go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/appengine/gaemiddleware/standard/urlfetch.go (about)

     1  // Copyright 2018 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package standard
    16  
    17  import (
    18  	"context"
    19  	"net/http"
    20  
    21  	"go.chromium.org/luci/gae/service/urlfetch"
    22  )
    23  
    24  var background = context.Background()
    25  
    26  // contextAwareURLFetch implements http.RoundTripper by instantiating GAE's
    27  // urlfetch.Transport for each request.
    28  //
    29  // Requests done through GAE's urlfetch.Transport inherit the deadline of
    30  // a context used to create the transport, totally ignoring the deadline in the
    31  // request's context. This leads to surprising bugs.
    32  //
    33  // contextAwareURLFetch works around this problem by instantiating a new
    34  // urlfetch.Transport for each request, using request's context as a basis
    35  // (if available), and falling back to the context provided during the creation
    36  // otherwise.
    37  type contextAwareURLFetch struct {
    38  	ctx context.Context
    39  }
    40  
    41  // RoundTrip is part of http.RoundTripper interface.
    42  func (c *contextAwareURLFetch) RoundTrip(r *http.Request) (*http.Response, error) {
    43  	ctx := r.Context()
    44  	// We assume context.Background() always returns exact same object.
    45  	if ctx == background {
    46  		ctx = c.ctx
    47  	}
    48  	return urlfetch.Get(ctx).RoundTrip(r)
    49  }