Summary

Complements the DNS sinkhole from #410 with transport-layer filtering. Guests can no longer bypass the allowlist by connecting to raw IPs.

• Port 443: Extracts hostname from TLS ClientHello SNI extension
• Port 80: Extracts hostname from HTTP Host header
• Other ports: Filters by IP/CIDR rules only
• Zero overhead when no allowlist is configured (filter=nil)

Uses bufio.Reader.Peek() + crypto/tls.Server.GetConfigForClient for non-consuming SNI extraction (same technique as inet.af/tcpproxy). Overrides gvproxy's TCP handler via reflect to inject the filter after virtualnetwork.New() — guarded by structural test.

Behavior by port

Files

New Go files (7):

• tcp_filter.go — AllowNet matcher (IP/CIDR/hostname/wildcard)
• tcp_filter_test.go — 12 unit tests
• sni_peek.go — TLS SNI + HTTP Host extraction via bufio.Peek()
• sni_peek_test.go — 10 unit tests
• forked_tcp.go — TCP forwarder with filter + SNI inspection
• forked_network.go — Override TCP handler via reflect
• forked_network_test.go — Structural guard test

Modified:

• main.go — Wire filter after virtualnetwork.New()
• network_spec.rs — 2 new ignored VM integration tests
• types.rs — Fix pre-existing server test (wrong serde format)

New Python tests:

• test_tcp_filter.py — 21 end-to-end VM integration tests across 7 categories

Test plan

• 25 Go unit tests pass (filter, SNI peek, structural guard)
• 6 Rust network_spec tests pass (non-ignored)
• 68 boxlite-server tests pass (including fixed deserialization test)
• 21 Python VM integration tests pass (default access, hostname allowlist, wildcard, IP/CIDR, mixed rules, disabled network, edge cases)
• CI: Run make test:integration:rust FILTER=network_spec for VM tests