Protect TCP_NODELAY changes while sending headers

src/connection.toit

@@ -144,10 +144,11 @@ class Connection:
     // Set this before doing blocking operations on the socket, so that we
     // don't let another task start another request on the same connection.
     if has-body: current-writer_ = body-writer
-    socket_.no-delay = false
 
     headers-written := false
+    no-delay-restored := false
     try:
+      socket_.no-delay = false
       writer.write status
       headers.write-to writer
       if is-client-request and host_:
@@ -157,13 +158,19 @@ class Connection:
       writer.write "\r\n"
       headers-written = true
     finally:
-      // If we failed to write the headers the connection is unusable: the
-      // peer may have received a partial header. Close it, which also
-      // resets $current-writer_ so that later attempts to respond don't
-      // fail with "Previous request not completed".
-      if not headers-written: close
+      // The TCP_NODELAY setter can throw if the peer has gone away. The nested
+      // finally ensures that we still close while its exception propagates.
+      try:
+        if headers-written:
+          socket_.no-delay = true
+          no-delay-restored = true
+      finally:
+        // A partial header or a failed TCP_NODELAY restoration makes the
+        // connection unusable. Closing also resets $current-writer_.
+        if not headers-written or
+            not no-delay-restored:
+          close
 
-    socket_.no-delay = true
     return body-writer
 
   // Gets the next request from the client. If the client closes the

tests/server-peer-gone-test.toit

@@ -4,9 +4,7 @@
 
 // A client that connects, sends a request and closes before the server
 // writes the response must be treated as a normal disconnect: the server
-// keeps serving and doesn't log any extraneous traces. The only acceptable
-// trace is the one the server emits when the handler lets the socket error
-// itself escape.
+// keeps serving and doesn't log "Previous request not completed".
 
 import expect show *
 import http
@@ -49,12 +47,9 @@ main:
         print "---------------------------------------"
         recorder.traces.clear
         test --max-tasks=max-tasks --scenario=scenario
-        traces-seen := recorder.traces.size
-        // The OS may report the disconnect during the response write or when
-        // the server next reads from the connection.
-        maximum := scenario == PROPAGATE ? 1 : 0
-        if traces-seen > maximum:
-          failures.add "$scenario/max-tasks=$max-tasks ($traces-seen > $maximum)"
+        recorder.traces.do: | trace/ByteArray |
+          if trace.to-string.contains "Previous request not completed":
+            failures.add "$scenario/max-tasks=$max-tasks"
   finally:
     recorder.uninstall
   expect failures.is-empty --message="$failures"