From ed34451cb32c7ee553ce26c8936f9498e9c44e70 Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Fri, 20 Aug 2021 18:54:18 -0700
Subject: [PATCH 1/7] Infrastructure to provide REST-specific handlers via
 hooks

NEXT:
- clean up init function for go view creator
- add custom operation for unknown enum
---
 .../google/showcase/v1beta1/compliance.proto  | 11 +++++
 server/genrest/compliance_manual.go           | 47 +++++++++++++++++++
 server/services/compliance_service.go         |  4 ++
 util/genrest/goviewcreator.go                 | 18 +++++++
 4 files changed, 80 insertions(+)
 create mode 100644 server/genrest/compliance_manual.go

diff --git a/schema/google/showcase/v1beta1/compliance.proto b/schema/google/showcase/v1beta1/compliance.proto
index 6b55407c6..3905f9a52 100644
--- a/schema/google/showcase/v1beta1/compliance.proto
+++ b/schema/google/showcase/v1beta1/compliance.proto
@@ -96,6 +96,17 @@ service Compliance {
     };
   }
 
+  // This method returns an unknown enum value. Client libraries should either error gracefully (not
+  // crash), ignore the value, or, depending on the API, set it to the zero default.
+  //
+  // This only works over REST currently. Requests over gRPC will echo the request and should
+  // succeed on the client side
+  rpc RepeatWithUnknownEnum(RepeatRequest) returns (RepeatResponse) {
+    option (google.api.http) = {
+      post: "/v1beta1/repeat:invalidenum"
+      body: "*"
+    };
+  }
 }
 
 message RepeatRequest {
diff --git a/server/genrest/compliance_manual.go b/server/genrest/compliance_manual.go
new file mode 100644
index 000000000..376ea2c1e
--- /dev/null
+++ b/server/genrest/compliance_manual.go
@@ -0,0 +1,47 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package genrest
+
+import (
+	"context"
+	"net/http"
+
+	genprotopb "github.com/googleapis/gapic-showcase/server/genproto"
+	"github.com/googleapis/gapic-showcase/util/genrest/resttools"
+)
+
+// .google.showcase.v1beta1.Compliance.HandleRepeatDataBody
+func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest) {
+	marshaler := resttools.ToJSON()
+
+	response, err := backend.ComplianceServer.RepeatWithUnknownEnum(context.Background(), request)
+	if err != nil {
+		// TODO: Properly handle error. Is StatusInternalServerError (500) the right response?
+		backend.Error(w, http.StatusInternalServerError, "server error: %s", err.Error())
+		return
+	}
+
+	// FIXME: change response field to sentinel enum
+
+	json, err := marshaler.Marshal(response)
+	if err != nil {
+		backend.Error(w, http.StatusInternalServerError, "error json-encoding response: %s", err.Error())
+		return
+	}
+
+	// FIXME: change sentinel to unknown value
+
+	w.Write(json)
+}
diff --git a/server/services/compliance_service.go b/server/services/compliance_service.go
index e3b40f0e1..fdc85b4f1 100644
--- a/server/services/compliance_service.go
+++ b/server/services/compliance_service.go
@@ -98,6 +98,10 @@ func (csi *complianceServerImpl) RepeatDataBodyPatch(ctx context.Context, in *pb
 	return csi.Repeat(ctx, in)
 }
 
+func (csi *complianceServerImpl) RepeatWithUnknownEnum(ctx context.Context, in *pb.RepeatRequest) (*pb.RepeatResponse, error) {
+	return csi.Repeat(ctx, in)
+}
+
 // complianceSuiteBytes contains the contents of the compliance suite JSON file. This requires Go
 // 1.16. Note that embedding can only be applied to global variables at package scope.
 //go:embed compliance_suite.json
diff --git a/util/genrest/goviewcreator.go b/util/genrest/goviewcreator.go
index afc0ff48e..b5bec2ccb 100644
--- a/util/genrest/goviewcreator.go
+++ b/util/genrest/goviewcreator.go
@@ -24,6 +24,14 @@ import (
 	"github.com/googleapis/gapic-showcase/util/genrest/resttools"
 )
 
+var customFunctions map[string]string
+
+func init() {
+	customFunctions = map[string]string{
+		".google.showcase.v1beta1.Compliance.RepeatWithUnknownEnum": "customRepeatWithUnknownEnum",
+	}
+}
+
 // NewView creates a a new goview.View (a series of files to be output) from a gomodel.Model. The
 // current approach is to generate one file per service, with that file containing all the service's
 // RPCs. An additional file `genrest.go` is also created to register all these handlers with a
@@ -189,6 +197,16 @@ func NewView(model *gomodel.Model) (*goview.View, error) {
 			source.P("  requestJSON, _ := marshaler.Marshal(%s)", handler.RequestVariable)
 			source.P(`  backend.StdLog.Printf("  request: %%s", requestJSON)`)
 			source.P("")
+
+			methodId := fmt.Sprintf("%s.%s", service.ProtoPath, handler.GoMethod)
+			customHandler, _ := customFunctions[methodId]
+			source.P("  // %s", methodId)
+			if len(customHandler) > 0 {
+				source.P("  backend.%s(w, r, request)  // %s", customHandler, methodId)
+				source.P("}")
+				continue
+			}
+
 			// TODO: In the future, we may want to redirect all REST-endpoint requests to the gRPC endpoint so that the gRPC-registered observers get invoked.
 			source.P("  %s, err := backend.%sServer.%s(context.Background(), %s)", handler.ResponseVariable, service.ShortName, handler.GoMethod, handler.RequestVariable)
 			source.P("  if err != nil {")

From 5bfe059185c2b15d364c47b875c4c3c064bdf983 Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Sat, 21 Aug 2021 12:51:37 -0700
Subject: [PATCH 2/7] Provide an unknown enum

NEXT: need tests, clean up code
---
 server/genrest/README.md                              |  6 ++++--
 .../{compliance_manual.go => compliance_custom.go}    | 11 ++++++++---
 2 files changed, 12 insertions(+), 5 deletions(-)
 rename server/genrest/{compliance_manual.go => compliance_custom.go} (70%)

diff --git a/server/genrest/README.md b/server/genrest/README.md
index 192b71c78..259e0c624 100644
--- a/server/genrest/README.md
+++ b/server/genrest/README.md
@@ -1,4 +1,6 @@
 # server/genrest
 
-This directory contains auto-generated files used to implement a REST endpoint
-for Showcase services.
+This directory contains mostly auto-generated files used to implement a REST
+endpoint for Showcase services. The `*_custom.go` files contain manually written
+REST-specific handlers, which are useful for helping generators test
+REST-specific functionality (such as invalid JSON).
diff --git a/server/genrest/compliance_manual.go b/server/genrest/compliance_custom.go
similarity index 70%
rename from server/genrest/compliance_manual.go
rename to server/genrest/compliance_custom.go
index 376ea2c1e..5214da269 100644
--- a/server/genrest/compliance_manual.go
+++ b/server/genrest/compliance_custom.go
@@ -15,6 +15,7 @@
 package genrest
 
 import (
+	"bytes"
 	"context"
 	"net/http"
 
@@ -22,7 +23,7 @@ import (
 	"github.com/googleapis/gapic-showcase/util/genrest/resttools"
 )
 
-// .google.showcase.v1beta1.Compliance.HandleRepeatDataBody
+// customRepeatWithUnknownEnum provides REST-specific handling for a RepeatWithUnknownEnum request. It returns a JSON response with an unknown enum symbol string in an enum field.
 func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest) {
 	marshaler := resttools.ToJSON()
 
@@ -33,7 +34,10 @@ func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r
 		return
 	}
 
-	// FIXME: change response field to sentinel enum
+	// Make sure we have at least one sentinel value before serializing properly.
+	sentinelValue := genprotopb.ComplianceData_LIFE_KINGDOM_UNSPECIFIED
+	sentinelString := genprotopb.ComplianceData_LifeKingdom_name[int32(sentinelValue)]
+	response.Request.Info.FKingdom = sentinelValue
 
 	json, err := marshaler.Marshal(response)
 	if err != nil {
@@ -41,7 +45,8 @@ func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r
 		return
 	}
 
-	// FIXME: change sentinel to unknown value
+	// Change the sentinel string to an unknown value.
+	json = bytes.ReplaceAll(json, []byte(sentinelString), []byte("LIFE_KINGDOM_NEW"))
 
 	w.Write(json)
 }

From acba666543276ad3e03e51d7c0e6dc75667a8930 Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Tue, 24 Aug 2021 16:53:57 -0700
Subject: [PATCH 3/7] Added test for TestRepeatWithUnknownEnum

Asa  result of the test, also fixed NPE by ensuring submessages are present before referencing them.
---
 cmd/gapic-showcase/compliance_custom_test.go | 101 +++++++++++++++++++
 cmd/gapic-showcase/compliance_suite_test.go  |   2 +-
 server/genrest/compliance_custom.go          |   6 ++
 3 files changed, 108 insertions(+), 1 deletion(-)
 create mode 100644 cmd/gapic-showcase/compliance_custom_test.go

diff --git a/cmd/gapic-showcase/compliance_custom_test.go b/cmd/gapic-showcase/compliance_custom_test.go
new file mode 100644
index 000000000..d71c062aa
--- /dev/null
+++ b/cmd/gapic-showcase/compliance_custom_test.go
@@ -0,0 +1,101 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"io/ioutil"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/googleapis/gapic-showcase/server/genproto"
+	genprotopb "github.com/googleapis/gapic-showcase/server/genproto"
+	"github.com/googleapis/gapic-showcase/util/genrest/resttools"
+	"google.golang.org/protobuf/encoding/protojson"
+)
+
+// TestRepeatWithUnknownEnum
+func TestRepeatWithUnknownEnum(t *testing.T) {
+	_, server, err := complianceSuiteTestSetup()
+	if err != nil {
+		t.Fatal(err)
+	}
+	server.Start()
+	defer server.Close()
+
+	resttools.JSONMarshaler.Replace(nil)
+	defer resttools.JSONMarshaler.Restore()
+
+	request := &genprotopb.RepeatRequest{
+		FInt32: 23,
+	}
+
+	// First ensure the request would be otherwise successful
+	errorPrefix := `"repeat:body":`
+	responseBody, requestBody := getJSONResponse(t, request, server.URL+"/v1beta1/repeat:body", errorPrefix)
+	var response genproto.RepeatResponse
+	if err := protojson.Unmarshal(responseBody, &response); err != nil {
+		t.Fatalf("%s could not unmarshal httpResponse body: %s\n   response body: %s\n   request: %s\n",
+			errorPrefix, err, string(responseBody), string(requestBody))
+	}
+
+	// Then ensure the expected error occurs
+	errorPrefix = `"repeat:invalidenum":`
+	responseBody, requestBody = getJSONResponse(t, request, server.URL+"/v1beta1/repeat:invalidenum", errorPrefix)
+	err = protojson.Unmarshal(responseBody, &response)
+	if err == nil {
+		t.Fatalf("%s did not receive an error:\n   response body: %s\n   request: %s\n",
+			errorPrefix, string(responseBody), string(requestBody))
+	}
+	if !strings.Contains(err.Error(), "invalid value for enum type") {
+		t.Fatalf("%s received different error than expected: %s\n   response body: %s\n   request: %s\n",
+			errorPrefix, err, string(responseBody), string(requestBody))
+	}
+
+}
+
+func getJSONResponse(t *testing.T, request *genprotopb.RepeatRequest, uri, errorPrefix string) (responseBody, requestBody []byte) {
+	verb := "POST"
+	requestBody, err := resttools.ToJSON().Marshal(request)
+	if err != nil {
+		t.Fatalf("%s error encoding request: %s", errorPrefix, err)
+	}
+
+	httpRequest, err := http.NewRequest(verb, uri, strings.NewReader(string(requestBody)))
+	if err != nil {
+		t.Fatalf("%s error creating request: %s", errorPrefix, err)
+	}
+	resttools.PopulateRequestHeaders(httpRequest)
+
+	httpResponse, err := http.DefaultClient.Do(httpRequest)
+	if err != nil {
+		t.Fatalf("%s error issuing call: %s", errorPrefix, err)
+	}
+
+	// Check for successful response.
+	if got, want := httpResponse.StatusCode, http.StatusOK; got != want {
+		t.Errorf("%s response code: got %d, want %d\n   %s %s\n\n",
+			errorPrefix, got, want, verb, uri)
+	}
+
+	responseBody, err = ioutil.ReadAll(httpResponse.Body)
+	httpResponse.Body.Close()
+	if err != nil {
+		t.Fatalf("%s could not read httpResponse body: %s", errorPrefix, err)
+	}
+	return responseBody, requestBody
+}
+
+// repeat wtih same message for invalidenum; check for error
diff --git a/cmd/gapic-showcase/compliance_suite_test.go b/cmd/gapic-showcase/compliance_suite_test.go
index 89f4d60ac..b9c30f05d 100644
--- a/cmd/gapic-showcase/compliance_suite_test.go
+++ b/cmd/gapic-showcase/compliance_suite_test.go
@@ -107,7 +107,7 @@ func TestComplianceSuite(t *testing.T) {
 				}
 
 				// Unmarshal httpResponse body, interpreted as JSON.
-				// should do this.
+				// GAPIC generators should do this in their tests.
 				responseBody, err := ioutil.ReadAll(httpResponse.Body)
 				httpResponse.Body.Close()
 				if err != nil {
diff --git a/server/genrest/compliance_custom.go b/server/genrest/compliance_custom.go
index 5214da269..b8c50ad50 100644
--- a/server/genrest/compliance_custom.go
+++ b/server/genrest/compliance_custom.go
@@ -37,6 +37,12 @@ func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r
 	// Make sure we have at least one sentinel value before serializing properly.
 	sentinelValue := genprotopb.ComplianceData_LIFE_KINGDOM_UNSPECIFIED
 	sentinelString := genprotopb.ComplianceData_LifeKingdom_name[int32(sentinelValue)]
+	if response.Request == nil {
+		response.Request = &genprotopb.RepeatRequest{}
+	}
+	if response.Request.Info == nil {
+		response.Request.Info = &genprotopb.ComplianceData{}
+	}
 	response.Request.Info.FKingdom = sentinelValue
 
 	json, err := marshaler.Marshal(response)

From 11434063bc3cd3950e4bb945ae8b69191626891d Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Tue, 24 Aug 2021 20:10:06 -0700
Subject: [PATCH 4/7] Add and implement RepeatWithUnknownOptionalEnum RPC

Need to test this next.
---
 .../google/showcase/v1beta1/compliance.proto  | 12 +++++++++++
 server/genrest/compliance_custom.go           | 21 ++++++++++++++++++-
 server/services/compliance_service.go         |  4 ++++
 util/genrest/goviewcreator.go                 |  3 ++-
 4 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/schema/google/showcase/v1beta1/compliance.proto b/schema/google/showcase/v1beta1/compliance.proto
index 3905f9a52..3e4ecc8eb 100644
--- a/schema/google/showcase/v1beta1/compliance.proto
+++ b/schema/google/showcase/v1beta1/compliance.proto
@@ -107,6 +107,18 @@ service Compliance {
       body: "*"
     };
   }
+
+  // This method returns an unknown enum value. Client libraries should either error gracefully (not
+  // crash), ignore the value, or, depending on the API, set it to the zero default.
+  //
+  // This only works over REST currently. Requests over gRPC will echo the request and should
+  // succeed on the client side
+  rpc RepeatWithUnknownOptionalEnum(RepeatRequest) returns (RepeatResponse) {
+    option (google.api.http) = {
+      post: "/v1beta1/repeat:invalidoptionalenum"
+      body: "*"
+    };
+  }
 }
 
 message RepeatRequest {
diff --git a/server/genrest/compliance_custom.go b/server/genrest/compliance_custom.go
index b8c50ad50..da1d85bc5 100644
--- a/server/genrest/compliance_custom.go
+++ b/server/genrest/compliance_custom.go
@@ -25,6 +25,22 @@ import (
 
 // customRepeatWithUnknownEnum provides REST-specific handling for a RepeatWithUnknownEnum request. It returns a JSON response with an unknown enum symbol string in an enum field.
 func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest) {
+	mutator := func(data *genprotopb.ComplianceData, sentinelValue genprotopb.ComplianceData_LifeKingdom) {
+		data.FKingdom = sentinelValue
+	}
+	backend.customRepeatWithUnknownEnumMethod(w, r, request, mutator)
+}
+
+// customRepeatWithUnknownOptionalEnum provides REST-specific handling for a RepeatWithUnknownOptionalEnum request. It returns a JSON response with an unknown enum symbol string in an enum field.
+func (backend *RESTBackend) customRepeatWithUnknownOptionalEnum(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest) {
+	mutator := func(data *genprotopb.ComplianceData, sentinelValue genprotopb.ComplianceData_LifeKingdom) {
+		data.PKingdom = &sentinelValue
+	}
+	backend.customRepeatWithUnknownEnumMethod(w, r, request, mutator)
+}
+
+// customRepeatWithUnknownEnumMethod provides REST-specific handling for the RepeatWithUnknown*Enum request. It returns a JSON response with an unknown enum symbol string in an enum field.
+func (backend *RESTBackend) customRepeatWithUnknownEnumMethod(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest, mutate enumMutator) {
 	marshaler := resttools.ToJSON()
 
 	response, err := backend.ComplianceServer.RepeatWithUnknownEnum(context.Background(), request)
@@ -43,7 +59,7 @@ func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r
 	if response.Request.Info == nil {
 		response.Request.Info = &genprotopb.ComplianceData{}
 	}
-	response.Request.Info.FKingdom = sentinelValue
+	mutate(response.Request.Info, sentinelValue)
 
 	json, err := marshaler.Marshal(response)
 	if err != nil {
@@ -56,3 +72,6 @@ func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r
 
 	w.Write(json)
 }
+
+// enumMutator represents a function that modifies data in place using sentinelValue.
+type enumMutator func(data *genprotopb.ComplianceData, sentinelValue genprotopb.ComplianceData_LifeKingdom)
diff --git a/server/services/compliance_service.go b/server/services/compliance_service.go
index fdc85b4f1..4fe7f8406 100644
--- a/server/services/compliance_service.go
+++ b/server/services/compliance_service.go
@@ -102,6 +102,10 @@ func (csi *complianceServerImpl) RepeatWithUnknownEnum(ctx context.Context, in *
 	return csi.Repeat(ctx, in)
 }
 
+func (csi *complianceServerImpl) RepeatWithUnknownOptionalEnum(ctx context.Context, in *pb.RepeatRequest) (*pb.RepeatResponse, error) {
+	return csi.Repeat(ctx, in)
+}
+
 // complianceSuiteBytes contains the contents of the compliance suite JSON file. This requires Go
 // 1.16. Note that embedding can only be applied to global variables at package scope.
 //go:embed compliance_suite.json
diff --git a/util/genrest/goviewcreator.go b/util/genrest/goviewcreator.go
index b5bec2ccb..43b369bdc 100644
--- a/util/genrest/goviewcreator.go
+++ b/util/genrest/goviewcreator.go
@@ -28,7 +28,8 @@ var customFunctions map[string]string
 
 func init() {
 	customFunctions = map[string]string{
-		".google.showcase.v1beta1.Compliance.RepeatWithUnknownEnum": "customRepeatWithUnknownEnum",
+		".google.showcase.v1beta1.Compliance.RepeatWithUnknownEnum":         "customRepeatWithUnknownEnum",
+		".google.showcase.v1beta1.Compliance.RepeatWithUnknownOptionalEnum": "customRepeatWithUnknownOptionalEnum",
 	}
 }
 

From 1ee9d48d2bdd582ffa664f7f1ebc2c957203ef21 Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Tue, 24 Aug 2021 20:24:42 -0700
Subject: [PATCH 5/7] Add test for RepeatWithUnknownOptionalEnum

---
 cmd/gapic-showcase/compliance_custom_test.go | 43 +++++++++++---------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/cmd/gapic-showcase/compliance_custom_test.go b/cmd/gapic-showcase/compliance_custom_test.go
index d71c062aa..c361b2c3c 100644
--- a/cmd/gapic-showcase/compliance_custom_test.go
+++ b/cmd/gapic-showcase/compliance_custom_test.go
@@ -15,6 +15,7 @@
 package main
 
 import (
+	"fmt"
 	"io/ioutil"
 	"net/http"
 	"strings"
@@ -42,28 +43,30 @@ func TestRepeatWithUnknownEnum(t *testing.T) {
 		FInt32: 23,
 	}
 
-	// First ensure the request would be otherwise successful
-	errorPrefix := `"repeat:body":`
-	responseBody, requestBody := getJSONResponse(t, request, server.URL+"/v1beta1/repeat:body", errorPrefix)
-	var response genproto.RepeatResponse
-	if err := protojson.Unmarshal(responseBody, &response); err != nil {
-		t.Fatalf("%s could not unmarshal httpResponse body: %s\n   response body: %s\n   request: %s\n",
-			errorPrefix, err, string(responseBody), string(requestBody))
-	}
+	for idx, variant := range []string{"invalidenum", "invalidoptionalenum"} {
+		errorPrefix := fmt.Sprintf("[%d %q]", idx, variant)
 
-	// Then ensure the expected error occurs
-	errorPrefix = `"repeat:invalidenum":`
-	responseBody, requestBody = getJSONResponse(t, request, server.URL+"/v1beta1/repeat:invalidenum", errorPrefix)
-	err = protojson.Unmarshal(responseBody, &response)
-	if err == nil {
-		t.Fatalf("%s did not receive an error:\n   response body: %s\n   request: %s\n",
-			errorPrefix, string(responseBody), string(requestBody))
-	}
-	if !strings.Contains(err.Error(), "invalid value for enum type") {
-		t.Fatalf("%s received different error than expected: %s\n   response body: %s\n   request: %s\n",
-			errorPrefix, err, string(responseBody), string(requestBody))
-	}
+		// First ensure the request would be otherwise successful
+		responseBody, requestBody := getJSONResponse(t, request, server.URL+"/v1beta1/repeat:body", errorPrefix)
+		var response genproto.RepeatResponse
+		if err := protojson.Unmarshal(responseBody, &response); err != nil {
+			t.Fatalf("%s could not unmarshal valid response body: %s\n   response body: %s\n   request: %s\n",
+				errorPrefix, err, string(responseBody), string(requestBody))
+		}
 
+		// Then ensure the expected error occurs
+		responseBody, requestBody = getJSONResponse(t, request,
+			fmt.Sprintf("%s/v1beta1/repeat:%s", server.URL, variant), errorPrefix)
+		err = protojson.Unmarshal(responseBody, &response)
+		if err == nil {
+			t.Fatalf("%s did not receive an error:\n   response body: %s\n   request: %s\n",
+				errorPrefix, string(responseBody), string(requestBody))
+		}
+		if !strings.Contains(err.Error(), "invalid value for enum type") {
+			t.Fatalf("%s received different error than expected: %s\n   response body: %s\n   request: %s\n",
+				errorPrefix, err, string(responseBody), string(requestBody))
+		}
+	}
 }
 
 func getJSONResponse(t *testing.T, request *genprotopb.RepeatRequest, uri, errorPrefix string) (responseBody, requestBody []byte) {

From ea6a882448ca9b8006d219ac2fef60ecf272f190 Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Wed, 25 Aug 2021 09:16:40 -0700
Subject: [PATCH 6/7] Use non-zero value as a sentinel

This allows isolating unknown enum values in specific fields.
---
 server/genrest/compliance_custom.go | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/server/genrest/compliance_custom.go b/server/genrest/compliance_custom.go
index da1d85bc5..5ae651216 100644
--- a/server/genrest/compliance_custom.go
+++ b/server/genrest/compliance_custom.go
@@ -50,8 +50,11 @@ func (backend *RESTBackend) customRepeatWithUnknownEnumMethod(w http.ResponseWri
 		return
 	}
 
-	// Make sure we have at least one sentinel value before serializing properly.
-	sentinelValue := genprotopb.ComplianceData_LIFE_KINGDOM_UNSPECIFIED
+	// Make sure we have at least one sentinel value before serializing properly; we will then
+	// replace the sentinel value in the JSON with an unknown value. The sentinel value should
+	// be a non-zero value, since unset non-proto-optional fields will serialize with the zero
+	// value, which would result in all of these always getting the new, unknown value
+	sentinelValue := genprotopb.ComplianceData_ANIMALIA
 	sentinelString := genprotopb.ComplianceData_LifeKingdom_name[int32(sentinelValue)]
 	if response.Request == nil {
 		response.Request = &genprotopb.RepeatRequest{}

From 3b54211b1f79b3a19c59399ddd20286acf35b063 Mon Sep 17 00:00:00 2001
From: Victor Chudnovsky <vchudnov@google.com>
Date: Wed, 25 Aug 2021 10:27:57 -0700
Subject: [PATCH 7/7] Cosmetic fixes.

---
 cmd/gapic-showcase/compliance_custom_test.go  | 10 ++++----
 .../google/showcase/v1beta1/compliance.proto  | 16 ++++++-------
 server/genrest/compliance_custom.go           | 12 ++++++----
 server/services/compliance_service_test.go    |  2 ++
 util/genrest/goviewcreator.go                 | 24 ++++++++++---------
 5 files changed, 35 insertions(+), 29 deletions(-)

diff --git a/cmd/gapic-showcase/compliance_custom_test.go b/cmd/gapic-showcase/compliance_custom_test.go
index c361b2c3c..d2d35d4c8 100644
--- a/cmd/gapic-showcase/compliance_custom_test.go
+++ b/cmd/gapic-showcase/compliance_custom_test.go
@@ -27,7 +27,7 @@ import (
 	"google.golang.org/protobuf/encoding/protojson"
 )
 
-// TestRepeatWithUnknownEnum
+// TestRepeatWithUnknownEnum tests both RepeatWithUnknownEnum and RepeatWithUnknownOptionalEnum
 func TestRepeatWithUnknownEnum(t *testing.T) {
 	_, server, err := complianceSuiteTestSetup()
 	if err != nil {
@@ -39,9 +39,7 @@ func TestRepeatWithUnknownEnum(t *testing.T) {
 	resttools.JSONMarshaler.Replace(nil)
 	defer resttools.JSONMarshaler.Restore()
 
-	request := &genprotopb.RepeatRequest{
-		FInt32: 23,
-	}
+	request := &genprotopb.RepeatRequest{}
 
 	for idx, variant := range []string{"invalidenum", "invalidoptionalenum"} {
 		errorPrefix := fmt.Sprintf("[%d %q]", idx, variant)
@@ -69,6 +67,8 @@ func TestRepeatWithUnknownEnum(t *testing.T) {
 	}
 }
 
+// getJSONResponse is a helper function for TestRepeatWithUnknownEnum. It issues the REST request to
+// the given URI and returns both the response and request JSON bodies.
 func getJSONResponse(t *testing.T, request *genprotopb.RepeatRequest, uri, errorPrefix string) (responseBody, requestBody []byte) {
 	verb := "POST"
 	requestBody, err := resttools.ToJSON().Marshal(request)
@@ -100,5 +100,3 @@ func getJSONResponse(t *testing.T, request *genprotopb.RepeatRequest, uri, error
 	}
 	return responseBody, requestBody
 }
-
-// repeat wtih same message for invalidenum; check for error
diff --git a/schema/google/showcase/v1beta1/compliance.proto b/schema/google/showcase/v1beta1/compliance.proto
index 3e4ecc8eb..8386f98c2 100644
--- a/schema/google/showcase/v1beta1/compliance.proto
+++ b/schema/google/showcase/v1beta1/compliance.proto
@@ -96,11 +96,11 @@ service Compliance {
     };
   }
 
-  // This method returns an unknown enum value. Client libraries should either error gracefully (not
-  // crash), ignore the value, or, depending on the API, set it to the zero default.
+  // This method returns an unknown value for a non-optional enum field. Client libraries should
+  // either error gracefully (not crash), ignore the value, or, depending on the API, set it to the
+  // zero default.
   //
-  // This only works over REST currently. Requests over gRPC will echo the request and should
-  // succeed on the client side
+  // This only works over REST currently. Requests over gRPC will simply echo the request.
   rpc RepeatWithUnknownEnum(RepeatRequest) returns (RepeatResponse) {
     option (google.api.http) = {
       post: "/v1beta1/repeat:invalidenum"
@@ -108,11 +108,11 @@ service Compliance {
     };
   }
 
-  // This method returns an unknown enum value. Client libraries should either error gracefully (not
-  // crash), ignore the value, or, depending on the API, set it to the zero default.
+  // This method returns an unknown value for an optional enum field. Client libraries should either
+  // error gracefully (not crash), ignore the value, or, depending on the API, set it to the zero
+  // default.
   //
-  // This only works over REST currently. Requests over gRPC will echo the request and should
-  // succeed on the client side
+  // This only works over REST currently. Requests over gRPC will simply echo the request.
   rpc RepeatWithUnknownOptionalEnum(RepeatRequest) returns (RepeatResponse) {
     option (google.api.http) = {
       post: "/v1beta1/repeat:invalidoptionalenum"
diff --git a/server/genrest/compliance_custom.go b/server/genrest/compliance_custom.go
index 5ae651216..a4bd2d7f8 100644
--- a/server/genrest/compliance_custom.go
+++ b/server/genrest/compliance_custom.go
@@ -23,7 +23,8 @@ import (
 	"github.com/googleapis/gapic-showcase/util/genrest/resttools"
 )
 
-// customRepeatWithUnknownEnum provides REST-specific handling for a RepeatWithUnknownEnum request. It returns a JSON response with an unknown enum symbol string in an enum field.
+// customRepeatWithUnknownEnum provides REST-specific handling for a RepeatWithUnknownEnum
+// request. It returns a JSON response with an unknown enum symbol string in an enum field.
 func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest) {
 	mutator := func(data *genprotopb.ComplianceData, sentinelValue genprotopb.ComplianceData_LifeKingdom) {
 		data.FKingdom = sentinelValue
@@ -31,7 +32,9 @@ func (backend *RESTBackend) customRepeatWithUnknownEnum(w http.ResponseWriter, r
 	backend.customRepeatWithUnknownEnumMethod(w, r, request, mutator)
 }
 
-// customRepeatWithUnknownOptionalEnum provides REST-specific handling for a RepeatWithUnknownOptionalEnum request. It returns a JSON response with an unknown enum symbol string in an enum field.
+// customRepeatWithUnknownOptionalEnum provides REST-specific handling for a
+// RepeatWithUnknownOptionalEnum request. It returns a JSON response with an unknown enum symbol
+// string in an enum field.
 func (backend *RESTBackend) customRepeatWithUnknownOptionalEnum(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest) {
 	mutator := func(data *genprotopb.ComplianceData, sentinelValue genprotopb.ComplianceData_LifeKingdom) {
 		data.PKingdom = &sentinelValue
@@ -39,7 +42,8 @@ func (backend *RESTBackend) customRepeatWithUnknownOptionalEnum(w http.ResponseW
 	backend.customRepeatWithUnknownEnumMethod(w, r, request, mutator)
 }
 
-// customRepeatWithUnknownEnumMethod provides REST-specific handling for the RepeatWithUnknown*Enum request. It returns a JSON response with an unknown enum symbol string in an enum field.
+// customRepeatWithUnknownEnumMethod provides REST-specific handling for the RepeatWithUnknown*Enum
+// request. It returns a JSON response with an unknown enum symbol string in an enum field.
 func (backend *RESTBackend) customRepeatWithUnknownEnumMethod(w http.ResponseWriter, r *http.Request, request *genprotopb.RepeatRequest, mutate enumMutator) {
 	marshaler := resttools.ToJSON()
 
@@ -76,5 +80,5 @@ func (backend *RESTBackend) customRepeatWithUnknownEnumMethod(w http.ResponseWri
 	w.Write(json)
 }
 
-// enumMutator represents a function that modifies data in place using sentinelValue.
+// enumMutator represents a function that modifies `data` in place using `sentinelValue`.
 type enumMutator func(data *genprotopb.ComplianceData, sentinelValue genprotopb.ComplianceData_LifeKingdom)
diff --git a/server/services/compliance_service_test.go b/server/services/compliance_service_test.go
index a2e6ce122..670286277 100644
--- a/server/services/compliance_service_test.go
+++ b/server/services/compliance_service_test.go
@@ -57,6 +57,8 @@ func TestComplianceRepeats(t *testing.T) {
 		server.RepeatDataPathTrailingResource,
 		server.RepeatDataBodyPut,
 		server.RepeatDataBodyPatch,
+		server.RepeatWithUnknownEnum,
+		server.RepeatWithUnknownOptionalEnum,
 	} {
 		response, err := rpc(context.Background(), request)
 		if err != nil {
diff --git a/util/genrest/goviewcreator.go b/util/genrest/goviewcreator.go
index 43b369bdc..8b52e179e 100644
--- a/util/genrest/goviewcreator.go
+++ b/util/genrest/goviewcreator.go
@@ -24,15 +24,6 @@ import (
 	"github.com/googleapis/gapic-showcase/util/genrest/resttools"
 )
 
-var customFunctions map[string]string
-
-func init() {
-	customFunctions = map[string]string{
-		".google.showcase.v1beta1.Compliance.RepeatWithUnknownEnum":         "customRepeatWithUnknownEnum",
-		".google.showcase.v1beta1.Compliance.RepeatWithUnknownOptionalEnum": "customRepeatWithUnknownOptionalEnum",
-	}
-}
-
 // NewView creates a a new goview.View (a series of files to be output) from a gomodel.Model. The
 // current approach is to generate one file per service, with that file containing all the service's
 // RPCs. An additional file `genrest.go` is also created to register all these handlers with a
@@ -201,9 +192,8 @@ func NewView(model *gomodel.Model) (*goview.View, error) {
 
 			methodId := fmt.Sprintf("%s.%s", service.ProtoPath, handler.GoMethod)
 			customHandler, _ := customFunctions[methodId]
-			source.P("  // %s", methodId)
 			if len(customHandler) > 0 {
-				source.P("  backend.%s(w, r, request)  // %s", customHandler, methodId)
+				source.P("  backend.%s(w, r, request)", customHandler)
 				source.P("}")
 				continue
 			}
@@ -372,7 +362,19 @@ func (namer *Namer) Get(newName string) string {
 
 var license string
 
+// customFunctions contains a map of fully qualified RPC names to their manually written REST
+// handlers (in package gapic-showcase/server/genrest). For these RPCs, the generated code created
+// by this file calls these custom handlers, instead of delegating to the core gRPC server
+// implementation as most of the REST handlers do. This allows Showcase to provide REST-specific
+// behavior in some scenarios.
+var customFunctions map[string]string
+
 func init() {
+	customFunctions = map[string]string{
+		".google.showcase.v1beta1.Compliance.RepeatWithUnknownEnum":         "customRepeatWithUnknownEnum",
+		".google.showcase.v1beta1.Compliance.RepeatWithUnknownOptionalEnum": "customRepeatWithUnknownOptionalEnum",
+	}
+
 	license = fmt.Sprintf(`// Copyright %d Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");