[PATCH 2 of 3 V4] chg: use validate to make sure the server is up to date

[Jun Wu]

# HG changeset patch
# User Jun Wu <quark at fb.com>
# Date 1456913782 0
#      Wed Mar 02 10:16:22 2016 +0000
# Node ID 29fb9d1f0ace0f4a96469d95fac6af081189185f
# Parent  64fc0ca8f5d7df4dfb133817708fcafb53f6b89f
chg: use validate to make sure the server is up to date

This patch uses the newly added validate method to make sure the server has
loaded the up-to-date config and extensions. If the server cannot validate
itself, the client will receive instructions and follow them to try to reach
another server that is more likely to validate itself. The instructions can
be a redirect (connect to another server address) and/or an unlink (stops an
out-dated server).

diff --git a/contrib/chg/chg.c b/contrib/chg/chg.c
--- a/contrib/chg/chg.c
+++ b/contrib/chg/chg.c
@@ -31,6 +31,7 @@
 
 struct cmdserveropts {
 	char sockname[UNIX_PATH_MAX];
+	char redirectsockname[UNIX_PATH_MAX];
 	char lockfile[UNIX_PATH_MAX];
 	char pidfile[UNIX_PATH_MAX];
 	size_t argsize;
@@ -270,18 +271,27 @@
 /* Connect to a cmdserver. Will start a new server on demand. */
 static hgclient_t *connectcmdserver(struct cmdserveropts *opts)
 {
-	hgclient_t *hgc = hgc_open(opts->sockname);
+	const char *sockname = opts->redirectsockname[0] ?
+		opts->redirectsockname : opts->sockname;
+	hgclient_t *hgc = hgc_open(sockname);
 	if (hgc)
 		return hgc;
 
 	lockcmdserver(opts);
-	hgc = hgc_open(opts->sockname);
+	hgc = hgc_open(sockname);
 	if (hgc) {
 		unlockcmdserver(opts);
 		debugmsg("cmdserver is started by another process");
 		return hgc;
 	}
 
+	/* prevent us from being connected to an outdated server: we were
+	 * told by a server to redirect to opts->redirectsockname and that
+	 * address does not work. we do not want to connect to the server
+	 * again because it will probably tell us the same thing. */
+	if (sockname == opts->redirectsockname)
+		unlink(opts->sockname);
+
 	debugmsg("start cmdserver at %s", opts->sockname);
 
 	pid_t pid = fork();
@@ -448,6 +458,28 @@
 	abortmsg("failed to prepare pager (errno = %d)", errno);
 }
 
+/* Run instructions sent from the server like unlink and set redirect path */
+static void runinstructions(struct cmdserveropts *opts, const char **insts)
+{
+	assert(insts);
+	opts->redirectsockname[0] = '\0';
+	const char **pinst;
+	for (pinst = insts; *pinst; pinst++) {
+		debugmsg("instruction: %s", *pinst);
+		if (strncmp(*pinst, "unlink ", 7) == 0) {
+			unlink(*pinst + 7);
+		} else if (strncmp(*pinst, "redirect ", 9) == 0) {
+			int r = snprintf(opts->redirectsockname,
+					 sizeof(opts->redirectsockname),
+					 "%s", *pinst + 9);
+			if (r < 0 || r >= (int)sizeof(opts->redirectsockname))
+				abortmsg("redirect path is too long (%d)", r);
+		} else {
+			abortmsg("unknown instruction: %s", *pinst);
+		}
+	}
+}
+
 /*
  * Test whether the command is unsupported or not. This is not designed to
  * cover all cases. But it's fast, does not depend on the server and does
@@ -516,12 +548,20 @@
 		}
 	}
 
-	hgclient_t *hgc = connectcmdserver(&opts);
-	if (!hgc)
-		abortmsg("cannot open hg client");
+	hgclient_t *hgc;
+	while (1) {
+		hgc = connectcmdserver(&opts);
+		if (!hgc)
+			abortmsg("cannot open hg client");
+		hgc_setenv(hgc, envp);
+		const char **insts = hgc_validate(hgc, argv + 1, argc - 1);
+		if (insts == NULL)
+			break;
+		runinstructions(&opts, insts);
+		hgc_close(hgc);
+	}
 
 	setupsignalhandler(hgc_peerpid(hgc));
-	hgc_setenv(hgc, envp);
 	setuppager(hgc, argv + 1, argc - 1);
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	hgc_close(hgc);