Merge pull request #33 from nblumhardt/request-uri-bug

Correctly follow relative redirect locations

Author: nblumhardt

README.md

@@ -16,4 +16,3 @@ Periodically GET an HTTP resource and write response metrics to Seq. These can t
    - if the URL is an HTTPS URL, the Seq server must trust the SSL certificate used by the server
    - the response will be fully downloaded on every check, so ideally the resource won't be more than a few kB
 7. Enter a probing interval in seconds; each event is stored internally in Seq, so be aware that shorter intervals will consume more space
-

src/Seq.Input.HealthCheck/HttpHealthCheck.cs

@@ -71,7 +71,7 @@ public async Task<HealthCheckResult> CheckNow(CancellationToken cancel)
         var redirectCount = 0;
 
         var probeId = Nonce.Generate(12);
-        var probedUrl = _bypassHttpCaching ? UrlHelper.AppendParameter(_targetUrl, ProbeIdParameterName, probeId) : _targetUrl;
+        var probedUrl = _bypassHttpCaching ? UriHelper.AppendParameter(_targetUrl, ProbeIdParameterName, probeId) : _targetUrl;
 
         var finalUrl = probedUrl;
 
@@ -80,7 +80,7 @@ public async Task<HealthCheckResult> CheckNow(CancellationToken cancel)
 
         try
         {
-            (var response, finalUrl, redirectCount) = await SendRequest(cancel, probedUrl, probeId);
+            (var response, finalUrl, redirectCount) = await SendRequest(probedUrl, probeId, cancel);
 
             statusCode = (int) response.StatusCode;
             contentType = response.Content.Headers.ContentType?.ToString();
@@ -136,25 +136,25 @@ void AddHeadersToRequest(HttpRequestMessage request, string probeId)
             request.Headers.CacheControl = new CacheControlHeaderValue {NoStore = true};
     }
 
-    async Task<(HttpResponseMessage, string, int)> SendRequest(CancellationToken cancel, string requestUri, string correlationId)
+    async Task<(HttpResponseMessage, string, int)> SendRequest(string requestUri, string correlationId, CancellationToken cancel)
     {
         HttpResponseMessage response = null!;
         var totalRedirects = 0;
 
-        for (int i = 0; i <= MaxRedirectCount; i++)
+        for (var i = 0; i <= MaxRedirectCount; i++)
         {
             var request = new HttpRequestMessage(HttpMethod.Get, requestUri);
             AddHeadersToRequest(request, correlationId);
 
             response = await _httpClient.SendAsync(request, cancel);
             var statusCode = (int) response.StatusCode;
 
-            if (_shouldFollowRedirects && statusCode is >= 300 and <= 399)
+            if (_shouldFollowRedirects && statusCode is >= 300 and < 400)
             {
                 var locationHeader = response.Headers.Location;
                 if (locationHeader is not null)
                 {
-                    requestUri = locationHeader.ToString();
+                    requestUri = UriHelper.MakeAbsoluteLocation(requestUri, locationHeader.ToString());
                     continue;
                 }
             }

src/Seq.Input.HealthCheck/Util/UrlHelper.cs renamed to src/Seq.Input.HealthCheck/Util/UriHelper.cs

@@ -18,7 +18,7 @@
 
 namespace Seq.Input.HealthCheck.Util;
 
-static class UrlHelper
+static class UriHelper
 {
     public static string AppendParameter(string targetUrl, string name, string value)
     {
@@ -31,4 +31,13 @@ public static string AppendParameter(string targetUrl, string name, string value
             [name] = value
         });
     }
+
+    public static string MakeAbsoluteLocation(string requestUri, string locationHeader)
+    {
+        var location = new Uri(locationHeader, UriKind.RelativeOrAbsolute);
+        if (location.IsAbsoluteUri) return locationHeader;
+
+        var baseUri = new Uri(requestUri, UriKind.Absolute);
+        return new Uri(baseUri, location).ToString();
+    }
 }

test/Seq.Input.HealthCheck.Tests/Seq.Input.HealthCheck.Tests.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>net8.0</TargetFramework>
-
+    <Nullable>enable</Nullable>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 

test/Seq.Input.HealthCheck.Tests/Util/UriHelperTests.cs

@@ -0,0 +1,31 @@
+using Seq.Input.HealthCheck.Util;
+using Xunit;
+
+namespace Seq.Input.HealthCheck.Tests.Util;
+
+public class UriHelperTests
+{
+    [Theory]
+    [InlineData("https://example.com", "https://example.com?q=42")]
+    [InlineData("https://example.com/p", "https://example.com/p?q=42")]
+    [InlineData("https://example.com/p/", "https://example.com/p/?q=42")]
+    [InlineData("https://example.com?a", "https://example.com?a&q=42")]
+    [InlineData("https://example.com?a=1", "https://example.com?a=1&q=42")]
+    public void ParametersAreAppendedCorrectly(string initial, string expected)
+    {
+        var actual = UriHelper.AppendParameter(initial, "q", "42");
+        Assert.Equal(expected, actual);
+    }
+
+    [Theory]
+    [InlineData("https://example.com", "https://www.example.com", null)]
+    [InlineData("https://example.com", "https://example.datalust.co", null)]
+    [InlineData("https://example.com", "https://example.com:1234/test?x=y", null)]
+    [InlineData("https://example.com", "/test", "https://example.com/test")]
+    [InlineData("https://example.com/health?x=y", "/test", "https://example.com/test")]
+    public void LocationHeadersAreMadeAbsolute(string requestUri, string locationHeader, string? expected)
+    {
+        var actual = UriHelper.MakeAbsoluteLocation(requestUri, locationHeader);
+        Assert.Equal(expected ?? locationHeader, actual);
+    }
+}