前面介绍了 webrtc 音视频流的通信， 根据自己粗浅的理解简单介绍了下， 今天花了点时间看了下DataChannel， 如何通过rtc发送文件，开始的步骤还是一样的 通过websocket 把 offer answer icecandidate 点对点建立

这次的主要提下 createDataChannel
本地端创建

sendChannel = local.createDataChannel(name, options)；
sendChannel.addEventListener('open', onSendChannelStateChange); //打开之后才可以传输数据 
sendChannel.addEventListener('close', onSendChannelStateChange);
sendChannel.send(JSON.stringify({
	  	name: file.name,
	  	type: file.type,
	  	size: file.size
	  }));
//也可以发送arraybuffer;
fileReader.onload = (e) => { sendChannel.send(e.target.result)};

参数可以参考 https://developer.mozilla.org/zh-CN/docs/Web/API/RTCPeerConnection/createDataChannel#RTCDataChannelInit_dictionary

remote.addEventListener('datachannel', callback);

//接受data
function callback(event){
	  // console.log('recive', event);
	  receiveChannel = event.channel;
	  receiveChannel.binaryType = 'arraybuffer';
	  receiveChannel.onmessage = onReceiveMessageCallback;
}

function onReceiveMessageCallback(event) {
		if (typeof event.data == 'string') {
			rcname = JSON.parse(event.data)['name'];
			rcsize = JSON.parse(event.data)['size'];
			document.getElementById('box').style.display = 'none';
			document.getElementById('msg').style.display = 'block';
			document.getElementById('msg').innerHTML = "<p>文件共计"+(rcsize/1024/1024).toFixed(2)+"MB</p>";
			return;
		};
		receiveBuffer.push(event.data);
		receivedSize += event.data.byteLength;
		document.querySelector('#bars p').style.width = (receivedSize/rcsize) * 100 +"%"
		if (receivedSize == rcsize) {
			let resultfile = new Blob(receiveBuffer);
			let url = URL.createObjectURL(resultfile);
			receivedSize = 0;
			let a = document.createElement('a');
			a.download = rcname;
			a.innerHTML = '点击保存';
			a.href=url;
			receiveChannel.close();
			document.getElementById('msg').appendChild(a);
		}
	}

发送成功