c# - 阅读HttpContent的前n个字符

Question

我想在visual c web api程序中记录有关httprequestmessage响应的信息。我想使用这样的消息处理程序（从delegatinghandler继承）：

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) 
{
    // log request.Method & request.RequestUri
    var result = await base.SendAsync(request, cancellationToken);
    // log first 100 chars of result.Content
    return result
}

问题是 result.Content有时会很大，所以我想限制它只打印前n个字符（大约50个）。
我试过的：
用 toString()和 SubString将整个内容复制到字符串中。这正是我想要的，但是把大量的字符串读入内存，然后只使用前几个字符似乎是浪费——我觉得一定有更好的方法。
各种各样的解决方案，从互联网上阅读的字符，但删除他们从流。我需要把所有的信息都发回去。

Answer 1

通过这个，您可以从流中复制所需的信息，并将响应传递到要去的地方。

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) {
    // log request.Method & request.RequestUri
    var response = await base.SendAsync(request, cancellationToken);
    // log first 100 chars of response.Content
    var N = 100;
    var first_100_Chars = await ReadFirstNCharsOfHttpContent(response.Content, N);

    return response;
}

private static async Task<string> ReadFirstNCharsOfHttpContent(HttpContent httpContent, int N = 100) {
    //get the content Stream
    var contentStream = await httpContent.ReadAsStreamAsync().ConfigureAwait(false);
    //How big is it
    var streamLength = contentStream.Length;
    // Get the size of the buffer to be read
    var bufferSize = (int)(streamLength > N ? N : (N > streamLength ? streamLength : N));
    var ms = new System.IO.MemoryStream(bufferSize);
    //copy only the needed length
    await contentStream.CopyToAsync(ms, bufferSize);

    // The StreamReader will read from the current 
    // position of the MemoryStream which is currently 
    // set at the end of the data we just copied to it.

    // We need to set the position to 0 in order to read 
    // from the beginning.
    ms.Position = 0;
    //reset content position just to be safe.
    contentStream.Position = 0;

    var sr = new System.IO.StreamReader(ms);
    var logString = sr.ReadToEnd();

    return logString;
}