[rosterloh]

picoparams.c mis-decodes SetParameters requests with more than one entry, and trusts several wire-supplied lengths. Found while running a Pico-ROS parameter server against rmw_zenoh_cpp on ESP32 boards. Independent of #25 (different file), and merges cleanly with it in either order.

Decode every entry of a SetParameters request

deserialize_ros_ParameterValue() returned straight after the scalar it was asked for, leaving string_value and the five array lengths unread. The second Parameter was therefore decoded from the middle of the first and came back as "Parameter not found": setting x and z in one call lost z. All ten fields are now read. Array contents are still not skipped, so array-typed values remain one per request.

Refuse bad input in set_params_value()

• It looped on the parameter count from the wire, up to 2^32 times on the zenoh read task for a 12-byte request.
• It reused the previous name when one failed to decode.
• It skipped an unknown name's value, misaligning every later entry.
• It could act on a value cut short.

It now stops at the first undecodable entry, reads each value before looking up its name, and writes the result count last. A request cut short gets one result per entry it actually carried, rather than the count it claimed.

params_server_handler() and set_parameters_atomically

• request_size - 4 was computed unchecked, so an empty request produced a buffer length that wrapped the address space. It now sends no reply.
• set_parameters_atomically replied with a bare CDR header, which clients fail to decode. It now refuses with a well-formed SetParametersResult.

Well-formed single-parameter requests decode exactly as before.

Testing

• Built into Zephyr firmware for an ESP32 board (Zephyr 4.5.0-rc3, CONFIG_PICOROS_PARAMS=y) on top of b739fc7 together with Bound string decoding, echo request identity in service replies, check z_malloc #25. No new warnings from picoparams.c.
• Carried downstream as a local patch. There is no host test for picoparams in test/ yet; happy to add one if you'd like it covered the way Bound string decoding, echo request identity in service replies, check z_malloc #25 covers picoserdes.

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