fix(vmess): add h2c support for h2 and grpc transport

[greenhat616]

• grpc with h2c: test ok as expect
• h2 with h2c: small page can read as expect
• huge page, like: https://www.aliyun.com or https://cloud.tencent.com could read really small - seems can't finish in a minute.
• I haven't tested it in h2 with tls

It seems buffer is really small?

[ibigbug]

to claifiry - h2c is just HTTP/2 without TLS right?

[greenhat616]

to claifiry - h2c is just HTTP/2 without TLS right?

Yes, It is.

ref: https://httpd.apache.org/docs/2.4/howto/http2.html

h2c is HTTP/2 over TCP.

[ibigbug]

so the possible setups could be

• vmess/trojan over h2c
• vmess/trojan over grpc over h2c

?

[greenhat616]

so the possible setups could be

• vmess/trojan over h2c
• vmess/trojan over grpc over h2c

?

Yes.
ref: https://www.v2ray.com/chapter_02/transport/h2.html

V2Ray 4.20 中对服务端的TLS配置的强制条件移除，为了在特殊用途的分流部署环境中，由外部网关组件完成TLS层对话，V2Ray作为后端应用，网关和V2Ray间使用称为h2c的明文http/2进行通讯。

It also defined in grpc: https://xtls.github.io/config/transports/grpc.html

[ibigbug]

thank you!