fix(http): compress empty encoded responses

[yordis]

• Prevents clients from receiving a declared gzip or deflate response that has no compressed payload to decode.
• Keeps HTTP compression behavior consistent for empty and non-empty responses.

[cursor]

PR Summary

Medium Risk
Changes HTTP response encoding behavior for empty bodies by emitting non-empty gzip/deflate payloads; could affect clients/proxies that rely on prior zero-length behavior or content-length handling. Scope is limited and covered by new unit tests for both direct compression and end-to-end Reply writes.

Overview
Ensures HTTP replies that advertise gzip/deflate always include a decodable compressed body, even when the uncompressed response is empty.

HttpEntityManager.CompressResponse now returns precomputed "empty" gzip/deflate members for zero-length inputs, and Reply is reordered so compression occurs before deciding whether to write/close. Adds tests that validate empty compressed bodies can be decompressed and that end-to-end Reply writes a non-empty payload while still decompressing to 0 bytes.

^{Reviewed by Cursor Bugbot for commit b78b901. Bugbot is set up for automated code reviews on this repo. Configure here.}

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 819ed943-a092-4501-8dfa-1c49e9aab27c

📥 Commits

Reviewing files that changed from the base of the PR and between 7aea47d and b78b901.

📒 Files selected for processing (1)

• src/EventStore.Core.Tests/Services/Transport/Http/compress_response_should.cs

Walkthrough

Empty HTTP responses are now compressed when clients advertise Content-Encoding support. HttpEntityManager applies compression via precomputed gzip/deflate payloads for empty inputs, producing valid compressed bodies. Tests verify compression produces non-empty, valid, and decompress-to-empty results.

Changes

Empty Payload Compression

Layer / File(s)	Summary
Core Implementation src/EventStore.Transport.Http/EntityManagement/HttpEntityManager.cs	Added precomputed static byte arrays EmptyGzipResponse and EmptyDeflateResponse representing valid compressed payloads for zero-length input. Modified CompressResponse to return these arrays when input is empty and gzip/deflate is requested. Updated Reply to always pass response ?? Array.Empty<byte>() through compression before checking payload length, enabling compressed empty bodies to be written.
Tests src/EventStore.Core.Tests/Services/Transport/Http/compress_response_should.cs	Added three tests: unit tests verify gzip/deflate compression of empty data yields non-empty compressed bytes that decompress to empty strings. Integration test constructs DefaultHttpContext with gzip encoding, sends empty reply via HttpEntityManager, asserts Content-Encoding: gzip header presence and valid gzip body. Updated using directives for ASP.NET Core HTTP types.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 Empty payloads once would flee,
But now they're compressed in gzip glee!
Precomputed bytes, so wise and small,
Make valid streams from none at all. ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately captures the main change: applying compression to empty encoded HTTP responses in the EventStore transport layer.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem (clients receiving declared but uncompressed responses) and the solution (consistent compression behavior).
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch yordis/fix-gzip-empty-responses

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[coderabbitai]

🧹 Nitpick comments (1)

src/EventStore.Core.Tests/Services/Transport/Http/compress_response_should.cs (1)

84-112: 💤 Low value

Consider adding a symmetric integration test for deflate.

There's empty_gzip_reply_has_a_valid_gzip_body but no equivalent empty_deflate_reply_has_a_valid_deflate_body. Since the Reply code path treats both algorithms identically and unit-level coverage exists for deflate, this is low risk—but adding the test would ensure complete parity.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In
`@src/EventStore.Core.Tests/Services/Transport/Http/compress_response_should.cs`
around lines 84 - 112, Add a parallel test to
empty_gzip_reply_has_a_valid_gzip_body that verifies deflate behavior: create a
new test method (e.g., empty_deflate_reply_has_a_valid_deflate_body) that sets
context.Request.Headers["Accept-Encoding"] = CompressionAlgorithms.Deflate,
calls manager.Reply(Array.Empty<byte>(), 200, "OK", "text/plain", Encoding.UTF8,
null, ex => error = ex) on the same HttpEntity/manager setup, assert the
response header context.Response.Headers["Content-Encoding"] equals
CompressionAlgorithms.Deflate, confirm responseBody.Length > 0 and then
decompress using System.IO.Compression.DeflateStream to verify the uncompressed
output length is 0 and error is null and the completed event was signaled.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In
`@src/EventStore.Core.Tests/Services/Transport/Http/compress_response_should.cs`:
- Around line 84-112: Add a parallel test to
empty_gzip_reply_has_a_valid_gzip_body that verifies deflate behavior: create a
new test method (e.g., empty_deflate_reply_has_a_valid_deflate_body) that sets
context.Request.Headers["Accept-Encoding"] = CompressionAlgorithms.Deflate,
calls manager.Reply(Array.Empty<byte>(), 200, "OK", "text/plain", Encoding.UTF8,
null, ex => error = ex) on the same HttpEntity/manager setup, assert the
response header context.Response.Headers["Content-Encoding"] equals
CompressionAlgorithms.Deflate, confirm responseBody.Length > 0 and then
decompress using System.IO.Compression.DeflateStream to verify the uncompressed
output length is 0 and error is null and the completed event was signaled.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 504582cd-0f22-4e52-9ad8-c8c88746aeef

📥 Commits

Reviewing files that changed from the base of the PR and between 13a7bb2 and 7aea47d.

📒 Files selected for processing (2)

• src/EventStore.Core.Tests/Services/Transport/Http/compress_response_should.cs
• src/EventStore.Transport.Http/EntityManagement/HttpEntityManager.cs