fix(stargate): enforce protocol input and header contracts - #1818

Why

Valid IPv6 backend URLs and owned or escaped JSON enum values were rejected. Proxies also removed Connection itself while forwarding fields named by it. Schema-generation tests duplicated configuration through test-only build-script paths instead of checking generated behavior.

Examples

• IPv6 registration: quic://[::1]:4433 is a valid direct backend address. Previously, extracting the host as text left IPv6 brackets in the string passed to the IP parser, so admission or dialing rejected it. Both paths now use the same parser and retain the URL parser's typed IPv6 address.
• JSON settings: "http\u0033" means "http3", and an owned JSON value containing "http3" is also valid input. The enums previously required a borrowed string, which those deserialization paths cannot supply. Reading an owned string accepts these representations while preserving validation of supported values.
• Connection-specific headers: a request with Connection: x-private-hop and X-Private-Hop: internal-value previously lost the Connection header but forwarded X-Private-Hop. The recipient could no longer tell that the field applied only to the previous connection. Forwarding now removes both fields, in both request and response directions, including repeated Connection fields and mixed-case names.
• Build verification: the removed tests checked facts such as the number of configured proto files and called test-only build-script functions. They could pass without exercising schema generation. This is a maintenance and verification defect: the build scripts now call the generators directly, and existing generated-message serialization tests remain in place and run through Bazel.

What changed

• Share direct QUIC URL validation with dialing and accept typed IPv6 hosts.
• Deserialize transport and connectivity enums from owned strings.
• Apply the shared hop-header and Connection-option filter once at each forwarding boundary, then apply tunnel-specific exclusions.
• Keep schema generation directly in build.rs, remove duplicate plan scaffolding and redundant dev dependencies, and expose the existing generated-protobuf behavior test through Bazel.

Customer Release Notes

Stargate accepts IPv6 backend addresses and valid JSON transport settings, and correctly removes connection-specific HTTP headers.

Plan Summary

Not applicable.

Usage

Existing registration and proxy interfaces apply.

Testing

The YAGNI follow-up passed all 39 existing tunnel tests and all-target Stargate Clippy with warnings denied in an isolated worktree. It inlines the remaining H3 Host exclusion and removes its one-comparison wrapper and mirrored test. Formatting and whitespace checks passed.

Earlier combined-stack validation passed 1,611 Cargo workspace tests, with 3 existing performance tests ignored, workspace Clippy, and 6 scoped Bazel targets. Regression coverage includes IPv6, owned and escaped JSON, serialization, both header-forwarding directions, and tunnel-specific exclusions. The full workspace and Bazel suites were not rerun for this local simplification. No live-cluster QA is required for this layer.

Notes

Layer 1 of the Stargate maintenance stack. No runtime architecture or wire-schema change.

Issues

Relates to #1817

References

HTTP connection fields

Related Pull Requests

Next layer: #1820. Stack, bottom to top: #1818, #1820, #1823, #1826.

Dependencies

No dependency versions were added or upgraded. Removed duplicate capnpc and tonic-prost-build dev declarations; both remain build dependencies. No license or NOTICE changes.

Summary by CodeRabbit

• Bug Fixes
  • Improved HTTP header forwarding by removing hop-by-hop headers, including headers listed in Connection, while preserving valid repeated headers such as Set-Cookie.
  • Applied consistent header filtering across HTTP proxies and QUIC/HTTP3 tunnels.
  • Improved QUIC address validation and added support for IPv4 and IPv6 socket addresses.
  • Improved deserialization for connectivity and transport protocol settings, including escaped JSON values.
  • Added coverage for header filtering and IPv6 direct registrations.