Resolve @dynamic Retry-After for any status code in GenericRandomErrorPlugin

DevProxy.Integration.Tests/BehaviorPluginsIntegrationTests.cs

@@ -64,6 +64,53 @@ public async Task GenericRandomError_Rate100_OverridesOriginWithConfiguredError(
         Assert.Equal(HttpStatusCode.ServiceUnavailable, response.StatusCode);
     }
 
+    [Fact]
+    public async Task GenericRandomError_DynamicRetryAfterOnNon429_IsResolved()
+    {
+        await using var origin = await FakeOrigin.StartAsync();
+        var urls = KestrelProxyHarness.BuildUrlsToWatch(origin.Host);
+
+        var config = PluginConfig.FromJson($$"""
+            {
+              "rate": 100,
+              "errors": [
+                {
+                  "request": { "url": "http://{{origin.Host}}/*" },
+                  "responses": [
+                    {
+                      "statusCode": 503,
+                      "headers": [ { "name": "RETRY-after", "value": "@dynamic=7" } ]
+                    }
+                  ]
+                }
+              ]
+            }
+            """);
+        var plugin = new GenericRandomErrorPlugin(
+            SharedHttpClient,
+            NullLogger<GenericRandomErrorPlugin>.Instance,
+            urls,
+            ProxyConfig,
+            config);
+        var retryAfter = new RetryAfterPlugin(
+            NullLogger<RetryAfterPlugin>.Instance,
+            urls);
+
+        await using var proxy = await KestrelProxyHarness.StartAsync(
+            origin.Host, [retryAfter, plugin]);
+        using var client = proxy.CreateHttpClient();
+
+        using var response = await client.GetAsync(new Uri($"http://{origin.Host}/get"));
+        // an immediate retry must be throttled by RetryAfterPlugin, proving the
+        // non-429 error registered the request for throttling
+        using var retry = await client.GetAsync(new Uri($"http://{origin.Host}/get"));
+
+        Assert.Equal(HttpStatusCode.ServiceUnavailable, response.StatusCode);
+        Assert.True(response.Headers.TryGetValues("Retry-After", out var values));
+        Assert.Equal("7", Assert.Single(values));
+        Assert.Equal(HttpStatusCode.TooManyRequests, retry.StatusCode);
+    }
+
     [Fact]
     public async Task Latency_AddsConfiguredDelayBeforeForwarding()
     {

DevProxy.Plugins/Behavior/GenericRandomErrorPlugin.cs

@@ -219,10 +219,11 @@ private void UpdateProxyResponse(ProxyRequestArgs e, GenericErrorResponseRespons
             headers.AddRange(error.Headers);
         }
 
-        if (error.StatusCode == (int)HttpStatusCode.TooManyRequests &&
-            error.Headers is not null)
+        // Retry-After can be sent with any status code (eg. 429, 503, 529),
+        // so resolve @dynamic regardless of the status code
+        if (error.Headers is not null)
         {
-            var retryAfterHeader = error.Headers.FirstOrDefault(h => h.Name is "Retry-After" or "retry-after");
+            var retryAfterHeader = error.Headers.FirstOrDefault(h => string.Equals(h.Name, "Retry-After", StringComparison.OrdinalIgnoreCase));
             if (retryAfterHeader?.Value is not null && retryAfterHeader.Value.StartsWith("@dynamic", StringComparison.OrdinalIgnoreCase))
             {
                 // Parse @dynamic or @dynamic=value syntax
@@ -257,7 +258,7 @@ private void UpdateProxyResponse(ProxyRequestArgs e, GenericErrorResponseRespons
                 var throttleKey = BuildThrottleKey(request);
                 throttledRequests?.Add(new(throttleKey, (req, key) => ShouldThrottle(req, key, retryAfterInSeconds), retryAfterDate));
                 // replace the header with the @dynamic value with the actual value
-                var h = headers.First(h => h.Name is "Retry-After" or "retry-after");
+                var h = headers.First(h => string.Equals(h.Name, "Retry-After", StringComparison.OrdinalIgnoreCase));
                 _ = headers.Remove(h);
                 headers.Add(new("Retry-After", retryAfterInSeconds.ToString(CultureInfo.InvariantCulture)));
             }