97 lines
3.2 KiB
Go
97 lines
3.2 KiB
Go
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package sctp
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import (
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"encoding/binary"
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"errors"
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"fmt"
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)
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/*
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chunkHeader represents a SCTP Chunk header, defined in https://tools.ietf.org/html/rfc4960#section-3.2
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The figure below illustrates the field format for the chunks to be
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transmitted in the SCTP packet. Each chunk is formatted with a Chunk
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Type field, a chunk-specific Flag field, a Chunk Length field, and a
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Value field.
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Chunk Type | Chunk Flags | Chunk Length |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Chunk Value |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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type chunkHeader struct {
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typ chunkType
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flags byte
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raw []byte
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}
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const (
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chunkHeaderSize = 4
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)
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var (
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errChunkHeaderTooSmall = errors.New("raw is too small for a SCTP chunk")
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errChunkHeaderNotEnoughSpace = errors.New("not enough data left in SCTP packet to satisfy requested length")
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errChunkHeaderPaddingNonZero = errors.New("chunk padding is non-zero at offset")
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)
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func (c *chunkHeader) unmarshal(raw []byte) error {
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if len(raw) < chunkHeaderSize {
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return fmt.Errorf("%w: raw only %d bytes, %d is the minimum length", errChunkHeaderTooSmall, len(raw), chunkHeaderSize)
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}
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c.typ = chunkType(raw[0])
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c.flags = raw[1]
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length := binary.BigEndian.Uint16(raw[2:])
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// Length includes Chunk header
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valueLength := int(length - chunkHeaderSize)
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lengthAfterValue := len(raw) - (chunkHeaderSize + valueLength)
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if lengthAfterValue < 0 {
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return fmt.Errorf("%w: remain %d req %d ", errChunkHeaderNotEnoughSpace, valueLength, len(raw)-chunkHeaderSize)
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} else if lengthAfterValue < 4 {
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// https://tools.ietf.org/html/rfc4960#section-3.2
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// The Chunk Length field does not count any chunk padding.
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// Chunks (including Type, Length, and Value fields) are padded out
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// by the sender with all zero bytes to be a multiple of 4 bytes
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// long. This padding MUST NOT be more than 3 bytes in total. The
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// Chunk Length value does not include terminating padding of the
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// chunk. However, it does include padding of any variable-length
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// parameter except the last parameter in the chunk. The receiver
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// MUST ignore the padding.
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for i := lengthAfterValue; i > 0; i-- {
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paddingOffset := chunkHeaderSize + valueLength + (i - 1)
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if raw[paddingOffset] != 0 {
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return fmt.Errorf("%w: %d ", errChunkHeaderPaddingNonZero, paddingOffset)
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}
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}
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}
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c.raw = raw[chunkHeaderSize : chunkHeaderSize+valueLength]
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return nil
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}
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func (c *chunkHeader) marshal() ([]byte, error) {
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raw := make([]byte, 4+len(c.raw))
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raw[0] = uint8(c.typ)
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raw[1] = c.flags
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binary.BigEndian.PutUint16(raw[2:], uint16(len(c.raw)+chunkHeaderSize))
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copy(raw[4:], c.raw)
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return raw, nil
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}
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func (c *chunkHeader) valueLength() int {
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return len(c.raw)
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}
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// String makes chunkHeader printable
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func (c chunkHeader) String() string {
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return c.typ.String()
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}
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