github.com/jlmucb/cloudproxy@v0.0.0-20170830161738-b5aa0b619bc4/go/apps/mixnet/encoding.go (about)

     1  // Copyright (c) 2016, 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 mixnet
    16  
    17  import (
    18  	"encoding/binary"
    19  
    20  	"github.com/golang/protobuf/proto"
    21  )
    22  
    23  // GetID returns the cell (circuit) ID.
    24  func getID(cell []byte) uint64 {
    25  	id := binary.LittleEndian.Uint64(cell[ID:])
    26  	return id
    27  }
    28  
    29  // Transform a directive into a cell, encoding its length and padding it to the
    30  // length of a cell.
    31  func marshalDirective(id uint64, d *Directive) ([]byte, error) {
    32  	db, err := proto.Marshal(d)
    33  	if err != nil {
    34  		return nil, err
    35  	}
    36  	dirBytes := uint64(len(db))
    37  
    38  	cell := make([]byte, CellBytes)
    39  	binary.LittleEndian.PutUint64(cell[ID:], id)
    40  
    41  	cell[TYPE] = dirCell
    42  	binary.LittleEndian.PutUint64(cell[BODY:], dirBytes)
    43  
    44  	// Throw an error if encoded Directive doesn't fit into a cell.
    45  	if dirBytes+LEN_SIZE+1 > CellBytes {
    46  		return nil, errCellLength
    47  	}
    48  	copy(cell[BODY+LEN_SIZE:], db)
    49  
    50  	return cell, nil
    51  }
    52  
    53  // Parse a directive from a cell.
    54  func unmarshalDirective(cell []byte, d *Directive) error {
    55  	if cell[TYPE] != dirCell {
    56  		return errCellType
    57  	}
    58  
    59  	dirBytes := binary.LittleEndian.Uint64(cell[BODY:])
    60  	if err := proto.Unmarshal(cell[BODY+LEN_SIZE:BODY+LEN_SIZE+int(dirBytes)], d); err != nil {
    61  		return err
    62  	}
    63  
    64  	return nil
    65  }