config: introduce new read-only in-memory backend

Now that we have abstracted away how to store and retrieve config
entries, it became trivial to implement a new in-memory backend by
making use of this. And thus we do so.

This commit implements a new read-only in-memory backend that can parse
a chunk of memory into a `git_config_backend` structure.

1 files changed, 224 insertions, 0 deletions

diff --git a/src/config_mem.c b/src/config_mem.c
new file mode 100644
index 000000000..fbb6373c3
--- /dev/null
+++ b/src/config_mem.c
@@ -0,0 +1,224 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "config.h"
+
+#include "config_backend.h"
+#include "config_parse.h"
+#include "config_entries.h"
+
+typedef struct {
+	git_config_backend parent;
+	git_config_entries *entries;
+	git_buf cfg;
+} config_memory_backend;
+
+typedef struct {
+	git_config_entries *entries;
+	git_config_level_t level;
+} config_memory_parse_data;
+
+static int config_error_readonly(void)
+{
+	giterr_set(GITERR_CONFIG, "this backend is read-only");
+	return -1;
+}
+
+static int read_variable_cb(
+	git_config_parser *reader,
+	const char *current_section,
+	const char *var_name,
+	const char *var_value,
+	const char *line,
+	size_t line_len,
+	void *payload)
+{
+	config_memory_parse_data *parse_data = (config_memory_parse_data *) payload;
+	git_buf buf = GIT_BUF_INIT;
+	git_config_entry *entry;
+	const char *c;
+	int result;
+
+	GIT_UNUSED(reader);
+	GIT_UNUSED(line);
+	GIT_UNUSED(line_len);
+
+	if (current_section) {
+		/* TODO: Once warnings land, we should likely warn
+		 * here. Git appears to warn in most cases if it sees
+		 * un-namespaced config options.
+		 */
+		git_buf_puts(&buf, current_section);
+		git_buf_putc(&buf, '.');
+	}
+
+	for (c = var_name; *c; c++)
+		git_buf_putc(&buf, git__tolower(*c));
+
+	if (git_buf_oom(&buf))
+		return -1;
+
+	entry = git__calloc(1, sizeof(git_config_entry));
+	GITERR_CHECK_ALLOC(entry);
+	entry->name = git_buf_detach(&buf);
+	entry->value = var_value ? git__strdup(var_value) : NULL;
+	entry->level = parse_data->level;
+	entry->include_depth = 0;
+
+	if ((result = git_config_entries_append(parse_data->entries, entry)) < 0)
+		return result;
+
+	return result;
+}
+
+static int config_memory_open(git_config_backend *backend, git_config_level_t level, const git_repository *repo)
+{
+	config_memory_backend *memory_backend = (config_memory_backend *) backend;
+	config_memory_parse_data parse_data;
+	git_config_parser reader;
+
+	GIT_UNUSED(repo);
+
+	if (memory_backend->cfg.size == 0)
+		return 0;
+
+	git_parse_ctx_init(&reader.ctx, memory_backend->cfg.ptr, memory_backend->cfg.size);
+	reader.file = NULL;
+	parse_data.entries = memory_backend->entries;
+	parse_data.level = level;
+
+	return git_config_parse(&reader, NULL, read_variable_cb, NULL, NULL, &parse_data);
+}
+
+static int config_memory_get(git_config_backend *backend, const char *key, git_config_entry **out)
+{
+	config_memory_backend *memory_backend = (config_memory_backend *) backend;
+	return git_config_entries_get(out, memory_backend->entries, key);
+}
+
+static int config_memory_iterator(
+	git_config_iterator **iter,
+	git_config_backend *backend)
+{
+	config_memory_backend *memory_backend = (config_memory_backend *) backend;
+	git_config_entries *entries;
+	int error;
+
+	if ((error = git_config_entries_dup(&entries, memory_backend->entries)) < 0)
+		goto out;
+
+	if ((error = git_config_entries_iterator_new(iter, entries)) < 0)
+		goto out;
+
+out:
+	/* Let iterator delete duplicated entries when it's done */
+	git_config_entries_free(entries);
+	return error;
+}
+
+static int config_memory_set(git_config_backend *backend, const char *name, const char *value)
+{
+	GIT_UNUSED(backend);
+	GIT_UNUSED(name);
+	GIT_UNUSED(value);
+	return config_error_readonly();
+}
+
+static int config_memory_set_multivar(
+	git_config_backend *backend, const char *name, const char *regexp, const char *value)
+{
+	GIT_UNUSED(backend);
+	GIT_UNUSED(name);
+	GIT_UNUSED(regexp);
+	GIT_UNUSED(value);
+	return config_error_readonly();
+}
+
+static int config_memory_delete(git_config_backend *backend, const char *name)
+{
+	GIT_UNUSED(backend);
+	GIT_UNUSED(name);
+	return config_error_readonly();
+}
+
+static int config_memory_delete_multivar(git_config_backend *backend, const char *name, const char *regexp)
+{
+	GIT_UNUSED(backend);
+	GIT_UNUSED(name);
+	GIT_UNUSED(regexp);
+	return config_error_readonly();
+}
+
+static int config_memory_lock(git_config_backend *backend)
+{
+	GIT_UNUSED(backend);
+	return config_error_readonly();
+}
+
+static int config_memory_unlock(git_config_backend *backend, int success)
+{
+	GIT_UNUSED(backend);
+	GIT_UNUSED(success);
+	return config_error_readonly();
+}
+
+static int config_memory_snapshot(git_config_backend **out, git_config_backend *backend)
+{
+	GIT_UNUSED(out);
+	GIT_UNUSED(backend);
+	giterr_set(GITERR_CONFIG, "this backend does not support snapshots");
+	return -1;
+}
+
+static void config_memory_free(git_config_backend *_backend)
+{
+	config_memory_backend *backend = (config_memory_backend *)_backend;
+
+	if (backend == NULL)
+		return;
+
+	git_config_entries_free(backend->entries);
+	git_buf_dispose(&backend->cfg);
+	git__free(backend);
+}
+
+int git_config_backend_from_string(git_config_backend **out, const char *cfg)
+{
+	config_memory_backend *backend;
+
+	backend = git__calloc(1, sizeof(config_memory_backend));
+	GITERR_CHECK_ALLOC(backend);
+
+	if (git_config_entries_new(&backend->entries) < 0) {
+		git__free(backend);
+		return -1;
+	}
+
+	if (git_buf_sets(&backend->cfg, cfg) < 0) {
+		git_config_entries_free(backend->entries);
+		git__free(backend);
+		return -1;
+	}
+
+	backend->parent.version = GIT_CONFIG_BACKEND_VERSION;
+	backend->parent.readonly = 1;
+	backend->parent.open = config_memory_open;
+	backend->parent.get = config_memory_get;
+	backend->parent.set = config_memory_set;
+	backend->parent.set_multivar = config_memory_set_multivar;
+	backend->parent.del = config_memory_delete;
+	backend->parent.del_multivar = config_memory_delete_multivar;
+	backend->parent.iterator = config_memory_iterator;
+	backend->parent.lock = config_memory_lock;
+	backend->parent.unlock = config_memory_unlock;
+	backend->parent.snapshot = config_memory_snapshot;
+	backend->parent.free = config_memory_free;
+
+	*out = (git_config_backend *)backend;
+
+	return 0;
+}