rpc: refactor read limit test (#32494)

closes #32240 #32232

The main cause for the time out is the slow json encoding of large data.
In #32240 they tried to resolve the issue by reducing the size of the
test. However as Felix pointed out, the test is still kind of confusing.

I've refactored the test so it is more understandable and have reduced
the amount of data needed to be json encoded. I think it is still
important to ensure that the default read limit is not active, so I have
retained one large (~32 MB) test case, but it's at least smaller than
the existing ~64 MB test case.

rpc/websocket_test.go

@@ -121,57 +121,50 @@ func TestWebsocketLargeRead(t *testing.T) {
 		srv     = newTestServer()
 		httpsrv = httptest.NewServer(srv.WebsocketHandler([]string{"*"}))
 		wsURL   = "ws:" + strings.TrimPrefix(httpsrv.URL, "http:")
+		buffer  = 64
 	)
 	defer srv.Stop()
 	defer httpsrv.Close()
 
-	testLimit := func(limit *int64) {
-		opts := []ClientOption{}
-		expLimit := int64(wsDefaultReadLimit)
-		if limit != nil && *limit >= 0 {
-			opts = append(opts, WithWebsocketMessageSizeLimit(*limit))
-			if *limit > 0 {
-				expLimit = *limit // 0 means infinite
-			}
+	for _, tt := range []struct {
+		size  int
+		limit int
+		err   bool
+	}{
+		{200, 200, false},                       // Small, successful request and limit
+		{2048, 1024, true},                      // Normal, failed request
+		{wsDefaultReadLimit + buffer, 0, false}, // Large, successful request, infinite limit
+	} {
+		func() {
+			if tt.limit != 0 {
+				// Some buffer is added to the limit to account for JSON encoding. It's
+				// skipped when the limit is zero since the intention is for the limit
+				// to be infinite.
+				tt.limit += buffer
 			}
+			opts := []ClientOption{WithWebsocketMessageSizeLimit(int64(tt.limit))}
 			client, err := DialOptions(context.Background(), wsURL, opts...)
 			if err != nil {
-			t.Fatalf("can't dial: %v", err)
+				t.Fatalf("failed to dial test server: %v", err)
 			}
 			defer client.Close()
-		// Remove some bytes for json encoding overhead.
-		underLimit := int(expLimit - 128)
-		overLimit := expLimit + 1
-		if expLimit == wsDefaultReadLimit {
-			// No point trying the full 32MB in tests. Just sanity-check that
-			// it's not obviously limited.
-			underLimit = 1024
-			overLimit = -1
-		}
+
 			var res string
-		// Check under limit
-		if err = client.Call(&res, "test_repeat", "A", underLimit); err != nil {
-			t.Fatalf("unexpected error with limit %d: %v", expLimit, err)
+			err = client.Call(&res, "test_repeat", "A", tt.size)
+			if tt.err && err == nil {
+				t.Fatalf("expected error, got none")
 			}
-		if len(res) != underLimit || strings.Count(res, "A") != underLimit {
+			if !tt.err {
+				if err != nil {
+					t.Fatalf("unexpected error with limit %d: %v", tt.limit, err)
+				}
+				if strings.Count(res, "A") != tt.size {
 					t.Fatal("incorrect data")
 				}
-		// Check over limit
-		if overLimit > 0 {
-			err = client.Call(&res, "test_repeat", "A", expLimit+1)
-			if err == nil || err != websocket.ErrReadLimit {
-				t.Fatalf("wrong error with limit %d: %v expecting %v", expLimit, err, websocket.ErrReadLimit)
 			}
+		}()
 	}
 }
-	ptr := func(v int64) *int64 { return &v }
-
-	testLimit(ptr(-1)) // Should be ignored (use default)
-	testLimit(ptr(0))  // Should be ignored (use default)
-	testLimit(nil)     // Should be ignored (use default)
-	testLimit(ptr(200))
-	testLimit(ptr(wsDefaultReadLimit * 2))
-}
 
 func TestWebsocketPeerInfo(t *testing.T) {
 	t.Parallel()