mobileproxy clib

[daniellacosse]

Command to run:

cd outline-sdk
CGO_ENABLED=1 go build -buildmode=c-shared ./x/examples/mobileproxy-clib

Header file output:

#include <stdint.h>  // uintptr_t

typedef uintptr_t StreamDialer;
typedef uintptr_t Proxy;

extern StreamDialer NewStreamDialerFromConfig(char* config);
extern void ReleaseStreamDialer(StreamDialer dialerHandle);
extern Proxy RunProxy(char* address, StreamDialer dialerHandle);
extern void AddURLProxy(Proxy proxyHandle, char* url, StreamDialer dialerHandle);
extern void StopProxy(Proxy proxyHandle, unsigned int timeoutSeconds);
extern void ReleaseProxy(Proxy proxyHandle);

TODOs:

• return tuple from main.go functions so we can have an error message
• demo: implement error handling
• demo: use signal to read Enter and shut down the server

[jyyi1]

We still need to use unsafe.Pointer as the type. cgo.Handle only allows you to pass object without pinning.

[fortuna]

We need to see this in action to be confident it works.

Please add a program that uses this library.
Some possibilities would be a c program, or a go program that calls this library via cgo.

[daniellacosse]

Okay, great! We're already at that stage I guess!

[daniellacosse]

In the interest of timing, maybe I can move this into experimental for now?

[fortuna]

I don't know what you mean with moving to experimental.
The binary can be in the examples folder, but we need it in order to know it works.

[daniellacosse]

Sorry, I meant examples! Okay, sure, I'll commit the binary to examples, and we can go from there

[fortuna]

If you'd like to use Abseil for flags, etc: https://abseil.io/docs/cpp/quickstart

[daniellacosse]

I'm not saying we shouldn't have a program! Just that given timing, I'd like to get the library in so a test program can be written around it, rather than it just hanging in the air. Do you feel a program blocks this PR @jyyi1 or can it be added in a follow-up?

[fortuna]

I would like to have this code checked in only when we have proof it works. I see no harm in keeping it in a branch if we can't produce a program that can use it.

[daniellacosse]

"Can't" is a strong word, we certainly can, but maybe not by the end of the week since I'm learning C as we go here: I'll see what I can do.

[daniellacosse]

I have started the program based on @jyyi1's initial draft and will review that with him today.

[fortuna]

We must have a way to return errors. Go Mobile returns a struct instead.

[daniellacosse]

@jyyi1 you can return a tuple right?

[jyyi1]

Yes, you can return a tuple and paste the header here.

@fortuna, do you mean a more C-friendly way of returning errors, like below?

Proxy *proxy;
int err = CreateProxy(&proxy);

[fortuna]

We need a way to return an error meesage.

Also, which design should we use?

• Return error (proxy reference)
• Return proxy (error reference)
• Return tuple
• return nothing (error and proxy reference)

I think Go Mobile on ios returns the value and writes the error to an input reference.

[daniellacosse]

I lean towards tuple with two pointers in it. Since we're throwing around unsafe pointers, with the tuple approach the caller doesn't have to do any guesswork around what kind of pointer they've received. But maybe there's a C way to do it? @jyyi1 thoughts?

[daniellacosse]

@jyyi1 should we be using errno? https://www.geeksforgeeks.org/error-handling-in-c/#

[jyyi1]

errno is very Unix specific. But sure, we can introduce our own errno. That's actually my code above, we'll return an int, and put the proxy into a "output parameter".

[fortuna]

We need a way to return an error message too. Errno is not enough.

[daniellacosse]

I'm going with tuple w/ error message as second optional argument

[fortuna]

There's no call to read the Enter here.

Consider sigaction: https://stackoverflow.com/a/19059462

[daniellacosse]

Yeah, this file is in progress. Converting this PR back to draft!

[jyyi1]

sigaction is not cross-platform. I'd rather use a standard library function.

[fortuna]

What do you mean? It's in the POSIX standard: https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaction.html

Does Windows not implement it? I guess signal is probably fine too.

[jyyi1]

Not sigaction, but signal is good.

[fortuna]

We need error handling.

[daniellacosse]

Yep, converting this to draft as we figure out that piece.