gvfs: add gvfs.sessionKey config

In different engineering systems, there may already be pseudonymous
identifiers stored in the local Git config. For Office and 1JS, this is
present in the 'otel.trace2.id' config value.

We'd like to be able to collect server-side telemetry based on these
pseudonymous identifiers, so prefxing the X-Session-Id header with this
value is helpful.

We could create a single 'gvfs.sessionPrefix' config key that stores
this value, but then we'd need to duplicate the identifier and risk
drift in the value. For now, we create this indirection by saying "what
config _key_ should Git use to look up the value to add as a prefix?"

Signed-off-by: Derrick Stolee <stolee@gmail.com>

Author: derrickstolee

Documentation/config/gvfs.adoc

@@ -26,3 +26,11 @@ gvfs.fallback::
 	If set to `false`, then never fallback to the origin server when the cache
 	server fails to connect. This will alert users to failures with the cache
 	server, but avoid causing throttling on the origin server.
+
+gvfs.sessionKey::
+	If set to a string, then the value is a config key name that will be used
+	to set a prefix in the `X-Session-Id` header sent to the server for all
+	GVFS Protocol calls. This allows engineering systems to improve support
+	across client and server behavior, including any End User Pseodynomous
+	Identifiers (EUPI) that may be configured. The `X-Session-Id` will
+	include the SID of the current process in either case.

gvfs-helper.c

@@ -467,8 +467,28 @@ static char *build_session_id_header(void)
 {
 	struct strbuf header = STRBUF_INIT;
 	const char *sid = tr2_sid_get();
+	char *session_key = NULL;
+	char *prefix = NULL;
+
+	/* Read gvfs.sessionkey to see if it points to a config key */
+	if (!repo_config_get_string(the_repository, "gvfs.sessionkey", &session_key) &&
+	    session_key) {
+		/* Try to read the config key that session_key points to */
+		if (!repo_config_get_string(the_repository, session_key, &prefix) &&
+		    prefix) {
+			/* We have a prefix, format as: X-Session-Id: <prefix>:<SID> */
+			strbuf_addf(&header, "X-Session-Id: %s:%s", prefix, sid);
+			free(prefix);
+		} else {
+			/* Config key doesn't exist, use just SID */
+			strbuf_addf(&header, "X-Session-Id: %s", sid);
+		}
 
-	strbuf_addf(&header, "X-Session-Id: %s", sid);
+		free(session_key);
+	} else {
+		/* No gvfs.sessionkey configured, use just SID */
+		strbuf_addf(&header, "X-Session-Id: %s", sid);
+	}
 
 	return strbuf_detach(&header, NULL);
 }

t/t5793-gvfs-helper-integration.sh

@@ -173,6 +173,7 @@ test_expect_success 'integration: X-Session-Id header with and without prefix' '
 	test_when_finished "per_test_cleanup" &&
 	start_gvfs_protocol_server &&
 
+	# Case 1: No gvfs.sessionkey configured - should send just SID
 	git -C "$REPO_T1" gvfs-helper \
 		--cache-server=disable \
 		--remote=origin \
@@ -182,7 +183,34 @@ test_expect_success 'integration: X-Session-Id header with and without prefix' '
 	# Verify X-Session-Id contains SID (with process ID marker "-P")
 	test_grep "X-Session-Id:.*-P" "$SERVER_LOG" >OUT.case1 &&
 	# Verify no slash (no prefix)
-	test_grep ! "X-Session-Id:.*:" OUT.case1
+	test_grep ! "X-Session-Id:.*:" OUT.case1 &&
+
+	# Case 2: gvfs.sessionkey points to non-existent config - should send just SID
+	rm -f OUT.output* OUT.case* &&
+	git -C "$REPO_T1" -c gvfs.sessionkey="test.id" gvfs-helper \
+		--cache-server=disable \
+		--remote=origin \
+		get \
+		<"$OID_ONE_BLOB_FILE" >OUT.output2 &&
+
+	# Verify X-Session-Id still contains just SID (no prefix)
+	test_grep "X-Session-Id:.*-P" "$SERVER_LOG" >OUT.case2 &&
+	test_grep ! "X-Session-Id:.*:" OUT.case2 &&
+
+	# Case 3: gvfs.sessionkey points to existing config - should send prefix/SID
+	rm -f OUT.output* OUT.case* &&
+	git -C "$REPO_T1" \
+		-c gvfs.sessionkey="test.id" \
+		-c test.id="my-trace-12345" \
+		gvfs-helper \
+		--cache-server=disable \
+		--remote=origin \
+		get \
+		<"$OID_ONE_BLOB_FILE" >OUT.output3 &&
+
+	# Verify X-Session-Id contains prefix, slash, and SID
+	test_grep "X-Session-Id:.*my-trace-12345:" "$SERVER_LOG" >OUT.case3 &&
+	test_grep "X-Session-Id:.*my-trace-12345:.*-P" OUT.case3
 '
 
 test_done