inviteMessage := "INVITE sip:[email protected] SIP/2.0\r\nCall-ID: 4d4d84b0cc83fc90aca41e295cd8ff43@0:0:0:0:0:0:0:0\r\nCSeq: 2 INVITE\r\nFrom: \"1001\" <sip:[email protected]>;tag=99f35805\r\nTo: <sip:[email protected]>\r\nMax-Forwards: 70\r\nContact: \"1001\" <sip:[email protected]:5060;transport=udp;registering_acc=192_168_58_203>\r\nUser-Agent: Jitsi2.11.20200408Linux\r\nContent-Type: application/sdp\r\nVia: SIP/2.0/UDP 192.168.58.201:5060;branch=z9hG4bK-393139-939e89686023b86822cb942ede452b62\r\nProxy-Authorization: Digest username=\"1001\",realm=\"192.168.58.203\",nonce=\"XruO2167ja8uRODnSv8aXqv+/hqPJiXh\",uri=\"sip:[email protected]\",response=\"5b814c709d1541d72ea778599c2e48a4\"\r\nContent-Length: 897\r\n\r\nv=0\r\no=1001-jitsi.org 0 0 IN IP4 192.168.58.201\r\ns=-\r\nc=IN IP4 192.168.58.201\r\nt=0 0\r\nm=audio 5000 RTP/AVP 96 97 98 9 100 102 0 8 103 3 104 101\r\na=rtpmap:96 opus/48000/2\r\na=fmtp:96 usedtx=1\r\na=ptime:20\r\na=rtpmap:97 SILK/24000\r\na=rtpmap:98 SILK/16000\r\na=rtpmap:9 G722/8000\r\na=rtpmap:100 speex/32000\r\na=rtpmap:102 speex/16000\r\na=rtpmap:0 PCMU/8000\r\na=rtpmap:8 PCMA/8000\r\na=rtpmap:103 iLBC/8000\r\na=rtpmap:3 GSM/8000\r\na=rtpmap:104 speex/8000\r\na=rtpmap:101 telephone-event/8000\r\na=extmap:1 urn:ietf:params:rtp-hdrext:csrc-audio-level\r\na=extmap:2 urn:ietf:params:rtp-hdrext:ssrc-audio-level\r\na=rtcp-xr:voip-metrics\r\nm=video 5002 RTP/AVP 105 99\r\na=recvonly\r\na=rtpmap:105 h264/90000\r\na=fmtp:105 profile-level-id=42E01f;packetization-mode=1\r\na=imageattr:105 send * recv [x=[1:1920],y=[1:1080]]\r\na=rtpmap:\r\n"

message, err := NewMessage(inviteMessage)
if err != nil {
    panic(err)
}

fmt.Println(message.MethodFrom("Request"))