Proposal: optee-utee: support no-std net.

[ivila]

Background

Currently, Teaclave has a net module provided by mssun (#31) four years ago, which can only be accessed in a std environment. However, during my development, I frequently perform HTTP requests to the REE (some services inside Kubernetes) from within the TEE. At present, I am using unsafe and optee_utee_sys directly. However, I believe it would be more elegant for Teaclave to officially support no_std TcpStream and hide the unsafe code and optee_utee_sys from developers.

Proposal

The changes are quite small, so I'll just summarize them:

1. Introduced SocketError: an enum that encompasses all the error values returned by the GP TEE Sockets API.
2. Introduced Socket struct and SocketAdapter trait: The Socket struct handles socket operations (open, send, recv), while SocketAdapter accommodates various implementations of the GP TEE Sockets API.
3. Introduced TcpAdapter and UdpAdapter for OP-TEE: using them to construct TcpStream and UdpSocket.

You can check this commit at my fork for details

[mssun]

That's a great proposal! Thanks @ivila.

[b49020]

@ivila Nice, feel free to create a corresponding PR. Also, please update examples: https://github.com/apache/incubator-teaclave-trustzone-sdk/tree/main/examples/tcp_client-rs and https://github.com/apache/incubator-teaclave-trustzone-sdk/tree/main/examples/udp_socket-rs such that they can be supported in no-std environment too.