Move diff max_size to public API

This commit adds a max_size value in the public `git_diff_options`
structure so that the user can automatically flag blobs over a
certain size as binary regardless of other properties.

Also, and perhaps more importantly, this moves binary detection
to be as early as possible in the diff traversal inner loop and
makes sure that we stop loading objects as soon as we decide that
they are binary.

include/git2/diff.h

@@ -56,7 +56,13 @@ enum {
  * values.  Similarly, passing NULL for the options structure will
  * give the defaults.  The default values are marked below.
  *
- * @todo Most of the parameters here are not actually supported at this time.
+ * - flags: a combination of the GIT_DIFF_... values above
+ * - context_lines: number of lines of context to show around diffs
+ * - interhunk_lines: min lines between diff hunks to merge them
+ * - old_prefix: "directory" to prefix to old file names (default "a")
+ * - new_prefix: "directory" to prefix to new file names (default "b")
+ * - pathspec: array of paths / patterns to constrain diff
+ * - max_size: maximum blob size to diff, above this treated as binary
  */
 typedef struct {
 	uint32_t flags;				/**< defaults to GIT_DIFF_NORMAL */
@@ -65,6 +71,7 @@ typedef struct {
 	char *old_prefix;			/**< defaults to "a" */
 	char *new_prefix;			/**< defaults to "b" */
 	git_strarray pathspec;		/**< defaults to show all paths */
+	git_off_t max_size;			/**< defaults to 512Mb */
 } git_diff_options;
 
 /**

src/diff_output.c

@@ -172,7 +172,7 @@ static void update_delta_is_binary(git_diff_delta *delta)
 	if ((delta->old_file.flags & GIT_DIFF_FILE_BINARY) != 0 ||
 		(delta->new_file.flags & GIT_DIFF_FILE_BINARY) != 0)
 		delta->binary = 1;
-	else if ((delta->old_file.flags & GIT_DIFF_FILE_NOT_BINARY) != 0 ||
+	else if ((delta->old_file.flags & GIT_DIFF_FILE_NOT_BINARY) != 0 &&
 			 (delta->new_file.flags & GIT_DIFF_FILE_NOT_BINARY) != 0)
 		delta->binary = 0;
 	/* otherwise leave delta->binary value untouched */
@@ -219,34 +219,46 @@ static int diff_delta_is_binary_by_attr(diff_delta_context *ctxt)
 	return error;
 }
 
-static int diff_delta_is_binary_by_content(diff_delta_context *ctxt)
+static int diff_delta_is_binary_by_content(
+	diff_delta_context *ctxt, git_diff_file *file, git_map *map)
 {
-	git_diff_delta *delta = ctxt->delta;
 	git_buf search;
 
-	if ((delta->old_file.flags & BINARY_DIFF_FLAGS) == 0) {
-		search.ptr  = ctxt->old_data.data;
-		search.size = min(ctxt->old_data.len, 4000);
+	if ((file->flags & BINARY_DIFF_FLAGS) == 0) {
+		search.ptr  = map->data;
+		search.size = min(map->len, 4000);
 
 		if (git_buf_is_binary(&search))
-			delta->old_file.flags |= GIT_DIFF_FILE_BINARY;
+			file->flags |= GIT_DIFF_FILE_BINARY;
 		else
-			delta->old_file.flags |= GIT_DIFF_FILE_NOT_BINARY;
+			file->flags |= GIT_DIFF_FILE_NOT_BINARY;
 	}
 
-	if ((delta->new_file.flags & BINARY_DIFF_FLAGS) == 0) {
-		search.ptr  = ctxt->new_data.data;
-		search.size = min(ctxt->new_data.len, 4000);
+	update_delta_is_binary(ctxt->delta);
 
-		if (git_buf_is_binary(&search))
-			delta->new_file.flags |= GIT_DIFF_FILE_BINARY;
-		else
-			delta->new_file.flags |= GIT_DIFF_FILE_NOT_BINARY;
+	return 0;
+}
+
+static int diff_delta_is_binary_by_size(
+	diff_delta_context *ctxt, git_diff_file *file)
+{
+	git_off_t threshold = MAX_DIFF_FILESIZE;
+
+	if ((file->flags & BINARY_DIFF_FLAGS) != 0)
+		return 0;
+
+	if (ctxt && ctxt->opts) {
+		if (ctxt->opts->max_size < 0)
+			return 0;
+
+		if (ctxt->opts->max_size > 0)
+			threshold = ctxt->opts->max_size;
 	}
 
-	update_delta_is_binary(delta);
+	if (file->size > threshold)
+		file->flags |= GIT_DIFF_FILE_BINARY;
 
-	/* TODO: if value != NULL, implement diff drivers */
+	update_delta_is_binary(ctxt->delta);
 
 	return 0;
 }
@@ -274,53 +286,56 @@ static void setup_xdiff_options(
 }
 
 static int get_blob_content(
-	git_repository *repo,
+	diff_delta_context *ctxt,
 	git_diff_file *file,
 	git_map *map,
 	git_blob **blob)
 {
 	int error;
-	git_odb *odb;
-	size_t len;
-	git_otype type;
 
 	if (git_oid_iszero(&file->oid))
 		return 0;
 
-	/* peek at object header to avoid loading if too large */
-	if ((error = git_repository_odb__weakptr(&odb, repo)) < 0 ||
-		(error = git_odb_read_header(&len, &type, odb, &file->oid)) < 0)
-		return error;
+	if (!file->size) {
+		git_odb *odb;
+		size_t len;
+		git_otype type;
 
-	assert(type == GIT_OBJ_BLOB);
+		/* peek at object header to avoid loading if too large */
+		if ((error = git_repository_odb__weakptr(&odb, ctxt->repo)) < 0 ||
+			(error = git_odb_read_header(&len, &type, odb, &file->oid)) < 0)
+			return error;
 
-	/* if blob is too large to diff, mark as binary */
-	if (len > MAX_DIFF_FILESIZE) {
-		file->flags |= GIT_DIFF_FILE_BINARY;
-		return 0;
-	}
+		assert(type == GIT_OBJ_BLOB);
 
-	if (!file->size)
 		file->size = len;
+	}
 
-	if ((error = git_blob_lookup(blob, repo, &file->oid)) < 0)
+	/* if blob is too large to diff, mark as binary */
+	if ((error = diff_delta_is_binary_by_size(ctxt, file)) < 0)
+		return error;
+	if (ctxt->delta->binary == 1)
+		return 0;
+
+	if ((error = git_blob_lookup(blob, ctxt->repo, &file->oid)) < 0)
 		return error;
 
 	map->data = (void *)git_blob_rawcontent(*blob);
 	map->len  = git_blob_rawsize(*blob);
 
-	return 0;
+	return diff_delta_is_binary_by_content(ctxt, file, map);
 }
 
 static int get_workdir_content(
-	git_repository *repo,
+	diff_delta_context *ctxt,
 	git_diff_file *file,
 	git_map *map)
 {
 	int error = 0;
 	git_buf path = GIT_BUF_INIT;
+	const char *wd = git_repository_workdir(ctxt->repo);
 
-	if (git_buf_joinpath(&path, git_repository_workdir(repo), file->path) < 0)
+	if (git_buf_joinpath(&path, wd, file->path) < 0)
 		return -1;
 
 	if (S_ISLNK(file->mode)) {
@@ -358,13 +373,12 @@ static int get_workdir_content(
 		if (!file->size)
 			file->size = git_futils_filesize(fd);
 
-		/* if file is too large to diff, mark as binary */
-		if (file->size > MAX_DIFF_FILESIZE) {
-			file->flags |= GIT_DIFF_FILE_BINARY;
+		if ((error = diff_delta_is_binary_by_size(ctxt, file)) < 0 ||
+			ctxt->delta->binary == 1)
 			goto close_and_cleanup;
-		}
 
-		error = git_filters_load(&filters, repo, file->path, GIT_FILTER_TO_ODB);
+		error = git_filters_load(
+			&filters, ctxt->repo, file->path, GIT_FILTER_TO_ODB);
 		if (error < 0)
 			goto close_and_cleanup;
 
@@ -400,6 +414,9 @@ close_and_cleanup:
 			file->flags |= GIT_DIFF_FILE_VALID_OID;
 	}
 
+	if (!error)
+		error = diff_delta_is_binary_by_content(ctxt, file, map);
+
 cleanup:
 	git_buf_free(&path);
 	return error;
@@ -480,7 +497,6 @@ static int diff_delta_prep(diff_delta_context *ctxt)
 static int diff_delta_load(diff_delta_context *ctxt)
 {
 	int error = 0;
-	git_repository *repo  = ctxt->repo;
 	git_diff_delta *delta = ctxt->delta;
 	bool load_old = false, load_new = false, check_if_unmodified = false;
 
@@ -519,31 +535,35 @@ static int diff_delta_load(diff_delta_context *ctxt)
 
 	if (load_old && ctxt->old_src == GIT_ITERATOR_WORKDIR) {
 		if ((error = get_workdir_content(
-				repo, &delta->old_file, &ctxt->old_data)) < 0)
+				ctxt, &delta->old_file, &ctxt->old_data)) < 0)
 			goto cleanup;
-
-		if ((delta->old_file.flags & GIT_DIFF_FILE_BINARY) != 0)
+		if (delta->binary == 1)
 			goto cleanup;
 	}
 
 	if (load_new && ctxt->new_src == GIT_ITERATOR_WORKDIR) {
 		if ((error = get_workdir_content(
-				repo, &delta->new_file, &ctxt->new_data)) < 0)
+				ctxt, &delta->new_file, &ctxt->new_data)) < 0)
 			goto cleanup;
-
-		if ((delta->new_file.flags & GIT_DIFF_FILE_BINARY) != 0)
+		if (delta->binary == 1)
 			goto cleanup;
 	}
 
-	if (load_old && ctxt->old_src != GIT_ITERATOR_WORKDIR &&
-		(error = get_blob_content(
-			repo, &delta->old_file, &ctxt->old_data, &ctxt->old_blob)) < 0)
-		goto cleanup;
+	if (load_old && ctxt->old_src != GIT_ITERATOR_WORKDIR) {
+		if ((error = get_blob_content(
+				ctxt, &delta->old_file, &ctxt->old_data, &ctxt->old_blob)) < 0)
+			goto cleanup;
+		if (delta->binary == 1)
+			goto cleanup;
+	}
 
-	if (load_new && ctxt->new_src != GIT_ITERATOR_WORKDIR &&
-		(error = get_blob_content(
-			repo, &delta->new_file, &ctxt->new_data, &ctxt->new_blob)) < 0)
-		goto cleanup;
+	if (load_new && ctxt->new_src != GIT_ITERATOR_WORKDIR) {
+		if ((error = get_blob_content(
+				ctxt, &delta->new_file, &ctxt->new_data, &ctxt->new_blob)) < 0)
+			goto cleanup;
+		if (delta->binary == 1)
+			goto cleanup;
+	}
 
 	/* if we did not previously have the definitive oid, we may have
 	 * incorrect status and need to switch this to UNMODIFIED.
@@ -559,12 +579,6 @@ static int diff_delta_load(diff_delta_context *ctxt)
 	}
 
 cleanup:
-	/* if we have not already decided whether file is binary,
-	 * check the first 4K for nul bytes to decide...
-	 */
-	if (!error && delta->binary == -1)
-		error = diff_delta_is_binary_by_content(ctxt);
-
 	ctxt->loaded = !error;
 
 	/* flag if we would want to diff the contents of these files */
@@ -1069,9 +1083,13 @@ int git_diff_blobs(
 	if ((error = diff_delta_prep(&ctxt)) < 0)
 		goto cleanup;
 
-	if (delta.binary == -1 &&
-		(error = diff_delta_is_binary_by_content(&ctxt)) < 0)
-		goto cleanup;
+	if (delta.binary == -1) {
+		if ((error = diff_delta_is_binary_by_content(
+				&ctxt, &delta.old_file, &ctxt.old_data)) < 0 ||
+			(error = diff_delta_is_binary_by_content(
+				&ctxt, &delta.new_file, &ctxt.new_data)) < 0)
+			goto cleanup;
+	}
 
 	ctxt.loaded = 1;
 	ctxt.diffable = (delta.binary != 1 && delta.status != GIT_DELTA_UNMODIFIED);