Source: common.go in package google.golang.org/grpc/credentials/alts/internal/conn

* * 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"
)

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.

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)
	}

Frame is not complete yet.

		return nil, b, nil
	}
	return b[:MsgLenFieldSize+length], b[MsgLenFieldSize+length:], nil