package sctp import ( "encoding/binary" "errors" "fmt" ) /* chunkInitCommon represents an SCTP Chunk body of type INIT and INIT ACK 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 1 | Chunk Flags | Chunk Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Initiate Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertised Receiver Window Credit (a_rwnd) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Outbound Streams | Number of Inbound Streams | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Initial TSN | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Optional/Variable-Length Parameters | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The INIT chunk contains the following parameters. Unless otherwise noted, each parameter MUST only be included once in the INIT chunk. Fixed Parameters Status ---------------------------------------------- Initiate Tag Mandatory Advertised Receiver Window Credit Mandatory Number of Outbound Streams Mandatory Number of Inbound Streams Mandatory Initial TSN Mandatory */ type chunkInitCommon struct { initiateTag uint32 advertisedReceiverWindowCredit uint32 numOutboundStreams uint16 numInboundStreams uint16 initialTSN uint32 params []param } const ( initChunkMinLength = 16 initOptionalVarHeaderLength = 4 ) var ( errInitChunkParseParamTypeFailed = errors.New("failed to parse param type") errInitChunkUnmarshalParam = errors.New("failed unmarshalling param in Init Chunk") errInitAckMarshalParam = errors.New("unable to marshal parameter for INIT/INITACK") ) func (i *chunkInitCommon) unmarshal(raw []byte) error { i.initiateTag = binary.BigEndian.Uint32(raw[0:]) i.advertisedReceiverWindowCredit = binary.BigEndian.Uint32(raw[4:]) i.numOutboundStreams = binary.BigEndian.Uint16(raw[8:]) i.numInboundStreams = binary.BigEndian.Uint16(raw[10:]) i.initialTSN = binary.BigEndian.Uint32(raw[12:]) // https://tools.ietf.org/html/rfc4960#section-3.2.1 // // Chunk values of SCTP control chunks consist of a chunk-type-specific // header of required fields, followed by zero or more parameters. The // optional and variable-length parameters contained in a chunk are // defined in a Type-Length-Value format as shown below. // // 0 1 2 3 // 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 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // | Parameter Type | Parameter Length | // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // | | // | Parameter Value | // | | // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ offset := initChunkMinLength remaining := len(raw) - offset for remaining > 0 { if remaining > initOptionalVarHeaderLength { pType, err := parseParamType(raw[offset:]) if err != nil { return fmt.Errorf("%w: %v", errInitChunkParseParamTypeFailed, err) } p, err := buildParam(pType, raw[offset:]) if err != nil { return fmt.Errorf("%w: %v", errInitChunkUnmarshalParam, err) } i.params = append(i.params, p) padding := getPadding(p.length()) offset += p.length() + padding remaining -= p.length() + padding } else { break } } return nil } func (i *chunkInitCommon) marshal() ([]byte, error) { out := make([]byte, initChunkMinLength) binary.BigEndian.PutUint32(out[0:], i.initiateTag) binary.BigEndian.PutUint32(out[4:], i.advertisedReceiverWindowCredit) binary.BigEndian.PutUint16(out[8:], i.numOutboundStreams) binary.BigEndian.PutUint16(out[10:], i.numInboundStreams) binary.BigEndian.PutUint32(out[12:], i.initialTSN) for idx, p := range i.params { pp, err := p.marshal() if err != nil { return nil, fmt.Errorf("%w: %v", errInitAckMarshalParam, err) } out = append(out, pp...) // Chunks (including Type, Length, and Value fields) are padded out // by the sender with all zero bytes to be a multiple of 4 bytes // long. This padding MUST NOT be more than 3 bytes in total. The // Chunk Length value does not include terminating padding of the // chunk. *However, it does include padding of any variable-length // parameter except the last parameter in the chunk.* The receiver // MUST ignore the padding. if idx != len(i.params)-1 { out = padByte(out, getPadding(len(pp))) } } return out, nil } // String makes chunkInitCommon printable func (i chunkInitCommon) String() string { format := `initiateTag: %d advertisedReceiverWindowCredit: %d numOutboundStreams: %d numInboundStreams: %d initialTSN: %d` res := fmt.Sprintf(format, i.initiateTag, i.advertisedReceiverWindowCredit, i.numOutboundStreams, i.numInboundStreams, i.initialTSN, ) for i, param := range i.params { res += fmt.Sprintf("Param %d:\n %s", i, param) } return res }