/// <summary>
/// A callback that is invoked prior to sending the proxied request. All HttpRequestMessage fields are
/// initialized except RequestUri, which will be initialized after the callback if no value is provided.
/// See <see cref="RequestUtilities.MakeDestinationAddress(string, PathString, QueryString)"/> for constructing a custom request Uri.
/// The string parameter represents the destination URI prefix that should be used when constructing the RequestUri.
/// The headers are copied by the base implementation, excluding some protocol headers like HTTP/2 pseudo headers (":authority").
/// </summary>
/// <param name="httpContext">The incoming request.</param>
/// <param name="proxyRequest">The outgoing proxy request.</param>
/// <param name="destinationPrefix">The uri prefix for the selected destination server which can be used to create the RequestUri.</param>
public virtual ValueTask TransformRequestAsync(HttpContext httpContext, HttpRequestMessage proxyRequest, string destinationPrefix)
{
foreach (var header in httpContext.Request.Headers)
{
var headerName = header.Key;
var headerValue = header.Value;
if (RequestUtilities.ShouldSkipRequestHeader(headerName))
{
continue;
}
RequestUtilities.AddHeader(proxyRequest, headerName, headerValue);
}
// https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
// If a message is received with both a Transfer-Encoding and a
// Content-Length header field, the Transfer-Encoding overrides the
// Content-Length. Such a message might indicate an attempt to
// perform request smuggling (Section 9.5) or response splitting
// (Section 9.4) and ought to be handled as an error. A sender MUST
// remove the received Content-Length field prior to forwarding such
// a message downstream.
if (httpContext.Request.Headers.ContainsKey(HeaderNames.TransferEncoding) &&
httpContext.Request.Headers.ContainsKey(HeaderNames.ContentLength))
{
proxyRequest.Content?.Headers.Remove(HeaderNames.ContentLength);
}
// https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2.2
// The only exception to this is the TE header field, which MAY be
// present in an HTTP/2 request; when it is, it MUST NOT contain any
// value other than "trailers".
if (ProtocolHelper.IsHttp2OrGreater(httpContext.Request.Protocol))
{
var te = httpContext.Request.Headers.GetCommaSeparatedValues(HeaderNames.TE);
if (te != null)
{
for (var i = 0; i < te.Length; i++)
{
if (string.Equals(te[i], "trailers", StringComparison.OrdinalIgnoreCase))
{
var added = proxyRequest.Headers.TryAddWithoutValidation(HeaderNames.TE, te[i]);
Debug.Assert(added);
break;
}
}
}
}
return(default);
private static void CopyResponseHeaders(HttpContext httpContext, HttpHeaders source, IHeaderDictionary destination)
{
var isHttp2OrGreater = ProtocolHelper.IsHttp2OrGreater(httpContext.Request.Protocol);
foreach (var header in source)
{
var headerName = header.Key;
if (RequestUtilities.ShouldSkipResponseHeader(headerName, isHttp2OrGreater))
{
continue;
}
destination.Append(headerName, header.Value.ToArray());
}
}
private static Task CopyResponseStatusAndHeadersAsync(HttpResponseMessage source, HttpContext context, HttpTransformer transformer)
{
context.Response.StatusCode = (int)source.StatusCode;
if (!ProtocolHelper.IsHttp2OrGreater(context.Request.Protocol))
{
// Don't explicitly set the field if the default reason phrase is used
if (source.ReasonPhrase != ReasonPhrases.GetReasonPhrase((int)source.StatusCode))
{
context.Features.Get <IHttpResponseFeature>().ReasonPhrase = source.ReasonPhrase;
}
}
// Copies headers
return(transformer.TransformResponseAsync(context, source));
}
private StreamCopyHttpContent SetupRequestBodyCopy(HttpRequest request, bool isStreamingRequest, CancellationToken cancellation)
{
// If we generate an HttpContent without a Content-Length then for HTTP/1.1 HttpClient will add a Transfer-Encoding: chunked header
// even if it's a GET request. Some servers reject requests containing a Transfer-Encoding header if they're not expecting a body.
// Try to be as specific as possible about the client's intent to send a body. The one thing we don't want to do is to start
// reading the body early because that has side-effects like 100-continue.
var hasBody = true;
var contentLength = request.Headers.ContentLength;
var method = request.Method;
#if NET
var canHaveBodyFeature = request.HttpContext.Features.Get <IHttpRequestBodyDetectionFeature>();
if (canHaveBodyFeature != null)
{
// 5.0 servers provide a definitive answer for us.
hasBody = canHaveBodyFeature.CanHaveBody;
}
else
#endif
// https://tools.ietf.org/html/rfc7230#section-3.3.3
// All HTTP/1.1 requests should have Transfer-Encoding or Content-Length.
// Http.Sys/IIS will even add a Transfer-Encoding header to HTTP/2 requests with bodies for back-compat.
// HTTP/1.0 Connection: close bodies are only allowed on responses, not requests.
// https://tools.ietf.org/html/rfc1945#section-7.2.2
//
// Transfer-Encoding overrides Content-Length per spec
if (request.Headers.TryGetValue(HeaderNames.TransferEncoding, out var transferEncoding) &&
transferEncoding.Count == 1 &&
string.Equals("chunked", transferEncoding.ToString(), StringComparison.OrdinalIgnoreCase))
{
hasBody = true;
}
else if (contentLength.HasValue)
{
hasBody = contentLength > 0;
}
// Kestrel HTTP/2: There are no required headers that indicate if there is a request body so we need to sniff other fields.
else if (!ProtocolHelper.IsHttp2OrGreater(request.Protocol))
{
hasBody = false;
}
// https://tools.ietf.org/html/rfc7231#section-4.3.1
// A payload within a GET/HEAD/DELETE/CONNECT request message has no defined semantics; sending a payload body on a
// GET/HEAD/DELETE/CONNECT request might cause some existing implementations to reject the request.
// https://tools.ietf.org/html/rfc7231#section-4.3.8
// A client MUST NOT send a message body in a TRACE request.
else if (HttpMethods.IsGet(method) ||
HttpMethods.IsHead(method) ||
HttpMethods.IsDelete(method) ||
HttpMethods.IsConnect(method) ||
HttpMethods.IsTrace(method))
{
hasBody = false;
}
// else hasBody defaults to true
StreamCopyHttpContent requestContent = null;
if (hasBody)
{
if (isStreamingRequest)
{
DisableMinRequestBodyDataRateAndMaxRequestBodySize(request.HttpContext);
}
// Note on `autoFlushHttpClientOutgoingStream: isStreamingRequest`:
// The.NET Core HttpClient stack keeps its own buffers on top of the underlying outgoing connection socket.
// We flush those buffers down to the socket on every write when this is set,
// but it does NOT result in calls to flush on the underlying socket.
// This is necessary because we proxy http2 transparently,
// and we are deliberately unaware of packet structure used e.g. in gRPC duplex channels.
// Because the sockets aren't flushed, the perf impact of this choice is expected to be small.
// Future: It may be wise to set this to true for *all* http2 incoming requests,
// but for now, out of an abundance of caution, we only do it for requests that look like gRPC.
requestContent = new StreamCopyHttpContent(
source: request.Body,
autoFlushHttpClientOutgoingStream: isStreamingRequest,
clock: _clock,
cancellation: cancellation);
}
return(requestContent);
}
/// <summary>
/// Proxies the incoming request to the destination server, and the response back to the client.
/// </summary>
/// <remarks>
/// In what follows, as well as throughout in Reverse Proxy, we consider
/// the following picture as illustrative of the Proxy.
/// <code>
/// +-------------------+
/// | Destination +
/// +-------------------+
/// ▲ |
/// (b) | | (c)
/// | ▼
/// +-------------------+
/// | Proxy +
/// +-------------------+
/// ▲ |
/// (a) | | (d)
/// | ▼
/// +-------------------+
/// | Client +
/// +-------------------+
/// </code>
///
/// (a) and (b) show the *request* path, going from the client to the target.
/// (c) and (d) show the *response* path, going from the destination back to the client.
///
/// Normal proxying comprises the following steps:
/// (0) Disable ASP .NET Core limits for streaming requests
/// (1) Create outgoing HttpRequestMessage
/// (2) Setup copy of request body (background) Client --► Proxy --► Destination
/// (3) Copy request headers Client --► Proxy --► Destination
/// (4) Send the outgoing request using HttpMessageInvoker Client --► Proxy --► Destination
/// (5) Copy response status line Client ◄-- Proxy ◄-- Destination
/// (6) Copy response headers Client ◄-- Proxy ◄-- Destination
/// (7-A) Check for a 101 upgrade response, this takes care of WebSockets as well as any other upgradeable protocol.
/// (7-A-1) Upgrade client channel Client ◄--- Proxy ◄--- Destination
/// (7-A-2) Copy duplex streams and return Client ◄--► Proxy ◄--► Destination
/// (7-B) Copy (normal) response body Client ◄-- Proxy ◄-- Destination
/// (8) Copy response trailer headers and finish response Client ◄-- Proxy ◄-- Destination
/// (9) Wait for completion of step 2: copying request body Client --► Proxy --► Destination
///
/// ASP .NET Core (Kestrel) will finally send response trailers (if any)
/// after we complete the steps above and relinquish control.
/// </remarks>
public async ValueTask <ForwarderError> SendAsync(
HttpContext context,
string destinationPrefix,
HttpMessageInvoker httpClient,
ForwarderRequestConfig requestConfig,
HttpTransformer transformer)
{
_ = context ?? throw new ArgumentNullException(nameof(context));
_ = destinationPrefix ?? throw new ArgumentNullException(nameof(destinationPrefix));
_ = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
_ = requestConfig ?? throw new ArgumentNullException(nameof(requestConfig));
_ = transformer ?? throw new ArgumentNullException(nameof(transformer));
// HttpClient overload for SendAsync changes response behavior to fully buffered which impacts performance
// See discussion in https://github.com/microsoft/reverse-proxy/issues/458
if (httpClient is HttpClient)
{
throw new ArgumentException($"The http client must be of type HttpMessageInvoker, not HttpClient", nameof(httpClient));
}
ForwarderTelemetry.Log.ForwarderStart(destinationPrefix);
var activityCancellationSource = ActivityCancellationTokenSource.Rent(requestConfig?.ActivityTimeout ?? DefaultTimeout, context.RequestAborted);
try
{
var isClientHttp2OrGreater = ProtocolHelper.IsHttp2OrGreater(context.Request.Protocol);
// NOTE: We heuristically assume gRPC-looking requests may require streaming semantics.
// See https://github.com/microsoft/reverse-proxy/issues/118 for design discussion.
var isStreamingRequest = isClientHttp2OrGreater && ProtocolHelper.IsGrpcContentType(context.Request.ContentType);
// :: Step 1-3: Create outgoing HttpRequestMessage
var(destinationRequest, requestContent) = await CreateRequestMessageAsync(
context, destinationPrefix, transformer, requestConfig, isStreamingRequest, activityCancellationSource);
// :: Step 4: Send the outgoing request using HttpClient
HttpResponseMessage destinationResponse;
try
{
ForwarderTelemetry.Log.ForwarderStage(ForwarderStage.SendAsyncStart);
destinationResponse = await httpClient.SendAsync(destinationRequest, activityCancellationSource.Token);
ForwarderTelemetry.Log.ForwarderStage(ForwarderStage.SendAsyncStop);
// Reset the timeout since we received the response headers.
activityCancellationSource.ResetTimeout();
}
catch (Exception requestException)
{
return(await HandleRequestFailureAsync(context, requestContent, requestException, transformer, activityCancellationSource));
}
Log.ResponseReceived(_logger, destinationResponse);
try
{
// :: Step 5: Copy response status line Client ◄-- Proxy ◄-- Destination
// :: Step 6: Copy response headers Client ◄-- Proxy ◄-- Destination
var copyBody = await CopyResponseStatusAndHeadersAsync(destinationResponse, context, transformer);
if (!copyBody)
{
// The transforms callback decided that the response body should be discarded.
destinationResponse.Dispose();
if (requestContent is not null && requestContent.InProgress)
{
activityCancellationSource.Cancel();
await requestContent.ConsumptionTask;
}
return(ForwarderError.None);
}
}
catch (Exception ex)
{
destinationResponse.Dispose();
if (requestContent is not null && requestContent.InProgress)
{
activityCancellationSource.Cancel();
await requestContent.ConsumptionTask;
}
ReportProxyError(context, ForwarderError.ResponseHeaders, ex);
// Clear the response since status code, reason and some headers might have already been copied and we want clean 502 response.
context.Response.Clear();
context.Response.StatusCode = StatusCodes.Status502BadGateway;
return(ForwarderError.ResponseHeaders);
}
// :: Step 7-A: Check for a 101 upgrade response, this takes care of WebSockets as well as any other upgradeable protocol.
if (destinationResponse.StatusCode == HttpStatusCode.SwitchingProtocols)
{
Debug.Assert(requestContent?.Started != true);
return(await HandleUpgradedResponse(context, destinationResponse, activityCancellationSource));
}
// NOTE: it may *seem* wise to call `context.Response.StartAsync()` at this point
// since it looks like we are ready to send back response headers
// (and this might help reduce extra delays while we wait to receive the body from the destination).
// HOWEVER, this would produce the wrong result if it turns out that there is no content
// from the destination -- instead of sending headers and terminating the stream at once,
// we would send headers thinking a body may be coming, and there is none.
// This is problematic on gRPC connections when the destination server encounters an error,
// in which case it immediately returns the response headers and trailing headers, but no content,
// and clients misbehave if the initial headers response does not indicate stream end.
// :: Step 7-B: Copy response body Client ◄-- Proxy ◄-- Destination
var(responseBodyCopyResult, responseBodyException) = await CopyResponseBodyAsync(destinationResponse.Content, context.Response.Body, activityCancellationSource);
if (responseBodyCopyResult != StreamCopyResult.Success)
{
return(await HandleResponseBodyErrorAsync(context, requestContent, responseBodyCopyResult, responseBodyException !, activityCancellationSource));
}
// :: Step 8: Copy response trailer headers and finish response Client ◄-- Proxy ◄-- Destination
await CopyResponseTrailingHeadersAsync(destinationResponse, context, transformer);
if (isStreamingRequest)
{
// NOTE: We must call `CompleteAsync` so that Kestrel will flush all bytes to the client.
// In the case where there was no response body,
// this is also when headers and trailing headers are sent to the client.
// Without this, the client might wait forever waiting for response bytes,
// while we might wait forever waiting for request bytes,
// leading to a stuck connection and no way to make progress.
await context.Response.CompleteAsync();
}
// :: Step 9: Wait for completion of step 2: copying request body Client --► Proxy --► Destination
// NOTE: It is possible for the request body to NOT be copied even when there was an incoming requet body,
// e.g. when the request includes header `Expect: 100-continue` and the destination produced a non-1xx response.
// We must only wait for the request body to complete if it actually started,
// otherwise we run the risk of waiting indefinitely for a task that will never complete.
if (requestContent is not null && requestContent.Started)
{
var(requestBodyCopyResult, requestBodyException) = await requestContent.ConsumptionTask;
if (requestBodyCopyResult != StreamCopyResult.Success)
{
// The response succeeded. If there was a request body error then it was probably because the client or destination decided
// to cancel it. Report as low severity.
var error = requestBodyCopyResult switch
{
StreamCopyResult.InputError => ForwarderError.RequestBodyClient,
StreamCopyResult.OutputError => ForwarderError.RequestBodyDestination,
StreamCopyResult.Canceled => ForwarderError.RequestBodyCanceled,
_ => throw new NotImplementedException(requestBodyCopyResult.ToString())
};
ReportProxyError(context, error, requestBodyException !);
return(error);
}
}
}
finally
{
activityCancellationSource.Return();
ForwarderTelemetry.Log.ForwarderStop(context.Response.StatusCode);
}
return(ForwarderError.None);
}