Encode the 32-bit Global Identifier as 2 x 16-bit in the IPv6 address.

Without this patch we would encode the IPv6 address' last part as
::ffffffff instead of ::ffff:ffff when the GID is UINT32_MAX.

See: https://bugs.torproject.org/4700

src/core/or/connection_edge.c

@@ -623,8 +623,10 @@ export_hs_client_circuit_id_haproxy(const edge_connection_t *edge_conn,
   }
 
   /* Build the string */
-  tor_asprintf(&buf, "PROXY TCP6 %s:%x %s %d %d\r\n",
-               src_ipv6_prefix, gid, dst_ipv6, src_port, dst_port);
+  tor_asprintf(&buf, "PROXY TCP6 %s:%x:%x %s %d %d\r\n",
+               src_ipv6_prefix,
+               gid >> 16, gid & 0x0000ffff,
+               dst_ipv6, src_port, dst_port);
 
   connection_buf_add(buf, strlen(buf), conn);
 

src/test/test_hs_service.c

@@ -2061,6 +2061,32 @@ test_export_client_circuit_id(void *arg)
   export_hs_client_circuit_id_haproxy(edge_conn, conn);
   cp2 = buf_get_contents(conn->outbuf, &sz);
   tt_str_op(cp1, OP_NE, cp2);
+  tor_free(cp1);
+
+  /* Check that GID with UINT32_MAX works. */
+  or_circ->global_identifier = UINT32_MAX;
+
+  export_hs_client_circuit_id_haproxy(edge_conn, conn);
+  cp1 = buf_get_contents(conn->outbuf, &sz);
+  tt_str_op(cp1, OP_EQ,
+            "PROXY TCP6 fc00:dead:beef:4dad::ffff:ffff ::1 65535 42\r\n");
+  tor_free(cp1);
+
+  /* Check that GID with UINT16_MAX works. */
+  or_circ->global_identifier = UINT16_MAX;
+
+  export_hs_client_circuit_id_haproxy(edge_conn, conn);
+  cp1 = buf_get_contents(conn->outbuf, &sz);
+  tt_str_op(cp1, OP_EQ,
+            "PROXY TCP6 fc00:dead:beef:4dad::0:ffff ::1 65535 42\r\n");
+  tor_free(cp1);
+
+  /* Check that GID with UINT16_MAX + 7 works. */
+  or_circ->global_identifier = UINT16_MAX + 7;
+
+  export_hs_client_circuit_id_haproxy(edge_conn, conn);
+  cp1 = buf_get_contents(conn->outbuf, &sz);
+  tt_str_op(cp1, OP_EQ, "PROXY TCP6 fc00:dead:beef:4dad::1:6 ::1 6 42\r\n");
 
  done:
   UNMOCK(connection_write_to_buf_impl_);