github.com/jlmucb/cloudproxy@v0.0.0-20170830161738-b5aa0b619bc4/go/tao/auth/buffer.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 auth
    16  
    17  import (
    18  	"encoding/binary"
    19  	"errors"
    20  	"fmt"
    21  	"io"
    22  )
    23  
    24  // Buffer holds partially encoded or decode auth elemnts.
    25  // Note: We could do capacity-doubling, etc., but we favor simplicity for now.
    26  type Buffer struct {
    27  	buf []byte
    28  }
    29  
    30  // Bytes returns the unconsumed portion of the buffer.
    31  func (buf *Buffer) Bytes() []byte {
    32  	return buf.buf
    33  }
    34  
    35  // EncodeVarint encodes an int as a (non zig-zag) varint, growing the buffer.
    36  func (buf *Buffer) EncodeVarint(i int64) {
    37  	b := make([]byte, 10) // int64 as varint is max 10 bytes
    38  	n := binary.PutUvarint(b, uint64(i))
    39  	buf.buf = append(buf.buf, b[0:n]...)
    40  }
    41  
    42  // DecodeVarint decodes an int, shrinking the buffer.
    43  func (buf *Buffer) DecodeVarint() (int64, error) {
    44  	i, n := binary.Uvarint(buf.buf)
    45  	if n == 0 {
    46  		return 0, io.ErrUnexpectedEOF
    47  	} else if n < 0 {
    48  		return 0, errors.New("varint overflow")
    49  	}
    50  	buf.buf = buf.buf[n:]
    51  	return int64(i), nil
    52  }
    53  
    54  // EncodeBool converts b to an int then calls EncodeVarint.
    55  func (buf *Buffer) EncodeBool(b bool) {
    56  	if b {
    57  		buf.EncodeVarint(1)
    58  	} else {
    59  		buf.EncodeVarint(0)
    60  	}
    61  }
    62  
    63  // DecodeBool calls DecodeVarint then converts the result to a bool.
    64  func (buf *Buffer) DecodeBool() (bool, error) {
    65  	i, err := buf.DecodeVarint()
    66  	return (i == 1), err
    67  }
    68  
    69  // EncodeString encodes a string as a length and byte array, growing the buffer.
    70  func (buf *Buffer) EncodeString(s string) {
    71  	bytes := []byte(s)
    72  	buf.EncodeVarint(int64(len(bytes)))
    73  	buf.buf = append(buf.buf, bytes...)
    74  }
    75  
    76  // DecodeString decodes a string, shrinking the buffer.
    77  func (buf *Buffer) DecodeString() (string, error) {
    78  	n, err := buf.DecodeVarint()
    79  	if err != nil {
    80  		return "", err
    81  	}
    82  	if n < int64(0) || n > int64(len(buf.buf)) {
    83  		return "", fmt.Errorf("invalid length: %d", n)
    84  	}
    85  	s := string(buf.buf[:n])
    86  	buf.buf = buf.buf[n:]
    87  	return s, nil
    88  }