credentials: add "store" helper

This is like "cache", except that we actually put the
credentials on disk. This can be terribly insecure, of
course, but we do what we can to protect them by filesystem
permissions, and we warn the user in the documentation.

This is not unlike using .netrc to store entries, but it's a
little more user-friendly. Instead of putting credentials in
place ahead of time, we transparently store them after
prompting the user for them once.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -32,6 +32,7 @@
 /git-count-objects
 /git-credential-cache
 /git-credential-cache--daemon
+/git-credential-store
 /git-cvsexportcommit
 /git-cvsimport
 /git-cvsserver

Documentation/git-credential-store.txt

@@ -0,0 +1,75 @@
+git-credential-store(1)
+=======================
+
+NAME
+----
+git-credential-store - helper to store credentials on disk
+
+SYNOPSIS
+--------
+-------------------
+git config credential.helper 'store [options]'
+-------------------
+
+DESCRIPTION
+-----------
+
+NOTE: Using this helper will store your passwords unencrypted on disk,
+protected only by filesystem permissions. If this is not an acceptable
+security tradeoff, try linkgit:git-credential-cache[1], or find a helper
+that integrates with secure storage provided by your operating system.
+
+This command stores credentials indefinitely on disk for use by future
+git programs.
+
+You probably don't want to invoke this command directly; it is meant to
+be used as a credential helper by other parts of git. See
+linkgit:gitcredentials[7] or `EXAMPLES` below.
+
+OPTIONS
+-------
+
+--store=<path>::
+
+	Use `<path>` to store credentials. The file will have its
+	filesystem permissions set to prevent other users on the system
+	from reading it, but will not be encrypted or otherwise
+	protected. Defaults to `~/.git-credentials`.
+
+EXAMPLES
+--------
+
+The point of this helper is to reduce the number of times you must type
+your username or password. For example:
+
+------------------------------------------
+$ git config credential.helper store
+$ git push http://example.com/repo.git
+Username: <type your username>
+Password: <type your password>
+
+[several days later]
+$ git push http://example.com/repo.git
+[your credentials are used automatically]
+------------------------------------------
+
+STORAGE FORMAT
+--------------
+
+The `.git-credentials` file is stored in plaintext. Each credential is
+stored on its own line as a URL like:
+
+------------------------------
+https://user:pass@example.com
+------------------------------
+
+When git needs authentication for a particular URL context,
+credential-store will consider that context a pattern to match against
+each entry in the credentials file.  If the protocol, hostname, and
+username (if we already have one) match, then the password is returned
+to git. See the discussion of configuration in linkgit:gitcredentials[7]
+for more information.
+
+GIT
+---
+Part of the linkgit:git[1] suite

Documentation/gitcredentials.txt

@@ -71,6 +71,11 @@ cache::
 	Cache credentials in memory for a short period of time. See
 	linkgit:git-credential-cache[1] for details.
 
+store::
+
+	Store credentials indefinitely on disk. See
+	linkgit:git-credential-store[1] for details.
+
 You may also have third-party helpers installed; search for
 `credential-*` in the output of `git help -a`, and consult the
 documentation of individual helpers.  Once you have selected a helper,

Makefile

@@ -429,6 +429,7 @@ PROGRAM_OBJS += show-index.o
 PROGRAM_OBJS += upload-pack.o
 PROGRAM_OBJS += http-backend.o
 PROGRAM_OBJS += sh-i18n--envsubst.o
+PROGRAM_OBJS += credential-store.o
 
 PROGRAMS += $(patsubst %.o,git-%$X,$(PROGRAM_OBJS))
 

credential-store.c

@@ -0,0 +1,157 @@
+#include "cache.h"
+#include "credential.h"
+#include "string-list.h"
+#include "parse-options.h"
+
+static struct lock_file credential_lock;
+
+static void parse_credential_file(const char *fn,
+				  struct credential *c,
+				  void (*match_cb)(struct credential *),
+				  void (*other_cb)(struct strbuf *))
+{
+	FILE *fh;
+	struct strbuf line = STRBUF_INIT;
+	struct credential entry = CREDENTIAL_INIT;
+
+	fh = fopen(fn, "r");
+	if (!fh) {
+		if (errno != ENOENT)
+			die_errno("unable to open %s", fn);
+		return;
+	}
+
+	while (strbuf_getline(&line, fh, '\n') != EOF) {
+		credential_from_url(&entry, line.buf);
+		if (entry.username && entry.password &&
+		    credential_match(c, &entry)) {
+			if (match_cb) {
+				match_cb(&entry);
+				break;
+			}
+		}
+		else if (other_cb)
+			other_cb(&line);
+	}
+
+	credential_clear(&entry);
+	strbuf_release(&line);
+	fclose(fh);
+}
+
+static void print_entry(struct credential *c)
+{
+	printf("username=%s\n", c->username);
+	printf("password=%s\n", c->password);
+}
+
+static void print_line(struct strbuf *buf)
+{
+	strbuf_addch(buf, '\n');
+	write_or_die(credential_lock.fd, buf->buf, buf->len);
+}
+
+static void rewrite_credential_file(const char *fn, struct credential *c,
+				    struct strbuf *extra)
+{
+	if (hold_lock_file_for_update(&credential_lock, fn, 0) < 0)
+		die_errno("unable to get credential storage lock");
+	if (extra)
+		print_line(extra);
+	parse_credential_file(fn, c, NULL, print_line);
+	if (commit_lock_file(&credential_lock) < 0)
+		die_errno("unable to commit credential store");
+}
+
+static void store_credential(const char *fn, struct credential *c)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	/*
+	 * Sanity check that what we are storing is actually sensible.
+	 * In particular, we can't make a URL without a protocol field.
+	 * Without either a host or pathname (depending on the scheme),
+	 * we have no primary key. And without a username and password,
+	 * we are not actually storing a credential.
+	 */
+	if (!c->protocol || !(c->host || c->path) ||
+	    !c->username || !c->password)
+		return;
+
+	strbuf_addf(&buf, "%s://", c->protocol);
+	strbuf_addstr_urlencode(&buf, c->username, 1);
+	strbuf_addch(&buf, ':');
+	strbuf_addstr_urlencode(&buf, c->password, 1);
+	strbuf_addch(&buf, '@');
+	if (c->host)
+		strbuf_addstr_urlencode(&buf, c->host, 1);
+	if (c->path) {
+		strbuf_addch(&buf, '/');
+		strbuf_addstr_urlencode(&buf, c->path, 0);
+	}
+
+	rewrite_credential_file(fn, c, &buf);
+	strbuf_release(&buf);
+}
+
+static void remove_credential(const char *fn, struct credential *c)
+{
+	/*
+	 * Sanity check that we actually have something to match
+	 * against. The input we get is a restrictive pattern,
+	 * so technically a blank credential means "erase everything".
+	 * But it is too easy to accidentally send this, since it is equivalent
+	 * to empty input. So explicitly disallow it, and require that the
+	 * pattern have some actual content to match.
+	 */
+	if (c->protocol || c->host || c->path || c->username)
+		rewrite_credential_file(fn, c, NULL);
+}
+
+static int lookup_credential(const char *fn, struct credential *c)
+{
+	parse_credential_file(fn, c, print_entry, NULL);
+	return c->username && c->password;
+}
+
+int main(int argc, const char **argv)
+{
+	const char * const usage[] = {
+		"git credential-store [options] <action>",
+		NULL
+	};
+	const char *op;
+	struct credential c = CREDENTIAL_INIT;
+	char *file = NULL;
+	struct option options[] = {
+		OPT_STRING(0, "file", &file, "path",
+			   "fetch and store credentials in <path>"),
+		OPT_END()
+	};
+
+	umask(077);
+
+	argc = parse_options(argc, argv, NULL, options, usage, 0);
+	if (argc != 1)
+		usage_with_options(usage, options);
+	op = argv[0];
+
+	if (!file)
+		file = expand_user_path("~/.git-credentials");
+	if (!file)
+		die("unable to set up default path; use --file");
+
+	if (credential_read(&c, stdin) < 0)
+		die("unable to read credential");
+
+	if (!strcmp(op, "get"))
+		lookup_credential(file, &c);
+	else if (!strcmp(op, "erase"))
+		remove_credential(file, &c);
+	else if (!strcmp(op, "store"))
+		store_credential(file, &c);
+	else
+		; /* Ignore unknown operation. */
+
+	return 0;
+}

t/t0302-credential-store.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+test_description='credential-store tests'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-credential.sh
+
+helper_test store
+
+test_done