feat: Add C API for host functions + support for C++, Python, Go, Node, OCaml

[zshipko]

• New types:

  • ExtismValType - Enum of WebAssembly types
  • ExtismValUnion - A union of the possible WebAssembly types
  • ExtismVal - A struct with ExtismValType and ExtismValUnion
  • ExtismFunction - The host function wrapper type
  • ExtismFunctionType - The type of the host function callback
  • ExtismCurrentPlugin - Provides access to the currently running plugin from inside a host function

• New functions:

  • extism_function_new - Create a new ExtismFunction
  • extism_function_free - Free an ExtismFunction
  • extism_current_plugin_memory, extism_current_plugin_memory_alloc, extism_current_plugin_memory_free, extism_current_plugin_memory_length - Manage plugin memory from inside a host functions

• Updated functions

  • extism_plugin_new and extsim_plugin_update - now accept two extra parameters for ExtismFunction* array and length of that array

Notes

• Host functions take a user-data argument, which is owned by the resulting ExtismFunction and will be cleaned up when extism_function_free is called (if a cleanup function was passed in with the user data)
• Host functions in every SDK require working with ExtismVal arguments directly, this is pretty low-level for what is kind of a high-level feature. We could work on adding some types to the SDKs that make working with pointers to plugin data more accessible, maybe something similar to how the Rust PDK handes input/output data.
• In each language the host functions more-or-less share a signature: (CurrentPlugin plugin, Val inputs[], Val outputs[], userData)
  • C, C++, OCaml and Go take a single userData argument but Python and Node take a "rest" argument which allows passing any number of user-data values
• Go requires the host function to be exported:

  extism/go/main.go

  Lines 13 to 26 in f9eb5ed

  	#include <extism.h>
  	EXTISM_GO_FUNCTION(hello_world);
  	*/
  	import "C"
  	//export hello_world
  	func hello_world(plugin *C.ExtismCurrentPlugin, inputs *C.ExtismVal, nInputs C.ExtismSize, outputs *C.ExtismVal, nOutputs C.ExtismSize, userData unsafe.Pointer) {
  	fmt.Println("Hello from Go!")
  	s := *(*interface{})(userData)
  	fmt.Println(s.(string))
  	inputSlice := unsafe.Slice(inputs, nInputs)
  	outputSlice := unsafe.Slice(outputs, nOutputs)
  	outputSlice[0] = inputSlice[0]
  	}

• Zig and Ruby should be relatively simple to add host functions to next but I haven't really looked into Elixir, .NET or Java yet.
• Also closes reminder: consider inlining -l/-L paths vs. pkg-config in go sdk #20

[zshipko]

Just pushed the change to get rid of plugin_new_with_functions/plugin_update_with_functions and add the parameters to extism_plugin_new/extism_plugin_update and updated all the SDKs

[nilslice]

This is awesome, @zshipko! Will be testing these out over the course of the week. For those following along, this is definitely a candidate for an upcoming v0.2.0 release, and if anyone can help test or add more of the bindings to other SDKs that would be excellent.

cc/ other SDK contributors for awareness:
@usdogu @thomasdarimont @mhmd-azeez @alistairjevans

[mhmd-azeez]

@nilslice I will try to add bindings to the .NET sdk after the PR is merged and the new binaries are released

[nilslice]

@mhmd-azeez that would be awesome. thanks!