Crate fit 

Garmin FIT protocol SDK for Rust — pure-Rust decoder + encoder for v21.200 .fit files (workouts, activities, courses, settings, etc.).

Quick start

use fit::{Decoder, Encoder};

let bytes = std::fs::read("Activity.fit")?;

// Decode every message with all transforms applied (DateTime, enum
// strings, scale/offset, components, sub-fields, dev fields).
let (messages, errors) = Decoder::builder(&bytes).build().read_all();
assert!(errors.is_empty());

// Encode the typed messages back into a FIT binary.
let encoded: Vec<u8> = Encoder::new().encode(&messages)?;
fit::check_integrity(&encoded)?;

Module map

API	Purpose
is_fit / check_integrity	Quick file-level validation
FileHeader / ByteStream	Low-level header + byte cursor
Decoder / RawMessage	Streaming raw-message iterator
DecoderBuilder / TypedDecoder / Message	Profile-aware typed pipeline
Encoder / EncoderBuilder	Round-trip back to FIT binary
crc / base_type / record_header	Protocol primitives
profile	Generated Profile.xlsx tables (see MesgNum, MesgInfo, FieldInfo)
transforms	Re-exports of the M5 transform helpers (datetime / enum / scale / components)
merge_heart_rates / decode_memo_glob	M6 post-processing helpers
FitError	Single error type used by every fallible operation

See the repository for the milestone log and companion tools.

Re-exports

pub use base_type::BaseType;

pub use dev_fields::DevFieldInfo;

pub use dev_fields::DevFieldRegistry;

pub use transforms::decode_memo_glob;

pub use transforms::merge_heart_rates;

Modules

base_type

FIT base types — the 17 primitive wire types referenced by every Definition message’s field-type byte.

crc

CRC-16 calculation for FIT files.

datetime

FIT timestamp conversions.

dev_fields

Developer field schema registry.

output_stream

Growing byte buffer with little-endian write helpers.

profile

FIT profile metadata: enum types, message numbers, and per-field schema.

transforms

Transform pipeline that converts a RawMessage into a typed Message.

Structs

ByteStream

A read cursor over a borrowed byte slice.

Decoder

The streaming decoder. Implements Iterator yielding one Result<RawMessage, FitError> per Data record.

DecoderBuilder

Builder for TypedDecoder. Created by Decoder::builder.

DeveloperFieldDefinition

One developer-field reference inside a Definition.

Encoder

FIT file encoder.

EncoderBuilder

Chainable builder for Encoder. Defaults match Encoder::new.

Field

One field of a fully-transformed message.

FieldDefinition

One field’s wire-level shape inside a Definition message.

FileHeader

Parsed FIT file header.

LocalDefinitions

The 16-slot local-definition table.

Message

A fully-transformed FIT message.

MessageDefinition

A complete Definition message.

RawDevField

A developer field’s wire bytes, awaiting M6 schema resolution.

RawField

A standard field’s decoded value.

RawMessage

One decoded FIT message.

TransformOptions

Toggleable transforms. All default to true (matches the JS SDK’s “decode richly” preset). Disable individually to get cheaper / less opinionated output.

TypedDecoder

Typed-message iterator. Yields one Message per Data record from the underlying Decoder.

Enums

Endian

Endianness selector for multi-byte reads.

FieldKind

Provenance of a field — distinguishes Profile-declared standard fields from runtime-registered developer fields.

FieldTooLargeKind

Tag identifying which protocol field exceeded its 255-byte u8 cap. Kept separate so FitError stays heap-free.

FitError

Anything that can go wrong while reading a FIT file.

RawValue

A decoded field value.

RecordHeader

Classification of a single record-header byte.

Value

A fully-transformed field value.

Constants

LOCAL_DEFINITION_SLOTS

Maximum number of simultaneously valid local message definitions.

Functions

check_integrity

Fully verify a FIT file’s CRCs.

crc16

Compute the CRC-16 over a byte slice. Thin wrapper around crc::calculate.

is_fit

Quick check: does this byte slice plausibly hold a FIT file?