go语言作为近十年来优秀的现代开发语言的代表，由于继承了c语言的简洁和很多现代语言的表达方式，在广泛的应用场景中得到众多爱好者的喜爱，如何将go和c、c++进行联合开发，拓展整个开发生态，不用重复造轮子，掌握cgo可以让你得心应手的在c和go之间传递信息，打通任督二脉。

    go在流媒体传输领域也有很强大的生态和优秀的轮子，比起传统的ffmpeg这种大而全的库，可以选择性的用一些小巧强悍的go语言写的库来替代ffmpeg，比如rtsp拉流，笔者用ffmpeg在android下写了一个推拉流的播放器，但是由于ffmpeg自成体系，在灵活定制方面有一些局限性，于是尝试用go rtsp来代替ffmpeg的rtsp拉流。

    首先我们需要利用cgo的交叉编译特性封装一个可以被c/c++调用的动态库，其中用到了cgo 进行设置和回调函数，并传递了类的指针，从而实现了c++ class的特性，达到了面向对象多路连接的设计目标。以下是go写的动态库源码，由于go的包管理做的特别棒，你可以用很少的代码实现一个多路拉流的应用。感觉比c++爽多了。

 

 

package main

import (
	"fmt"
	"sync"
	"time"
	"unsafe"

	"github.com/deepch/vdk/av"
	"github.com/deepch/vdk/codec/h264parser"
	"github.com/deepch/vdk/format/rtsp"
)

/*
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#cgo CFLAGS: -I.
void OnSendPacket(void * callclass,unsigned char *data, int len,int mediatype);
typedef void (*CallbackFunc)(unsigned char *,int,int);
*/
import "C"

// 导出的回调函数类型
// type
// void SendcallbackFunc(unsigned char* data, int length);
// extern CallbackFunc _callback;
//
//	static void setCallbackWrapper(CallbackFunc callback) {
//	    _callback = callback;
//	}
type CallbackFunc func(*byte, int, int)

// 接口定义
type MediaInterface interface {
	SetCallback(callback CallbackFunc)
}

// 结构体实现接口
type MediaImplementation struct {
	id       int
	callback CallbackFunc
	// C._callback
	callclass unsafe.Pointer // 修改为unsafe.Pointer类型
}

var (
	instances     = make(map[int]*MediaImplementation)
	instancesLock sync.Mutex
	callbackLock  sync.Mutex
)

func (m *MediaImplementation) SendData(data []byte, length int, mediatype int) {
	// if C._callback != nil {
	fmt.Println("callback data len", length, mediatype)
	// arr := (*C.uchar)(unsafe.Pointer(&data[0]))
	// C.OnSendPacket(arr, C.int(length), C.int(mediatype))
}

func (m *MediaImplementation) CallBackData(data *byte, length int, mediatype int) {
	goSlice := (*[1 << 30]byte)(unsafe.Pointer(data))[:length:length]
	m.SendData(goSlice, length, mediatype)
}

func (m *MediaImplementation) RtspClientStart(uri string) {
	// m.rtsp = unsafe.Pointer(&Rtspclient{
	// 	callback: m.CallBackData,
	// })
	// ((*Rtspclient)(m.rtsp)).rtspclient(uri)
	m.rtspConsumer(uri)
}

func (m *MediaImplementation) SetCallback(callback CallbackFunc) {
	m.callback = callback
}

//export CallRtspClientStart
func CallRtspClientStart(impl unsafe.Pointer, data *C.char) {
	if impl == nil {
		fmt.Println("Invalid implementation")
		return
	}
	m := (*MediaImplementation)(impl)
	m.rtspConsumer(C.GoString(data))
	// m.RtspClientStart(C.GoString(data))
}

//export NewMediaImplementation
func NewMediaImplementation() uintptr {
	instancesLock.Lock()
	defer instancesLock.Unlock()

	id := len(instances) + 1

	instance := &MediaImplementation{
		id: id,
	}

	instances[id] = instance

	return uintptr(unsafe.Pointer(instance))
}

//export GetMediaInstanceByID
func GetMediaInstanceByID(id C.int) uintptr { // 修改返回类型为uintptr
	instancesLock.Lock()
	defer instancesLock.Unlock()

	if instance, ok := instances[int(id)]; ok {
		return uintptr(unsafe.Pointer(instance))
	}

	return uintptr(0) // 返回表示未找到实例
}

//export CallSendData
func CallSendData(impl unsafe.Pointer, data *C.uchar, length C.int, mediatype C.int) {
	if impl == nil {
		fmt.Println("Invalid implementation")
		return
	}

	goSlice := (*[1 << 30]byte)(unsafe.Pointer(data))[:length:length]
	m := (*MediaImplementation)(impl)
	go m.SendData(goSlice, int(length), int(mediatype))
}

//export SetCallbackWrapper
func SetCallbackWrapper(impl unsafe.Pointer, callback unsafe.Pointer) {
	if impl == nil {
		fmt.Println("Invalid implementation")
		return
	}
	m := (*MediaImplementation)(impl)
	m.callclass = callback
	fmt.Println("SetCallbackWrapper callback", m.callback, callback)
	// C._callback = callbackFunc
	// m.SetCallback(callbackFunc)
}

func main() {}

func (m *MediaImplementation) rtspConsumer(uri string) {
	annexbNALUStartCode := func() []byte { return []byte{0x00, 0x00, 0x00, 0x01} }
	//fmt.Println("rtspConsumer starting...")

	session, err := rtsp.DialTimeout(uri, 10*time.Second)
	// defer session.Close()
	if err != nil {
		fmt.Errorf("rtsp Dial Error: %v", err)
		return
		//panic(err)
	}

	//session.RtpKeepAliveTimeout = 10 * time.Second
	session.RtpTimeout = 20 * time.Second
	session.RtpKeepAliveTimeout = 5 * time.Second
	session.RtspTimeout = 20 * time.Second
	codecs, err := session.Streams()
	if err != nil {
		fmt.Errorf("stream error: %v", err)
		// continue
		//panic(err)
	}
	for i, t := range codecs {
		fmt.Printf("Stream", i, "is of type", t.Type().String())
	}

	if codecs[0].Type() != av.H264 {
		//fmt.Println("RTSP feed must begin with a H264 codec")
		// continue
		//panic("RTSP feed must begin with a H264 codec")
	}
	if len(codecs) != 1 {
		//fmt.Println("Ignoring all but the first stream.")
	}

	// var previousTime time.Duration
	for {
		// select {
		// case <-rtspsrcch:
		// default:
		// if KVMrtsp.BInUse != true {
		// 	break
		// }
		pkt, err := session.ReadPacket()
		if err != nil {
			break
		}

		// if pkt.Idx != 0 {
		// 	//audio or other stream, skip it
		// 	continue
		// }
		if codecs[pkt.Idx].Type().IsVideo() {
			pkt.Data = pkt.Data[4:]

			// For every key-frame pre-pend the SPS and PPS
			if pkt.IsKeyFrame {
				pkt.Data = append(annexbNALUStartCode(), pkt.Data...)
				pkt.Data = append(codecs[0].(h264parser.CodecData).PPS(), pkt.Data...)
				pkt.Data = append(annexbNALUStartCode(), pkt.Data...)
				pkt.Data = append(codecs[0].(h264parser.CodecData).SPS(), pkt.Data...)
				pkt.Data = append(annexbNALUStartCode(), pkt.Data...)
			} else {
				pkt.Data = append(annexbNALUStartCode(), pkt.Data...)
			}

			// bufferDuration := pkt.Time - previousTime
			// previousTime = pkt.Time
			// m.CallBackData(pkt.Data,len(pkt.Data))
			fmt.Println("Is Video IsKeyFrame", pkt.IsKeyFrame, codecs[pkt.Idx].Type(), pkt.Time)
			mediatype := 0
			switch codecs[pkt.Idx].Type() {
			case av.H264:
				mediatype = 1
			case av.H265:
				mediatype = 2
			}
			length := len(pkt.Data)
			arr := (*C.uchar)(unsafe.Pointer(&pkt.Data[0]))
			C.OnSendPacket(m.callclass, arr, C.int(length), C.int(mediatype))
			// if err = KVMrtsp.Track.WriteSample(media.Sample{Data: pkt.Data, Duration: bufferDuration}); err != nil && err != io.ErrClosedPipe {
			// 	logger.Errorf("WriteSample error %v", err)
			// 	break
			// 	//panic(err)
			// }
		} else if codecs[pkt.Idx].Type().IsAudio() {
			// codecs, err = session.Streams()
			// if err != nil {
			// 	fmt.Println("Error getting streams")
			// 	break
			// }
			codec := codecs[pkt.Idx].(av.AudioCodecData)
			duration, err := codec.PacketDuration(pkt.Data)
			if err != nil {
				fmt.Println("Failed to get duration for audio:", err)
				break
			}
			fmt.Println("IS Audio Packet duration:", duration)
			mediatype := 0
			switch codecs[pkt.Idx].Type() {
			case av.AAC:
				mediatype = 3
			case av.PCM_MULAW:
				mediatype = 4
			case av.PCM_ALAW:
				mediatype = 5
			case av.SPEEX:
				mediatype = 6
			case av.NELLYMOSER:
				mediatype = 7
			case av.PCM:
				mediatype = 8
			case av.OPUS:
				mediatype = 9
			}
			length := len(pkt.Data)
			arr := (*C.uchar)(unsafe.Pointer(&pkt.Data[0]))
			C.OnSendPacket(m.callclass, arr, C.int(length), C.int(mediatype))
			// m.CallBackData(pkt.Data,len(pkt.Data))
			// err = audioTrack.WriteSample(media.Sample{Data: pkt.Data, Duration: duration})
			// if err != nil {
			// 	//fmt.Println("Failed to write audio sample", err)
			// 	break
			// }
		}
	}

	if err = session.Close(); err != nil {
		fmt.Errorf("session Close error %v", err)
		return
	}

	// time.Sleep(5 * time.Second)

	// }
}