Asp.Net Core 2.0实现HttpResponse中繁切换

随笔背景：因为项目中有个简单的功能是需要实现中文简体到繁体的切换，数据库中存储的源数据都是中文简体的，为了省事就想着通过HttpHeader的方式来控制Api返回对应的繁体数据。

实现方式：通过Asp.Net Core 中的中间件来拦截HttpResponse，然后通过转换字符编码来实现中文繁体切换。

实现代码如下：

HttpContextMiddleware 中间件

public class HttpContextMiddleware
{
private readonly RequestDelegate _next;
public HttpContextMiddleware(RequestDelegate next)
{
_next = next;
}

public async Task Invoke(HttpContext context)
{
var originalBodyStream = context.Response.Body;

using (var responseBody = new MemoryStream())
{
context.Response.Body = responseBody;
await _next(context);
var result = await FormatResponse(context.Response);
if (context.Request.Headers.Keys.Contains(Constants.HttpHeaderLanguage))
{
var lang = context.Request.Headers.GetCommaSeparatedValues(Constants.HttpHeaderLanguage).GetValue(0).ToString();
if (lang == "zh-tw")
{
var traditionresult = ConvertHelper.ToTraditional(result);
byte[] array = Encoding.UTF8.GetBytes(traditionresult);
MemoryStream stream = new MemoryStream(array);
try
{
await stream.CopyToAsync(originalBodyStream);
}
catch (Exception ex)
{

throw ex;
}
}
else
{
try
{
await responseBody.CopyToAsync(originalBodyStream);
}
catch (Exception ex)
{

throw ex;
}
}
}
else
{
await responseBody.CopyToAsync(originalBodyStream);
}

}
}

private async Task<string> FormatResponse(HttpResponse response)
{
response.Body.Seek(0, SeekOrigin.Begin);
var text = await new StreamReader(response.Body).ReadToEndAsync();
response.Body.Seek(0, SeekOrigin.Begin);

return $"{text}";
}
}

Startup.cs

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseDefaultFiles();
app.UseAuthentication();
app.UseStaticFiles();
//在Mvc之前注入到管道中
app.UseMiddleware<HttpContextMiddleware>();
app.UseMvc();
}

ConvertHelper 中文简体繁体转换工具类

public static  class ConvertHelper
{
private const int LOCALE_SYSTEM_DEFAULT = 0x0800;
private const int LCMAP_SIMPLIFIED_CHINESE = 0x02000000;
private const int LCMAP_TRADITIONAL_CHINESE = 0x04000000;

[DllImport("kernel32", CharSet = CharSet.Auto, SetLastError = true)]
private static extern int LCMapString(int Locale, int dwMapFlags, string lpSrcStr, int cchSrc, [Out] string lpDestStr, int cchDest);

/// <summary>
/// 将字符转换成简体中文
/// </summary>
/// <param name="source">输入要转换的字符串</param>
/// <returns>转换完成后的字符串</returns>
public static string ToSimplified(string source)
{
String target = new String(' ', source.Length);
int ret = LCMapString(LOCALE_SYSTEM_DEFAULT, LCMAP_SIMPLIFIED_CHINESE, source, source.Length, target, source.Length);
return target;
}

/// <summary>
/// 将字符转换为繁体中文
/// </summary>
/// <param name="source">输入要转换的字符串</param>
/// <returns>转换完成后的字符串</returns>
public static string ToTraditional(string source)
{
String target = new String(' ', source.Length);
int ret = LCMapString(LOCALE_SYSTEM_DEFAULT, LCMAP_TRADITIONAL_CHINESE, source, source.Length, target, source.Length);
return target;
}
}

以上源代码就是所有关键代码了，中间件注入以后，不用再在action里或controller里单独拦截，经测试，会拦截所有api的响应结果。这里有个插曲是我之前尝试过使用ResultFilter来拦截，但没法做到在响应后拦截响应结果。不知出于什么原因，最后我放弃了Filter的方式，选择了这种中间件的拦截方式。

本文参考如下：

https://elanderson.net/2017/02/log-requests-and-responses-in-asp-net-core/

本文如有不对的地方，欢迎指正！愿与君共勉。

最后，感谢您的阅读！