/// <summary>
/// Proxies the incoming request to the upstream server, and the response back to our client.
/// </summary>
/// <remarks>
/// In what follows, as well as throughout in Reverse Proxy, we consider
/// the following picture as illustrative of the Proxy.
/// <code>
/// +-------------------+
/// | Upstream server +
/// +-------------------+
/// ▲ |
/// (b) | | (c)
/// | ▼
/// +-------------------+
/// | Proxy +
/// +-------------------+
/// ▲ |
/// (a) | | (d)
/// | ▼
/// +-------------------+
/// | Downstream client +
/// +-------------------+
/// </code>
///
/// (a) and (b) show the *request* path, going *upstream* from the client to the target.
/// (c) and (d) show the *response* path, going *downstream* from the target back to the client.
/// </remarks>
/// <param name="longCancellation">This should be linked to a client disconnect notification like <see cref="HttpContext.RequestAborted"/>
/// to avoid leaking long running requests.</param>
public Task ProxyAsync(
HttpContext context,
string destinationPrefix,
Transforms transforms,
IProxyHttpClientFactory httpClientFactory,
ProxyTelemetryContext proxyTelemetryContext,
CancellationToken shortCancellation,
CancellationToken longCancellation)
{
Contracts.CheckValue(context, nameof(context));
Contracts.CheckValue(destinationPrefix, nameof(destinationPrefix));
Contracts.CheckValue(transforms, nameof(transforms));
Contracts.CheckValue(httpClientFactory, nameof(httpClientFactory));
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 1: Create outgoing HttpRequestMessage
var upgradeFeature = context.Features.Get <IHttpUpgradeFeature>();
var isUpgrade = upgradeFeature?.IsUpgradableRequest ?? false;
// Default to HTTP/1.1 for proxying upgradable requests. This is already the default as of .NET Core 3.1
// Otherwise request HTTP/2 and let HttpClient fallback to HTTP/1.1 if it cannot establish HTTP/2 with the target.
// This is done without extra round-trips thanks to ALPN. We can detect a downgrade after calling HttpClient.SendAsync
// (see Step 3 below). TBD how this will change when HTTP/3 is supported.
var version = isUpgrade ? ProtocolHelper.Http11Version : ProtocolHelper.Http2Version;
var request = CreateRequestMessage(context, destinationPrefix, version, transforms.RequestTransforms);
if (isUpgrade)
{
return(UpgradableProxyAsync(context, upgradeFeature, request, transforms, httpClientFactory.CreateUpgradableClient(), proxyTelemetryContext, shortCancellation, longCancellation));
}
else
{
return(NormalProxyAsync(context, request, transforms, httpClientFactory.CreateNormalClient(), proxyTelemetryContext, shortCancellation, longCancellation));
}
}
/// <summary>
/// Proxies the incoming request to the upstream server, and the response back to our client.
/// </summary>
/// <remarks>
/// In what follows, as well as throughout in Reverse Proxy, we consider
/// the following picture as illustrative of the Proxy.
/// <code>
/// +-------------------+
/// | Upstream server +
/// +-------------------+
/// ▲ |
/// (b) | | (c)
/// | ▼
/// +-------------------+
/// | Proxy +
/// +-------------------+
/// ▲ |
/// (a) | | (d)
/// | ▼
/// +-------------------+
/// | Downstream client +
/// +-------------------+
/// </code>
///
/// (a) and (b) show the *request* path, going *upstream* from the client to the target.
/// (c) and (d) show the *response* path, going *downstream* from the target back to the client.
/// </remarks>
/// <param name="longCancellation">This should be linked to a client disconnect notification like <see cref="HttpContext.RequestAborted"/>
/// to avoid leaking long running requests.</param>
public Task ProxyAsync(
HttpContext context,
Uri targetUri,
IProxyHttpClientFactory httpClientFactory,
ProxyTelemetryContext proxyTelemetryContext,
CancellationToken shortCancellation,
CancellationToken longCancellation)
{
Contracts.CheckValue(context, nameof(context));
Contracts.CheckValue(targetUri, nameof(targetUri));
Contracts.CheckValue(httpClientFactory, nameof(httpClientFactory));
var upgradeFeature = context.Features.Get <IHttpUpgradeFeature>();
if (upgradeFeature == null || !upgradeFeature.IsUpgradableRequest)
{
return(NormalProxyAsync(context, targetUri, httpClientFactory.CreateNormalClient(), proxyTelemetryContext, shortCancellation, longCancellation));
}
else
{
return(UpgradableProxyAsync(context, upgradeFeature, targetUri, httpClientFactory.CreateUpgradableClient(), proxyTelemetryContext, shortCancellation, longCancellation));
}
}
/// <summary>
/// Proxies the incoming request to the upstream server, and the response back to our client.
/// </summary>
/// <remarks>
/// In what follows, as well as throughout in Reverse Proxy, we consider
/// the following picture as illustrative of the Proxy.
/// <code>
/// +-------------------+
/// | Upstream server +
/// +-------------------+
/// ▲ |
/// (b) | | (c)
/// | ▼
/// +-------------------+
/// | Proxy +
/// +-------------------+
/// ▲ |
/// (a) | | (d)
/// | ▼
/// +-------------------+
/// | Downstream client +
/// +-------------------+
/// </code>
///
/// (a) and (b) show the *request* path, going *upstream* from the client to the target.
/// (c) and (d) show the *response* path, going *downstream* from the target back to the client.
/// </remarks>
/// <param name="longCancellation">This should be linked to a client disconnect notification like <see cref="HttpContext.RequestAborted"/>
/// to avoid leaking long running requests.</param>
public Task ProxyAsync(
HttpContext context,
string destinationPrefix,
Transforms transforms,
IProxyHttpClientFactory httpClientFactory,
ProxyTelemetryContext proxyTelemetryContext,
CancellationToken shortCancellation,
CancellationToken longCancellation)
{
_ = context ?? throw new ArgumentNullException(nameof(context));
_ = destinationPrefix ?? throw new ArgumentNullException(nameof(destinationPrefix));
_ = transforms ?? throw new ArgumentNullException(nameof(transforms));
_ = httpClientFactory ?? throw new ArgumentNullException(nameof(httpClientFactory));
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 1: Create outgoing HttpRequestMessage
var upgradeFeature = context.Features.Get <IHttpUpgradeFeature>();
var isUpgrade = (upgradeFeature?.IsUpgradableRequest ?? false)
// Mitigate https://github.com/microsoft/reverse-proxy/issues/255, IIS considers all requests upgradeable.
&& string.Equals("WebSocket", context.Request.Headers[HeaderNames.Upgrade], StringComparison.OrdinalIgnoreCase);
// Default to HTTP/1.1 for proxying upgradeable requests. This is already the default as of .NET Core 3.1
// Otherwise request HTTP/2 and let HttpClient fallback to HTTP/1.1 if it cannot establish HTTP/2 with the target.
// This is done without extra round-trips thanks to ALPN. We can detect a downgrade after calling HttpClient.SendAsync
// (see Step 3 below). TBD how this will change when HTTP/3 is supported.
var version = isUpgrade ? ProtocolHelper.Http11Version : ProtocolHelper.Http2Version;
var request = CreateRequestMessage(context, destinationPrefix, version, transforms.RequestTransforms);
if (isUpgrade)
{
return(UpgradableProxyAsync(context, upgradeFeature, request, transforms, httpClientFactory.CreateClient(), proxyTelemetryContext, shortCancellation, longCancellation));
}
else
{
return(NormalProxyAsync(context, request, transforms, httpClientFactory.CreateClient(), proxyTelemetryContext, shortCancellation, longCancellation));
}
}
/// <summary>
/// Proxies an upgradable request to the upstream server, treating the upgraded stream as an opaque duplex channel.
/// </summary>
/// <remarks>
/// Upgradable request proxying comprises the following steps:
/// (1) Create outgoing HttpRequestMessage
/// (2) Copy request headers Downstream ---► Proxy ---► Upstream
/// (3) Send the outgoing request using HttpMessageInvoker Downstream ---► Proxy ---► Upstream
/// (4) Copy response status line Downstream ◄--- Proxy ◄--- Upstream
/// (5) Copy response headers Downstream ◄--- Proxy ◄--- Upstream
/// Scenario A: upgrade with upstream worked (got 101 response)
/// (A-6) Upgrade downstream channel (also sends response headers) Downstream ◄--- Proxy ◄--- Upstream
/// (A-7) Copy duplex streams Downstream ◄--► Proxy ◄--► Upstream
/// ---- or ----
/// Scenario B: upgrade with upstream failed (got non-101 response)
/// (B-6) Send response headers Downstream ◄--- Proxy ◄--- Upstream
/// (B-7) Copy response body Downstream ◄--- Proxy ◄--- Upstream
///
/// This takes care of WebSockets as well as any other upgradable protocol.
/// </remarks>
private async Task UpgradableProxyAsync(
HttpContext context,
IHttpUpgradeFeature upgradeFeature,
Uri targetUri,
HttpMessageInvoker httpClient,
ProxyTelemetryContext proxyTelemetryContext,
CancellationToken shortCancellation,
CancellationToken longCancellation)
{
Contracts.CheckValue(context, nameof(context));
Contracts.CheckValue(upgradeFeature, nameof(upgradeFeature));
Contracts.CheckValue(targetUri, nameof(targetUri));
Contracts.CheckValue(httpClient, nameof(httpClient));
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 1: Create outgoing HttpRequestMessage
var upstreamRequest = new HttpRequestMessage(HttpUtilities.GetHttpMethod(context.Request.Method), targetUri)
{
// Default to HTTP/1.1 for proxying upgradable requests. This is already the default as of .NET Core 3.1
Version = new Version(1, 1),
};
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 2: Copy request headers Downstream --► Proxy --► Upstream
CopyHeadersToUpstream(context, upstreamRequest);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 3: Send the outgoing request using HttpMessageInvoker
var upstreamResponse = await httpClient.SendAsync(upstreamRequest, shortCancellation);
var upgraded = upstreamResponse.StatusCode == HttpStatusCode.SwitchingProtocols && upstreamResponse.Content != null;
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 4: Copy response status line Downstream ◄-- Proxy ◄-- Upstream
context.Response.StatusCode = (int)upstreamResponse.StatusCode;
context.Features.Get <IHttpResponseFeature>().ReasonPhrase = upstreamResponse.ReasonPhrase;
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 5: Copy response headers Downstream ◄-- Proxy ◄-- Upstream
CopyHeadersToDownstream(upstreamResponse, context.Response.Headers);
if (!upgraded)
{
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step B-6: Send response headers Downstream ◄-- Proxy ◄-- Upstream
// This is important to avoid any extra delays in sending response headers
// e.g. if the upstream server is slow to provide its response body.
await context.Response.StartAsync(shortCancellation);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step B-7: Copy response body Downstream ◄-- Proxy ◄-- Upstream
await CopyBodyDownstreamAsync(upstreamResponse.Content, context.Response.Body, proxyTelemetryContext, longCancellation);
return;
}
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step A-6: Upgrade the downstream channel. This will send all response headers too.
using var downstreamStream = await upgradeFeature.UpgradeAsync();
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step A-7: Copy duplex streams
var upstreamStream = await upstreamResponse.Content.ReadAsStreamAsync();
var upstreamCopier = new StreamCopier(
_metrics,
new StreamCopyTelemetryContext(
direction: "upstream",
backendId: proxyTelemetryContext.BackendId,
routeId: proxyTelemetryContext.RouteId,
destinationId: proxyTelemetryContext.DestinationId));
var upstreamTask = upstreamCopier.CopyAsync(downstreamStream, upstreamStream, longCancellation);
var downstreamCopier = new StreamCopier(
_metrics,
new StreamCopyTelemetryContext(
direction: "downstream",
backendId: proxyTelemetryContext.BackendId,
routeId: proxyTelemetryContext.RouteId,
destinationId: proxyTelemetryContext.DestinationId));
var downstreamTask = downstreamCopier.CopyAsync(upstreamStream, downstreamStream, longCancellation);
await Task.WhenAll(upstreamTask, downstreamTask);
}
/// <summary>
/// Proxies a normal (i.e. non-upgradable) request to the upstream server, and the response back to our client.
/// </summary>
/// <remarks>
/// 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) Downstream --► Proxy --► Upstream
/// (3) Copy request headers Downstream --► Proxy --► Upstream
/// (4) Send the outgoing request using HttpMessageInvoker Downstream --► Proxy --► Upstream
/// (5) Copy response status line Downstream ◄-- Proxy ◄-- Upstream
/// (6) Copy response headers Downstream ◄-- Proxy ◄-- Upstream
/// (7) Copy response body Downstream ◄-- Proxy ◄-- Upstream
/// (8) Copy response trailer headers and finish response Downstream ◄-- Proxy ◄-- Upstream
/// (9) Wait for completion of step 2: copying request body Downstream --► Proxy --► Upstream
///
/// ASP .NET Core (Kestrel) will finally send response trailers (if any)
/// after we complete the steps above and relinquish control.
/// </remarks>
private async Task NormalProxyAsync(
HttpContext context,
Uri targetUri,
HttpMessageInvoker httpClient,
ProxyTelemetryContext proxyTelemetryContext,
CancellationToken shortCancellation,
CancellationToken longCancellation)
{
Contracts.CheckValue(context, nameof(context));
Contracts.CheckValue(targetUri, nameof(targetUri));
Contracts.CheckValue(httpClient, nameof(httpClient));
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 0: Disable ASP .NET Core limits for streaming requests
var isIncomingHttp2 = ProtocolHelper.IsHttp2(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 = isIncomingHttp2 && ProtocolHelper.IsGrpcContentType(context.Request.ContentType);
if (isStreamingRequest)
{
DisableMinRequestBodyDataRateAndMaxRequestBodySize(context);
}
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 1: Create outgoing HttpRequestMessage
var upstreamRequest = new HttpRequestMessage(HttpUtilities.GetHttpMethod(context.Request.Method), targetUri)
{
// We request HTTP/2, but HttpClient will fallback to HTTP/1.1 if it cannot establish HTTP/2 with the target.
// This is done without extra round-trips thanks to ALPN. We can detect a downgrade after calling HttpClient.SendAsync
// (see Step 3 below). TBD how this will change when HTTP/3 is supported.
Version = Http2Version,
};
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 2: Setup copy of request body (background) Downstream --► Proxy --► Upstream
// Note that we must do this before step (3) because step (3) may also add headers to the HttpContent that we set up here.
var bodyToUpstreamContent = SetupCopyBodyUpstream(context.Request.Body, upstreamRequest, in proxyTelemetryContext, isStreamingRequest, longCancellation);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 3: Copy request headers Downstream --► Proxy --► Upstream
CopyHeadersToUpstream(context, upstreamRequest);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 4: Send the outgoing request using HttpClient
////this.logger.LogInformation($" Starting Proxy --> upstream request");
var upstreamResponse = await httpClient.SendAsync(upstreamRequest, shortCancellation);
// Detect connection downgrade, which may be problematic for e.g. gRPC.
if (isIncomingHttp2 && upstreamResponse.Version.Major != 2)
{
// TODO: Do something on connection downgrade...
Log.HttpDowngradeDeteced(_logger);
}
// Assert that, if we are proxying content upstream, it must have started by now
// (since HttpClient.SendAsync has already completed asynchronously).
// If this check fails, there is a coding defect which would otherwise
// cause us to wait forever in step 9, so fail fast here.
if (bodyToUpstreamContent != null && !bodyToUpstreamContent.Started)
{
// TODO: bodyToUpstreamContent is never null. HttpClient might would not need to read the body in some scenarios, such as an early auth failure with Expect: 100-continue.
throw new InvalidOperationException("Proxying the downstream request body to the upstream server hasn't started. This is a coding defect.");
}
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 5: Copy response status line Downstream ◄-- Proxy ◄-- Upstream
////this.logger.LogInformation($" Setting downstream <-- Proxy status: {(int)upstreamResponse.StatusCode} {upstreamResponse.ReasonPhrase}");
context.Response.StatusCode = (int)upstreamResponse.StatusCode;
context.Features.Get <IHttpResponseFeature>().ReasonPhrase = upstreamResponse.ReasonPhrase;
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 6: Copy response headers Downstream ◄-- Proxy ◄-- Upstream
CopyHeadersToDownstream(upstreamResponse, context.Response.Headers);
// 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 upstream).
// HOWEVER, this would produce the wrong result if it turns out that there is no content
// from the upstream -- 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 upstream 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.
// TODO: Some of the tasks in steps (7) - (9) may go unobserved depending on what fails first. Needs more consideration.
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 7: Copy response body Downstream ◄-- Proxy ◄-- Upstream
await CopyBodyDownstreamAsync(upstreamResponse.Content, context.Response.Body, proxyTelemetryContext, longCancellation);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 8: Copy response trailer headers and finish response Downstream ◄-- Proxy ◄-- Upstream
CopyTrailingHeadersToDownstream(upstreamResponse, context);
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 Downstream --► Proxy --► Upstream
if (bodyToUpstreamContent != null)
{
////this.logger.LogInformation($" Waiting for downstream --> Proxy --> upstream body proxying to complete");
await bodyToUpstreamContent.ConsumptionTask;
}
}
/// <summary>
/// Proxies an upgradable request to the upstream server, treating the upgraded stream as an opaque duplex channel.
/// </summary>
/// <remarks>
/// Upgradable request proxying comprises the following steps:
/// (1) Create outgoing HttpRequestMessage
/// (2) Copy request headers Downstream ---► Proxy ---► Upstream
/// (3) Send the outgoing request using HttpMessageInvoker Downstream ---► Proxy ---► Upstream
/// (4) Copy response status line Downstream ◄--- Proxy ◄--- Upstream
/// (5) Copy response headers Downstream ◄--- Proxy ◄--- Upstream
/// Scenario A: upgrade with upstream worked (got 101 response)
/// (A-6) Upgrade downstream channel (also sends response headers) Downstream ◄--- Proxy ◄--- Upstream
/// (A-7) Copy duplex streams Downstream ◄--► Proxy ◄--► Upstream
/// ---- or ----
/// Scenario B: upgrade with upstream failed (got non-101 response)
/// (B-6) Send response headers Downstream ◄--- Proxy ◄--- Upstream
/// (B-7) Copy response body Downstream ◄--- Proxy ◄--- Upstream
///
/// This takes care of WebSockets as well as any other upgradable protocol.
/// </remarks>
private async Task UpgradableProxyAsync(
HttpContext context,
IHttpUpgradeFeature upgradeFeature,
HttpRequestMessage upstreamRequest,
Transforms transforms,
HttpMessageInvoker httpClient,
ProxyTelemetryContext proxyTelemetryContext,
CancellationToken shortCancellation,
CancellationToken longCancellation)
{
_ = context ?? throw new ArgumentNullException(nameof(context));
_ = upgradeFeature ?? throw new ArgumentNullException(nameof(upgradeFeature));
_ = upstreamRequest ?? throw new ArgumentNullException(nameof(upstreamRequest));
_ = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 2: Copy request headers Downstream --► Proxy --► Upstream
CopyHeadersToUpstream(context, upstreamRequest, transforms.CopyRequestHeaders, transforms.RequestHeaderTransforms);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 3: Send the outgoing request using HttpMessageInvoker
var upstreamResponse = await httpClient.SendAsync(upstreamRequest, shortCancellation);
var upgraded = upstreamResponse.StatusCode == HttpStatusCode.SwitchingProtocols && upstreamResponse.Content != null;
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 4: Copy response status line Downstream ◄-- Proxy ◄-- Upstream
context.Response.StatusCode = (int)upstreamResponse.StatusCode;
context.Features.Get <IHttpResponseFeature>().ReasonPhrase = upstreamResponse.ReasonPhrase;
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step 5: Copy response headers Downstream ◄-- Proxy ◄-- Upstream
CopyHeadersToDownstream(upstreamResponse, context, transforms.ResponseHeaderTransforms);
if (!upgraded)
{
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step B-6: Send response headers Downstream ◄-- Proxy ◄-- Upstream
// This is important to avoid any extra delays in sending response headers
// e.g. if the upstream server is slow to provide its response body.
await context.Response.StartAsync(shortCancellation);
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step B-7: Copy response body Downstream ◄-- Proxy ◄-- Upstream
await CopyBodyDownstreamAsync(upstreamResponse.Content, context.Response.Body, proxyTelemetryContext, longCancellation);
return;
}
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step A-6: Upgrade the downstream channel. This will send all response headers too.
using var downstreamStream = await upgradeFeature.UpgradeAsync();
// :::::::::::::::::::::::::::::::::::::::::::::
// :: Step A-7: Copy duplex streams
var upstreamStream = await upstreamResponse.Content.ReadAsStreamAsync();
var upstreamCopier = new StreamCopier(
_metrics,
new StreamCopyTelemetryContext(
direction: "upstream",
clusterId: proxyTelemetryContext.ClusterId,
routeId: proxyTelemetryContext.RouteId,
destinationId: proxyTelemetryContext.DestinationId));
var upstreamTask = upstreamCopier.CopyAsync(downstreamStream, upstreamStream, longCancellation);
var downstreamCopier = new StreamCopier(
_metrics,
new StreamCopyTelemetryContext(
direction: "downstream",
clusterId: proxyTelemetryContext.ClusterId,
routeId: proxyTelemetryContext.RouteId,
destinationId: proxyTelemetryContext.DestinationId));
var downstreamTask = downstreamCopier.CopyAsync(upstreamStream, downstreamStream, longCancellation);
await Task.WhenAll(upstreamTask, downstreamTask);
}
/// <summary>
/// Proxies the incoming request to the destination server, and the response back to our 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>
/// <param name="longCancellation">This should be linked to a client disconnect notification like <see cref="HttpContext.RequestAborted"/>
/// to avoid leaking long running requests.</param>
public async Task ProxyAsync(
HttpContext context,
string destinationPrefix,
HttpMessageInvoker httpClient,
RequestProxyOptions proxyOptions,
ProxyTelemetryContext proxyTelemetryContext)
{
_ = context ?? throw new ArgumentNullException(nameof(context));
_ = destinationPrefix ?? throw new ArgumentNullException(nameof(destinationPrefix));
_ = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
_ = proxyOptions ?? throw new ArgumentNullException(nameof(proxyOptions));
var requestAborted = context.RequestAborted;
// :: Step 1: Create outgoing HttpRequestMessage
var upgradeFeature = context.Features.Get <IHttpUpgradeFeature>();
var isUpgradeRequest = (upgradeFeature?.IsUpgradableRequest ?? false)
// Mitigate https://github.com/microsoft/reverse-proxy/issues/255, IIS considers all requests upgradeable.
&& string.Equals("WebSocket", context.Request.Headers[HeaderNames.Upgrade], StringComparison.OrdinalIgnoreCase);
var destinationRequest = CreateRequestMessage(context, destinationPrefix, isUpgradeRequest, proxyOptions.Transforms.RequestTransforms);
var isClientHttp2 = ProtocolHelper.IsHttp2(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 = isClientHttp2 && ProtocolHelper.IsGrpcContentType(context.Request.ContentType);
// :: Step 2: Setup copy of request body (background) Client --► Proxy --► Destination
// Note that we must do this before step (3) because step (3) may also add headers to the HttpContent that we set up here.
var requestContent = SetupRequestBodyCopy(context.Request, destinationRequest, in proxyTelemetryContext, isStreamingRequest, requestAborted);
// :: Step 3: Copy request headers Client --► Proxy --► Destination
CopyRequestHeaders(context, destinationRequest, proxyOptions.Transforms);
// :: Step 4: Send the outgoing request using HttpClient
HttpResponseMessage destinationResponse;
var requestTimeoutSource = CancellationTokenSource.CreateLinkedTokenSource(requestAborted);
requestTimeoutSource.CancelAfter(proxyOptions.RequestTimeout);
var requestTimeoutToken = requestTimeoutSource.Token;
try
{
destinationResponse = await httpClient.SendAsync(destinationRequest, requestTimeoutToken);
}
catch (OperationCanceledException canceledException)
{
if (!requestAborted.IsCancellationRequested && requestTimeoutToken.IsCancellationRequested)
{
ReportProxyError(context, ProxyError.RequestTimedOut, canceledException);
context.Response.StatusCode = StatusCodes.Status504GatewayTimeout;
return;
}
ReportProxyError(context, ProxyError.RequestCanceled, canceledException);
context.Response.StatusCode = StatusCodes.Status502BadGateway;
return;
}
catch (Exception requestException)
{
await HandleRequestFailureAsync(context, requestContent, requestException);
return;
}
finally
{
requestTimeoutSource.Dispose();
}
// Detect connection downgrade, which may be problematic for e.g. gRPC.
if (isClientHttp2 && destinationResponse.Version.Major != 2)
{
// TODO: Do something on connection downgrade...
Log.HttpDowngradeDetected(_logger);
}
// Assert that, if we are proxying content to the destination, it must have started by now
// (since HttpClient.SendAsync has already completed asynchronously).
// If this check fails, there is a coding defect which would otherwise
// cause us to wait forever in step 9, so fail fast here.
if (requestContent != null && !requestContent.Started)
{
// TODO: HttpClient might not need to read the body in some scenarios, such as an early auth failure with Expect: 100-continue.
throw new InvalidOperationException("Proxying the Client request body to the Destination server hasn't started. This is a coding defect.");
}
// :: Step 5: Copy response status line Client ◄-- Proxy ◄-- Destination
// :: Step 6: Copy response headers Client ◄-- Proxy ◄-- Destination
CopyResponseStatusAndHeaders(destinationResponse, context, proxyOptions.Transforms.ResponseHeaderTransforms);
// :: 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)
{
await HandleUpgradedResponse(context, upgradeFeature, destinationResponse, proxyTelemetryContext, requestAborted);
return;
}
// 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, proxyTelemetryContext, requestAborted);
if (responseBodyCopyResult != StreamCopyResult.Success)
{
await HandleResponseBodyErrorAsync(context, requestContent, responseBodyCopyResult, responseBodyException);
return;
}
// :: Step 8: Copy response trailer headers and finish response Client ◄-- Proxy ◄-- Destination
CopyResponseTrailingHeaders(destinationResponse, context, proxyOptions.Transforms.ResponseTrailerTransforms);
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
if (requestContent != null)
{
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 => ProxyError.RequestBodyClient,
StreamCopyResult.OutputError => ProxyError.RequestBodyDestination,
StreamCopyResult.Canceled => ProxyError.RequestBodyCanceled,
_ => throw new NotImplementedException(requestBodyCopyResult.ToString())
};
ReportProxyError(context, error, requestBodyException);
}
}
}
