Re: Revamping the git protocol

From: Junio C Hamano <junkio@cox.net>
Date: Oct 20, 2005, 06:11 UTC
Message-ID: <7vwtk8pvju.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <43571DA1.6030907@zytor.com>

Wow.

That's elaborate. And all this is to replace the beginning of execute() part of daemon.c? What I am assuming is that after exchanging command-response initially, you still plan to eventually have the protocol driver such as upload-pack to take things over, once "send-pack <path>" is issued, but is my assumption correct? Or are you also thinking about redoing upload-pack as well (otherwise you cannot issue 5.4 errors)?

I am wondering if we can just get away with a simpler scheme Linus outlined instead. One drawback of that approach is it does not easily allow things like challenge-response uniformly across different commands (admittedly we only have "upload-pack" command right now, but we could add list of supported commands easily in execute()), but you could do something along this, I presume?

When daemon is started with --require-challenge-response, the client needs to issue "challenge-me" command and complete challenge_response successfully before being able to issue any other commands.

NOTE: this is just an outline, not a compilable patch.  You need to
fill in the details of challenge response, definition of
"require_challenge_response" variable of type bool, and a
command line parsing to set that variable.

---

git diff

diff --git a/daemon.c b/daemon.c
index c3381b3..8a8746a 100644
--- a/daemon.c
+++ b/daemon.c
@@ -204,20 +204,55 @@ static int upload(char *dir)
 	return -1;
 }
 
-static int execute(void)
+static int challenge_response(const char *me)
 {
-	static char line[1000];
-	int len;
+	char line[1000];
 
-	alarm(init_timeout ? init_timeout : timeout);
+	packet_write(1, "here comes your challenge");
+
+	alarm(timeout);
 	len = packet_read_line(0, line, sizeof(line));
 	alarm(0);
 
 	if (len && line[len-1] == '\n')
 		line[--len] = 0;
 
-	if (!strncmp("git-upload-pack /", line, 17))
-		return upload(line+16);
+	if ("validate response we obtained in line here")
+		return 1;
+	return 0;
+}
+
+static int execute(void)
+{
+	static char line[1000];
+	int len;
+	int client_ok = !require_challenge_response;
+	unsigned int time_out = init_timeout;
+
+	while (1) {
+
+		alarm(time_out);
+		time_out = timeout;
+		len = packet_read_line(0, line, sizeof(line));
+		alarm(0);
+		if (len && line[len-1] == '\n')
+			line[--len] = 0;
+
+		if (!strncmp("challenge-me ", line, 13)) {
+			client_ok = challenge_response(line+13);
+			continue;
+		}
+
+		if (!client_ok)
+			break;
+
+		if (!strncmp("git-upload-pack /", line, 17))
+			return upload(line+16);
+
+		/* more commands here later */
+
+		break;
+	}
 
 	logerror("Protocol error: '%s'", line);
 	return -1;