feat(v2/callctx): add new callctx package

v2/callctx/callctx.go

@@ -0,0 +1,75 @@
+// Copyright 2023, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Package callctx provides helpers for storing and retrieving values out of
+// [context.Context]. These values are used by our client libraries in various
+// ways across the stack.
+package callctx
+
+import (
+	"context"
+)
+
+const (
+	headerKey = contextKey("header")
+)
+
+// contextKey is a private type used to store/retrieve context values.
+type contextKey string
+
+// HeadersFromContext retrieves headers set from [SetHeaders]. These headers
+// can then be cast to http.Header or metadata.MD to send along on requests.
+func HeadersFromContext(ctx context.Context) map[string][]string {
+	m, ok := ctx.Value(headerKey).(map[string][]string)
+	if !ok {
+		return nil
+	}
+	return m
+}
+
+// SetHeaders stores key value pairs in the returned context that can later
+// be retrieved by [HeadersFromContext]. Values stored in this manner will
+// automatically be retrieved by client libraries and sent as outgoing headers
+// on all requests. keyvals should have a corresponding value for every key
+// provided. If there is an odd number of keyvals the context passed to this
+// method will be returned and no values will be stored in the context.
+func SetHeaders(ctx context.Context, keyvals ...string) context.Context {
+	if len(keyvals)%2 != 0 {
+		// TODO(codyoss): maybe eventually log here when we have the facilities
+		return ctx
+	}
+	h, ok := ctx.Value(headerKey).(map[string][]string)
+	if !ok {
+		h = make(map[string][]string)
+	}
+	for i := 0; i < len(keyvals); i = i + 2 {
+		h[keyvals[i]] = append(h[keyvals[i]], keyvals[i+1])
+	}
+	return context.WithValue(ctx, headerKey, h)
+}

v2/callctx/callctx_example_test.go

@@ -0,0 +1,49 @@
+// Copyright 2023, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package callctx_test
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/googleapis/gax-go/v2/callctx"
+)
+
+func ExampleSetHeaders() {
+	ctx := context.Background()
+	ctx = callctx.SetHeaders(ctx, "key", "value")
+
+	// Send the returned context to the request you are making. Later on these
+	// values will be retrieved and set on outgoing requests.
+
+	headers := callctx.HeadersFromContext(ctx)
+	fmt.Println(headers["key"][0])
+	// Output: value
+}

v2/callctx/callctx_test.go

@@ -0,0 +1,74 @@
+// Copyright 2023, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package callctx
+
+import (
+	"context"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestAll(t *testing.T) {
+	testCases := []struct {
+		name  string
+		pairs []string
+		want  map[string][]string
+	}{
+		{
+			name:  "standard",
+			pairs: []string{"key", "value"},
+			want:  map[string][]string{"key": {"value"}},
+		},
+		{
+			name:  "multiple values",
+			pairs: []string{"key", "value", "key2", "value2"},
+			want:  map[string][]string{"key": {"value"}, "key2": {"value2"}},
+		},
+		{
+			name:  "multiple values with same key",
+			pairs: []string{"key", "value", "key", "value2"},
+			want:  map[string][]string{"key": {"value", "value2"}},
+		},
+		{
+			name:  "odd key value pairs",
+			pairs: []string{"key", "value", "key"},
+			want:  nil,
+		},
+	}
+	for _, tc := range testCases {
+		ctx := context.Background()
+		ctx = SetHeaders(ctx, tc.pairs...)
+		got := HeadersFromContext(ctx)
+		if diff := cmp.Diff(tc.want, got); diff != "" {
+			t.Errorf("HeadersFromContext() mismatch (-want +got):\n%s", diff)
+		}
+	}
+}