genai: add WithAttribution client option

Add an option that lets Google products identify which calls
are made with this client.

genai/client.go

@@ -87,7 +87,15 @@ Import the option package as "google.golang.org/api/option".`)
 	if err != nil {
 		return nil, fmt.Errorf("creating discovery client: %w", err)
 	}
-	gc.SetGoogleClientInfo("gccl", "v"+internal.Version, "genai-go", internal.Version)
+
+	kvs := []string{"gccl", "v" + internal.Version, "genai-go", internal.Version}
+	if a, ok := optionOfType[*attribution](opts); ok {
+		kvs = append(kvs, a.key, a.value)
+	}
+	gc.SetGoogleClientInfo(kvs...)
+	mc.SetGoogleClientInfo(kvs...)
+	fc.SetGoogleClientInfo(kvs...)
+
 	return &Client{gc, mc, fc, cc, ds}, nil
 }
 

genai/client_test.go

@@ -864,3 +864,16 @@ func uploadFile(t *testing.T, ctx context.Context, client *Client, filename stri
 	})
 	return file
 }
+
+func TestAttribution(t *testing.T) {
+	a := WithAttribution("k", "v")
+	opts := []option.ClientOption{option.WithAPIKey("x"), a, option.WithEndpoint("e")}
+	got, ok := optionOfType[*attribution](opts)
+	if !ok {
+		t.Fatal("not found")
+	}
+	want := a.(*attribution)
+	if got.key != want.key || got.value != want.value {
+		t.Errorf("got %q, %q, want %q, %q", got.key, got.value, want.key, want.value)
+	}
+}

genai/option.go

@@ -0,0 +1,41 @@
+// Copyright 2024 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
+//
+//      http://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 genai
+
+import (
+	"google.golang.org/api/option"
+	"google.golang.org/api/option/internaloption"
+)
+
+// WithAttribution sets request information identifying the
+// product that is calling this client.
+func WithAttribution(key, value string) option.ClientOption {
+	return &attribution{key: key, value: value}
+}
+
+type attribution struct {
+	internaloption.EmbeddableAdapter
+	key, value string
+}
+
+func optionOfType[T option.ClientOption](opts []option.ClientOption) (T, bool) {
+	for _, opt := range opts {
+		if opt, ok := opt.(T); ok {
+			return opt, true
+		}
+	}
+	var z T
+	return z, false
+}