Question

我正在将HttpRequestBase包裹为HttpRequestMessage，这需要复制所有标头。但由于HttpRequestMessage特别关于哪些标头应用于请求对象与Content对象，因此下面的httpRequest.Headers.Add行有时会抛出InvalidOperationException。

public static HttpRequestMessage AsHttpRequestMessage(this HttpRequestBase request) {
    Requires.NotNull(request, "request");

    var httpRequest = new HttpRequestMessage(new HttpMethod(request.HttpMethod), request.Url);
    foreach (string header in request.Headers) {
        httpRequest.Headers.Add(header, request.Headers.GetValues(header));
    }

    if (request.Form != null) {
        // Avoid a request message that will try to read the request stream twice for already parsed data.
        httpRequest.Content = new FormUrlEncodedContent(request.Form.AsKeyValuePairs());
    } else if (request.InputStream != null) {
        httpRequest.Content = new StreamContent(request.InputStream);
    }

    return httpRequest;
}

显然，我希望我的代码不会抛出异常，而是将每个标头适当地应用到适当的对象。我怎么预测呢？我是否可以使用任何方法来测试标题的适用性，而不是生成和捕获异常的标题？

Answer 1

事实证明这很简单。这个片段受到ASP.NET's own open sourced source code的启发。

/// <summary>
/// Clones an <see cref="HttpWebRequest" /> in order to send it again.
/// </summary>
/// <param name="message">The message to set headers on.</param>
/// <param name="request">The request with headers to clone.</param>
internal static void CopyHeadersFrom(this HttpRequestMessage message, HttpRequestBase request) {
    Requires.NotNull(request, "request");
    Requires.NotNull(message, "message");

    foreach (string headerName in request.Headers) {
        string[] headerValues = request.Headers.GetValues(headerName);
        if (!message.Headers.TryAddWithoutValidation(headerName, headerValues)) {
            message.Content.Headers.TryAddWithoutValidation(headerName, headerValues);
        }
    }
}

Answer 2

您应该可以使用TryAddWithoutValidation而不是Add来避免抛出。根据是否要缓冲请求，您需要注意是否调用GetBufferlessStream。请参阅以下类中的ConvertRequest方法：http://aspnetwebstack.codeplex.com/SourceControl/changeset/view/4764b0111b91#src/System.Web.Http.WebHost/HttpControllerHandler.cs

考虑标题名称，如何将HttpRequestBase转换为HttpRequestMessage？

2 个答案: