Handle JSON RPC errors. Resolves issue #672. (#673)

* Handle JSON RPC errors. Resolves issue #672.

* Refactor decode func to receive JSON RPC response. Remove error func.

* Comment tweaks.

examples/addsvc/pkg/addtransport/jsonrpc.go

@@ -137,9 +137,12 @@ func encodeSumResponse(_ context.Context, obj interface{}) (json.RawMessage, err
 	return b, nil
 }
 
-func decodeSumResponse(_ context.Context, msg json.RawMessage) (interface{}, error) {
-	var res addendpoint.SumResponse
-	err := json.Unmarshal(msg, &res)
+func decodeSumResponse(_ context.Context, res jsonrpc.Response) (interface{}, error) {
+	if res.Error != nil {
+		return nil, *res.Error
+	}
+	var sumres addendpoint.SumResponse
+	err := json.Unmarshal(res.Result, &sumres)
 	if err != nil {
 		return nil, fmt.Errorf("couldn't unmarshal body to SumResponse: %s", err)
 	}
@@ -185,9 +188,12 @@ func encodeConcatResponse(_ context.Context, obj interface{}) (json.RawMessage,
 	return b, nil
 }
 
-func decodeConcatResponse(_ context.Context, msg json.RawMessage) (interface{}, error) {
-	var res addendpoint.ConcatResponse
-	err := json.Unmarshal(msg, &res)
+func decodeConcatResponse(_ context.Context, res jsonrpc.Response) (interface{}, error) {
+	if res.Error != nil {
+		return nil, *res.Error
+	}
+	var concatres addendpoint.ConcatResponse
+	err := json.Unmarshal(res.Result, &concatres)
 	if err != nil {
 		return nil, fmt.Errorf("couldn't unmarshal body to ConcatResponse: %s", err)
 	}

transport/http/jsonrpc/client.go

@@ -67,10 +67,14 @@ func DefaultRequestEncoder(_ context.Context, req interface{}) (json.RawMessage,
 	return json.Marshal(req)
 }
 
-// DefaultResponseDecoder unmarshals the given JSON to interface{}.
-func DefaultResponseDecoder(_ context.Context, res json.RawMessage) (interface{}, error) {
+// DefaultResponseDecoder unmarshals the result to interface{}, or returns an
+// error, if found.
+func DefaultResponseDecoder(_ context.Context, res Response) (interface{}, error) {
+	if res.Error != nil {
+		return nil, *res.Error
+	}
 	var result interface{}
-	err := json.Unmarshal(res, &result)
+	err := json.Unmarshal(res.Result, &result)
 	if err != nil {
 		return nil, err
 	}
@@ -203,7 +207,7 @@ func (c Client) Endpoint() endpoint.Endpoint {
 			ctx = f(ctx, resp)
 		}
 
-		return c.dec(ctx, rpcRes.Result)
+		return c.dec(ctx, rpcRes)
 	}
 }
 

transport/http/jsonrpc/client_test.go

@@ -62,12 +62,12 @@ func TestClientHappyPath(t *testing.T) {
 		fin             = func(ctx context.Context, err error) {
 			finalizerCalled = true
 		}
-		decode = func(ctx context.Context, res json.RawMessage) (interface{}, error) {
+		decode = func(ctx context.Context, res jsonrpc.Response) (interface{}, error) {
 			if ac := ctx.Value(afterCalledKey); ac == nil {
 				t.Fatal("after not called")
 			}
 			var result int
-			err := json.Unmarshal(res, &result)
+			err := json.Unmarshal(res.Result, &result)
 			if err != nil {
 				return nil, err
 			}
@@ -206,6 +206,51 @@ func TestCanUseDefaults(t *testing.T) {
 	}
 }
 
+func TestClientCanHandleJSONRPCError(t *testing.T) {
+	var testbody = `{
+		"jsonrpc": "2.0",
+		"error": {
+			"code": -32603,
+			"message": "Bad thing happened."
+		}
+	}`
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(testbody))
+	}))
+
+	sut := jsonrpc.NewClient(mustParse(server.URL), "add")
+
+	_, err := sut.Endpoint()(context.Background(), 5)
+	if err == nil {
+		t.Fatal("Expected error, got none.")
+	}
+
+	{
+		want := "Bad thing happened."
+		got := err.Error()
+		if got != want {
+			t.Fatalf("error message: want=%s, got=%s", want, got)
+		}
+	}
+
+	type errorCoder interface {
+		ErrorCode() int
+	}
+	ec, ok := err.(errorCoder)
+	if !ok {
+		t.Fatal("Error is not errorCoder")
+	}
+
+	{
+		want := -32603
+		got := ec.ErrorCode()
+		if got != want {
+			t.Fatalf("error code: want=%d, got=%d", want, got)
+		}
+	}
+}
+
 func TestDefaultAutoIncrementer(t *testing.T) {
 	sut := jsonrpc.NewAutoIncrementID(0)
 	var want uint64

transport/http/jsonrpc/encode_decode.go

@@ -20,29 +20,29 @@ type EndpointCodec struct {
 // EndpointCodecMap maps the Request.Method to the proper EndpointCodec
 type EndpointCodecMap map[string]EndpointCodec
 
-// DecodeRequestFunc extracts a user-domain request object from an raw JSON
-// It's designed to be used in HTTP servers, for server-side endpoints.
+// DecodeRequestFunc extracts a user-domain request object from raw JSON
+// It's designed to be used in JSON RPC servers, for server-side endpoints.
 // One straightforward DecodeRequestFunc could be something that unmarshals
 // JSON from the request body to the concrete request type.
 type DecodeRequestFunc func(context.Context, json.RawMessage) (request interface{}, err error)
 
-// EncodeResponseFunc encodes the passed response object to a JSON RPC response.
+// EncodeResponseFunc encodes the passed response object to a JSON RPC result.
 // It's designed to be used in HTTP servers, for server-side endpoints.
 // One straightforward EncodeResponseFunc could be something that JSON encodes
 // the object directly.
 type EncodeResponseFunc func(context.Context, interface{}) (response json.RawMessage, err error)
 
 // Client-Side Codec
 
-// EncodeRequestFunc encodes the passed request object to raw JSON.
+// EncodeRequestFunc encodes the given request object to raw JSON.
 // It's designed to be used in JSON RPC clients, for client-side
 // endpoints. One straightforward EncodeResponseFunc could be something that
 // JSON encodes the object directly.
 type EncodeRequestFunc func(context.Context, interface{}) (request json.RawMessage, err error)
 
-// DecodeResponseFunc extracts a user-domain response object from an HTTP
-// request object. It's designed to be used in JSON RPC clients, for
-// client-side endpoints. One straightforward DecodeRequestFunc could be
-// something that JSON decodes from the request body to the concrete
-// response type.
-type DecodeResponseFunc func(context.Context, json.RawMessage) (response interface{}, err error)
+// DecodeResponseFunc extracts a user-domain response object from an JSON RPC
+// response object. It's designed to be used in JSON RPC clients, for
+// client-side endpoints. It is the responsibility of this function to decide
+// whether any error present in the JSON RPC response should be surfaced to the
+// client endpoint.
+type DecodeResponseFunc func(context.Context, Response) (response interface{}, err error)