fix(binarycodec): guard BinaryParser::read bounds + limit STObject decode depth

[e-desouza]

Why

BinaryParser::read(n) sliced self.0[..n] before calling skip_bytes(n), which is where the bounds check lived. On a truncated binary XRPL blob, read panicked instead of returning an error — reachable from any network-sourced binary data via decode().

decode_st_object and decode_field_value form a mutually recursive pair with no depth limit. A crafted binary blob embedding deeply nested STObject headers (~4–16 KB) overflows the stack. Stack overflows abort the process unconditionally — they are not catchable with catch_unwind.

What changed

• BinaryParser::read: added if n > self.0.len() guard returning UnexpectedParserSkipOverflow { max, found } before the slice.
• Added const MAX_DECODE_DEPTH: u32 = 32.
• Added MaxDecodeDepthExceeded { max: u32 } variant to XRPLBinaryCodecException.
• decode_st_object, decode_field_value, decode_st_array now accept a depth: u32 parameter; the public decode() entry passes depth: 0.
• decode_st_object returns Err(MaxDecodeDepthExceeded) when depth > MAX_DECODE_DEPTH.

How to validate

cargo test --release

New tests: test_binary_parser_read_truncated_returns_error, test_decode_st_object_depth_limit.

[codecov]

Codecov Report

❌ Patch coverage is 94.64286% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.72%. Comparing base (c83df4f) to head (778d2ed).

Files with missing lines	Patch %	Lines
src/core/binarycodec/binary_wrappers.rs	94.54%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #344   +/-   ##
=======================================
  Coverage   86.71%   86.72%           
=======================================
  Files         252      252           
  Lines       32630    32676   +46     
=======================================
+ Hits        28296    28339   +43     
- Misses       4334     4337    +3     

Flag	Coverage Δ
integration	71.32% <ø> (ø)
unit	87.34% <94.64%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/core/binarycodec/exceptions.rs	0.00% <ø> (ø)
src/core/binarycodec/mod.rs	90.55% <100.00%> (ø)
src/core/binarycodec/binary_wrappers.rs	89.94% <94.54%> (+0.30%)	⬆️

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[Copilot]

Pull request overview

This PR hardens the XRPL binary decoder against malformed or adversarial inputs by preventing panics in BinaryParser::read and bounding recursive decoding of nested STObject/STArray structures.

Changes:

• Added an explicit bounds check in BinaryParser::read(n) to return an error instead of panicking on out-of-bounds slices.
• Introduced a maximum decode depth (MAX_DECODE_DEPTH) and a new MaxDecodeDepthExceeded error to prevent stack overflows from deeply nested payloads.
• Updated decoding helpers to thread a depth counter through recursive calls, and added regression tests for both failure modes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/core/binarycodec/mod.rs	Updates the decode() entrypoint to initialize recursive decoding with depth = 0.
src/core/binarycodec/exceptions.rs	Adds MaxDecodeDepthExceeded to the binary codec exception set for depth-limit enforcement.
src/core/binarycodec/binary_wrappers.rs	Implements read() bounds guard, adds decode depth limit enforcement, threads depth through decode functions, and adds regression tests.

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