feat: Prohibit streaming on paging methods.

docs/rules/0158/response-unary.md

@@ -0,0 +1,68 @@
+---
+rule:
+  aip: 158
+  name: [core, '0158', response-unary]
+  summary: Paginated responses must not use streaming.
+permalink: /158/response-unary
+redirect_from:
+  - /0158/response-unary
+---
+
+# Paginated methods: Unary responses
+
+This rule enforces that all paginated methods (`List` and `Search` methods, or
+methods with pagination fields) use unary responses, as mandated in
+[AIP-158][].
+
+## Details
+
+This rule looks at any message matching `List*Response` or `Search*Response`,
+or any response message that has `next_page_token` field, and complains if the
+method uses gRPC server streaming (the `stream` keyword).
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+// Streaming is prohibited on paginated responses.
+rpc ListBooks(ListBooksRequest) returns (stream ListBooksResponse) {
+  option (google.api.http) = {
+    get: "/v1/{parent=publishers/*}/books"
+  };
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+rpc ListBooks(ListBooksRequest) returns (ListBooksResponse) {
+  option (google.api.http) = {
+    get: "/v1/{parent=publishers/*}/books"
+  };
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the message or
+above the field. Remember to also include an [aip.dev/not-precedent][] comment
+explaining why.
+
+```proto
+// (-- api-linter: core::0158::response-unary
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+rpc ListBooks(ListBooksRequest) returns (stream ListBooksResponse) {
+  option (google.api.http) = {
+    get: "/v1/{parent=publishers/*}/books"
+  };
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-158]: https://aip.dev/158
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

rules/aip0158/aip0158.go

@@ -31,6 +31,7 @@ func AddRules(r lint.RuleRegistry) error {
 		responsePaginationNextPageToken,
 		responseRepeatedFirstField,
 		responsePluralFirstField,
+		responseUnary,
 	)
 }
 
@@ -46,3 +47,7 @@ func isPaginatedRequestMessage(m *desc.MessageDescriptor) bool {
 func isPaginatedResponseMessage(m *desc.MessageDescriptor) bool {
 	return paginatedRes.MatchString(m.GetName()) || m.FindFieldByName("next_page_token") != nil
 }
+
+func isPaginatedMethod(m *desc.MethodDescriptor) bool {
+	return isPaginatedRequestMessage(m.GetInputType()) && isPaginatedResponseMessage(m.GetOutputType())
+}

rules/aip0158/response_unary.go

@@ -0,0 +1,36 @@
+// Copyright 2019 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 aip0158
+
+import (
+	"github.com/googleapis/api-linter/lint"
+	"github.com/googleapis/api-linter/locations"
+	"github.com/jhump/protoreflect/desc"
+)
+
+var responseUnary = &lint.MethodRule{
+	Name:   lint.NewRuleName(158, "response-unary"),
+	OnlyIf: isPaginatedMethod,
+	LintMethod: func(m *desc.MethodDescriptor) []lint.Problem {
+		if m.IsServerStreaming() {
+			return []lint.Problem{{
+				Message:    "Paginated responses must be unary, not streaming.",
+				Descriptor: m,
+				Location:   locations.MethodResponseType(m),
+			}}
+		}
+		return nil
+	},
+}

rules/aip0158/response_unary_test.go

@@ -0,0 +1,54 @@
+// Copyright 2020 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 aip0158
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+)
+
+func TestResponseUnary(t *testing.T) {
+	for _, test := range []struct {
+		name          string
+		Stream        string
+		Response      string
+		NextPageToken string
+		problems      testutils.Problems
+	}{
+		{"Vaild", "", "ListFoosResponse", "next_page_token", nil},
+		{"Invalid", "stream ", "ListFoosResponse", "next_page_token", testutils.Problems{{Message: "unary, not stream"}}},
+		{"Irrelevant", "stream ", "FrobFoosResponse", "not_paginated_response", nil},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+				service Foos {
+					rpc ListFoos(ListFoosRequest) returns ({{.Stream}}{{.Response}});
+				}
+				message ListFoosRequest {
+					int32 page_size = 1;
+					string page_token = 2;
+				}
+				message {{.Response}} {
+					string {{.NextPageToken}} = 1;
+				}
+			`, test)
+			m := f.GetServices()[0].GetMethods()[0]
+			if diff := test.problems.SetDescriptor(m).Diff(responseUnary.Lint(f)); diff != "" {
+				t.Errorf(diff)
+			}
+		})
+	}
+}