Allow JSON lowerCamelCase names

internal/twirptest/json_serialization/json_serialization_test.go

@@ -17,6 +17,7 @@ import (
 	bytes "bytes"
 	"context"
 	json "encoding/json"
+	io "io"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -58,13 +59,8 @@ func TestJSONSerializationServiceWithDefaults(t *testing.T) {
 	if resp.StatusCode != 200 {
 		t.Fatalf("manual EchoJSON invalid status, have=%d, want=200", resp.StatusCode)
 	}
-	buf := new(bytes.Buffer)
-	_, _ = buf.ReadFrom(resp.Body)
-	var objmap map[string]json.RawMessage
-	err = json.Unmarshal(buf.Bytes(), &objmap)
-	if err != nil {
-		t.Fatalf("json.Unmarshal err=%q", err)
-	}
+
+	objmap := readJSONAsMap(t, resp.Body)
 	for _, field := range []string{"query", "page_number", "hell", "foobar", "snippets", "all_empty"} {
 		if _, ok := objmap[field]; !ok {
 			t.Fatalf("expected JSON response to include field %q", field)
@@ -213,3 +209,55 @@ func TestJSONSerializationServiceSkipDefaults(t *testing.T) {
 		t.Fatalf("invalid msg2.Snippets[0], have=%v, want=%v", have, want)
 	}
 }
+
+func TestJSONSerializationCamelCase(t *testing.T) {
+	s := httptest.NewServer(
+		NewJSONSerializationServer(
+			&JSONSerializationService{},
+			twirp.WithServerJSONCamelCaseNames(true),
+		),
+	)
+	defer s.Close()
+
+	reqBody := bytes.NewBuffer([]byte(`{"pageNumber": 123}`))
+	req, _ := http.NewRequest("POST", s.URL+"/twirp/JSONSerialization/EchoJSON", reqBody)
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("manual EchoJSON err=%q", err)
+	}
+	if resp.StatusCode != 200 {
+		t.Fatalf("manual EchoJSON invalid status, have=%d, want=200", resp.StatusCode)
+	}
+
+	objmap := readJSONAsMap(t, resp.Body)
+
+	// response includes camelCase names
+	for _, field := range []string{"query", "pageNumber", "hell", "foobar", "snippets", "allEmpty"} {
+		if _, ok := objmap[field]; !ok {
+			t.Fatalf("expected JSON response to include camelCase field %q", field)
+		}
+	}
+
+	// response does not include original snake_case names
+	for _, field := range []string{"page_number", "all_empty"} {
+		if _, ok := objmap[field]; ok {
+			t.Fatalf("expected JSON response to NOT include snake_case field %q", field)
+		}
+	}
+}
+
+//
+// Test helpers
+//
+
+func readJSONAsMap(t *testing.T, body io.Reader) map[string]json.RawMessage {
+	buf := new(bytes.Buffer)
+	_, _ = buf.ReadFrom(body)
+	var objmap map[string]json.RawMessage
+	err := json.Unmarshal(buf.Bytes(), &objmap)
+	if err != nil {
+		t.Fatalf("json.Unmarshal err=%q", err)
+	}
+	return objmap
+}

protoc-gen-twirp/generator.go

@@ -1151,6 +1151,7 @@ func (t *twirp) generateServer(file *descriptor.FileDescriptorProto, service *de
 	t.P(`  hooks     *`, t.pkgs["twirp"], `.ServerHooks`)
 	t.P(`  pathPrefix string // prefix for routing`)
 	t.P(`  jsonSkipDefaults bool // do not include unpopulated fields (default values) in the response`)
+	t.P(`  jsonCamelCase bool // JSON fields are serialized as lowerCamelCase rather than keeping the original proto names`)
 	t.P(`}`)
 	t.P()
 
@@ -1164,6 +1165,8 @@ func (t *twirp) generateServer(file *descriptor.FileDescriptorProto, service *de
 	t.P(`  // Using ReadOpt allows backwards and forwads compatibility with new options in the future`)
 	t.P(`  jsonSkipDefaults := false`)
 	t.P(`  _ = serverOpts.ReadOpt("jsonSkipDefaults", &jsonSkipDefaults)`)
+	t.P(`  jsonCamelCase := false`)
+	t.P(`  _ = serverOpts.ReadOpt("jsonCamelCase", &jsonCamelCase)`)
 	t.P(`  var pathPrefix string`)
 	t.P(`  if ok := serverOpts.ReadOpt("pathPrefix", &pathPrefix); !ok {`)
 	t.P(`    pathPrefix = "/twirp" // default prefix`)
@@ -1175,6 +1178,7 @@ func (t *twirp) generateServer(file *descriptor.FileDescriptorProto, service *de
 	t.P(`    interceptor: `, t.pkgs["twirp"], `.ChainInterceptors(serverOpts.Interceptors...),`)
 	t.P(`    pathPrefix: pathPrefix,`)
 	t.P(`    jsonSkipDefaults: jsonSkipDefaults,`)
+	t.P(`    jsonCamelCase: jsonCamelCase,`)
 	t.P(`  }`)
 	t.P(`}`)
 	t.P()
@@ -1358,7 +1362,7 @@ func (t *twirp) generateServerJSONMethod(service *descriptor.ServiceDescriptorPr
 	t.P()
 	t.P(`  ctx = callResponsePrepared(ctx, s.hooks)`)
 	t.P()
-	t.P(`  marshaler := &`, t.pkgs["protojson"], `.MarshalOptions{UseProtoNames: true, EmitUnpopulated: !s.jsonSkipDefaults}`)
+	t.P(`  marshaler := &`, t.pkgs["protojson"], `.MarshalOptions{UseProtoNames: !s.jsonCamelCase, EmitUnpopulated: !s.jsonSkipDefaults}`)
 	t.P(`  respBytes, err := marshaler.Marshal(respContent)`)
 	t.P(`  if err != nil {`)
 	t.P(`    s.writeError(ctx, resp, wrapInternal(err, "failed to marshal json response"))`)

server_options.go

@@ -61,6 +61,18 @@ func WithServerJSONSkipDefaults(skipDefaults bool) ServerOption {
 	}
 }
 
+// WithServerJSONCamelCaseNames configures JSON serialization to use
+// lowerCamelCase field names rather than the original proto field names.
+// It is disabled by default, because JSON is commonly used for manual
+// debugging, but sometimes converting to lowerCamelCase is needed
+// to match the default canonical encoding on other proto-json parsers.
+// See: https://developers.google.com/protocol-buffers/docs/proto3#json
+func WithServerJSONCamelCaseNames(jsonCamelCase bool) ServerOption {
+	return func(opts *ServerOptions) {
+		opts.setOpt("jsonCamelCase", jsonCamelCase)
+	}
+}
+
 // ServerHooks is a container for callbacks that can instrument a
 // Twirp-generated server. These callbacks all accept a context and return a
 // context. They can use this to add to the request context as it threads