fix(cdr): use decode_headerless_ros1 for ROS1 messages in DynCodec

[zhexuany]

Summary

When decoding ROS1 bag messages through the dynamic CDR codec path (DynCodec), the code was using decode() which expects standard CDR format with alignment padding. However, ROS1 messages are stored:

1. Without a CDR encapsulation header - just raw field data
2. With packed serialization - no alignment padding between fields

This mismatch caused decode errors for ROS1 bag messages, particularly those with string arrays or complex nested types.

Root Cause

The DynCodec::decode() method was unconditionally calling self.decoder.decode() for all message schemas. This works for standard CDR but fails for ROS1 serialized data.

Changes

• Added detection for ROS1 encoding by checking schema_encoding.contains("ros1")
• Route ROS1 messages to decode_headerless_ros1() instead of decode()
• Standard CDR messages continue using decode() as before

Fixes

Resolves decode errors in roboflow_sources when reading ROS1 bag files with messages like:

• kuavo_msgs/lejuClawState (contains string arrays)
• Other complex ROS1 message types with nested structures

Test

• Added examples/test_leju_state.rs for manual verification
• Added test fixture robocodec_test_24_leju_claw.bag

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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[greptile-apps]

Greptile Overview

Greptile Summary

This PR fixes ROS1 decoding through the dynamic CDR codec path by routing CDR schemas whose schema_encoding indicates ROS1 to CdrDecoder::decode_headerless_ros1() instead of decode(), avoiding the 4-byte CDR header + alignment expectations that don’t match ROS1 bag serialization.

It also adds a ROS1 bag fixture and a new test suite intended to cover the streaming/S3-like path (StreamingBagParser + CodecFactory + decode_dynamic()), plus a manual example for local verification.

Main issues to address before merge are in the new tests/example: the tests appear to map record.conn_id to channels via as u16, which can cause records to be skipped and the regression to become ineffective, and one test asserts all channels have schema_encoding == "ros1msg", which is brittle and fixture-dependent. The example also hardcodes an absolute local filesystem path, making it non-portable.

Confidence Score: 3/5

• This PR is likely correct functionally, but the added tests/example need fixes to be reliable and portable.
• Core change in CdrCodec::decode_dynamic() is small and aligns with documented ROS1 serialization differences. However, the new streaming regression tests have a probable channel-id mapping issue (conn_id as u16) that can silently skip decoding, and a schema_encoding assertion that is overly strict and may break on fixture changes. The manual example hardcodes an absolute path, which will not work for other environments.
• tests/ros1_decode_dynamic_tests.rs, examples/test_leju_state.rs

Important Files Changed

Filename	Overview
src/encoding/cdr/codec.rs	Routes ROS1-encoded CDR schemas to decode_headerless_ros1() in decode_dynamic() based on schema_encoding containing "ros1"; otherwise uses standard decode().
tests/ros1_decode_dynamic_tests.rs	Adds regression tests using a ROS1 bag fixture to exercise streaming decode_dynamic(); includes assertions about schema_encoding and allows partial decode success, but has a likely channel-id mapping bug (conn_id as u16) and a brittle assumption that all channels have schema_encoding == "ros1msg".
examples/test_leju_state.rs	Adds a manual example that hardcodes an absolute local file path and is not portable/reproducible as checked into the repo.
tests/fixtures/robocodec_test_24_leju_claw.bag	Adds a ~1.8MB ROS1 bag fixture used by new tests; review needed for repo policies on committing binary fixtures and test determinism.

Sequence Diagram

sequenceDiagram
    participant Caller as Client/Consumer
    participant Factory as CodecFactory
    participant Codec as CdrCodec (DynCodec)
    participant Schema as SchemaMetadata::Cdr
    participant Parser as schema parser
    participant Decoder as CdrDecoder

    Caller->>Factory: get_codec(Encoding::Cdr)
    Factory-->>Caller: &dyn DynCodec (CdrCodec)
    Caller->>Codec: decode_dynamic(data, schema)
    Codec->>Schema: match SchemaMetadata::Cdr
    Codec->>Parser: parse_schema_with_encoding_str(type_name, schema_text, schema_encoding)
    Parser-->>Codec: MessageSchema
    Codec->>Codec: is_ros1 = schema_encoding contains "ros1"
    alt ROS1 schema_encoding
        Codec->>Decoder: decode_headerless_ros1(parsed_schema, data, Some(type_name))
        Decoder-->>Codec: DecodedMessage
    else Standard CDR
        Codec->>Decoder: decode(parsed_schema, data, Some(type_name))
        Decoder-->>Codec: DecodedMessage
    end
    Codec-->>Caller: Result<DecodedMessage>

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