JITSU-163: klauspost/gzip on the ingest and Mixpanel read paths

[sahiltyagi-jitsu]

First of the small PRs for JITSU-163, covering the half the ticket calls "independent of the zstd work and can ship first".

Swaps compress/gzip for klauspost/compress/gzip on two decode paths: the s2s batch request body (router_batch_handler.go) and the Mixpanel partial-failure response (mixpanel.go). Both are named in the ticket's swap scope — "the HTTP wire formats below" and "Mixpanel".

Readers only

Both sites are reads, so nothing written changes and no consumer is affected. Decode is ~33% cheaper per the ticket's benchmarks. Writers follow separately.

Verification

Behaviour is identical to compress/gzip across valid, truncated (half and single-byte), empty, garbage, multi-member, bad-CRC and bogus-flag inputs — same accept/reject decisions and the same error strings, so anything matching on error text is unaffected.

Also checked against a live local stack: a batch compressed with GNU gzip(1) decodes and its writeKey is parsed out of the body; corrupt bytes return a clean 400 gzip: invalid header. Confirmed the running binary actually linked v1.19.1 rather than the previous v1.18.7, since the build container reports success even when it fails to copy source.

gzip_compat_test.go is new and covers the round trip both directions. Not asked for in the ticket — happy to drop it.

Dependency

klauspost/compress was already indirect in both modules; promoted to direct and aligned on v1.19.1 (what admin already uses; the ticket benchmarked v1.19.2). Deliberately no go mod tidy — it ignores the workspace and resolves the sibling modules from the proxy, which rewrites the whole graph.

Risk

No format, config, schema or contract change. No deploy ordering; mixed old/new pods are fine. Revert is one import line per file. Not covered: very large bodies under memory pressure.

Blocking the next PR

"All five warehouse adapters" isn't actionable as written — those files contain no gzip calls. The compression lives in bulkerlib/types/marshaller.go and sql/abstract_transactional.go. Which did you mean?

🤖 Generated with Claude Code

[jitsu-code-review]

Reviewed the gzip reader substitution in the ingest batch and Mixpanel error-reporting paths, along with the module updates and compatibility coverage.

No actionable correctness, security, or user-visible regression found.