Decode the protobuf wire format in Gleam!
protobin.hexdocs.pm/
gleam
protobuf
gtfs tests
Gavin Morrow
(Sep 28, 2025, 9:04 PM EDT)
dec19769
191e768f
+117
-22
test/gtfs-short.pb
test/gtfs-short.pb
This is a binary file and will not be displayed.
+37
test/gtfs-short.protoscope.txt
+37
test/gtfs-short.protoscope.txt
···
1
+
1: {"1.0"}
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3: 1758224061i64
3
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1001: {
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1: {"1.0"}
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2: {
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1: {"1"}
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2: {2: 1758224061i64}
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}
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2: {
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1: {"2"}
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2: {2: 1758224061i64}
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}
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# 2: {
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# 1: {6:SGROUP}
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# 2: {2: 1758224061i64}
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# }
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# 2: {
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# 1: {6:EGROUP}
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# 2: {2: 1758224061i64}
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# }
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2: {
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1: {"5"}
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2: {2: 1758224061i64}
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}
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2: {
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1: {"6"}
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2: {2: 1758224061i64}
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}
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2: {
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1: {"7"}
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2: {2: 1758224061i64}
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}
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# 2: {
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# 1: {10:SGROUP}
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# 2: {2: 1758224061i64}
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# }
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}
+80
-22
test/protobuf_decode_gleam_test.gleam
+80
-22
test/protobuf_decode_gleam_test.gleam
···
40
40
)
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use day <- decode.field(5, decoders.fixed(32))
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-
decode.success(Person(id:, age:, score:, self: person, day:))
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+
Person(id:, age:, score:, self: person, day:) |> decode.success
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}
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pub fn person_pb_test() {
···
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use id <- decode.field(1, decoders.uint())
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use age <- decode.field(2, decoders.uint())
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decode.success(Test(id:, age:))
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+
Test(id:, age:) |> decode.success
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}
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pub fn two_ints_test() {
···
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assert data == Test(id: 150, age: 80_150)
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}
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-
type Gtfs {
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-
Gtfs(header: FeedHeader)
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+
pub type FeedHeader {
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FeedHeader(gtfs_realtime_version: String, timestamp: Int, nyct: NyctHeader)
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}
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-
fn gtfs_decoder() -> Decoder(Gtfs) {
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-
use header <- decode.field(
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1,
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decoders.protobuf(
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-
using: feed_header_decoder,
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named: "FeedHeader",
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-
default: feed_header_default,
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-
),
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+
pub type NyctHeader {
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NyctHeader(
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+
version: String,
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+
trip_replacement_periods: List(TripReplacementPeriod),
110
106
)
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-
decode.success(Gtfs(header:))
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107
}
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-
type FeedHeader {
115
-
FeedHeader(version: String)
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+
pub type TripReplacementPeriod {
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TripReplacementPeriod(route_id: String, replacement_period: Int)
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111
}
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112
118
-
const feed_header_default = FeedHeader(version: "0.0")
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const nyct_header_default = NyctHeader(
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version: "1.0",
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trip_replacement_periods: [],
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)
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+
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const trip_replacement_period_default = TripReplacementPeriod(
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route_id: "",
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replacement_period: 0,
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)
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fn feed_header_decoder() -> Decoder(FeedHeader) {
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-
use version <- decode.field(1, decode_string())
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-
decode.success(FeedHeader(version:))
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+
use gtfs_realtime_version <- decode.field(1, decoders.string())
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use timestamp <- decode.field(3, decoders.fixed(64))
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use nyct <- decode.field(
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1001,
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decoders.protobuf(
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using: nyct_header_decoder,
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named: "NyctHeader",
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+
default: nyct_header_default,
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+
),
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+
)
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FeedHeader(gtfs_realtime_version:, timestamp:, nyct:) |> decode.success
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+
}
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+
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+
fn nyct_header_decoder() -> Decoder(NyctHeader) {
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+
use version <- decode.field(1, decoders.string())
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+
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+
use trip_replacement_periods <- decode.field(
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2,
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+
decode.list(of: decoders.protobuf(
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using: trip_replacement_period_decoder,
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named: "TripReplacementPeriod",
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default: trip_replacement_period_default,
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+
)),
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+
)
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+
149
+
NyctHeader(version:, trip_replacement_periods:) |> decode.success
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+
}
151
+
152
+
fn trip_replacement_period_decoder() -> Decoder(TripReplacementPeriod) {
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+
use route_id <- decode.field(1, decoders.string())
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+
use replacement_period <- decode.field(
155
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2,
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+
decoders.protobuf(
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using: trip_replacement_period_time_range_decoder,
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named: "TripReplacePeriod.TimeRange",
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default: 0,
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),
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)
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TripReplacementPeriod(route_id:, replacement_period:) |> decode.success
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+
}
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+
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fn trip_replacement_period_time_range_decoder() -> Decoder(Int) {
166
+
use time <- decode.field(2, decoders.fixed(64))
167
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time |> decode.success
123
168
}
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169
125
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pub fn gtfs_test() {
126
171
let path = "./test/gtfs-short.pb"
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let assert Ok(bits) = file.read_bits(from: path)
128
-
let assert Ok(gtfs) = parse(from: bits, using: gtfs_decoder())
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+
let assert Ok(header) = parse(from: bits, using: feed_header_decoder())
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174
130
-
echo gtfs
131
-
132
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Nil
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+
assert header
176
+
== Parsed(
177
+
FeedHeader(
178
+
"1.0",
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1_758_224_061,
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NyctHeader("1.0", [
181
+
TripReplacementPeriod("7", 1_758_224_061),
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+
TripReplacementPeriod("6", 1_758_224_061),
183
+
TripReplacementPeriod("5", 1_758_224_061),
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+
TripReplacementPeriod("2", 1_758_224_061),
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TripReplacementPeriod("1", 1_758_224_061),
186
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]),
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),
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<<>>,
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+
102,
190
+
)
133
191
}