Add git_config_refresh() API to reload config

This adds a new API that allows users to reload the config if the
file has changed on disk.  A new config callback function to
refresh the config was added.

The modified time and file size are used to test if the file needs
to be reloaded (and are now stored in the disk backend object).

In writing tests, just using mtime was a problem / race, so I
wanted to check file size as well.  To support that, I extended
`git_futils_readbuffer_updated` to optionally check file size in
addition to mtime, and I added a new function `git_filebuf_stats`
to fetch the mtime and size for an open filebuf (so that the
config could be easily refreshed after a write).

Lastly, I moved some similar file checking code for attributes
into filebuf.  It is still only being used for attrs, but it
seems potentially reusable, so I thought I'd move it over.

1 files changed, 43 insertions, 6 deletions

diff --git a/src/config_file.c b/src/config_file.c
index 92fe13296..1eae8b9ac 100644
--- a/src/config_file.c
+++ b/src/config_file.c
@@ -75,7 +75,11 @@ typedef struct {
 		int eof;
 	} reader;
 
-	char *file_path;
+	char  *file_path;
+	time_t file_mtime;
+	size_t file_size;
+
+	unsigned int level;
 } diskfile_backend;
 
 static int config_parse(diskfile_backend *cfg_file, unsigned int level);
@@ -150,25 +154,53 @@ static int config_open(git_config_file *cfg, unsigned int level)
 	int res;
 	diskfile_backend *b = (diskfile_backend *)cfg;
 
+	b->level = level;
+
 	b->values = git_strmap_alloc();
 	GITERR_CHECK_ALLOC(b->values);
 
 	git_buf_init(&b->reader.buffer, 0);
-	res = git_futils_readbuffer(&b->reader.buffer, b->file_path);
+	res = git_futils_readbuffer_updated(
+		&b->reader.buffer, b->file_path, &b->file_mtime, &b->file_size, NULL);
 
 	/* It's fine if the file doesn't exist */
 	if (res == GIT_ENOTFOUND)
 		return 0;
 
-	if (res < 0 || config_parse(b, level) <  0) {
+	if (res < 0 || (res = config_parse(b, level)) < 0) {
 		free_vars(b->values);
 		b->values = NULL;
-		git_buf_free(&b->reader.buffer);
-		return -1;
 	}
 
 	git_buf_free(&b->reader.buffer);
-	return 0;
+	return res;
+}
+
+static int config_refresh(git_config_file *cfg)
+{
+	int res, updated = 0;
+	diskfile_backend *b = (diskfile_backend *)cfg;
+	git_strmap *old_values;
+
+	res = git_futils_readbuffer_updated(
+		&b->reader.buffer, b->file_path, &b->file_mtime, &b->file_size, &updated);
+	if (res < 0 || !updated)
+		return (res == GIT_ENOTFOUND) ? 0 : res;
+
+	/* need to reload - store old values and prep for reload */
+	old_values = b->values;
+	b->values = git_strmap_alloc();
+	GITERR_CHECK_ALLOC(b->values);
+
+	if ((res = config_parse(b, b->level)) < 0) {
+		free_vars(b->values);
+		b->values = old_values;
+	} else {
+		free_vars(old_values);
+	}
+
+	git_buf_free(&b->reader.buffer);
+	return res;
 }
 
 static void backend_free(git_config_file *_backend)
@@ -527,6 +559,7 @@ int git_config_file__ondisk(git_config_file **out, const char *path)
 	backend->parent.set_multivar = config_set_multivar;
 	backend->parent.del = config_delete;
 	backend->parent.foreach = file_foreach;
+	backend->parent.refresh = config_refresh;
 	backend->parent.free = backend_free;
 
 	*out = (git_config_file *)backend;
@@ -1197,8 +1230,12 @@ static int config_write(diskfile_backend *cfg, const char *key, const regex_t *p
 	git__free(section);
 	git__free(current_section);
 
+	/* refresh stats - if this errors, then commit will error too */
+	(void)git_filebuf_stats(&cfg->file_mtime, &cfg->file_size, &file);
+
 	result = git_filebuf_commit(&file, GIT_CONFIG_FILE_MODE);
 	git_buf_free(&cfg->reader.buffer);
+
 	return result;
 
 rewrite_fail: