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package dmpkg
import (
"bytes"
"compress/zlib"
"fmt"
"github.com/andybalholm/brotli"
"github.com/lunixbochs/struc"
"io"
)
type DanmakuExchangeHeader struct {
// Length total remaining bytes of this exchange, excluding `Length` itself
Length uint32
// HeaderLength = Length - len(Body) + 4, always equals to 16
HeaderLength uint16
ProtocolVer ProtocolVer
Operation Operation
// SequenceId is always 1
SequenceId uint32
}
// DanmakuExchange represents an actual message sent from client or server. This is an atomic unit.
type DanmakuExchange struct {
DanmakuExchangeHeader
Body []byte
}
func (e *DanmakuExchange) String() string {
return fmt.Sprintf("DanmakuExchange{length=%v, protocol=%v, operation=%v, body=%v}",
e.Length, e.ProtocolVer, e.Operation, e.Body)
}
const kHeaderLength = 16
const kSequenceId = 1
type ProtocolVer uint16
const (
// ProtoPlainJson the body is plain JSON text
ProtoPlainJson ProtocolVer = 0
// ProtoMinimal the body is uint32 watcher count (big endian)
ProtoMinimal ProtocolVer = 1
// ProtoZlib the body is a zlib compressed package
ProtoZlib ProtocolVer = 2
// ProtoBrotli the body is a brotli compressed package
ProtoBrotli ProtocolVer = 3
)
const kUidGuest = 0
const kPlatformWeb = "web"
const kAuthTypeDefault = 2 // magic number, not sure what does it mean
func (e *DanmakuExchange) Marshal() (data []byte, err error) {
var buffer bytes.Buffer
// only unpack header with struc, since it does not support indirect variable field length calculation
err = struc.Pack(&buffer, &e.DanmakuExchangeHeader)
if err != nil {
err = fmt.Errorf("cannot pack an exchange into binary form: %w", err)
return
}
data = buffer.Bytes()
data = append(data, e.Body...)
return
}
// Inflate decompresses the body if it is compressed
func (e *DanmakuExchange) Inflate() (ret DanmakuExchange, err error) {
switch e.ProtocolVer {
case ProtoMinimal:
fallthrough
case ProtoPlainJson:
ret = *e
case ProtoBrotli:
var data []byte
rd := brotli.NewReader(bytes.NewReader(e.Body))
data, err = io.ReadAll(rd)
if err != nil {
err = fmt.Errorf("cannot decompress exchange body: %w", err)
return
}
var nestedExchange DanmakuExchange
nestedExchange, err = DecodeExchange(data)
if err != nil {
err = fmt.Errorf("cannot decode nested exchange: %w", err)
return
}
return nestedExchange.Inflate()
case ProtoZlib:
var data []byte
var rd io.ReadCloser
rd, err = zlib.NewReader(bytes.NewReader(e.Body))
if err != nil {
err = fmt.Errorf("cannot create zlib reader: %w", err)
return
}
data, err = io.ReadAll(rd)
if err != nil {
err = fmt.Errorf("cannot decompress exchange body: %w", err)
return
}
var nestedExchange DanmakuExchange
nestedExchange, err = DecodeExchange(data)
if err != nil {
err = fmt.Errorf("cannot decode nested exchange: %w", err)
return
}
return nestedExchange.Inflate()
}
return
}
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