# ASP.NET Core modify post request data
###### tags: `C#`

有時會想在 middleware 統一對 request 資料做些修改，或變更 router 路徑，可以這麼做

using Newtonsoft.Json;
using System.Net;
using System.Text;

public class UserDefineMiddleware
{
    private readonly RequestDelegate _next;

    public UserDefineMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext httpContext)
    {
        var path = httpContext.Request.Path.ToString().ToLower();

        if (!path.Contains("/api/wallet"))
        {
            await _next(httpContext);
            return;
        }

        //讀取本來的 request
        httpContext.Request.EnableBuffering();
        using var sr = new StreamReader(httpContext.Request.Body, Encoding.UTF8);
        var body = await sr.ReadToEndAsync();
        var dataSource = JsonConvert.DeserializeObject<RequestDto>(body);
        if (dataSource == null)
        {
            httpContext.Response.StatusCode = (int)HttpStatusCode.BadRequest;
            return;
        }

        //修改 request 內容並重新塞回去
        dataSource.name = dataSource.name.Towlower();
        var jsonString = JsonConvert.SerializeObject(dataSource);
        var requestContent = new StringContent(jsonString, Encoding.UTF8, "application/json");
        httpContext.Request.Body = await requestContent.ReadAsStreamAsync();

        //重新 router 路徑
        httpContext.Request.Path = $"/aaa/test";
        httpContext.Request.Body.Position = 0;
        await _next(httpContext);
    }
}

### read form data from request

if (context.Request.HasFormContentType)
{
    IFormCollection form;
    form = context.Request.Form; // sync
    // Or
    form = await context.Request.ReadFormAsync(); // async

    string param1 = form["param1"];
    string param2 = form["param2"];
 }

### 相關連結
[ASP.NET Core modify/substitute request body](https://stackoverflow.com/a/44500627/19304838)
[.Net Core Middleware - Getting Form Data from Request](https://stackoverflow.com/a/56056862/19304838)