THRIFT-6139: Validate Ruby CompactProtocol integer ranges

[kpumuk]

Ruby's CompactProtocol writers accept integers outside the widths declared by the Thrift type system. An out-of-range value can therefore be serialized without an error, change when decoded, and behave differently depending on whether the native extension is loaded.

This change validates fixed-width integers, field identifiers, message sequence identifiers, and collection or binary sizes before writing bytes or changing protocol state. Native and pure-Ruby implementations now follow the same bounds, while protocol-owned header bytes continue to use their unsigned wire representation.

The pure-Ruby varint writers also collect multi-byte values into a single transport write. This avoids a performance penalty from the added validation and reduces temporary allocations without changing valid wire encodings.

Benchmarks

The protocol benchmark was run in seven fresh processes for both upstream/master and this change. Pure-Ruby runs additionally set THRIFT_BENCHMARK_SKIP_NATIVE=1.

ruby ../../test/rb/benchmarks/protocol_benchmark.rb \
  --small-runs 30000 \
  --large-runs 2 \
  --scenarios rb-cmp-write-small,rb-cmp-write-large,hdr-cmp-write-small \
  --json

Mode and scenario	Master median	Proposed median	Change
Native Compact, small structures	0.155830s	0.154606s	-0.79%
Native Compact, large structure	0.209833s	0.209450s	-0.18%
Native Header/Compact, small structures	0.377205s	0.372075s	-1.36%
Pure-Ruby Compact, small structures	0.467134s	0.450486s	-3.56%
Pure-Ruby Compact, large structure	0.643928s	0.631595s	-1.92%
Pure-Ruby Header/Compact, small structures	0.621219s	0.607185s	-2.26%

A targeted allocation benchmark encoding 500,000 representative varints reduced temporary allocations from 4,500,009 to 1,400,004.

These measurements used Ruby 4.0.6 on aarch64 Linux; they do not represent a cross-version or cross-platform benchmark matrix.

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• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
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[Copilot]

Pull request overview

This PR tightens Ruby CompactProtocol write-side validation so fixed-width integers, field IDs, sequence IDs, and container/binary sizes are checked against Thrift’s declared bounds before any bytes are written or protocol state is mutated. It also optimizes pure-Ruby varint emission by buffering multi-byte encodings into a single transport write.

Changes:

• Add spec coverage for rejecting out-of-range / non-integer / nil values without writing partial output.
• Add range/type validation for BYTE/I16/I32/I64, field IDs, sequence IDs, and size-prefixed values in the pure-Ruby CompactProtocol.
• Reduce pure-Ruby varint write overhead by batching bytes into a single string write.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
lib/rb/spec/compact_protocol_spec.rb	Adds behavioral specs ensuring invalid inputs raise and do not write/append bytes.
lib/rb/lib/thrift/protocol/compact_protocol.rb	Implements pure-Ruby validation for integer widths/IDs/sizes and batches varint writes.
lib/rb/ext/compact_protocol.c	Aligns native extension write-side validation with Thrift integer/size bounds.

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