DotNetCore HttpClient User-Agent & Encoding {id="DotNetCore-HttpClient-User-Agent-And-Encoding"}

DotNetCore HttpClient User-Agent & Encoding

編碼部分 DotNetCore 只保留常用編碼所以Big5需要額外安裝套件

Install-Package System.Text.Encoding.CodePages

在程式起始處初始化該套件 Startup (Web) 或 Main (Console)

Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

之後就跟以往用法一樣

再來是 User-Agent 部分

有些網站會依照此設定值返回不同內容

不設定有時會拿到預期之外的Response

client.DefaultRequestHeaders.UserAgent.TryParseAdd(
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36");

或是

client.DefaultRequestHeaders.Add(
    "User-Agent",
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36");

其他Header也可以依序新增進去

最後應該長這樣 User-Agent

static async Task Main()
{
    Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
    using (HttpClient client = new HttpClient())
    {
        client.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36");
        try
        {
        HttpResponseMessage response = await client.GetAsync("https://tw.yahoo.com/");
        response.EnsureSuccessStatusCode();
        string responseBody = await response.Content.ReadAsStringAsync();
        File.WriteAllText(@"E:\Users\jakeu\Desktop\WriteText.txt", responseBody);
        }catch{}
    }
}

因為網頁內容太長所以我最後寫到檔案

Encoding Big5

static async Task Main()
{
    Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
    using (HttpClient client = new HttpClient())
    {
        client.DefaultRequestHeaders.UserAgent.TryParseAdd(
            "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36");
        try
        {
        HttpResponseMessage response = await client.GetAsync("https://tw.yahoo.com/");
        response.EnsureSuccessStatusCode();
        var responseBytes = await response.Content.ReadAsByteArrayAsync();
        var responseBody = Encoding.GetEncoding("big5").GetString(responseBytes, 0, responseBytes.Length - 1); ;
        File.WriteAllText(@"E:\Users\jakeu\Desktop\WriteText.txt", responseBody);
        }catch{}
    }
}

這邊要把 Url 改到一個 Big5 的網站測試 (Yahoo不是Big5編碼)

小心.NET HttpClient

參考文件：小心.NET HttpClient

[ASP.NET][C#] 使用 HtmlAgilityPack 擷取新聞 (爬文機器人)

參考文件： [ASP.NET][C#] 使用 HtmlAgilityPack 擷取新聞 (爬文機器人)

PS5

C#
.Net Core
HttpClinet
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14 October 2025