From c942b6f8edb182e0079dd69bbfc44bf70a18c5ea Mon Sep 17 00:00:00 2001
From: eaon <eaon@posteo.net>
Date: Tue, 24 Feb 2026 20:12:16 +0000
Subject: [PATCH] Add byte decoder

---
 src/protobin.gleam | 9 +++++++++
 test/protobin_test.gleam | 41 +++++++++++++++++++++++++++++++++++++++++
 2 file(s) changed, 50 insertion(s)(+), 0 deletion(s)(-)

diff --git a/src/protobin.gleam b/src/protobin.gleam
--- a/src/protobin.gleam
+++ b/src/protobin.gleam
@@ -346,6 +346,15 @@
   single_or_raw(of: decode.bit_array, named: "BitArray", default: <<>>)
 }
 
+/// Decode a `bytes` field. The result is guaranteed to be byte-aligned.
+pub fn decode_bytes() -> Decoder(BitArray) {
+  use bits <- decode.then(single_or_raw_bit_array())
+  case bits {
+    <<_:bytes>> -> decode.success(bits)
+    _ -> decode.failure(<<>>, "Bytes")
+  }
+}
+
 pub fn decode_protobuf(
   // Passed as a function so recursive decoders are easier
   using decoder: fn() -> Decoder(t),
diff --git a/test/protobin_test.gleam b/test/protobin_test.gleam
--- a/test/protobin_test.gleam
+++ b/test/protobin_test.gleam
@@ -282,6 +282,47 @@
     )
 }
 
+type BytesFields {
+  BytesFields(data: BitArray, tag: BitArray)
+}
+
+fn bytes_fields_decoder() -> Decoder(BytesFields) {
+  use data <- decode.field(3, protobin.decode_bytes())
+  use tag <- decode.field(9, protobin.decode_bytes())
+  BytesFields(data:, tag:) |> decode.success
+}
+
+pub fn bytes_fields_test() {
+  let bits = <<
+    // field 3
+    0x1a,
+    0x03,
+    0x01,
+    0x02,
+    0x03,
+    // field 9
+    0x4a,
+    0x04,
+    0x0a,
+    0x0b,
+    0x0c,
+    0x0d,
+  >>
+  let assert Ok(parsed) = parse(from: bits, using: bytes_fields_decoder())
+
+  assert parsed
+    == Parsed(
+      value: BytesFields(data: <<0x01, 0x02, 0x03>>, tag: <<
+        0x0a,
+        0x0b,
+        0x0c,
+        0x0d,
+      >>),
+      rest: <<>>,
+      pos: 11,
+    )
+}
+
 pub fn does_not_ignore_groups_test() {
   let path = "./test/ignores-groups.pb"
   let assert Ok(bits) = file.read_bits(from: path)

--
tangled.sh