[PATCH 1/3] Add function git_config_set()

@@ -384,6 +384,7 @@ extern int git_default_config(const char
 extern int git_config(config_fn_t fn);
 extern int git_config_int(const char *, const char *);
 extern int git_config_bool(const char *, const char *);
+extern int git_config_set(const char *, const char *);
 
 #define MAX_GITNAME (1000)
 extern char git_default_email[MAX_GITNAME];

@@ -247,3 +247,148 @@ int git_config(config_fn_t fn)
 	}
 	return ret;
 }
+
+static struct {
+	int baselen;
+	const char* key;
+	const char* value;
+	off_t offset;
+	enum { START, SECTION_SEEN, SECTION_END_SEEN, KEY_SEEN } state;
+} store;
+
+static int store_aux(const char* key, const char* value)
+{
+	switch (store.state) {
+		case KEY_SEEN:
+			if (!strcmp(key, store.key))
+				store.offset = ftell(config_file);
+			break;
+		case SECTION_SEEN:
+			if (strncmp(key, store.key, store.baselen+1)) {
+				store.offset = ftell(config_file);
+				store.state = SECTION_END_SEEN;
+				break;
+			}
+		case SECTION_END_SEEN:
+		case START:
+			if (!strcmp(key, store.key)) {
+				store.offset = ftell(config_file);
+				store.state = KEY_SEEN;
+			} else if(!strncmp(key, store.key, store.baselen))
+				store.state = SECTION_SEEN;
+	}
+	return 0;
+}
+
+static void store_write_section(int fd)
+{
+	write(fd, "[", 1);
+	write(fd, store.key, store.baselen);
+	write(fd, "]\n", 2);
+}
+
+static void store_write_pair(int fd)
+{
+	int i;
+
+	write(fd, "\t", 1);
+	write(fd, store.key+store.baselen+1,
+		strlen(store.key+store.baselen+1));
+	write(fd, " = ", 3);
+	for (i = 0; store.value[i]; i++)
+		switch (store.value[i]) {
+		case '\n': write(fd, "\\n", 2); break;
+		case '\t': write(fd, "\\t", 2); break;
+		case '"': case '\\': write(fd, "\\", 1);
+		default: write(fd, store.value+i, 1);
+	}
+	write(fd, "\n", 1);
+}
+
+int git_config_set(const char* key, const char* value)
+{
+	int i;
+	struct stat st;
+	int fd;
+	char* config_file = strdup(git_path("config"));
+	char* lock_file = strdup(git_path("config.lock"));
+
+	for (store.baselen = 0;
+			key[store.baselen] != '.' && key[store.baselen];
+			store.baselen++);
+	if (!key[store.baselen]) {
+		fprintf(stderr, "key does not contain a section: %s\n", key);
+		return 2;
+	}
+
+	for (i = 0; key[i]; i++)
+		if (i != store.baselen && !isalpha(key[i])) {
+			fprintf(stderr, "invalid key: %s\n", key);
+			return 1;
+		}
+
+	store.key = key;
+	store.value = value;
+
+	fd = open(lock_file, O_WRONLY | O_CREAT | O_EXCL, 0666);
+	if (fd < 0) {
+		fprintf(stderr, "could not lock config file\n");
+		return -1;
+	}
+
+	if (stat(config_file, &st)) {
+		/* write new file */
+		static const char contents[] =
+			"#\n"
+			"# This is the config file\n"
+			"#\n"
+			"\n";
+
+		write(fd, contents, sizeof(contents)-1);
+		store_write_section(fd);
+		store_write_pair(fd);
+	} else{
+		int in_fd;
+		char* contents;
+		int offset;
+
+		store.offset = 0;
+		store.state = START;
+
+		if (git_config(store_aux)) {
+			fprintf(stderr, "invalid config file\n");
+			return 3;
+		}
+
+		in_fd = open(config_file, O_RDONLY, 0666);
+		contents = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, in_fd, 0);
+		close(in_fd);
+
+		if (store.offset == 0)
+			offset = st.st_size;
+		else {
+			for (offset = store.offset-2; offset > 0 
+					&& contents[offset] != '\n'; offset--);
+			offset++;
+		}
+		write(fd, contents, offset);
+		if (store.state == START)
+			store_write_section(fd);
+		store_write_pair(fd);
+		if (store.offset > offset)
+			write(fd, contents + store.offset,
+				st.st_size - store.offset);
+		
+		unlink(config_file);
+	}
+
+	close(fd);
+
+	if (rename(lock_file, config_file) < 0) {
+		fprintf(stderr, "Could not rename the lock file?\n");
+		return 4;
+	}
+
+	return 0;
+}
+