/// <summary>
/// Removes and returns the current trailer value by first checking the HttpResponse
/// and falling back to the value from HttpResponseMessage only if
/// <see cref="ResponseTrailersTransformContext.HeadersCopied"/> is not set.
/// This ordering allows multiple transforms to mutate the same header.
/// </summary>
/// <param name="headerName">The name of the header to take.</param>
/// <returns>The response header value, or StringValues.Empty if none.</returns>
public static StringValues TakeHeader(ResponseTrailersTransformContext context, string headerName)
{
if (context is null)
{
throw new System.ArgumentNullException(nameof(context));
}
if (string.IsNullOrEmpty(headerName))
{
throw new System.ArgumentException($"'{nameof(headerName)}' cannot be null or empty.", nameof(headerName));
}
var existingValues = StringValues.Empty;
var responseTrailersFeature = context.HttpContext.Features.Get <IHttpResponseTrailersFeature>();
var responseTrailers = responseTrailersFeature.Trailers;
// Support should have already been checked by the caller.
Debug.Assert(responseTrailers != null);
Debug.Assert(!responseTrailers.IsReadOnly);
if (responseTrailers.TryGetValue(headerName, out var responseValues))
{
responseTrailers.Remove(headerName);
existingValues = responseValues;
}
else if (!context.HeadersCopied &&
context.ProxyResponse.TrailingHeaders.TryGetValues(headerName, out var values))
{
existingValues = (string[])values;
}
return(existingValues);
}
/// <inheritdoc/>
public override ValueTask ApplyAsync(ResponseTrailersTransformContext context)
{
if (context is null)
{
throw new ArgumentNullException(nameof(context));
}
Debug.Assert(context.ProxyResponse != null);
Debug.Assert(!context.HeadersCopied);
// See https://github.com/microsoft/reverse-proxy/blob/51d797986b1fea03500a1ad173d13a1176fb5552/src/ReverseProxy/Forwarder/HttpTransformer.cs#L85-L99
// NOTE: Deliberately not using `context.Response.SupportsTrailers()`, `context.Response.AppendTrailer(...)`
// because they lookup `IHttpResponseTrailersFeature` for every call. Here we do it just once instead.
var responseTrailersFeature = context.HttpContext.Features.Get <IHttpResponseTrailersFeature>();
var outgoingTrailers = responseTrailersFeature?.Trailers;
if (outgoingTrailers != null && !outgoingTrailers.IsReadOnly)
{
// Note that trailers, if any, should already have been declared in Proxy's response
CopyResponseHeaders(context.ProxyResponse.TrailingHeaders, outgoingTrailers);
}
context.HeadersCopied = true;
return(default);
/// <summary>
/// Sets the given trailer on the HttpResponse.
/// </summary>
public static void SetHeader(ResponseTrailersTransformContext context, string headerName, StringValues values)
{
var responseTrailersFeature = context.HttpContext.Features.Get <IHttpResponseTrailersFeature>();
var responseTrailers = responseTrailersFeature.Trailers;
// Support should have already been checked by the caller.
Debug.Assert(responseTrailers != null);
Debug.Assert(!responseTrailers.IsReadOnly);
responseTrailers[headerName] = values;
}
// Assumes the response status code has been set on the HttpContext already.
/// <inheritdoc/>
public override ValueTask ApplyAsync(ResponseTrailersTransformContext context)
{
if (context is null)
{
throw new ArgumentNullException(nameof(context));
}
if (Always || Success(context))
{
var responseTrailersFeature = context.HttpContext.Features.Get <IHttpResponseTrailersFeature>();
var responseTrailers = responseTrailersFeature.Trailers;
// Support should have already been checked by the caller.
Debug.Assert(responseTrailers != null);
Debug.Assert(!responseTrailers.IsReadOnly);
responseTrailers.Remove(HeaderName);
}
return(default);
// Assumes the response status code has been set on the HttpContext already.
/// <inheritdoc/>
public override ValueTask ApplyAsync(ResponseTrailersTransformContext context)
{
if (context is null)
{
throw new ArgumentNullException(nameof(context));
}
if (Always || Success(context))
{
var existingHeader = TakeHeader(context, HeaderName);
if (Append)
{
var value = StringValues.Concat(existingHeader, Value);
SetHeader(context, HeaderName, value);
}
else
{
SetHeader(context, HeaderName, Value);
}
}
return(default);
internal static bool Success(ResponseTrailersTransformContext context)
{
// TODO: How complex should this get? Compare with http://nginx.org/en/docs/http/ngx_http_headers_module.html#add_header
return(context.HttpContext.Response.StatusCode < 400);
}
/// <summary> /// Transforms the given response trailers. The trailers will have (optionally) already been /// copied to the <see cref="HttpResponse"/> and any changes should be made there. /// </summary> public abstract ValueTask ApplyAsync(ResponseTrailersTransformContext context);
/// <inheritdoc/>
public override ValueTask ApplyAsync(ResponseTrailersTransformContext context)
{
return(_func(context));
}
