Support uploading FIT files (and zipped exports) alongside GPX
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Maptool::Fit reads Garmin's binary FIT format directly rather than
adding a gem — the one Ruby option depends on activesupport, unmaintained
since 2022, for a single-purpose binary parser. Only "record" messages
are read (position + altitude; everything else is skipped by byte
length, never interpreted); field numbers and scale/offset are
Garmin's own (fit-python-sdk's profile.py), and the framing plus all
extracted values were checked byte-for-byte against 5 real device
files from python-fitparse's test suite before this shipped.

A .zip upload (Garmin's bulk/FIT export format) is expanded into its
.gpx/.fit entries via rubyzip — that one's an actual dependency, since
ZIP's own format isn't the kind of narrow, single-purpose parsing FIT
above is.
This commit is contained in:
randy committed 2026-09-07 12:23:37 +02:00
1 parent 8d3c126a14
commit fc174d4267
8 files changed
+338 -29

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@@ -0,0 +1,232 @@
module Maptool
# Converts a Garmin FIT file (binary — see https://developer.garmin.com/fit/)
# to a GeoJSON FeatureCollection, in the same shape Gpx.to_geojson produces
# for a <trk>: one Feature per file, geometry MultiLineString, "kind" =>
# "track". Only positioned "record" messages are read — FIT also carries
# laps/sessions/events/device info/developer fields, none of which this
# app has anywhere to show, so they're skipped by byte-length rather than
# interpreted.
module Fit
class ParseError < StandardError; end
FIT_EPOCH = Time.utc(1989, 12, 31).to_i
RECORD_MESSAGE_NUM = 20
FIELD_POSITION_LAT = 0
FIELD_POSITION_LONG = 1
FIELD_ALTITUDE = 2
FIELD_ENHANCED_ALTITUDE = 78
SEMICIRCLE_TO_DEGREES = 180.0 / (2**31)
Definition = Struct.new(:global_mesg_num, :little_endian, :fields, :total_size)
def self.kinds(path)
to_geojson(path)["features"].empty? ? [] : ["track"]
rescue ParseError
[]
end
def self.to_geojson(path)
points = parse(File.binread(path))
features = points.empty? ? [] : [track_feature(points)]
{ "type" => "FeatureCollection", "features" => features }
end
def self.track_feature(points)
{
"type" => "Feature",
"geometry" => { "type" => "MultiLineString", "coordinates" => [points] },
"properties" => { "kind" => "track", "name" => nil },
}
end
private_class_method :track_feature
def self.parse(data)
raise ParseError, "not a FIT file" if data.bytesize < 12 || data.byteslice(8, 4) != ".FIT"
header_size = data.getbyte(0)
data_size = data.byteslice(4, 4).unpack1("L<")
data_end = header_size + data_size
raise ParseError, "truncated file" if data_end > data.bytesize
offset = header_size
definitions = {}
points = []
while offset < data_end
header = data.getbyte(offset)
offset += 1
if header & 0x80 != 0
local_type = (header >> 5) & 0x3
definition = definitions[local_type] or raise ParseError, "data message before its definition"
offset = read_data_message(data, offset, definition, points)
elsif header & 0x40 != 0
local_type = header & 0x0F
definition, offset = read_definition(data, offset, header & 0x20 != 0)
definitions[local_type] = definition
else
local_type = header & 0x0F
definition = definitions[local_type] or raise ParseError, "data message before its definition"
offset = read_data_message(data, offset, definition, points)
end
end
points
rescue ArgumentError, NoMethodError => e
raise ParseError, e.message
end
private_class_method :parse
def self.read_definition(data, offset, has_developer_fields)
architecture = data.getbyte(offset + 1)
little_endian = architecture.zero?
global_mesg_num = data.byteslice(offset + 2, 2).unpack1(little_endian ? "S<" : "S>")
num_fields = data.getbyte(offset + 4)
offset += 5
fields = []
num_fields.times do
fields << [data.getbyte(offset), data.getbyte(offset + 1)]
offset += 3
end
if has_developer_fields
num_dev_fields = data.getbyte(offset)
offset += 1
num_dev_fields.times do
fields << [nil, data.getbyte(offset + 1)]
offset += 3
end
end
total_size = fields.sum { |_field_num, size| size }
[Definition.new(global_mesg_num, little_endian, fields, total_size), offset]
end
private_class_method :read_definition
def self.read_data_message(data, offset, definition, points)
if definition.global_mesg_num == RECORD_MESSAGE_NUM
point = extract_point(data, offset, definition)
points << point if point
end
offset + definition.total_size
end
private_class_method :read_data_message
# Only reads the 3 fields the map needs; every other field in the
# message (heart rate, cadence, power, ...) is walked past via its
# declared size without being interpreted.
def self.extract_point(data, offset, definition)
lat = lon = altitude = nil
pos = offset
definition.fields.each do |field_num, size|
case field_num
when FIELD_POSITION_LAT
lat = unpack_int(data, pos, size, definition.little_endian, signed: true)
when FIELD_POSITION_LONG
lon = unpack_int(data, pos, size, definition.little_endian, signed: true)
when FIELD_ALTITUDE, FIELD_ENHANCED_ALTITUDE
altitude ||= unpack_int(data, pos, size, definition.little_endian, signed: false)
end
pos += size
end
return nil if lat.nil? || lon.nil? || invalid?(lat, 4) || invalid?(lon, 4)
coordinate = [lon * SEMICIRCLE_TO_DEGREES, lat * SEMICIRCLE_TO_DEGREES]
coordinate << (altitude / 5.0 - 500) if altitude && !invalid?(altitude, 2) && !invalid?(altitude, 4)
coordinate
end
private_class_method :extract_point
UNPACK_FORMATS = {
[1, true] => "c", [1, false] => "C",
[2, true] => "s", [2, false] => "S",
[4, true] => "l", [4, false] => "L",
[8, true] => "q", [8, false] => "Q",
}.freeze
def self.unpack_int(data, offset, size, little_endian, signed:)
format = UNPACK_FORMATS[[size, signed]]
return nil unless format
format += little_endian ? "<" : ">" if size > 1
data.byteslice(offset, size)&.unpack1(format)
end
private_class_method :unpack_int
# FIT's per-base-type "field not present" sentinel: all bits set for an
# unsigned/positive-only reading, the same pattern for signed. Good
# enough for the two fields this cares about (position, altitude)
# without needing every base type's exact invalid value.
def self.invalid?(value, size)
value == (1 << (size * 8 - 1)) - 1 || value == -1 || value == (1 << (size * 8)) - 1
end
private_class_method :invalid?
end
end
if __FILE__ == $0
require "tmpdir"
# A hand-built minimal FIT file: header + one definition message (local
# type 0, global mesg 20 "record", fields position_lat/position_long,
# both sint32) + two data messages + a throwaway CRC. Exercises the
# header/definition/data framing without external fixtures.
def le32(n)
[n].pack("l<")
end
def build_fit(records)
definition = [0, 0].pack("CC") + [20].pack("S<") + [2].pack("C") +
[0, 4, 0x85].pack("C3") + [1, 4, 0x85].pack("C3")
definition_header = [0b01000000].pack("C")
data = records.map do |lat, lon|
[0b00000000].pack("C") + le32(lat) + le32(lon)
end.join
body = definition_header + definition + data
header = [12, 16, 0, 0].pack("C2S<") + le32(body.bytesize) + ".FIT"
header + body + "\x00\x00"
end
Dir.mktmpdir do |dir|
path = File.join(dir, "test.fit")
File.binwrite(path, build_fit([[100_000_000, 200_000_000], [100_000_100, 200_000_100]]))
geojson = Maptool::Fit.to_geojson(path)
coords = geojson["features"][0]["geometry"]["coordinates"][0]
raise "expected 2 points" unless coords.size == 2
expected_lat = 100_000_000 * Maptool::Fit::SEMICIRCLE_TO_DEGREES
expected_lon = 200_000_000 * Maptool::Fit::SEMICIRCLE_TO_DEGREES
raise "bad coordinate: #{coords[0]}" unless (coords[0][1] - expected_lat).abs < 1e-9 && (coords[0][0] - expected_lon).abs < 1e-9
raise "expected kind track" unless Maptool::Fit.kinds(path) == ["track"]
empty_path = File.join(dir, "empty.fit")
File.binwrite(empty_path, build_fit([]))
raise "expected no features for a pointless file" unless Maptool::Fit.to_geojson(empty_path)["features"].empty?
raise "expected no kinds for a pointless file" unless Maptool::Fit.kinds(empty_path) == []
raise "expected ParseError for garbage" rescue nil
begin
Maptool::Fit.to_geojson(File.join(dir, "nonexistent.fit"))
raise "expected an error reading a missing file"
rescue Errno::ENOENT
# fine — this app only ever calls to_geojson with a path it already
# knows exists
end
garbage_path = File.join(dir, "garbage.fit")
File.binwrite(garbage_path, "not a fit file at all")
begin
Maptool::Fit.to_geojson(garbage_path)
raise "expected ParseError for garbage input"
rescue Maptool::Fit::ParseError
# expected
end
end
puts "ok"
end
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@@ -1,12 +1,17 @@
require "fileutils"
require_relative "gpx"
require_relative "fit"
module Maptool
# Filesystem-backed store for uploaded GPX files, organized in
# Filesystem-backed store for uploaded GPX/FIT files, organized in
# user-chosen folders (arbitrary nesting). All paths coming from the
# outside (folder names, file paths in URLs) are resolved and checked
# against the store root before touching the filesystem, so path
# traversal (e.g. "../../etc") can't escape it.
#
# A .zip upload (Garmin exports FIT files zipped) isn't handled here —
# the caller (app.rb) unpacks it and calls save() once per extracted
# file, same as it would for several files dropped in at once.
class GpxStore
class InvalidPath < StandardError; end
@@ -16,12 +21,12 @@ module Maptool
end
# Nested { type:, name:, path:, children: } hash describing every
# folder and .gpx file under the store root.
# folder and .gpx/.fit file under the store root.
def tree
{ "type" => "folder", "name" => "root", "path" => "", "children" => list_children(@root, "") }
end
# Saves `io`'s contents as a .gpx file under `folder` (created if
# Saves `io`'s contents as a .gpx/.fit file under `folder` (created if
# needed), deriving a safe filename from `filename`. Returns the
# stored file's path relative to the store root.
def save(folder:, filename:, io:)
@@ -91,10 +96,12 @@ module Maptool
path == @root || path.start_with?(@root + File::SEPARATOR)
end
TRACK_EXTENSIONS = %w[.gpx .fit].freeze
def safe_filename(filename)
base = File.basename(filename.to_s)
base = "upload.gpx" if base.empty? || base == "." || base == ".."
base = "#{base}.gpx" unless base.downcase.end_with?(".gpx")
base = "#{base}.gpx" unless TRACK_EXTENSIONS.any? { |ext| base.downcase.end_with?(ext) }
base
end
@@ -119,6 +126,8 @@ module Maptool
{ "type" => "folder", "name" => entry, "path" => rel, "children" => list_children(full, rel) }
elsif entry.downcase.end_with?(".gpx")
{ "type" => "file", "name" => entry, "path" => rel, "kinds" => Gpx.kinds(full) }
elsif entry.downcase.end_with?(".fit")
{ "type" => "file", "name" => entry, "path" => rel, "kinds" => Fit.kinds(full) }
end
end
end