github.com/jlmucb/cloudproxy@v0.0.0-20170830161738-b5aa0b619bc4/go/util/messagestream.go (about)

     1  // Copyright (c) 2014, Kevin Walsh.  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 util
    16  
    17  import (
    18  	"encoding/binary"
    19  	"errors"
    20  	"io"
    21  	"math"
    22  
    23  	"github.com/golang/glog"
    24  	"github.com/golang/protobuf/proto"
    25  )
    26  
    27  // A MessageStream is an io.ReadWriteCloser that can also read and write strings
    28  // and protobuf messages. Boundaries are preserved for strings and protobuf
    29  // messages using a 32-bit (network byte order) length prefix before the
    30  // contents of the string or marshalled protobuf message. MessageStream can also
    31  // enforce an upper-limit on the size of received messages.
    32  type MessageStream struct {
    33  	MaxMessageSize int // Negative means unlimited
    34  	io.ReadWriteCloser
    35  }
    36  
    37  // DefaultMaxMessageSize gives the default max for messages sent on a
    38  // MessageStream.
    39  const DefaultMaxMessageSize = 20 * 1024 * 1024
    40  
    41  // ErrMessageTooLarge is the error message returned when a message larger than
    42  // DefaultMaxMessageSize is sent on a MessageStream.
    43  var ErrMessageTooLarge = errors.New("messagestream: message is too large")
    44  
    45  // WriteString writes a 32-bit length followed by the string.
    46  func (ms *MessageStream) WriteString(s string) (int, error) {
    47  	n := len(s)
    48  	if n > math.MaxUint32 {
    49  		return 0, ErrMessageTooLarge
    50  	}
    51  	var sizebytes [4]byte
    52  	binary.BigEndian.PutUint32(sizebytes[:], uint32(n))
    53  	n, err := ms.Write(sizebytes[:])
    54  	if err != nil {
    55  		return n, Logged(err)
    56  	}
    57  	m, err := ms.Write([]byte(s))
    58  	return n + m, Logged(err)
    59  }
    60  
    61  // ReadString reads a 32-bit length followed by a string.
    62  func (ms *MessageStream) ReadString() (string, error) {
    63  	var sizebytes [4]byte
    64  	_, err := io.ReadFull(ms, sizebytes[:])
    65  	if err != nil {
    66  		return "", err
    67  	}
    68  	n := binary.BigEndian.Uint32(sizebytes[:])
    69  	max := ms.MaxMessageSize
    70  	// We also check for int(n) to overflow so allocation below doesn't fail.
    71  	if int(n) < 0 || (max > 0 && int(n) > max) {
    72  		glog.Errorf("String on wire is too large: %d bytes\n", n)
    73  		return "", Logged(ErrMessageTooLarge)
    74  	}
    75  	strbytes := make([]byte, int(n))
    76  	_, err = io.ReadFull(ms, strbytes)
    77  	if err != nil {
    78  		return "", Logged(err)
    79  	}
    80  	return string(strbytes), nil
    81  }
    82  
    83  // WriteMessage writes 32-bit length followed by a protobuf message. If m is
    84  // nil, a blank message is written instead.
    85  func (ms *MessageStream) WriteMessage(m proto.Message) (int, error) {
    86  	if m == nil {
    87  		return ms.WriteString("")
    88  	}
    89  	bytes, err := proto.Marshal(m)
    90  	if err != nil {
    91  		return 0, Logged(err)
    92  	}
    93  	return ms.WriteString(string(bytes))
    94  }
    95  
    96  // ReadMessage reads a 32-bit length followed by a protobuf message. If m is
    97  // nil, the incoming message is discarded.
    98  func (ms *MessageStream) ReadMessage(m proto.Message) error {
    99  	s, err := ms.ReadString()
   100  	if err != nil {
   101  		return err
   102  	}
   103  	if m != nil {
   104  		err = proto.Unmarshal([]byte(s), m)
   105  		if err != nil {
   106  			return Logged(err)
   107  		}
   108  	}
   109  	return nil
   110  }
   111  
   112  // NewMessageStream creates a MessageStream for the given pipe with a reception
   113  // limit of DefaultMaxMessageSize.
   114  func NewMessageStream(pipe io.ReadWriteCloser) *MessageStream {
   115  	return &MessageStream{DefaultMaxMessageSize, pipe}
   116  }