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mcp: refactor the streamable client test to be more flexible

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Use a fake streamable server to facilitate testing client behavior.
For this commit, just update the existing test (moved to a new file for
isolation). Subsequent CLs will add more tests.

Improve one client error message that occurred while debuging tests.

For #393
This commit is contained in:
Rob Findley 2025-09-04 15:34:39 +00:00 • committed by Robert Findley
commit a4313f92bf
1 changed files with 193 additions and 72 deletions
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71
mcp/streamable_test.go
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@ -1035,77 +1035,6 @@ func mustMarshal(v any) json.RawMessage {
return data
}
func TestStreamableClientTransport(t *testing.T) {
// This test verifies various behavior of the streamable client transport:
// - check that it can handle application/json responses
// - check that it sends the negotiated protocol version
//
// TODO(rfindley): make this test more comprehensive, similar to
// [TestStreamableServerTransport].
ctx := context.Background()
resp := func(id int64, result any, err error) *jsonrpc.Response {
return &jsonrpc.Response{
ID: jsonrpc2.Int64ID(id),
Result: mustMarshal(result),
Error: err,
}
}
initResult := &InitializeResult{
Capabilities: &ServerCapabilities{
Completions: &CompletionCapabilities{},
Logging: &LoggingCapabilities{},
Tools: &ToolCapabilities{ListChanged: true},
},
ProtocolVersion: latestProtocolVersion,
ServerInfo: &Implementation{Name: "testServer", Version: "v1.0.0"},
}
initResp := resp(1, initResult, nil)
var reqN atomic.Int32 // request count
serverHandler := func(w http.ResponseWriter, r *http.Request) {
rN := reqN.Add(1)
// TODO(rfindley): if the status code is NoContent or Accepted, we should
// probably be tolerant of when the content type is not application/json.
w.Header().Set("Content-Type", "application/json")
if rN == 1 {
data, err := jsonrpc2.EncodeMessage(initResp)
if err != nil {
t.Errorf("encoding failed: %v", err)
}
w.Header().Set("Mcp-Session-Id", "123")
w.Write(data)
} else {
if v := r.Header.Get(protocolVersionHeader); v != latestProtocolVersion {
t.Errorf("bad protocol version header: got %q, want %q", v, latestProtocolVersion)
}
}
}
httpServer := httptest.NewServer(http.HandlerFunc(serverHandler))
defer httpServer.Close()
transport := &StreamableClientTransport{Endpoint: httpServer.URL}
client := NewClient(testImpl, nil)
session, err := client.Connect(ctx, transport, nil)
if err != nil {
t.Fatalf("client.Connect() failed: %v", err)
}
if err := session.Close(); err != nil {
t.Errorf("closing session: %v", err)
}
if got, want := reqN.Load(), int32(3); got < want {
// Expect at least 3 requests: initialize, initialized, and DELETE.
// We may or may not observe the GET, depending on timing.
t.Errorf("unexpected number of requests: got %d, want at least %d", got, want)
}
if diff := cmp.Diff(initResult, session.state.InitializeResult); diff != "" {
t.Errorf("mismatch (-want, +got):\n%s", diff)
}
}
func TestEventID(t *testing.T) {
tests := []struct {
sid StreamID