如何在golang中使用数组作为Web汇编代码？

Question

我想使用Webassembly计算一个数组的总和。我的锈代码看起来像这样

use std::os::raw::c_int;

#[no_mangle]
pub extern fn bar(my_array: *const c_int, length: c_int) -> *mut c_int{
    let slice = unsafe { slice::from_raw_parts(my_array, length as usize) };
    let resp: i32 = slice.iter().sum();

    resp as *mut c_int
}

将此锈代码编译为wasm。现在，我在golang中调用此函数。

package main

import (
    "encoding/binary"
    "encoding/hex"
    "fmt"

    wasm "github.com/wasmerio/go-ext-wasm/wasmer"
)

const length int32 = 4

func main() {
    // Instantiate the module.
    wasmbyte, _ := wasm.ReadBytes("test.wasm")
    instance, _ := wasm.NewInstance(wasmbyte)
    defer instance.Close()
    hasmemory := instance.HasMemory()
    fmt.Println("it has memory:", (hasmemory))

    a := []int32{1, 2, 3, 4}
    var i int32
    var ptr [length]*int32

    for i = 0; i < length; i++ {
        ptr[i] = &a[i]
        fmt.Printf("Value of a[%d] = %d\n", i, *ptr[i])

        // pass int value
        // lengths := binary.LittleEndian.Uint32(a)
        // fmt.Printf("customLen=%d\n", int32(lengths))
        // result := int32(lengths)

        allocateResult, err := instance.Exports["bar"](*ptr[i], length)
        if err != nil {
            fmt.Println("error is here", err)
        }

        binary.LittleEndian.PutUint32(instance.Memory.Data()[0:4], uint32(length))

        inputPointer := allocateResult.ToI32()

        //  Write the subject into the memory.
        memory := instance.Memory.Data()[inputPointer:]
        binary.LittleEndian.Uint32(memory)

        resp := hex.EncodeToString(memory)
        fmt.Println("resp:", resp)

    }
}

但是此代码没有给我结果。我的代码的逻辑是计算一个数组的总和。在运行时给数组的值我需要做哪些更改？

谢谢

Answer 1

将数据复制到WebAssembly内存（例如WebAssembly内存地址0）：

    a := []int32{10, 20, 30, 40}
    // Copy data to wasm memory:
    bytes := instance.Memory.Data()
    for i, v := range a {
        binary.LittleEndian.PutUint32(bytes[4*i:], uint32(v))
    }

从WebAssembly实例获取bar导出的函数：

    bar := instance.Exports["bar"]

用WebAssembly的内存地址和长度调用导出的函数：

    result, err := bar(0, 4)
    if err != nil {
        panic(err)
    }

    fmt.Println(result)

代码：

package main

import (
    "encoding/binary"
    "fmt"

    wasm "github.com/wasmerio/go-ext-wasm/wasmer"
)

func main() {
    // Instantiate the module.
    wasmbyte, err := wasm.ReadBytes("test.wasm")
    if err != nil {
        panic(err)
    }

    instance, err := wasm.NewInstance(wasmbyte)
    if err != nil {
        panic(err)
    }

    defer instance.Close()
    hasmemory := instance.HasMemory()
    fmt.Println("it has memory:", hasmemory)

    a := []int32{10, 20, 30, 40}
    // Copy data to wasm memory:
    bytes := instance.Memory.Data()
    for i, v := range a {
        binary.LittleEndian.PutUint32(bytes[4*i:], uint32(v))
    }

    bar := instance.Exports["bar"]

    result, err := bar(0, 4)
    if err != nil {
        panic(err)
    }

    fmt.Println(result)
}

输出：

it has memory: true
100