Failed to construct ‘RTCIceCandidate‘ sdpMid and sdpMLineIndex are both null

最近在搞webrtc，在编写函数处理远端传递来的candidate时报错了，具体信息如下。国内关于webrtc的资料很少，所以去国外社区转了一圈，回来记录一下报错的解决方案

其实这个bug也好解决，根据报错信息可以判断是RTCIceCandidate的sdpMid和sdpMlineIndex为null了，看了看RTCIceCandidate的原码，基本就能判断出应该是对端传递candidate的时候没传递这两个值

interface RTCIceCandidate {
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/address) */
    readonly address: string | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/candidate) */
    readonly candidate: string;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/component) */
    readonly component: RTCIceComponent | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/foundation) */
    readonly foundation: string | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/port) */
    readonly port: number | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/priority) */
    readonly priority: number | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/protocol) */
    readonly protocol: RTCIceProtocol | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/relatedAddress) */
    readonly relatedAddress: string | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/relatedPort) */
    readonly relatedPort: number | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/sdpMLineIndex) */
    readonly sdpMLineIndex: number | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/sdpMid) */
    readonly sdpMid: string | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/tcpType) */
    readonly tcpType: RTCIceTcpCandidateType | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/type) */
    readonly type: RTCIceCandidateType | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/usernameFragment) */
    readonly usernameFragment: string | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/RTCIceCandidate/toJSON) */
    toJSON(): RTCIceCandidateInit;
}

于是我检查发送来的数据是这么构造的

我丢你的雷姆，这俩参数我压根就没传递。我们修改一下传递的json数据

tip：上述修改方式任然过于繁杂，const candidateJson = JSON.stringfy(event.candidate)即可实现预期效果

然后重启项目我们会发现报错消失了，并且也能显示出我们想要的效果，webrtc能够正常搭建

这篇文章提供了上面这个项目的源码（前端+后端）但还未整理，后续我会发布有关webrtc入门demo的文章和各位分享

webRTC详解文章
【前后端的那些事】2万字详解WebRTC（附加入门demo代码解析）