github.com/letsencrypt/trillian@v1.1.2-0.20180615153820-ae375a99d36a/crypto/keys/handlers.go (about)

     1  // Copyright 2017 Google Inc. All Rights Reserved.
     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 keys
    16  
    17  import (
    18  	"context"
    19  	"crypto"
    20  	"fmt"
    21  
    22  	"github.com/golang/glog"
    23  	"github.com/golang/protobuf/proto"
    24  )
    25  
    26  // ProtoHandler uses the information in a protobuf message to obtain a crypto.Signer.
    27  // For example, the protobuf message may contain a key or identify where a key can be found.
    28  type ProtoHandler func(context.Context, proto.Message) (crypto.Signer, error)
    29  
    30  // handlers convert a protobuf message into a crypto.Signer.
    31  var handlers = make(map[string]ProtoHandler)
    32  
    33  // RegisterHandler enables transformation of protobuf messages of the same
    34  // type as keyProto into crypto.Signer by invoking the provided handler.
    35  // The keyProto need only be an empty example of the type of protobuf message that
    36  // the handler can process - only its type is examined.
    37  // If a handler for this type of protobuf message has already been added, it will
    38  // be replaced.
    39  func RegisterHandler(keyProto proto.Message, handler ProtoHandler) {
    40  	keyProtoType := proto.MessageName(keyProto)
    41  
    42  	if _, alreadyExists := handlers[keyProtoType]; alreadyExists {
    43  		glog.Warningf("Overridding ProtoHandler for protobuf %q", keyProtoType)
    44  	}
    45  
    46  	handlers[keyProtoType] = handler
    47  }
    48  
    49  // UnregisterHandler removes a previously-added protobuf message handler.
    50  // See RegisterHandler().
    51  func UnregisterHandler(keyProto proto.Message) {
    52  	delete(handlers, proto.MessageName(keyProto))
    53  }
    54  
    55  // NewSigner uses a registered ProtoHandler (see RegisterHandler()) to convert a
    56  // protobuf message into a crypto.Signer.
    57  // If there is no ProtoHandler registered for this type of protobuf message, an
    58  // error will be returned.
    59  func NewSigner(ctx context.Context, keyProto proto.Message) (crypto.Signer, error) {
    60  	keyProtoType := proto.MessageName(keyProto)
    61  
    62  	if handler, ok := handlers[keyProtoType]; ok {
    63  		return handler(ctx, keyProto)
    64  	}
    65  
    66  	return nil, fmt.Errorf("no ProtoHandler registered for protobuf %q", keyProtoType)
    67  }