Add test to check when proxy times-out mid-write to upstream

I've add to add code to allow the environment to specify the upstream
tiemout so we don't have to wait 30s for this test to happen.

src/proxy/proxy.c

@@ -58,6 +58,20 @@ struct proxier *proxy_create(char *s_downstream_address,
     out->downstream_fd = -1;
     out->upstream_fd = -1;
 
+    int upstream_timeout = UPSTREAM_TIMEOUT;
+
+    char *env_upstream_timeout = getenv("FLEXNBD_UPSTREAM_TIMEOUT");
+    if (NULL != env_upstream_timeout) {
+	int ut = atoi(env_upstream_timeout);
+        warn("Got %i from atoi\n", ut);
+	if (ut > 0) {
+	    upstream_timeout = ut;
+	}
+    }
+
+    out->upstream_timeout = upstream_timeout;
+    out->upstream_timeout_ms = (long unsigned int) upstream_timeout * 1000;
+
     out->prefetch = NULL;
     if (s_cache_bytes) {
 	int cache_bytes = atoi(s_cache_bytes);
@@ -781,6 +795,9 @@ void proxy_session(struct proxier *proxy)
 	};
 
 	if (select_timeout.tv_sec > 0) {
+	    if (select_timeout.tv_sec > proxy->upstream_timeout) {
+		select_timeout.tv_sec = proxy->upstream_timeout;
+	    }
 	    select_timeout_ptr = &select_timeout;
 	}
 
@@ -854,7 +871,7 @@ void proxy_session(struct proxier *proxy)
 	/* In these states, we're interested in restarting after a timeout.
 	 */
 	if (old_state == state && proxy_state_upstream(state)) {
-	    if ((monotonic_time_ms()) - state_started > UPSTREAM_TIMEOUT) {
+	    if ((monotonic_time_ms()) - state_started > proxy->upstream_timeout_ms) {
 		warn("Timed out in state %s while communicating with upstream", proxy_session_state_names[state]);
 		state = CONNECT_TO_UPSTREAM;
 	    }

src/proxy/proxy.h

@@ -14,10 +14,10 @@
 #endif
 
 /** UPSTREAM_TIMEOUT
- * How long ( in ms ) to allow for upstream to respond. If it takes longer
+ * How long (in s) to allow for upstream to respond. If it takes longer
  * than this, we will cancel the current request-response to them and resubmit
  */
-#define UPSTREAM_TIMEOUT 30 * 1000
+#define UPSTREAM_TIMEOUT 30
 
 struct proxier {
 	/** address/port to bind to */
@@ -72,6 +72,16 @@ struct proxier {
     uint64_t req_count;
     int hello_sent;
 
+    /*
+     * How long (in s) to allow for upstream to respond. If it takes longer
+     * than this, we will cancel the current request-response to them and
+     * resubmit
+     *
+     * Defaults to UPSTREAM_TIMEOUT but can be overridden in the environment.
+     */
+     int upstream_timeout;
+     unsigned long int upstream_timeout_ms;
+
 	/** These are only used if we pass --cache on the command line */
 
     /* While the in-flight request has been munged by prefetch, these two are

tests/acceptance/flexnbd/fake_dest.rb

@@ -54,6 +54,10 @@ module FlexNBD
         write_reply(handle, 1)
       end
 
+      def nread
+        @sock.nread
+      end
+
       def disconnected?
         Timeout.timeout(2) do
           @sock.read(1).nil?
@@ -85,6 +89,10 @@ module FlexNBD
         @sock.write(len)
       end
 
+      def getsockopt(level, optname)
+        @sock.getsockopt(level, optname)
+      end
+
       def self.parse_be64(str)
         raise "String is the wrong length: 8 bytes expected (#{str.length} received)" unless
           str.length == 8

tests/acceptance/proxy_tests.rb

@@ -206,6 +206,56 @@ module ProxyTests
     end
   end
 
+  def test_write_request_retried_when_upstream_times_out_during_write_phase
+    ENV['FLEXNBD_UPSTREAM_TIMEOUT'] = '4'
+    maker = make_fake_server
+
+    with_ld_preload('setsockopt_logger') do
+      with_proxied_client(4096) do |client|
+        server, sc1 = maker.value
+
+        # Guess an approprate request size, based on the send buffer size.
+        sz = sc1.getsockopt(Socket::SOL_SOCKET, Socket::SO_SNDBUF).int * 4
+        data1 = (b * sz)
+
+        # Send the read request to the proxy
+        client.write(0, data1)
+
+        # ensure we're given the read request
+        req1 = sc1.read_request
+        assert_equal ::FlexNBD::REQUEST_MAGIC, req1[:magic]
+        assert_equal ::FlexNBD::REQUEST_WRITE, req1[:type]
+        assert_equal 0, req1[:from]
+        assert_equal data1.size, req1[:len]
+
+        # Need to sleep longer than the timeout set above
+        sleep 5
+        # Check the number of bytes that can be read from the socket without
+        # blocking.  If this equal to the size of the original request, then
+        # the whole request has been buffered.  If this is the case, then the
+        # proxy will not time-out in the WRITE_UPSTREAM statem which is what
+        # we're trying to test.
+        assert sc1.nread < sz, 'Request from proxy completely buffered. Test is useless'
+
+        # Kill the server again, now we're sure the read request has been sent once
+        sc1.close
+
+        # We expect the proxy to reconnect without our client doing anything.
+        sc2 = server.accept
+        sc2.write_hello
+
+        # And once reconnected, it should resend an identical request.
+        req2 = sc2.read_request
+        assert_equal req1, req2
+        data2 = sc2.read_data(req2[:len])
+        assert_equal data1, data2
+
+        sc2.close
+        server.close
+      end
+    end
+  end
+
   def test_only_one_client_can_connect_to_proxy_at_a_time
     with_proxied_client do |_client|
       c2 = nil