;
 
-	return error;
+fail:
+	git_iterator_free(old);
+	git_iterator_free(new);
+	git_diff_list_free(diff);
+	*diff_ptr = NULL;
+	return -1;
 }
 
 
@@ -478,14 +471,13 @@ int git_diff_tree_to_tree(
 	git_tree *new,
 	git_diff_list **diff)
 {
-	int error;
 	git_iterator *a = NULL, *b = NULL;
 
 	assert(repo && old && new && diff);
 
-	if ((error = git_iterator_for_tree(repo, old, &a)) < GIT_SUCCESS ||
-		(error = git_iterator_for_tree(repo, new, &b)) < GIT_SUCCESS)
-		return error;
+	if (git_iterator_for_tree(repo, old, &a) < 0 ||
+		git_iterator_for_tree(repo, new, &b) < 0)
+		return -1;
 
 	return diff_from_iterators(repo, opts, a, b, diff);
 }
@@ -496,14 +488,13 @@ int git_diff_index_to_tree(
 	git_tree *old,
 	git_diff_list **diff)
 {
-	int error;
 	git_iterator *a = NULL, *b = NULL;
 
 	assert(repo && old && diff);
 
-	if ((error = git_iterator_for_tree(repo, old, &a)) < GIT_SUCCESS ||
-		(error = git_iterator_for_index(repo, &b)) < GIT_SUCCESS)
-		return error;
+	if (git_iterator_for_tree(repo, old, &a) < 0 ||
+		git_iterator_for_index(repo, &b) < 0)
+		return -1;
 
 	return diff_from_iterators(repo, opts, a, b, diff);
 }
@@ -513,14 +504,13 @@ int git_diff_workdir_to_index(
 	const git_diff_options *opts,
 	git_diff_list **diff)
 {
-	int error;
 	git_iterator *a = NULL, *b = NULL;
 
 	assert(repo && diff);
 
-	if ((error = git_iterator_for_index(repo, &a)) < GIT_SUCCESS ||
-		(error = git_iterator_for_workdir(repo, &b)) < GIT_SUCCESS)
-		return error;
+	if (git_iterator_for_index(repo, &a) < 0 ||
+		git_iterator_for_workdir(repo, &b) < 0)
+		return -1;
 
 	return diff_from_iterators(repo, opts, a, b, diff);
 }
@@ -532,14 +522,13 @@ int git_diff_workdir_to_tree(
 	git_tree *old,
 	git_diff_list **diff)
 {
-	int error;
 	git_iterator *a = NULL, *b = NULL;
 
 	assert(repo && old && diff);
 
-	if ((error = git_iterator_for_tree(repo, old, &a)) < GIT_SUCCESS ||
-		(error = git_iterator_for_workdir(repo, &b)) < GIT_SUCCESS)
-		return error;
+	if (git_iterator_for_tree(repo, old, &a) < 0 ||
+		git_iterator_for_workdir(repo, &b) < 0)
+		return -1;
 
 	return diff_from_iterators(repo, opts, a, b, diff);
 }
@@ -548,16 +537,15 @@ int git_diff_merge(
 	git_diff_list *onto,
 	const git_diff_list *from)
 {
-	int error;
+	int error = 0;
 	unsigned int i = 0, j = 0;
 	git_vector onto_new;
 	git_diff_delta *delta;
 
-	error = git_vector_init(&onto_new, onto->deltas.length, diff_delta__cmp);
-	if (error < GIT_SUCCESS)
-		return error;
+	if (git_vector_init(&onto_new, onto->deltas.length, diff_delta__cmp) < 0)
+		return -1;
 
-	while (i < onto->deltas.length || j < from->deltas.length) {
+	while (!error && (i < onto->deltas.length || j < from->deltas.length)) {
 		git_diff_delta       *o = git_vector_get(&onto->deltas, i);
 		const git_diff_delta *f = git_vector_get_const(&from->deltas, j);
 		const char *opath = !o ? NULL : o->old.path ? o->old.path : o->new.path;
@@ -575,16 +563,10 @@ int git_diff_merge(
 			j++;
 		}
 
-		if (!delta)
-			error = GIT_ENOMEM;
-		else
-			error = git_vector_insert(&onto_new, delta);
-
-		if (error != GIT_SUCCESS)
-			break;
+		error = !delta ? -1 : git_vector_insert(&onto_new, delta);
 	}
 
-	if (error == GIT_SUCCESS) {
+	if (error == 0) {
 		git_vector_swap(&onto->deltas, &onto_new);
 		onto->new_src = from->new_src;
 	}
diff --git a/src/diff_output.c b/src/diff_output.c
index 9c34dcf71..638cabca5 100644
--- a/src/diff_output.c
+++ b/src/diff_output.c
@@ -34,31 +34,39 @@ static int read_next_int(const char **str, int *value)
 		v = (v * 10) + (*scan - '0');
 	*str = scan;
 	*value = v;
-	return (digits > 0) ? GIT_SUCCESS : GIT_ENOTFOUND;
+	return (digits > 0) ? 0 : -1;
 }
 
 static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 {
-	int err = GIT_SUCCESS;
 	diff_output_info *info = priv;
 
 	if (len == 1 && info->hunk_cb) {
 		git_diff_range range = { -1, 0, -1, 0 };
+		const char *scan = bufs[0].ptr;
 
 		/* expect something of the form "@@ -%d[,%d] +%d[,%d] @@" */
-		if (bufs[0].ptr[0] == '@') {
-			const char *scan = bufs[0].ptr;
-			if (!(err = read_next_int(&scan, &range.old_start)) && *scan == ',')
-				err = read_next_int(&scan, &range.old_lines);
-			if (!err &&
-				!(err = read_next_int(&scan, &range.new_start)) && *scan == ',')
-				err = read_next_int(&scan, &range.new_lines);
-			if (!err && range.old_start >= 0 && range.new_start >= 0)
-				err = info->hunk_cb(
-					info->cb_data, info->delta, &range, bufs[0].ptr, bufs[0].size);
-		}
+		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;
+
+		return info->hunk_cb(
+			info->cb_data, info->delta, &range, bufs[0].ptr, bufs[0].size);
 	}
-	else if ((len == 2 || len == 3) && info->line_cb) {
+
+	if ((len == 2 || len == 3) && info->line_cb) {
 		int origin;
 
 		/* expect " "/"-"/"+", then data, then maybe newline */
@@ -67,41 +75,43 @@ static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 			(*bufs[0].ptr == '-') ? GIT_DIFF_LINE_DELETION :
 			GIT_DIFF_LINE_CONTEXT;
 
-		err = info->line_cb(
-			info->cb_data, info->delta, origin, bufs[1].ptr, bufs[1].size);
+		if (info->line_cb(
+			info->cb_data, info->delta, origin, bufs[1].ptr, bufs[1].size) < 0)
+			return -1;
 
 		/* deal with adding and removing newline at EOF */
-		if (err == GIT_SUCCESS && len == 3) {
+		if (len == 3) {
 			if (origin == GIT_DIFF_LINE_ADDITION)
 				origin = GIT_DIFF_LINE_ADD_EOFNL;
 			else
 				origin = GIT_DIFF_LINE_DEL_EOFNL;
 
-			err = info->line_cb(
+			return info->line_cb(
 				info->cb_data, info->delta, origin, bufs[2].ptr, bufs[2].size);
 		}
 	}
 
-	return err;
+	return 0;
 }
 
 #define BINARY_DIFF_FLAGS (GIT_DIFF_FILE_BINARY|GIT_DIFF_FILE_NOT_BINARY)
 
-static int set_file_is_binary_by_attr(git_repository *repo, git_diff_file *file)
+static int update_file_is_binary_by_attr(git_repository *repo, git_diff_file *file)
 {
 	const char *value;
-	int error = git_attr_get(repo, file->path, "diff", &value);
-	if (error != GIT_SUCCESS)
-		return error;
+	if (git_attr_get(repo, file->path, "diff", &value) < 0)
+		return -1;
+
 	if (GIT_ATTR_FALSE(value))
 		file->flags |= GIT_DIFF_FILE_BINARY;
 	else if (GIT_ATTR_TRUE(value))
 		file->flags |= GIT_DIFF_FILE_NOT_BINARY;
 	/* otherwise leave file->flags alone */
-	return error;
+
+	return 0;
 }
 
-static void set_delta_is_binary(git_diff_delta *delta)
+static void update_delta_is_binary(git_diff_delta *delta)
 {
 	if ((delta->old.flags & GIT_DIFF_FILE_BINARY) != 0 ||
 		(delta->new.flags & GIT_DIFF_FILE_BINARY) != 0)
@@ -116,7 +126,7 @@ static int file_is_binary_by_attr(
 	git_diff_list *diff,
 	git_diff_delta *delta)
 {
-	int error, mirror_new;
+	int error = 0, mirror_new;
 
 	delta->binary = -1;
 
@@ -127,7 +137,7 @@ static int file_is_binary_by_attr(
 		delta->old.flags |= GIT_DIFF_FILE_BINARY;
 		delta->new.flags |= GIT_DIFF_FILE_BINARY;
 		delta->binary = 1;
-		return GIT_SUCCESS;
+		return 0;
 	}
 
 	/* check if user is forcing us to text diff these files */
@@ -135,22 +145,21 @@ static int file_is_binary_by_attr(
 		delta->old.flags |= GIT_DIFF_FILE_NOT_BINARY;
 		delta->new.flags |= GIT_DIFF_FILE_NOT_BINARY;
 		delta->binary = 0;
-		return GIT_SUCCESS;
+		return 0;
 	}
 
 	/* check diff attribute +, -, or 0 */
-	error = set_file_is_binary_by_attr(diff->repo, &delta->old);
-	if (error != GIT_SUCCESS)
-		return error;
+	if (update_file_is_binary_by_attr(diff->repo, &delta->old) < 0)
+		return -1;
 
 	mirror_new = (delta->new.path == delta->old.path ||
 				  strcmp(delta->new.path, delta->old.path) == 0);
 	if (mirror_new)
 		delta->new.flags &= (delta->old.flags & BINARY_DIFF_FLAGS);
 	else
-		error = set_file_is_binary_by_attr(diff->repo, &delta->new);
+		error = update_file_is_binary_by_attr(diff->repo, &delta->new);
 
-	set_delta_is_binary(delta);
+	update_delta_is_binary(delta);
 
 	return error;
 }
@@ -179,11 +188,11 @@ static int file_is_binary_by_content(
 			delta->new.flags |= GIT_DIFF_FILE_NOT_BINARY;
 	}
 
-	set_delta_is_binary(delta);
+	update_delta_is_binary(delta);
 
 	/* TODO: if value != NULL, implement diff drivers */
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static void setup_xdiff_options(
@@ -214,17 +223,15 @@ static int get_blob_content(
 	git_map *map,
 	git_blob **blob)
 {
-	int error;
-
 	if (git_oid_iszero(oid))
-		return GIT_SUCCESS;
+		return 0;
 
-	if ((error = git_blob_lookup(blob, repo, oid)) == GIT_SUCCESS) {
-		map->data = (void *)git_blob_rawcontent(*blob);
-		map->len  = git_blob_rawsize(*blob);
-	}
+	if (git_blob_lookup(blob, repo, oid) < 0)
+		return -1;
 
-	return error;
+	map->data = (void *)git_blob_rawcontent(*blob);
+	map->len  = git_blob_rawsize(*blob);
+	return 0;
 }
 
 static int get_workdir_content(
@@ -232,35 +239,33 @@ static int get_workdir_content(
 	git_diff_file *file,
 	git_map *map)
 {
-	git_buf full_path = GIT_BUF_INIT;
-	int error = git_buf_joinpath(
-		&full_path, git_repository_workdir(repo), file->path);
-	if (error != GIT_SUCCESS)
-		return error;
+	int error = 0;
+	git_buf path = GIT_BUF_INIT;
+
+	if (git_buf_joinpath(&path, git_repository_workdir(repo), file->path) < 0)
+		return -1;
 
 	if (S_ISLNK(file->mode)) {
+		ssize_t read_len;
+
 		file->flags |= GIT_DIFF_FILE_FREE_DATA;
 		file->flags |= GIT_DIFF_FILE_BINARY;
 
 		map->data = git__malloc((size_t)file->size + 1);
-		if (map->data == NULL)
-			error = GIT_ENOMEM;
-		else {
-			ssize_t read_len =
-				p_readlink(full_path.ptr, map->data, (size_t)file->size + 1);
-			if (read_len != (ssize_t)file->size)
-				error = git__throw(
-					GIT_EOSERR, "Failed to read symlink %s", file->path);
-			else
-				map->len = read_len;
-
-		}
+		GITERR_CHECK_ALLOC(map->data);
+
+		read_len = p_readlink(path.ptr, map->data, (size_t)file->size + 1);
+		if (read_len != (ssize_t)file->size) {
+			giterr_set(GITERR_OS, "Failed to read symlink '%s'", file->path);
+			error = -1;
+		} else
+			map->len = read_len;
 	}
 	else {
-		error = git_futils_mmap_ro_file(map, full_path.ptr);
+		error = git_futils_mmap_ro_file(map, path.ptr);
 		file->flags |= GIT_DIFF_FILE_UNMAP_DATA;
 	}
-	git_buf_free(&full_path);
+	git_buf_free(&path);
 	return error;
 }
 
@@ -288,7 +293,7 @@ int git_diff_foreach(
 	git_diff_hunk_fn hunk_cb,
 	git_diff_line_fn line_cb)
 {
-	int error = GIT_SUCCESS;
+	int error = 0;
 	diff_output_info info;
 	git_diff_delta *delta;
 	xpparam_t    xdiff_params;
@@ -320,8 +325,7 @@ int git_diff_foreach(
 			(diff->opts.flags & GIT_DIFF_INCLUDE_UNTRACKED) == 0)
 			continue;
 
-		error = file_is_binary_by_attr(diff, delta);
-		if (error < GIT_SUCCESS)
+		if ((error = file_is_binary_by_attr(diff, delta)) < 0)
 			goto cleanup;
 
 		old_data.data = "";
@@ -345,7 +349,7 @@ int git_diff_foreach(
 			else
 				error = get_blob_content(
 					diff->repo, &delta->old.oid, &old_data, &old_blob);
-			if (error != GIT_SUCCESS)
+			if (error < 0)
 				goto cleanup;
 		}
 
@@ -359,13 +363,13 @@ int git_diff_foreach(
 			else
 				error = get_blob_content(
 					diff->repo, &delta->new.oid, &new_data, &new_blob);
-			if (error != GIT_SUCCESS)
+			if (error < 0)
 				goto cleanup;
 
 			if ((delta->new.flags | GIT_DIFF_FILE_VALID_OID) == 0) {
 				error = git_odb_hash(
 					&delta->new.oid, new_data.data, new_data.len, GIT_OBJ_BLOB);
-				if (error != GIT_SUCCESS)
+				if (error < 0)
 					goto cleanup;
 
 				/* since we did not have the definitive oid, we may have
@@ -384,7 +388,7 @@ int git_diff_foreach(
 		if (delta->binary == -1) {
 			error = file_is_binary_by_content(
 				diff, delta, &old_data, &new_data);
-			if (error < GIT_SUCCESS)
+			if (error < 0)
 				goto cleanup;
 		}
 
@@ -394,7 +398,7 @@ int git_diff_foreach(
 
 		if (file_cb != NULL) {
 			error = file_cb(data, delta, (float)info.index / diff->deltas.length);
-			if (error != GIT_SUCCESS)
+			if (error < 0)
 				goto cleanup;
 		}
 
@@ -417,7 +421,7 @@ cleanup:
 		release_content(&delta->old, &old_data, old_blob);
 		release_content(&delta->new, &new_data, new_blob);
 
-		if (error != GIT_SUCCESS)
+		if (error < 0)
 			break;
 	}
 
@@ -462,7 +466,7 @@ static int print_compact(void *data, git_diff_delta *delta, float progress)
 	}
 
 	if (!code)
-		return GIT_SUCCESS;
+		return 0;
 
 	old_suffix = pick_suffix(delta->old.mode);
 	new_suffix = pick_suffix(delta->new.mode);
@@ -482,8 +486,8 @@ static int print_compact(void *data, git_diff_delta *delta, float progress)
 	else
 		git_buf_printf(pi->buf, "%c\t%s\n", code, delta->old.path);
 
-	if (git_buf_oom(pi->buf) == true)
-		return GIT_ENOMEM;
+	if (git_buf_oom(pi->buf))
+		return -1;
 
 	return pi->print_cb(pi->cb_data, GIT_DIFF_LINE_FILE_HDR, pi->buf->ptr);
 }
@@ -535,14 +539,13 @@ static int print_oid_range(diff_print_info *pi, git_diff_delta *delta)
 	}
 
 	if (git_buf_oom(pi->buf))
-		return GIT_ENOMEM;
+		return -1;
 
 	return 0;
 }
 
 static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 {
-	int error;
 	diff_print_info *pi = data;
 	const char *oldpfx = pi->diff->opts.src_prefix;
 	const char *oldpath = delta->old.path;
@@ -553,8 +556,9 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 
 	git_buf_clear(pi->buf);
 	git_buf_printf(pi->buf, "diff --git %s%s %s%s\n", oldpfx, delta->old.path, newpfx, delta->new.path);
-	if ((error = print_oid_range(pi, delta)) < GIT_SUCCESS)
-		return error;
+
+	if (print_oid_range(pi, delta) < 0)
+		return -1;
 
 	if (git_oid_iszero(&delta->old.oid)) {
 		oldpfx = "";
@@ -571,18 +575,18 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	}
 
 	if (git_buf_oom(pi->buf))
-		return GIT_ENOMEM;
+		return -1;
 
-	error = pi->print_cb(pi->cb_data, GIT_DIFF_LINE_FILE_HDR, pi->buf->ptr);
-	if (error != GIT_SUCCESS || delta->binary != 1)
-		return error;
+	if (pi->print_cb(pi->cb_data, GIT_DIFF_LINE_FILE_HDR, pi->buf->ptr) < 0 ||
+		delta->binary != 1)
+		return -1;
 
 	git_buf_clear(pi->buf);
 	git_buf_printf(
 		pi->buf, "Binary files %s%s and %s%s differ\n",
 		oldpfx, oldpath, newpfx, newpath);
 	if (git_buf_oom(pi->buf))
-		return GIT_ENOMEM;
+		return -1;
 
 	return pi->print_cb(pi->cb_data, GIT_DIFF_LINE_BINARY, pi->buf->ptr);
 }
@@ -600,11 +604,10 @@ static int print_patch_hunk(
 	GIT_UNUSED(r);
 
 	git_buf_clear(pi->buf);
+	if (git_buf_printf(pi->buf, "%.*s", (int)header_len, header) < 0)
+		return -1;
 
-	if (git_buf_printf(pi->buf, "%.*s", (int)header_len, header) == GIT_SUCCESS)
-		return pi->print_cb(pi->cb_data, GIT_DIFF_LINE_HUNK_HDR, pi->buf->ptr);
-	else
-		return GIT_ENOMEM;
+	return pi->print_cb(pi->cb_data, GIT_DIFF_LINE_HUNK_HDR, pi->buf->ptr);
 }
 
 static int print_patch_line(
@@ -628,7 +631,7 @@ static int print_patch_line(
 		git_buf_printf(pi->buf, "%.*s", (int)content_len, content);
 
 	if (git_buf_oom(pi->buf))
-		return GIT_ENOMEM;
+		return -1;
 
 	return pi->print_cb(pi->cb_data, line_origin, pi->buf->ptr);
 }
@@ -721,5 +724,5 @@ int git_diff_blobs(
 
 	xdl_diff(&old, &new, &xdiff_params, &xdiff_config, &xdiff_callback);
 
-	return GIT_SUCCESS;
+	return 0;
 }
diff --git a/src/errors.c b/src/errors.c
index 548e44a32..c25fa7519 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -123,6 +123,8 @@ void giterr_set(int error_class, const char *string, ...)
 	char error_str[1024];
 	va_list arglist;
 	git_error *error;
+	const char *oserr =
+		(error_class == GITERR_OS && errno != 0) ? strerror(errno) : NULL;
 
 	error = &GIT_GLOBAL->error_t;
 	free(error->message);
@@ -131,6 +133,13 @@ void giterr_set(int error_class, const char *string, ...)
 	p_vsnprintf(error_str, sizeof(error_str), string, arglist);
 	va_end(arglist);
 
+	/* automatically suffix strerror(errno) for GITERR_OS errors */
+	if (oserr != NULL) {
+		strncat(error_str, ": ", sizeof(error_str));
+		strncat(error_str, oserr, sizeof(error_str));
+		errno = 0;
+	}
+
 	error->message = git__strdup(error_str);
 	error->klass = error_class;
 
diff --git a/src/filebuf.c b/src/filebuf.c
index e6e68014a..8297b4fcf 100644
--- a/src/filebuf.c
+++ b/src/filebuf.c
@@ -45,8 +45,8 @@ static int lock_file(git_filebuf *file, int flags)
 		source = p_open(file->path_original, O_RDONLY);
 		if (source < 0) {
 			giterr_set(GITERR_OS,
-				"Failed to open file '%s' for reading: %s",
-				file->path_original, strerror(errno));
+				"Failed to open file '%s' for reading",
+				file->path_original);
 			return -1;
 		}
 
diff --git a/src/fileops.c b/src/fileops.c
index c6a3be73d..c9fd2c5bc 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -37,7 +37,7 @@ int git_futils_mktmp(git_buf *path_out, const char *filename)
 
 	if ((fd = p_mkstemp(path_out->ptr)) < 0) {
 		giterr_set(GITERR_OS,
-			"Failed to create temporary file '%s': %s", path_out->ptr, strerror(errno));
+			"Failed to create temporary file '%s'", path_out->ptr);
 		return -1;
 	}
 
@@ -53,8 +53,7 @@ int git_futils_creat_withpath(const char *path, const mode_t dirmode, const mode
 
 	fd = p_creat(path, mode);
 	if (fd < 0) {
-		giterr_set(GITERR_OS,
-			"Failed to create file '%s': %s", path, strerror(errno));
+		giterr_set(GITERR_OS, "Failed to create file '%s'", path);
 		return -1;
 	}
 
@@ -65,8 +64,7 @@ int git_futils_creat_locked(const char *path, const mode_t mode)
 {
 	int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_EXCL, mode);
 	if (fd < 0) {
-		giterr_set(GITERR_OS,
-			"Failed to create locked file '%s': %s", path, strerror(errno));
+		giterr_set(GITERR_OS, "Failed to create locked file '%s'", path);
 		return -1;
 	}
 
@@ -115,10 +113,8 @@ int git_futils_readbuffer_updated(git_buf *buf, const char *path, time_t *mtime,
 	if (updated != NULL)
 		*updated = 0;
 
-	if ((fd = p_open(path, O_RDONLY)) < 0) {
-		giterr_set(GITERR_OS, "Failed to read file '%s': %s", path, strerror(errno));
-		return (errno == ENOENT) ? GIT_ENOTFOUND : -1;
-	}
+	if ((fd = git_futils_open_ro(path)) < 0)
+		return fd;
 
 	if (p_fstat(fd, &st) < 0 || S_ISDIR(st.st_mode) || !git__is_sizet(st.st_size+1)) {
 		close(fd);
@@ -154,8 +150,7 @@ int git_futils_readbuffer_updated(git_buf *buf, const char *path, time_t *mtime,
 
 		if (read_size < 0) {
 			close(fd);
-			giterr_set(GITERR_OS, "Failed to read descriptor for %s: %s",
-				path, strerror(errno));
+			giterr_set(GITERR_OS, "Failed to read descriptor for '%s'", path);
 			return -1;
 		}
 
diff --git a/src/fileops.h b/src/fileops.h
index ab57b6f38..c2ba8ffc8 100644
--- a/src/fileops.h
+++ b/src/fileops.h
@@ -77,6 +77,20 @@ extern int git_futils_mktmp(git_buf *path_out, const char *filename);
 extern int git_futils_mv_withpath(const char *from, const char *to, const mode_t dirmode);
 
 /**
+ * Open a file readonly and set error if needed
+ */
+GIT_INLINE(int) git_futils_open_ro(const char *path)
+{
+	int fd = p_open(path, O_RDONLY);
+	if (fd < 0) {
+		if (errno == ENOENT)
+			fd = GIT_ENOTFOUND;
+		giterr_set(GITERR_OS, "Failed to open '%s'", path);
+	}
+	return fd;
+}
+
+/**
  * Get the filesize in bytes of a file
  */
 extern git_off_t git_futils_filesize(git_file fd);
diff --git a/src/index.c b/src/index.c
index b646dfcbb..d5410a3a7 100644
--- a/src/index.c
+++ b/src/index.c
@@ -544,7 +544,7 @@ const git_index_entry_unmerged *git_index_get_unmerged_bypath(git_index *index,
 	if (!index->unmerged.length)
 		return NULL;
 
-	if ((pos = git_vector_bsearch2(&index->unmerged, unmerged_srch, path)) < GIT_SUCCESS)
+	if ((pos = git_vector_bsearch2(&index->unmerged, unmerged_srch, path)) < 0)
 		return NULL;
 
 	return git_vector_get(&index->unmerged, pos);
diff --git a/src/odb.c b/src/odb.c
index 53e07519d..edb9c72a0 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -32,10 +32,7 @@ static int format_object_header(char *hdr, size_t n, size_t obj_len, git_otype o
 {
 	const char *type_str = git_object_type2string(obj_type);
 	int len = p_snprintf(hdr, n, "%s %"PRIuZ, type_str, obj_len);
-
-	if (len < 0 || len >= (int)n)
-		return git__throw(GIT_ERROR, "Cannot format object header. Length is out of bounds");
-
+	assert(len > 0 && len <= (int)n);
 	return len+1;
 }
 
@@ -48,13 +45,11 @@ int git_odb__hashobj(git_oid *id, git_rawobj *obj)
 	assert(id && obj);
 
 	if (!git_object_typeisloose(obj->type))
-		return git__throw(GIT_ERROR, "Failed to hash object. Wrong object type");
-
+		return -1;
 	if (!obj->data && obj->len != 0)
-		return git__throw(GIT_ERROR, "Failed to hash object. No data given");
+		return -1;
 
-	if ((hdrlen = format_object_header(header, sizeof(header), obj->len, obj->type)) < 0)
-		return git__rethrow(hdrlen, "Failed to hash object");
+	hdrlen = format_object_header(header, sizeof(header), obj->len, obj->type);
 
 	vec[0].data = header;
 	vec[0].len = hdrlen;
@@ -63,7 +58,7 @@ int git_odb__hashobj(git_oid *id, git_rawobj *obj)
 
 	git_hash_vec(id, vec, 2);
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 
@@ -120,8 +115,6 @@ int git_odb__hashfd(git_oid *out, git_file fd, size_t size, git_otype type)
 	git_hash_ctx *ctx;
 
 	hdr_len = format_object_header(hdr, sizeof(hdr), size, type);
-	if (hdr_len < 0)
-		return git__throw(GIT_ERROR, "Failed to format blob header. Length is out of bounds");
 
 	ctx = git_hash_new_ctx();
 
@@ -132,7 +125,8 @@ int git_odb__hashfd(git_oid *out, git_file fd, size_t size, git_otype type)
 
 		if (read_len < 0) {
 			git_hash_free_ctx(ctx);
-			return git__throw(GIT_EOSERR, "Error when reading file: %s", strerror(errno));
+			giterr_set(GITERR_OS, "Error reading file");
+			return -1;
 		}
 
 		git_hash_update(ctx, buffer, read_len);
@@ -142,69 +136,69 @@ int git_odb__hashfd(git_oid *out, git_file fd, size_t size, git_otype type)
 	git_hash_final(out, ctx);
 	git_hash_free_ctx(ctx);
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int git_odb__hashlink(git_oid *out, const char *path)
 {
 	struct stat st;
-	int error;
 	git_off_t size;
+	int result;
 
-	error = p_lstat(path, &st);
-	if (error < 0)
-		return git__throw(GIT_EOSERR, "Failed to stat blob. %s", strerror(errno));
+	if (p_lstat(path, &st) < 0) {
+		giterr_set(GITERR_OS, "Failed to stat object '%s'", path);
+		return -1;
+	}
 
 	size = st.st_size;
 
-	if (!git__is_sizet(size))
-		return git__throw(GIT_EOSERR, "File size overflow for 32-bit systems");
+	if (!git__is_sizet(size)) {
+		giterr_set(GITERR_OS, "File size overflow for 32-bit systems");
+		return -1;
+	}
 
 	if (S_ISLNK(st.st_mode)) {
 		char *link_data;
 		ssize_t read_len;
 
 		link_data = git__malloc((size_t)size);
-		if (link_data == NULL)
-			return GIT_ENOMEM;
+		GITERR_CHECK_ALLOC(link_data);
 
 		read_len = p_readlink(path, link_data, (size_t)(size + 1));
-		if (read_len != (ssize_t)size)
-			return git__throw(GIT_EOSERR, "Failed to read symlink data");
+		if (read_len != (ssize_t)size) {
+			giterr_set(GITERR_OS, "Failed to read symlink data for '%s'", path);
+			return -1;
+		}
 
-		error = git_odb_hash(out, link_data, (size_t)size, GIT_OBJ_BLOB);
+		result = git_odb_hash(out, link_data, (size_t)size, GIT_OBJ_BLOB);
 		free(link_data);
 	} else { 
-		int fd;
-
-		if ((fd = p_open(path, O_RDONLY)) < 0)
-			return git__throw(GIT_ENOTFOUND, "Could not open '%s'", path);
-
-		error = git_odb__hashfd(out, fd, (size_t)size, GIT_OBJ_BLOB);
+		int fd = git_futils_open_ro(path);
+		if (fd < 0)
+			return -1;
+		result = git_odb__hashfd(out, fd, (size_t)size, GIT_OBJ_BLOB);
 		p_close(fd);
 	}
 
-	return error;
+	return result;
 }
 
 int git_odb_hashfile(git_oid *out, const char *path, git_otype type)
 {
-	int fd, error;
 	git_off_t size;
-
-	if ((fd = p_open(path, O_RDONLY)) < 0)
-		return git__throw(GIT_ENOTFOUND, "Could not open '%s'", path);
+	int result, fd = git_futils_open_ro(path);
+	if (fd < 0)
+		return -1;
 
 	if ((size = git_futils_filesize(fd)) < 0 || !git__is_sizet(size)) {
+		giterr_set(GITERR_OS, "File size overflow for 32-bit systems");
 		p_close(fd);
-		return git__throw(GIT_EOSERR,
-			"File size overflow. The object is too big to fit in 32-bit mode");
+		return -1;
 	}
 
-	error = git_odb__hashfd(out, fd, (size_t)size, type);
-
+	result = git_odb__hashfd(out, fd, (size_t)size, type);
 	p_close(fd);
-	return error;
+	return result;
 }
 
 int git_odb_hash(git_oid *id, const void *data, size_t len, git_otype type)
@@ -242,11 +236,11 @@ static int fake_wstream__write(git_odb_stream *_stream, const char *data, size_t
 	fake_wstream *stream = (fake_wstream *)_stream;
 
 	if (stream->written + len > stream->size)
-		return GIT_ENOMEM;
+		return -1;
 
 	memcpy(stream->buffer + stream->written, data, len);
 	stream->written += len;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static void fake_wstream__free(git_odb_stream *_stream)
@@ -262,15 +256,14 @@ static int init_fake_wstream(git_odb_stream **stream_p, git_odb_backend *backend
 	fake_wstream *stream;
 
 	stream = git__calloc(1, sizeof(fake_wstream));
-	if (stream == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(stream);
 
 	stream->size = size;
 	stream->type = type;
 	stream->buffer = git__malloc(size);
 	if (stream->buffer == NULL) {
 		git__free(stream);
-		return GIT_ENOMEM;
+		return -1;
 	}
 
 	stream->stream.backend = backend;
@@ -281,7 +274,7 @@ static int init_fake_wstream(git_odb_stream **stream_p, git_odb_backend *backend
 	stream->stream.mode = GIT_STREAM_WRONLY;
 
 	*stream_p = (git_odb_stream *)stream;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 /***********************************************************
@@ -305,26 +298,19 @@ static int backend_sort_cmp(const void *a, const void *b)
 
 int git_odb_new(git_odb **out)
 {
-	int error;
-
 	git_odb *db = git__calloc(1, sizeof(*db));
-	if (!db)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(db);
 
-	error = git_cache_init(&db->cache, GIT_DEFAULT_CACHE_SIZE, &free_odb_object);
-	if (error < GIT_SUCCESS) {
+	if (git_cache_init(&db->cache, GIT_DEFAULT_CACHE_SIZE, &free_odb_object) < 0 ||
+		git_vector_init(&db->backends, 4, backend_sort_cmp) < 0)
+	{
 		git__free(db);
-		return git__rethrow(error, "Failed to create object database");
-	}
-
-	if ((error = git_vector_init(&db->backends, 4, backend_sort_cmp)) < GIT_SUCCESS) {
-		git__free(db);
-		return git__rethrow(error, "Failed to create object database");
+		return -1;
 	}
 
 	*out = db;
 	GIT_REFCOUNT_INC(db);
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int add_backend_internal(git_odb *odb, git_odb_backend *backend, int priority, int is_alternate)
@@ -333,12 +319,11 @@ static int add_backend_internal(git_odb *odb, git_odb_backend *backend, int prio
 
 	assert(odb && backend);
 
-	if (backend->odb != NULL && backend->odb != odb)
-		return git__throw(GIT_EBUSY, "The backend is already owned by another ODB");
+	/* Check if the backend is already owned by another ODB */
+	assert(!backend->odb || backend->odb == odb);
 
 	internal = git__malloc(sizeof(backend_internal));
-	if (internal == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(internal);
 
 	internal->backend = backend;
 	internal->priority = priority;
@@ -346,12 +331,12 @@ static int add_backend_internal(git_odb *odb, git_odb_backend *backend, int prio
 
 	if (git_vector_insert(&odb->backends, internal) < 0) {
 		git__free(internal);
-		return GIT_ENOMEM;
+		return -1;
 	}
 
 	git_vector_sort(&odb->backends);
 	internal->backend->odb = odb;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int git_odb_add_backend(git_odb *odb, git_odb_backend *backend, int priority)
@@ -367,27 +352,18 @@ int git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority)
 static int add_default_backends(git_odb *db, const char *objects_dir, int as_alternates)
 {
 	git_odb_backend *loose, *packed;
-	int error;
 
 	/* add the loose object backend */
-	error = git_odb_backend_loose(&loose, objects_dir, -1, 0);
-	if (error < GIT_SUCCESS)
-		return error;
-
-	error = add_backend_internal(db, loose, GIT_LOOSE_PRIORITY, as_alternates);
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to add backend");
+	if (git_odb_backend_loose(&loose, objects_dir, -1, 0) < 0 ||
+		add_backend_internal(db, loose, GIT_LOOSE_PRIORITY, as_alternates) < 0)
+		return -1;
 
 	/* add the packed file backend */
-	error = git_odb_backend_pack(&packed, objects_dir);
-	if (error < GIT_SUCCESS)
-		return error;
-
-	error = add_backend_internal(db, packed, GIT_PACKED_PRIORITY, as_alternates);
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to add backend");
+	if (git_odb_backend_pack(&packed, objects_dir) < 0 ||
+		add_backend_internal(db, packed, GIT_PACKED_PRIORITY, as_alternates) < 0)
+		return -1;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int load_alternates(git_odb *odb, const char *objects_dir)
@@ -396,24 +372,22 @@ static int load_alternates(git_odb *odb, const char *objects_dir)
 	git_buf alternates_buf = GIT_BUF_INIT;
 	char *buffer;
 	const char *alternate;
-	int error;
+	int result = 0;
 
-	error = git_buf_joinpath(&alternates_path, objects_dir, GIT_ALTERNATES_FILE);
-	if (error < GIT_SUCCESS)
-		return error;
+	if (git_buf_joinpath(&alternates_path, objects_dir, GIT_ALTERNATES_FILE) < 0)
+		return -1;
 
 	if (git_path_exists(alternates_path.ptr) == false) {
 		git_buf_free(&alternates_path);
-		return GIT_SUCCESS;
+		return 0;
 	}
 
-	if (git_futils_readbuffer(&alternates_buf, alternates_path.ptr) < GIT_SUCCESS) {
+	if (git_futils_readbuffer(&alternates_buf, alternates_path.ptr) < 0) {
 		git_buf_free(&alternates_path);
-		return git__throw(GIT_EOSERR, "Failed to add backend. Can't read alternates");
+		return -1;
 	}
 
 	buffer = (char *)alternates_buf.ptr;
-	error = GIT_SUCCESS;
 
 	/* add each alternate as a new backend; one alternate per line */
 	while ((alternate = git__strtok(&buffer, "\r\n")) != NULL) {
@@ -422,48 +396,41 @@ static int load_alternates(git_odb *odb, const char *objects_dir)
 
 		/* relative path: build based on the current `objects` folder */
 		if (*alternate == '.') {
-			error = git_buf_joinpath(&alternates_path, objects_dir, alternate);
-			if (error < GIT_SUCCESS)
+			if ((result = git_buf_joinpath(&alternates_path, objects_dir, alternate)) < 0)
 				break;
 			alternate = git_buf_cstr(&alternates_path);
 		}
 
-		if ((error = add_default_backends(odb, alternate, 1)) < GIT_SUCCESS)
+		if ((result = add_default_backends(odb, alternate, 1)) < 0)
 			break;
 	}
 
 	git_buf_free(&alternates_path);
 	git_buf_free(&alternates_buf);
 
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to load alternates");
-	return error;
+	return result;
 }
 
 int git_odb_open(git_odb **out, const char *objects_dir)
 {
 	git_odb *db;
-	int error;
 
 	assert(out && objects_dir);
 
 	*out = NULL;
 
-	if ((error = git_odb_new(&db)) < 0)
-		return git__rethrow(error, "Failed to open ODB");
+	if (git_odb_new(&db) < 0)
+		return -1;
 
-	if ((error = add_default_backends(db, objects_dir, 0)) < GIT_SUCCESS)
-		goto cleanup;
-
-	if ((error = load_alternates(db, objects_dir)) < GIT_SUCCESS)
-		goto cleanup;
+	if (add_default_backends(db, objects_dir, 0) < 0 ||
+		load_alternates(db, objects_dir) < 0)
+	{
+		git_odb_free(db);
+		return -1;
+	}
 
 	*out = db;
-	return GIT_SUCCESS;
-
-cleanup:
-	git_odb_free(db);
-	return error; /* error already set - pass through */
+	return 0;
 }
 
 static void odb_free(git_odb *db)
@@ -497,13 +464,13 @@ int git_odb_exists(git_odb *db, const git_oid *id)
 {
 	git_odb_object *object;
 	unsigned int i;
-	int found = 0;
+	bool found = false;
 
 	assert(db && id);
 
 	if ((object = git_cache_get(&db->cache, id)) != NULL) {
 		git_odb_object_free(object);
-		return 1;
+		return (int)true;
 	}
 
 	for (i = 0; i < db->backends.length && !found; ++i) {
@@ -514,7 +481,7 @@ int git_odb_exists(git_odb *db, const git_oid *id)
 			found = b->exists(b, id);
 	}
 
-	return found;
+	return (int)found;
 }
 
 int git_odb_read_header(size_t *len_p, git_otype *type_p, git_odb *db, const git_oid *id)
@@ -529,7 +496,7 @@ int git_odb_read_header(size_t *len_p, git_otype *type_p, git_odb *db, const git
 		*len_p = object->raw.len;
 		*type_p = object->raw.type;
 		git_odb_object_free(object);
-		return GIT_SUCCESS;
+		return 0;
 	}
 
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
@@ -541,7 +508,7 @@ int git_odb_read_header(size_t *len_p, git_otype *type_p, git_odb *db, const git
 	}
 
 	if (error == GIT_EPASSTHROUGH)
-		return GIT_SUCCESS;
+		return 0;
 
 	/*
 	 * no backend could read only the header.
diff --git a/src/path.c b/src/path.c
index 8d0cf288f..1ff257a98 100644
--- a/src/path.c
+++ b/src/path.c
@@ -499,7 +499,7 @@ int git_path_direach(
 	wd_len = path->size;
 	dir = opendir(path->ptr);
 	if (!dir) {
-		giterr_set(GITERR_OS, "Failed to `opendir` %s: %s", path->ptr, strerror(errno));
+		giterr_set(GITERR_OS, "Failed to 'opendir' %s", path->ptr);
 		return -1;
 	}
 
diff --git a/src/refs.c b/src/refs.c
index 461b50719..e90cf5de1 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -1021,8 +1021,7 @@ static int reference_delete(git_reference *ref)
 		git_buf_free(&full_path); /* done with path at this point */
 
 		if (result < 0) {
-			giterr_set(GITERR_OS,
-				"Failed to unlink '%s': %s", full_path.ptr, strerror(errno));
+			giterr_set(GITERR_OS, "Failed to unlink '%s'", full_path.ptr);
 			return -1;
 		}
 
diff --git a/src/util.c b/src/util.c
index 1fb01170b..d2309124b 100644
--- a/src/util.c
+++ b/src/util.c
@@ -355,23 +355,26 @@ int git__bsearch(
 	int (*compare)(const void *, const void *),
 	size_t *position)
 {
-	int lim, cmp;
+	int lim, cmp = -1;
 	void **part, **base = array;
 
 	for (lim = array_len; lim != 0; lim >>= 1) {
 		part = base + (lim >> 1);
 		cmp = (*compare)(key, *part);
 		if (cmp == 0) {
-			*position = (part - array);
-			return GIT_SUCCESS;
-		} else if (cmp > 0) { /* key > p; take right partition */
+			base = part;
+			break;
+		}
+		if (cmp > 0) { /* key > p; take right partition */
 			base = part + 1;
 			lim--;
 		} /* else take left partition */
 	}
 
-	*position = (base - array);
-	return GIT_ENOTFOUND;
+	if (position)
+		*position = (base - array);
+
+	return (cmp == 0) ? 0 : -1;
 }
 
 /**
diff --git a/src/util.h b/src/util.h
index 803c63d73..01755b59e 100644
--- a/src/util.h
+++ b/src/util.h
@@ -115,6 +115,11 @@ extern int git__fnmatch(const char *pattern, const char *name, int flags);
 
 extern void git__tsort(void **dst, size_t size, int (*cmp)(const void *, const void *));
 
+/**
+ * @param position If non-NULL, this will be set to the position where the
+ * 		element is or would be inserted if not found.
+ * @return pos (>=0) if found or -1 if not found
+ */
 extern int git__bsearch(
 	void **array,
 	size_t array_len,
diff --git a/src/vector.c b/src/vector.c
index 7513ea3f0..d73c2b418 100644
--- a/src/vector.c
+++ b/src/vector.c
@@ -19,10 +19,9 @@ static int resize_vector(git_vector *v)
 		v->_alloc_size = minimum_size;
 
 	v->contents = git__realloc(v->contents, v->_alloc_size * sizeof(void *));
-	if (v->contents == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(v->contents);
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 void git_vector_free(git_vector *v)
@@ -52,30 +51,29 @@ int git_vector_init(git_vector *v, unsigned int initial_size, git_vector_cmp cmp
 	v->sorted = 1;
 
 	v->contents = git__malloc(v->_alloc_size * sizeof(void *));
-	if (v->contents == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(v->contents);
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int git_vector_insert(git_vector *v, void *element)
 {
 	assert(v);
 
-	if (v->length >= v->_alloc_size) {
-		if (resize_vector(v) < 0)
-			return GIT_ENOMEM;
-	}
+	if (v->length >= v->_alloc_size &&
+		resize_vector(v) < 0)
+		return -1;
 
 	v->contents[v->length++] = element;
 	v->sorted = 0;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
-int git_vector_insert_sorted(git_vector *v, void *element, int (*on_dup)(void **old, void *new))
+int git_vector_insert_sorted(
+	git_vector *v, void *element, int (*on_dup)(void **old, void *new))
 {
-	int error = GIT_SUCCESS;
+	int result;
 	size_t pos;
 
 	assert(v && v->_cmp);
@@ -83,22 +81,18 @@ int git_vector_insert_sorted(git_vector *v, void *element, int (*on_dup)(void **
 	if (!v->sorted)
 		git_vector_sort(v);
 
-	if (v->length >= v->_alloc_size) {
-		if (resize_vector(v) < 0)
-			return GIT_ENOMEM;
-	}
-
-	error = git__bsearch(v->contents, v->length, element, v->_cmp, &pos);
+	if (v->length >= v->_alloc_size &&
+		resize_vector(v) < 0)
+		return -1;
 
-	/* If we found the element and have a duplicate handler callback,
-	 * invoke it.  If it returns an error, then cancel insert, otherwise
+	/* If we find the element and have a duplicate handler callback,
+	 * invoke it.  If it returns non-zero, then cancel insert, otherwise
 	 * proceed with normal insert.
 	 */
-	if (error == GIT_SUCCESS && on_dup != NULL) {
-		error = on_dup(&v->contents[pos], element);
-		if (error != GIT_SUCCESS)
-			return error;
-	}
+	if (git__bsearch(v->contents, v->length, element, v->_cmp, &pos) >= 0 &&
+		on_dup != NULL &&
+		(result = on_dup(&v->contents[pos], element)) < 0)
+		return result;
 
 	/* shift elements to the right */
 	if (pos < v->length) {
@@ -108,8 +102,7 @@ int git_vector_insert_sorted(git_vector *v, void *element, int (*on_dup)(void **
 
 	v->contents[pos] = element;
 	v->length++;
-
-	return GIT_SUCCESS;
+	return 0;
 }
 
 void git_vector_sort(git_vector *v)
@@ -130,16 +123,14 @@ int git_vector_bsearch2(git_vector *v, git_vector_cmp key_lookup, const void *ke
 	assert(v && key && key_lookup);
 
 	/* need comparison function to sort the vector */
-	if (v->_cmp == NULL)
-		return git__throw(GIT_ENOTFOUND, "Can't sort vector. No comparison function set");
+	assert(v->_cmp != NULL);
 
 	git_vector_sort(v);
 
-	if (git__bsearch(v->contents, v->length, key, key_lookup,
-			&pos) == GIT_SUCCESS)
+	if (git__bsearch(v->contents, v->length, key, key_lookup, &pos) >= 0)
 		return (int)pos;
 
-	return git__throw(GIT_ENOTFOUND, "Can't find element");
+	return GIT_ENOTFOUND;
 }
 
 int git_vector_search2(git_vector *v, git_vector_cmp key_lookup, const void *key)
@@ -153,7 +144,7 @@ int git_vector_search2(git_vector *v, git_vector_cmp key_lookup, const void *key
 			return i;
 	}
 
-	return git__throw(GIT_ENOTFOUND, "Can't find element");
+	return GIT_ENOTFOUND;
 }
 
 static int strict_comparison(const void *a, const void *b)
@@ -178,13 +169,13 @@ int git_vector_remove(git_vector *v, unsigned int idx)
 	assert(v);
 
 	if (idx >= v->length || v->length == 0)
-		return git__throw(GIT_ENOTFOUND, "Can't remove element. Index out of bounds");
+		return GIT_ENOTFOUND;
 
 	for (i = idx; i < v->length - 1; ++i)
 		v->contents[i] = v->contents[i + 1];
 
 	v->length--;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 void git_vector_pop(git_vector *v)