c＃ReadOnlyMemory from Pointer

Question

[嗨，我有一个c本机库，正在将我的json作为char *返回。我想在c＃中做的是使用此指针并将其直接写到

this.ControllerContext.HttpContext.Response.BodyWriter;

我能够从ptr创建ReadOnlySpan，但据我所知，PipeWriter仅接受ReadOnlyMemory<byte>，该C0没有IntPtr的构造函数。有没有一种方法可以从IntPtr创建ReadOnlyMemory<byte>，还是可以通过其他方式从本地库写入我的字符串，而无需额外复制一次？]

Answer 1

public class Utility
{
    public System.ReadOnlyMemory<T> ConvertToReadOnlyMemory(System.ReadOnlySpan<T> input) {
        var tmp = new System.Memory<T>();
        input.CopyTo(tmp.Span);
        return (System.ReadOnlyMemory<T>)tmp;
    }
}

但是，我认为这将涉及将流完全复制到堆存储中，这可能不是您想要的...

Answer 2

namespace Helper
{
    using System;
    using System.Runtime.InteropServices;

    public static class CStringMapper
    {
        // convert unmanaged c string to managed c# string
        public string toCSharpString(char* unmanaged_c_string)
        {
             return Marshal.PtrToStringAnsi((IntPtr)unmanaged_c_string);
         }

         // Free unmanaged c pointer
         public void free(char* unmanaged_c_string)
         {
             Marshal.FreeHGlobal((IntPtr)unmanaged_c_string);
         }
     }
}

用法：

 using Helper;

 /* generate your unmanaged c string here */

 try
 {
     // eg. char* OO7c = cLibFunc();
     string cSharpString = CStringMapper.toCSharpString(OO7c);
 } 
 finally
 {
     // Make sure to  freeing the pointer
     CStringMapper.free(OO7c);
 }

Answer 3

所以我唯一能够实现这一目标的方法就是。

 await Response.StartAsync(HttpContext.RequestAborted);
 var dest = Response.BodyWriter.GetMemory((int)jsonLen).Pin();
 unsafe { memcpy(dest.Pointer), srcPtr, srcLen); }
 Response.BodyWriter.Advance(srcLen);
 await Response.BodyWriter.FlushAsync(HttpContext.RequestAborted);