feat: Prohibit streaming on long-running operations.

docs/rules/0151/response-unary.md

@@ -0,0 +1,69 @@
+---
+rule:
+  aip: 151
+  name: [core, '0151', response-unary]
+  summary: Long-running operations must not use streaming.
+permalink: /151/response-unary
+redirect_from:
+  - /0151/response-unary
+---
+
+# Paginated methods: Unary responses
+
+This rule enforces that all long-running operation methods use unary responses,
+as mandated in [AIP-151][].
+
+## Details
+
+This rule looks at any message returning a `google.longrunning.Operation`, and
+complains if the method uses gRPC server streaming (the `stream` keyword).
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+// Streaming is prohibited on long-running operations.
+rpc ReadBook(ReadBookRequest) returns (stream google.longrunning.Operation) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*/books/*}:read"
+    body: "*"
+  };
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+rpc ReadBook(ReadBookRequest) returns (google.longrunning.Operation) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*/books/*}:read"
+    body: "*"
+  };
+}
+```
+
+## 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::0151::response-unary
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+rpc ReadBook(ReadBookRequest) returns (stream google.longrunning.Operation) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*/books/*}:read"
+    body: "*"
+  };
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-151]: https://aip.dev/151
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

rules/aip0151/aip0151.go

@@ -30,6 +30,7 @@ func AddRules(r lint.RuleRegistry) error {
 		lroMetadataReachable,
 		lroResponse,
 		lroResponseReachable,
+		responseUnary,
 	)
 }
 

rules/aip0151/response_unary.go

@@ -0,0 +1,36 @@
+// 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 aip0151
+
+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(151, "response-unary"),
+	OnlyIf: isLRO,
+	LintMethod: func(m *desc.MethodDescriptor) []lint.Problem {
+		if m.IsServerStreaming() {
+			return []lint.Problem{{
+				Message:    "LRO responses must be unary, not streaming.",
+				Descriptor: m,
+				Location:   locations.MethodResponseType(m),
+			}}
+		}
+		return nil
+	},
+}

rules/aip0151/response_unary_test.go

@@ -0,0 +1,49 @@
+// 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 aip0151
+
+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
+		problems testutils.Problems
+	}{
+		{"Vaild", "", "google.longrunning.Operation", nil},
+		{"Invalid", "stream ", "google.longrunning.Operation", testutils.Problems{{Message: "unary, not stream"}}},
+		{"Irrelevant", "stream ", "ReadBookResponse", nil},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+				import "google/longrunning/operations.proto";
+				service Library {
+					rpc ReadBook(ReadBookRequest) returns ({{.Stream}}{{.Response}});
+				}
+				message ReadBookRequest {}
+				message ReadBookResponse {}
+			`, test)
+			m := f.GetServices()[0].GetMethods()[0]
+			if diff := test.problems.SetDescriptor(m).Diff(responseUnary.Lint(f)); diff != "" {
+				t.Errorf(diff)
+			}
+		})
+	}
+}