serial-codec

Byte-stream codecs for serial ports, with no runtime or framework dependencies. Used by tauri-plugin-serialplugin, usable on its own.

• framing: turn read chunks into frames. Same semantics as the Node.js @serialport/parser-* packages (their test suites are ported): delimiter, readline, byteLength, interByteTimeout, packetLength, ready, regex, startEnd, slip (plus slip_encode) and ccTalk.
• at: AT command response parsing (final result codes, URCs, verbose/numeric). Result codes are those of V.250, 27.007 (+CME ERROR) and 27.005 (+CMS ERROR), plus SEND OK / SEND FAIL (not V.250: the finals of module TCP stacks, kept for compatibility). Numeric mode (ATV0) accepts CR-only result codes (V.250 §5.7.1).
• urc / args: typed 3GPP TS 27.007 / 27.005 line parsers (registration, signal, calls, SMS headers, operators, +CGEV) and a quote-aware argument splitter.
• cmux: 3GPP TS 27.010 (GSM 07.10) CMUX frame encode/decode.
• sms: 3GPP TS 23.038 alphabets (GSM 7-bit with national tables, UCS2) and TS 23.040 PDUs for AT+CMGF=0: decode SMS-DELIVER / SUBMIT / STATUS-REPORT, encode SMS-SUBMIT with automatic concatenation, multipart reassembly.
• ussd: USSD 7-bit packing, CBS data coding schemes and the +CUSD line.

Framing

use serial_codec::framing::{Framer, FramerConfig};
use std::time::Instant;

let cfg: FramerConfig = serde_json::from_str(r#"{ "type": "readline", "delimiter": "\r\n" }"#).unwrap();
let mut framer = cfg.build().unwrap();

let mut frames = Vec::new();
framer.push(b"OK\r\nRI", Instant::now(), &mut frames);
framer.push(b"NG\r\n", Instant::now(), &mut frames);
assert_eq!(frames, vec![b"OK".to_vec(), b"RING".to_vec()]);

Time-based framers (interByteTimeout, ccTalk) take now instead of running timers: call poll(now, &mut frames) when deadline() passes. flush() returns the partial frame at end of stream.

Differences from Node (all deliberate, see the framing module docs): frames are bytes (encoding is accepted and ignored), buffered bytes are bounded (maxBufferSize, default 64 KiB, for every framer that buffers, packetLength included), the work per pushed byte is bounded (a stream without delimiters fed one byte at a time stays linear), unknown option names are rejected, empty frames are never emitted, ready and multi-byte packetLength delimiters are found after a false start, and regex keeps UTF-8 characters split across reads.

URCs and responses

urc parses one already-framed line into a serde-serializable (camelCase) type; each parser returns None for another command or a malformed line. urc::parse_any dispatches the unsolicited ones (+CREG/+CGREG/+CEREG/+C5GREG, +CLIP, +COLP, +CCWA, +CIEV, +CMTI, +CDSI, +CMT, +CDS, +CGEV). Response parsers: Csq, Cesq, Cpin, Clcc, CindValues/CindRanges, MessageHeader (+CMGL/+CMGR, header only: the body is the next line), MessageReference (+CMGS/+CMSS), CpmsStatus/CpmsSupport, Cnmi/CnmiSupport, Cops/CopsList. +CUSD lives in the USSD module.

use serial_codec::urc::{parse_any, Csq, RegStatus, Urc};

// `<n>,<stat>,...` (read response) and `<stat>,...` (URC) are told apart.
let Some(Urc::Registration(r)) = parse_any("+CREG: 2,5,\"0502\",\"0404736D\",2") else { panic!() };
assert_eq!((r.n, r.stat, r.lac), (Some(2), RegStatus::Roaming, Some(0x0502)));

assert_eq!(Csq::parse("+CSQ: 18,99").unwrap().rssi_dbm(), Some(-77));

args::split is the underlying splitter: commas inside quotes or parentheses do not split, \HH escapes are decoded (V.250 §5.4.2.2: a quote is \22; any other backslash is text), omitted fields stay as empty arguments.

SMS and USSD

use serial_codec::sms::pdu::{decode_hex, encode_submit, SubmitRequest, Tpdu};
use serial_codec::sms::concat::Reassembler;

// Decode what +CMGR / +CMT printed (SMSC prefix included).
let pdu = decode_hex("07911326040000F0040B910100000020F70000208062917314480CC8F71D14969741F977FD07").unwrap();
let Tpdu::Deliver(d) = &pdu.tpdu else { panic!() };
assert_eq!(d.originator.to_string(), "+10000000027");
assert_eq!(pdu.tpdu.text(), Some("How are you?"));
assert_eq!(d.scts.unwrap().to_string(), "2002-08-26T19:37:41-01:00");

// Encode: one (length for AT+CMGS, hex) pair per part. A message that needs more than
// one part needs a concatenation reference (keep a counter per recipient so two long
// messages in flight never share one); without it encode_submit returns
// PduError::MissingConcatRef.
let mut req = SubmitRequest::new("+15551234567", "x".repeat(200));
req.concat_ref = Some(42);
let parts = encode_submit(&req).unwrap();
assert_eq!(parts.len(), 2);

// Reassemble (also accepts parts out of order). At most 64 incomplete messages are held
// (Reassembler::with_max_pending to change it), the oldest is evicted first; call
// expire_before periodically.
let mut asm = Reassembler::new();
let text = parts
    .iter()
    .find_map(|(_, hex)| asm.push_tpdu(&decode_hex(hex).unwrap().tpdu, 0))
    .and_then(|m| m.text);
assert_eq!(text, Some("x".repeat(200)));

// +CUSD with a GSM 7-bit DCS: <str> is in the +CSCS character set (27.007 §7.15).
use serial_codec::ussd::{parse_cusd, Cscs};
let c = parse_cusd(r#"+CUSD: 0,"Balance 5.00",15"#).unwrap();
assert_eq!(c.text().as_deref(), Some("Balance 5.00")); // +CSCS="GSM"/"IRA"
let c = parse_cusd(r#"+CUSD: 0,"00310032",15"#).unwrap();
assert_eq!(c.text().as_deref(), Some("00310032"));
assert_eq!(c.text_as(Cscs::Ucs2).as_deref(), Some("12")); // +CSCS="UCS2"
// Some firmware (Huawei E160, ...) sends packed septets in hex instead: non-standard, opt in.
let c = parse_cusd(r#"+CUSD: 0,"AA58ACA6AA8D1A",15"#).unwrap();
assert_eq!(c.text_packed_hex().as_deref(), Some("*115*5#"));

Decoding is strict about lengths (TP-UDL beyond the data, odd UCS2 payloads and truncated fields are errors) and tolerant where 23.038/23.040 ask receivers to be: reserved DCS values read as GSM 7-bit, any TOA octet is accepted, an invalid SCTS decodes as None (raw octets kept), an unparseable optional TP-PI tail of a status report is ignored (the mandatory fields stay). A +CUSD DCS that is not 0–255 is kept in invalid_dcs; CbsDcs::language gives the language a CBS DCS names. The encoder picks GSM 7-bit, then the national tables you allow (locking_shift/single_shift) when they avoid UCS2, then UCS2; parts never split an escape pair or a surrogate pair, references above 255 switch to the 16-bit IE. National tables: Turkish, Spanish (single shift), Portuguese; the Indic tables of 23.038 Annex A are not included. Fixture sources and the known disagreements with other implementations are listed in tests/fixtures/sms/README.md and tests/fixtures/ussd/README.md.

Minimum Rust version: 1.85.

License

MPL-2.0. You can use the crate in any project, open or closed source, under any license. If you distribute a modified version of this crate's files, those files must stay MPL-2.0 and their source must be published.