github.com/ooni/psiphon/tunnel-core@v0.0.0-20230105123940-fe12a24c96ee/oovendor/quic-go/internal/wire/crypto_frame.go (about)

     1  package wire
     2  
     3  import (
     4  	"bytes"
     5  	"io"
     6  
     7  	"github.com/ooni/psiphon/tunnel-core/oovendor/quic-go/internal/protocol"
     8  	"github.com/ooni/psiphon/tunnel-core/oovendor/quic-go/quicvarint"
     9  )
    10  
    11  // A CryptoFrame is a CRYPTO frame
    12  type CryptoFrame struct {
    13  	Offset protocol.ByteCount
    14  	Data   []byte
    15  }
    16  
    17  func parseCryptoFrame(r *bytes.Reader, _ protocol.VersionNumber) (*CryptoFrame, error) {
    18  	if _, err := r.ReadByte(); err != nil {
    19  		return nil, err
    20  	}
    21  
    22  	frame := &CryptoFrame{}
    23  	offset, err := quicvarint.Read(r)
    24  	if err != nil {
    25  		return nil, err
    26  	}
    27  	frame.Offset = protocol.ByteCount(offset)
    28  	dataLen, err := quicvarint.Read(r)
    29  	if err != nil {
    30  		return nil, err
    31  	}
    32  	if dataLen > uint64(r.Len()) {
    33  		return nil, io.EOF
    34  	}
    35  	if dataLen != 0 {
    36  		frame.Data = make([]byte, dataLen)
    37  		if _, err := io.ReadFull(r, frame.Data); err != nil {
    38  			// this should never happen, since we already checked the dataLen earlier
    39  			return nil, err
    40  		}
    41  	}
    42  	return frame, nil
    43  }
    44  
    45  func (f *CryptoFrame) Write(b *bytes.Buffer, _ protocol.VersionNumber) error {
    46  	b.WriteByte(0x6)
    47  	quicvarint.Write(b, uint64(f.Offset))
    48  	quicvarint.Write(b, uint64(len(f.Data)))
    49  	b.Write(f.Data)
    50  	return nil
    51  }
    52  
    53  // Length of a written frame
    54  func (f *CryptoFrame) Length(_ protocol.VersionNumber) protocol.ByteCount {
    55  	return 1 + quicvarint.Len(uint64(f.Offset)) + quicvarint.Len(uint64(len(f.Data))) + protocol.ByteCount(len(f.Data))
    56  }
    57  
    58  // MaxDataLen returns the maximum data length
    59  func (f *CryptoFrame) MaxDataLen(maxSize protocol.ByteCount) protocol.ByteCount {
    60  	// pretend that the data size will be 1 bytes
    61  	// if it turns out that varint encoding the length will consume 2 bytes, we need to adjust the data length afterwards
    62  	headerLen := 1 + quicvarint.Len(uint64(f.Offset)) + 1
    63  	if headerLen > maxSize {
    64  		return 0
    65  	}
    66  	maxDataLen := maxSize - headerLen
    67  	if quicvarint.Len(uint64(maxDataLen)) != 1 {
    68  		maxDataLen--
    69  	}
    70  	return maxDataLen
    71  }
    72  
    73  // MaybeSplitOffFrame splits a frame such that it is not bigger than n bytes.
    74  // It returns if the frame was actually split.
    75  // The frame might not be split if:
    76  // * the size is large enough to fit the whole frame
    77  // * the size is too small to fit even a 1-byte frame. In that case, the frame returned is nil.
    78  func (f *CryptoFrame) MaybeSplitOffFrame(maxSize protocol.ByteCount, version protocol.VersionNumber) (*CryptoFrame, bool /* was splitting required */) {
    79  	if f.Length(version) <= maxSize {
    80  		return nil, false
    81  	}
    82  
    83  	n := f.MaxDataLen(maxSize)
    84  	if n == 0 {
    85  		return nil, true
    86  	}
    87  
    88  	newLen := protocol.ByteCount(len(f.Data)) - n
    89  
    90  	new := &CryptoFrame{}
    91  	new.Offset = f.Offset
    92  	new.Data = make([]byte, newLen)
    93  
    94  	// swap the data slices
    95  	new.Data, f.Data = f.Data, new.Data
    96  
    97  	copy(f.Data, new.Data[n:])
    98  	new.Data = new.Data[:n]
    99  	f.Offset += n
   100  
   101  	return new, true
   102  }