ASP.NET Core – 讀寫 Request / Response

需求

常見的需求就是從 request 里面讀取一些 information. 比如 

request URL, header, cookie, 

寫入 response header, cookie

 

實戰

Razor Page Model 中

// 讀取 request, header, cookie
var fullUrl = HttpContext.Request.GetDisplayUrl(); // https://192.168.1.152:44300/?value=v1&value=v2 (note: about 的話是 .../about?value=v1, 不是 .../about/?value=v1 哦)
var scheme = HttpContext.Request.Scheme; // https
var host = HttpContext.Request.Host.Host; // 192.168.1.152
var port = HttpContext.Request.Host.Port; // 44300
var path = HttpContext.Request.Path; // "/" <-- home page 的 path 是 /
var queryString = HttpContext.Request.QueryString.Value; // ?value=v1&value=v2
var query = HttpContext.Request.Query;
if (query.TryGetValue("value", out StringValues value))
{
    // same key won't combine
    var value1 = value.ElementAt(0); // v1
    var value2 = value.ElementAt(1); // v2
    var combineValue =  value.ToString(); // v1,v2
}
var remoteIp = HttpContext.Connection.RemoteIpAddress;

if (HttpContext.Request.Cookies.TryGetValue("cookie1", out var cookieValue)) 
{ 
        
}
var userAgent = HttpContext.Request.Headers.UserAgent.ToString();
var contentType = HttpContext.Request.Headers.ContentType.ToString();
if (HttpContext.Request.Headers.TryGetValue("Custom-Header", out StringValues customHeaderValue)) // h1,h2
{
    var h1 = customHeaderValue.ElementAt(0); // h1,h2
    var h2 = customHeaderValue.ElementAtOrDefault(1); // null
    var combineHeader = customHeaderValue.ToString(); // h1,h2
    // same key will combine become value1 value2
};

// 寫入 header, cookie
HttpContext.Response.Headers.Append("CustomResponseHeader", "value1");
HttpContext.Response.Cookies.Append("cookie1", "value1");

可以看到關鍵就是 HttpContext, request, response 都可以通過這個去讀寫.

header 和 query 如果遇到有 2 個 key (雖然我不知道什么情況下會需要這樣), header 是會 combine value 而 query 是不會的哦 

queryString 獲取的值就是 original 的值, 是含 encode 的, 調用 TryGetValue 的時候我們則不需要顧慮 encode, decode, 它會替我們處理好.

更多關於 query 的操控可以看這篇

 

razor .cshtml

我們依然可以調用到 HttpContext

@HttpContext.Request.Headers.UserAgent

 

Web API Controller

var userAgent = HttpContext.Request.Headers.UserAgent;

 

DI Service

要在 service 中獲取到 Httpcontext 就需要依賴注入. 

首先在 startup.cs

services.AddHttpContextAccessor();

源碼

然后在 Service.cs, 通過 HttpContextAccessor 就可以獲取到 HttpContext 了

public class CustomerService
{
    private readonly HttpContext _httpContext;
    public CustomerService(
      IHttpContextAccessor httpContextAccessor
    )
    {
        _httpContext = httpContextAccessor.HttpContext!;
    }

    public string GetUserAgent() 
    { 
        return _httpContext.Request.Headers.UserAgent;
    }
}

 

MVC View 中

Razor Pages 是 HttpContext 而 MVC VIew 是 Context 而已.