github.com/daeuniverse/quic-go@v0.0.0-20240413031024-943f218e0810/internal/wire/crypto_frame.go (about)

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