WebAssembly support

[brandonros]

I don't know why I expected this to work with WebAssembly (it compiles for the wasm32-unknown-unknown target if you disable any TLS/SSL features).

But you will get to JavaScript layer and have one of what I guess is many issues (how would it know to do HTTP over fetch()?):

panicked at 'time not implemented on this platform', library/std/src/sys/wasm/../unsupported/time.rs:13:9

Stack:

Error
    at http://localhost:8080/pkg/graphql_poc.js:188:21

Which comes from

 let agent = AgentBuilder::new()
        .timeout_read(Duration::from_secs(30))
        .timeout_write(Duration::from_secs(30))
        .build();

I read you can use Chrono::Duration (which does support WASM) but AgentBuilder would need to accept non std::time::Duration?

[algesten]

Hi @brandonros! Welcome to ureq!

I have never used WebAssembly myself, so I don't actually know what would be required to make that work. The Duration here are ultimately used as socket timeouts. Those sockets are std::net::TcpStream, and I'll imagine that even if we get past the Duration problems, we will get to a dead end for the sockets. I don't know if it would be possible to solve that – blocking sockets at the bottom of the call stack?

A possible direction for a ureq 3.0, would be to isolate the HTTP request/response function into a Sans IO pattern backing library without allocations, deliberately target no_std and webassembly. Then make nice higher level wrappers for std, no_std and webasm that sits on the same core.

[jsha]

I'm curious @brandonros, what's the use case for using ureq in WebAssembly?

If it's useful, we could probably do something where all the meaningful features are stubbed out to fetch, but we'd need some motivating use cases.

I do really like the idea of making a no_std version of ureq (with more user-friendly features stacked on top when std is present).

[algesten]

@jsha i've been thinking about the no_std thing.

Here's an experiment just fleshing out what a no_std low level API could look like: https://github.com/algesten/h1-call

Design goals:

• no_std and no alloc crate. Stack is enough
• Sans-IO. Bring your own transport.
• Allow flushing the buffer to the transport at any point. I.e. do not require all headers to be in the borrowed buffer at the same time.
• Encode protocol as types, i.e. let State mean "the state the call is currently in", Version means Http/1.0 or 1.1. Method means GET/HEAD/etc...
• Using types, constraint operations to only those that are valid. I.e. Version HTTP/1.0 cannot send a body unless the Method is POST (the others are GET/HEAD which cannot have a body).

I've fleshed out how this could look with HTTP/1.0 – but it looks pretty promising, albeit it's a type soup.

[brandonros]

I'm curious @brandonros, what's the use case for using ureq in WebAssembly?

If it's useful, we could probably do something where all the meaningful features are stubbed out to fetch, but we'd need some motivating use cases.

I do really like the idea of making a no_std version of ureq (with more user-friendly features stacked on top when std is present).

You're probably right. My "vision"/idea was probably due to a lack of understanding on how things should be done in wasm land but the argument was:

write once, be able to run it backend (native Rust binary) and/or in the browser with wasm without having to add logic like if backend, use ureq, otherwise, use web-sys fetch https://github.com/search?q=repo%3Arustwasm%2Fwasm-bindgen%20fetch_with_request&type=code