asp.net - 考虑到 header 名称，如何将HttpRequestBase转换为HttpRequestMessage？

Question

我将HttpRequestBase包装为HttpRequestMessage，这要求将所有 header 都复制过来。但是，由于HttpRequestMessage特定于哪些 header 应用于请求对象与内容对象，因此下面的httpRequest.Headers.Add行有时会引发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，我希望代码不引发异常，而是将每个 header 适本地应用于适当的对象。我该如何预测呢？我可以使用任何方法来测试 header 的适用性，该 header 不包括生成并捕获异常的 header 吗？

Answer 1

事实证明，这很简单。该片段受ASP.NET's own open sourced source code的启发很大。

/// <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);
        }
    }
}