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/*
*
* Copyright 2018 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package conn
import (
"encoding/binary"
"errors"
"fmt"
)
const (
// GcmTagSize is the GCM tag size is the difference in length between
// plaintext and ciphertext. From crypto/cipher/gcm.go in Go crypto
// library.
GcmTagSize = 16
)
// ErrAuth occurs on authentication failure.
var ErrAuth = errors.New("message authentication failed")
// SliceForAppend takes a slice and a requested number of bytes. It returns a
// slice with the contents of the given slice followed by that many bytes and a
// second slice that aliases into it and contains only the extra bytes. If the
// original slice has sufficient capacity then no allocation is performed.
func SliceForAppend(in []byte, n int) (head, tail []byte) {
if total := len(in) + n; cap(in) >= total {
head = in[:total]
} else {
head = make([]byte, total)
copy(head, in)
}
tail = head[len(in):]
return head, tail
}
// ParseFramedMsg parse the provided buffer and returns a frame of the format
// msgLength+msg and any remaining bytes in that buffer.
func ParseFramedMsg(b []byte, maxLen uint32) ([]byte, []byte, error) {
// If the size field is not complete, return the provided buffer as
// remaining buffer.
if len(b) < MsgLenFieldSize {
return nil, b, nil
}
msgLenField := b[:MsgLenFieldSize]
length := binary.LittleEndian.Uint32(msgLenField)
if length > maxLen {
return nil, nil, fmt.Errorf("received the frame length %d larger than the limit %d", length, maxLen)
}
if len(b) < int(length)+4 { // account for the first 4 msg length bytes.
// Frame is not complete yet.
return nil, b, nil
}
return b[:MsgLenFieldSize+length], b[MsgLenFieldSize+length:], nil
}
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