net/http: avoid leaking goroutines when TestServerGracefulClose retries

If the call to ReadString returns an error, the closure in
testServerGracefulClose will return an error and retry the test with a
longer timeout. If that happens, we need to wait for the conn.Write
goroutine to complete so that we don't leak connections across tests.

Updates #57084.
Fixes #62643.

Change-Id: Ia86c1bbd0a5e5d0aeccf4dfeb994c19d1fb10b00
Reviewed-on: https://go-review.googlesource.com/c/go/+/528398
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Damien Neil <[email protected]>

src/net/http/serve_test.go

@@ -3135,12 +3135,19 @@ func testServerGracefulClose(t *testing.T, mode testMode) {
  if err != nil {
  return err
  }
- defer conn.Close()
  writeErr := make(chan error)
  go func() {
  _, err := conn.Write(req)
  writeErr <- err
  }()
+ defer func() {
+ conn.Close()
+ // Wait for write to finish. This is a broken pipe on both
+ // Darwin and Linux, but checking this isn't the point of
+ // the test.
+ <-writeErr
+ }()
+
  br := bufio.NewReader(conn)
  lineNum := 0
  for {
@@ -3156,10 +3163,6 @@ func testServerGracefulClose(t *testing.T, mode testMode) {
  t.Errorf("Response line = %q; want a 401", line)
  }
  }
- // Wait for write to finish. This is a broken pipe on both
- // Darwin and Linux, but checking this isn't the point of
- // the test.
- <-writeErr
  return nil
  })
 }