Update (force-pushed)

This branch was rebased onto current main to pick up the unnecessary_cast clippy fix already on main (commit c9ef4d5), and one additional commit was added on top:

Map serde_repr variant rejections to ASCOM InvalidValue — fixes a remaining gap where Deserialize_repr enums (e.g. DriveRate) receiving an integer that parses but matches no variant (e.g. ConformU sending TrackingRate=5 or -1) still returned HTTP 400 instead of ASCOM InvalidValue. serde_repr rejects via Error::custom directly, so the deserializer's serde::de::Error for AlpacaParseError impl now routes custom to a new InvalidValue(String) variant, and response.rs maps it to ASCOMError::invalid_value. Three regression tests added.

Summary

Replace serde_plain::from_str with a custom deserializer so Alpaca integer parameters that parse successfully but don't fit the target type return ASCOM INVALID_VALUE (error 1025) instead of HTTP 400 BadRequest.

Closes #5

Motivation

The ASCOM Alpaca spec and ConformU conformance tests require INVALID_VALUE for parseable-but-out-of-range values — e.g. sending Id=999 to a Switch with only 4 ports should return HTTP 200 with ErrorNumber: 1025, not HTTP 400.

Previously, OpaqueParams::maybe_extract used serde_plain::from_str::<T>, which surfaces a single ParseIntError for every failure mode: malformed input, negative values for unsigned targets, and values too large for the target type. Everything collapsed into Error::BadParameter → HTTP 400, so ConformU's out-of-range checks were reported as protocol errors instead of device-level errors.

How it works

Integer parsing now goes through a two-step split:

1. str.parse::<i64>() — fails only for genuinely malformed input (AlpacaParseError::BadFormat → HTTP 400)
2. T::try_from(i64_value) — fails only for values that parse as integers but don't fit the target (AlpacaParseError::OutOfRange → ASCOM INVALID_VALUE)
3. Error::custom from external code (e.g. serde_repr rejecting an unknown enum variant) — surfaced as AlpacaParseError::InvalidValue → ASCOM INVALID_VALUE

i64 is the narrowest intermediate that covers the full range of every Alpaca numeric target (i8/i16/i32/u8/u16/u32/usize — including u32 transaction IDs up to 4.3B and negative i32 device values), so a single generic parse_integer<T: TryFrom<i64>> handles all of them without per-type dispatch.

The inner AlpacaParseError is carried on Error::BadParameter, and the ResponseWithTransaction<Result<T>> IntoResponse impl destructures the OutOfRange and InvalidValue variants to produce the ASCOM-formatted error response (HTTP 200 + 1025). BadFormat continues to return HTTP 400.

Changes

• src/server/params.rs:
  • New AlpacaParseError enum (BadFormat/OutOfRange/InvalidValue) and AlpacaDeserializer implementing serde::Deserializer
  • Integer methods parse via i64 with TryFrom narrowing; float/bool/char/enum/etc. paths preserved
  • serde::de::Error::custom impl routes to InvalidValue so serde_repr variant rejections (and similar external-code rejections of syntactically valid values) get ASCOM INVALID_VALUE treatment
  • Unit tests for range vs format classification, u32-above-i32::MAX, negative-as-OutOfRange, whitespace trimming, and Deserialize_repr enum variant rejection
• src/server/error.rs: Error::BadParameter now carries AlpacaParseError (was serde_plain::Error)
• src/server/response.rs: BadParameter { err: OutOfRange { .. } } and BadParameter { err: InvalidValue(_) } both map to ASCOMError::invalid_value
• Cargo.toml: drop serde_plain dependency (no longer needed)

Test plan

• cargo check --features server,all-devices passes
• cargo clippy --features server,all-devices clean
• CI clippy matrix (all 7 feature combos under RUSTFLAGS=-D warnings) clean from a clean target dir
• New unit tests in params.rs pass (13/13)
• Manual verification with ConformU: out-of-range Switch.Id returns ASCOM 1025, not HTTP 400
• Manual verification: malformed input (e.g. Id=abc) still returns HTTP 400
• Manual verification with ConformU: TrackingRate Write test no longer flags out-of-enum-range values (5, -1)