support setting bytes for stdin

[Tiziano Santoro]

Motivation

It is quite common to have to provide a pre-determined stdin value to a Wasm module, without having to expose a full file system to it.

Proposed solution

leverage this function:

https://docs.wasmtime.dev/c-api/wasi_8h.html#a525abd98ade58887a969b796ea05468e

would require modifying

wasmer-go/wasmer/packaged/include/wasmer.h

Lines 705 to 707 in ca60a45

 #if defined(WASMER_WASI_ENABLED) 
 void wasi_config_inherit_stdin(struct wasi_config_t *config); 
 #endif 

and

wasmer-go/wasmer/wasi.go

Lines 196 to 202 in ca60a45

 // InheritStdin configures the WASI module to inherit the stdin from 
 // the host. 
 func (self *WasiStateBuilder) InheritStdin() *WasiStateBuilder { 
 	C.wasi_config_inherit_stdin(self.inner()) 
  
 	return self 
 } 

Alternatives

The best alternative at the moment is passing the value as argument on the command line, but that's not great for large and / or binary values.

[Jaime Amate]

I'm currently facing the same issue on my project. It would be quite handy having somehow a setStdIn function.

Could you explain on more further details about the workaround to pass input data to the wasi module execution?

[Tiziano Santoro]

For the time being I just serialize the data as a string (base64 if necessary) and pass it as the first command line argument to the Wasm module, which then reads it as argv[1]

[Jaime Amate]

Thanks for the explanation, I think this wouldn't even work in my use case :(

I'm trying to embed a .wasm module compiled by Javy and according to this issue, it doesn't currently expose APIs to read environment variables or command line arguments.

[Tiziano Santoro]

Right, in that case fixing this issue wouldn't help you, since this is specific to WASI, which AFAICT you are not using. I think your best bet is to declare a custom function for the Wasm module to read the data into its own memory