peridot/vendor/github.com/googleapis/gax-go/v2/callctx/callctx.go

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// 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"
"fmt"
)
const (
// XGoogFieldMaskHeader is the canonical header key for the [System Parameter]
// that specifies the response read mask. The value(s) for this header
// must adhere to format described in [fieldmaskpb].
//
// [System Parameter]: https://cloud.google.com/apis/docs/system-parameters
// [fieldmaskpb]: https://google.golang.org/protobuf/types/known/fieldmaskpb
XGoogFieldMaskHeader = "x-goog-fieldmask"
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 this method will panic.
func SetHeaders(ctx context.Context, keyvals ...string) context.Context {
if len(keyvals)%2 != 0 {
panic(fmt.Sprintf("callctx: an even number of key value pairs must be provided, got %d", len(keyvals)))
}
h, ok := ctx.Value(headerKey).(map[string][]string)
if !ok {
h = make(map[string][]string)
} else {
h = cloneHeaders(h)
}
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)
}
// cloneHeaders makes a new key-value map while reusing the value slices.
// As such, new values should be appended to the value slice, and modifying
// indexed values is not thread safe.
//
// TODO: Replace this with maps.Clone when Go 1.21 is the minimum version.
func cloneHeaders(h map[string][]string) map[string][]string {
c := make(map[string][]string, len(h))
for k, v := range h {
vc := make([]string, len(v))
copy(vc, v)
c[k] = vc
}
return c
}