gopls/internal/cmd: wait for startup log in TestMCPCommandHTTP
This test continues to be flaky. The most recent flake occurred
because after eight connection attempts with exponential backoff,
the server still wasn't ready to accept client connections. Instead
of using retries, we check the server's output logs to verify that
it has started.
Change-Id: I3cae36ea3c240049aff84d2a983a4565230679bb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/687075
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
diff --git a/gopls/internal/cmd/mcp_test.go b/gopls/internal/cmd/mcp_test.go
index c456036..2be71fd 100644
--- a/gopls/internal/cmd/mcp_test.go
+++ b/gopls/internal/cmd/mcp_test.go
@@ -5,6 +5,7 @@
package cmd_test
import (
+ "bufio"
"bytes"
"fmt"
"net"
@@ -159,7 +160,6 @@
-- go.mod --
module example.com
go 1.18
-
-- a.go --
package a
@@ -176,7 +176,14 @@
goplsCmd.Env = append(os.Environ(), "ENTRYPOINT=goplsMain")
goplsCmd.Dir = tree
goplsCmd.Stdout = os.Stderr
- goplsCmd.Stderr = os.Stderr
+
+ // Pipe stderr to a scanner, so that we can wait for the log message that
+ // tells us the server has started.
+ stderr, err := goplsCmd.StderrPipe()
+ if err != nil {
+ t.Fatal(err)
+ }
+ // forward stdout to test output
if err := goplsCmd.Start(); err != nil {
t.Fatalf("starting gopls: %v", err)
}
@@ -190,23 +197,30 @@
goplsCmd.Wait()
}()
+ // Wait for the MCP server to start listening. The referenced log occurs
+ // after the connection is opened via net.Listen and the HTTP handlers are
+ // set up.
+ ready := make(chan bool)
+ go func() {
+ // Copy from the pipe to stderr, keeping an eye out for the "mcp http
+ // server listening" string.
+ scan := bufio.NewScanner(stderr)
+ for scan.Scan() {
+ line := scan.Text()
+ if strings.Contains(line, "mcp http server listening") {
+ ready <- true
+ }
+ fmt.Fprintln(os.Stderr, line)
+ }
+ if err := scan.Err(); err != nil {
+ t.Logf("reading from pipe: %v", err)
+ }
+ }()
+
+ <-ready
client := mcp.NewClient("client", "v0.0.1", nil)
ctx := t.Context()
- // Wait for http server to start listening.
- var (
- mcpSession *mcp.ClientSession
- err error
- )
- maxRetries := 8
- for i := range maxRetries {
- mcpSession, err = client.Connect(ctx, mcp.NewSSEClientTransport("http://"+addr, nil))
- if err == nil {
- t.Log("succeeded")
- break // success
- }
- t.Logf("failed to connect on attempt %d: %v, trying again", i, err)
- time.Sleep(50 * time.Millisecond << i) // retry with exponential backoff
- }
+ mcpSession, err := client.Connect(ctx, mcp.NewSSEClientTransport("http://"+addr, nil))
if err != nil {
t.Fatalf("connecting to server: %v", err)
}
diff --git a/gopls/internal/mcp/mcp.go b/gopls/internal/mcp/mcp.go
index de0c513..d00b34b 100644
--- a/gopls/internal/mcp/mcp.go
+++ b/gopls/internal/mcp/mcp.go
@@ -70,6 +70,7 @@
<-ctx.Done()
svr.Close() // ignore error
}()
+ log.Printf("mcp http server listening")
return svr.Serve(listener)
}
