fix: fall back when payload compression fails

.changeset/cold-buckets-gzip.md

@@ -0,0 +1,6 @@
+---
+'PostHog': patch
+'PostHog.AspNetCore': patch
+---
+
+Fall back to uncompressed batch uploads when local gzip compression fails.

src/PostHog/Library/HttpClientExtensions.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.IO.Compression;
 using System.Net;
 using System.Net.Http.Json;
@@ -12,6 +13,7 @@ namespace PostHog.Library;
 /// </summary>
 internal static class HttpClientExtensions
 {
+    internal static Func<object, CancellationToken, Task<ByteArrayContent>> CreateCompressedJsonContentAsync = CreateGzipJsonContentAsync;
     /// <summary>
     /// Sends a POST request to the specified Uri containing the value serialized as JSON in the request body.
     /// Returns the response body deserialized as <typeparamref name="TBody"/>.
@@ -69,7 +71,7 @@ internal static class HttpClientExtensions
             try
             {
                 response = enableCompression
-                    ? await PostCompressedJsonAsync(httpClient, requestUri, content, cancellationToken)
+                    ? await PostCompressedJsonWithFallbackAsync(httpClient, requestUri, content, cancellationToken)
                     : await httpClient.PostAsJsonAsync(
                         requestUri,
                         content,
@@ -268,13 +270,48 @@ static Task Delay(TimeProvider timeProvider, TimeSpan delay, CancellationToken c
 #endif
     }
 
-    static async Task<HttpResponseMessage> PostCompressedJsonAsync(
+    static async Task<HttpResponseMessage> PostCompressedJsonWithFallbackAsync(
         HttpClient httpClient,
         Uri requestUri,
         object content,
         CancellationToken cancellationToken)
     {
-        // Stream JSON directly into gzip to avoid intermediate allocation
+        var compressedContent = await TryCreateCompressedJsonContentAsync(content, cancellationToken);
+        if (compressedContent is null)
+        {
+            return await httpClient.PostAsJsonAsync(
+                requestUri,
+                content,
+                JsonSerializerHelper.Options,
+                cancellationToken);
+        }
+
+        using (compressedContent)
+        {
+            return await httpClient.PostAsync(requestUri, compressedContent, cancellationToken);
+        }
+    }
+
+    static async Task<ByteArrayContent?> TryCreateCompressedJsonContentAsync(
+        object content,
+        CancellationToken cancellationToken)
+    {
+        try
+        {
+            return await CreateCompressedJsonContentAsync(content, cancellationToken);
+        }
+        catch (Exception ex) when (ex is IOException or InvalidDataException or NotSupportedException or ObjectDisposedException)
+        {
+            Debug.WriteLine($"Failed to gzip request body, sending uncompressed: {ex}");
+            return null;
+        }
+    }
+
+    static async Task<ByteArrayContent> CreateGzipJsonContentAsync(
+        object content,
+        CancellationToken cancellationToken)
+    {
+        // Stream JSON directly into gzip to avoid intermediate allocation and honor cancellation during serialization.
         using var memoryStream = new MemoryStream(4096);
         using (var gzipStream = new GZipStream(memoryStream, CompressionLevel.Fastest, leaveOpen: true))
         {
@@ -286,13 +323,9 @@ static async Task<HttpResponseMessage> PostCompressedJsonAsync(
             ? new ByteArrayContent(buffer.Array!, buffer.Offset, buffer.Count)
             : new ByteArrayContent(memoryStream.ToArray());
 
-        using (compressedContent)
-        {
-            compressedContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
-            compressedContent.Headers.ContentEncoding.Add("gzip");
-
-            return await httpClient.PostAsync(requestUri, compressedContent, cancellationToken);
-        }
+        compressedContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
+        compressedContent.Headers.ContentEncoding.Add("gzip");
+        return compressedContent;
     }
 
     public static async Task EnsureSuccessfulApiCall(

tests/UnitTests/Library/HttpClientExtensionsTests.cs

@@ -605,6 +605,65 @@ public async Task CompressesRequestBodyWithGzip()
         Assert.Contains("api_key", decompressedJson, StringComparison.Ordinal);
     }
 
+    public static IEnumerable<object[]> CompressionFailureExceptions()
+    {
+        yield return [new IOException("gzip failed")];
+        yield return [new InvalidDataException("gzip failed")];
+        yield return [new NotSupportedException("gzip failed")];
+        yield return [new ObjectDisposedException("gzip")];
+    }
+
+    [Theory]
+    [MemberData(nameof(CompressionFailureExceptions))]
+    public async Task FallsBackToUncompressedRequestWhenCompressionFails(Exception compressionException)
+    {
+        string? capturedBody = null;
+        IEnumerable<string>? capturedContentEncoding = null;
+
+        var handler = new LambdaHttpMessageHandler(async request =>
+        {
+            capturedContentEncoding = request.Content?.Headers.ContentEncoding;
+            if (request.Content != null)
+            {
+                capturedBody = await request.Content.ReadAsStringAsync();
+            }
+            return new HttpResponseMessage(HttpStatusCode.OK)
+            {
+                Content = new StringContent("{\"status\": 1}")
+            };
+        });
+
+        using var httpClient = new HttpClient(handler);
+        var options = new PostHogOptions
+        {
+            ProjectToken = "test-api-key",
+            EnableCompression = true
+        };
+        var timeProvider = new FakeTimeProvider();
+        var payload = new { api_key = "test", batch = new[] { new { @event = "test-event" } } };
+        var originalCompressor = HttpClientExtensions.CreateCompressedJsonContentAsync;
+        HttpClientExtensions.CreateCompressedJsonContentAsync = (_, _) => Task.FromException<ByteArrayContent>(compressionException);
+
+        try
+        {
+            await httpClient.PostJsonWithRetryAsync<ApiResult>(
+                BatchUrl,
+                payload,
+                timeProvider,
+                options,
+                CancellationToken.None);
+        }
+        finally
+        {
+            HttpClientExtensions.CreateCompressedJsonContentAsync = originalCompressor;
+        }
+
+        Assert.Empty(capturedContentEncoding ?? Enumerable.Empty<string>());
+        Assert.NotNull(capturedBody);
+        Assert.Contains("test-event", capturedBody, StringComparison.Ordinal);
+        Assert.Contains("api_key", capturedBody, StringComparison.Ordinal);
+    }
+
     [Fact]
     public async Task DoesNotCompressWhenCompressionDisabled()
     {