Add conversion to/from gleam types for CBOR tags 1-4

gleam.toml

@@ -9,6 +9,7 @@ repository = { type = "github", user = "Beaudidly", repo = "gbor" }
 gleam_stdlib = ">= 0.44.0 and < 2.0.0"
 ieee_float = ">= 1.5.0 and < 2.0.0"
 gleam_erlang = ">= 1.2.0 and < 2.0.0"
+gleam_time = ">= 1.3.0 and < 2.0.0"
 
 [dev-dependencies]
 gleeunit = ">= 1.0.0 and < 2.0.0"

src/gbor.gleam

@@ -7,6 +7,8 @@
 /// > **Note**: This type may become opaque in future major types as we evaluate
 /// > the API needs for this package.
 ///
+import gleam/time/timestamp.{type Timestamp}
+
 pub type CBOR {
   CBInt(Int)
   CBString(String)
@@ -18,6 +20,7 @@ pub type CBOR {
   CBUndefined
   CBBinary(BitArray)
   CBTagged(Int, CBOR)
+  CBTime(Timestamp)
 }
 
 // Placeholder for LSP

src/gbor/decode.gleam

@@ -5,10 +5,13 @@ import gleam/bool
 import gleam/dynamic
 import gleam/dynamic/decode as gdd
 import gleam/erlang/atom
+import gleam/float
 import gleam/int
 import gleam/list
 import gleam/result
 import gleam/string
+import gleam/time/duration
+import gleam/time/timestamp
 
 import ieee_float as i
 
@@ -39,24 +42,29 @@ pub fn cbor_to_dynamic(cbor: g.CBOR) -> dynamic.Dynamic {
     g.CBUndefined -> dynamic.nil()
     g.CBBinary(v) -> dynamic.bit_array(v)
     g.CBTagged(tag, value) -> ffi_to_tagged(tag, cbor_to_dynamic(value))
+    g.CBTime(v) ->
+      ffi_to_tagged(
+        0,
+        dynamic.string(timestamp.to_rfc3339(v, duration.hours(0))),
+      )
   }
 }
 
 /// Decode a tagged CBOR value.
-/// 
+///
 /// Provided tag is the expected tag number for the value, and the decoder is run
 /// on the value corresponding to the tag.
-/// 
+///
 /// For example, for a CBOR value with a tag number of `0`, the expected data item
 /// is a text string representing a standard time string, so one would call:
-/// 
+///
 /// ```gleam
 /// import gleam/dynamic/decode as gdd
 /// tagged_decoder(0, gdd.string, "")
 /// ```
-/// 
+///
 /// Reference: [RFC 8949 : 3.4 Tagging of Items](https://www.rfc-editor.org/rfc/rfc8949.html#name-tagging-of-items)
-/// 
+///
 pub fn tagged_decoder(
   expected_tag: Int,
   decoder: gdd.Decoder(a),
@@ -78,11 +86,11 @@ pub fn tagged_decoder(
 }
 
 /// Decode a CBOR value from a bit array
-/// 
+///
 /// This function is the main entry point for decoding CBOR data into Gleam types.
-/// 
+///
 /// It takes a bit array and returns a result containing the decoded CBOR value
-/// 
+///
 pub fn from_bit_array(data: BitArray) -> Result(g.CBOR, CborDecodeError) {
   case decode_helper(data) {
     Ok(#(v, <<>>)) -> Ok(v)
@@ -392,8 +400,53 @@ fn decode_tagged(
   })
 
   use #(tag_value, rest) <- result.try(decode_helper(rest))
+  case tag_num {
+    0 | 1 | 2 | 3 ->
+      case decode_low_tag(tag_num, tag_value) {
+        Ok(val) -> Ok(#(val, rest))
+        Error(Nil) -> Error(MajorTypeError(6))
+      }
+    _ -> {
+      Ok(#(g.CBTagged(tag_num, tag_value), rest))
+    }
+  }
+}
+
+fn decode_low_tag(min: Int, value: g.CBOR) -> Result(g.CBOR, Nil) {
+  case min, value {
+    0, g.CBString(datetime) -> decode_datetime(datetime)
+    1, g.CBInt(time) -> Ok(g.CBTime(timestamp.from_unix_seconds(time)))
+    1, g.CBFloat(time) -> Ok(g.CBTime(decode_timestamp(time)))
+    2, g.CBBinary(value) -> {
+      let size = bit_array.byte_size(value)
+      case value {
+        <<res:unsigned-int-size(size)-unit(8)>> -> Ok(g.CBInt(res))
+        _ -> Error(Nil)
+      }
+    }
+    3, g.CBBinary(value) ->
+      case decode_low_tag(2, g.CBBinary(value)) {
+        Ok(g.CBInt(bigint)) -> Ok(g.CBInt({ -bigint } - 1))
+        u -> u
+      }
+    _, _ -> Error(Nil)
+  }
+}
 
-  Ok(#(g.CBTagged(tag_num, tag_value), rest))
+fn decode_datetime(dt: String) -> Result(g.CBOR, Nil) {
+  case timestamp.parse_rfc3339(dt) {
+    Ok(dt) -> Ok(g.CBTime(dt))
+    _ -> Error(Nil)
+  }
+}
+
+fn decode_timestamp(ts: Float) -> timestamp.Timestamp {
+  let seconds = float.floor(ts)
+  let nano = { ts -. seconds } *. 1.0e9
+  timestamp.from_unix_seconds_and_nanoseconds(
+    float.truncate(seconds),
+    float.truncate(nano),
+  )
 }
 
 @external(erlang, "erl_gbor", "to_tagged")

src/gbor/encode.gleam

@@ -1,9 +1,12 @@
 //// Module where we can find the functions used for getting the CBOR binary representation of a value
 
 import gleam/bit_array
+import gleam/int
 import gleam/list
 import gleam/result
 import gleam/string
+import gleam/time/duration
+import gleam/time/timestamp
 
 import ieee_float as i
 
@@ -28,6 +31,11 @@ pub fn to_bit_array(value: g.CBOR) -> Result(BitArray, EncodeError) {
     g.CBTagged(t, v) -> tagged_encode(t, v)
     g.CBNull -> Ok(null_encode())
     g.CBUndefined -> Ok(undefined_encode())
+    g.CBTime(v) ->
+      to_bit_array(g.CBTagged(
+        0,
+        g.CBString(timestamp.to_rfc3339(v, duration.hours(0))),
+      ))
   }
 }
 
@@ -39,7 +47,15 @@ fn uint_encode(value: Int) -> Result(BitArray, EncodeError) {
     v if v < 0x10000 -> Ok(<<0:3, 25:5, v:16>>)
     v if v < 0x100000000 -> Ok(<<0:3, 26:5, v:32>>)
     v if v < 0x10000000000000000 -> Ok(<<0:3, 27:5, v:64>>)
-    v -> Error(EncodeError("Int value too large: " <> string.inspect(v)))
+    v -> {
+      let l = string.length(int.to_base16(v))
+      let l = l - { l / 2 }
+      case l < 0b100000 {
+        True -> Ok(<<6:3, 2:5, 2:3, l:5, v:size(l)-unit(8)>>)
+        False ->
+          Error(EncodeError("Int value too large: " <> string.inspect(v)))
+      }
+    }
   }
 }
 
@@ -52,7 +68,17 @@ fn int_encode(value: Int) -> Result(BitArray, EncodeError) {
     v if v < 0x10000 -> Ok(<<1:3, 25:5, v:16>>)
     v if v < 0x100000000 -> Ok(<<1:3, 26:5, v:32>>)
     v if v < 0x10000000000000000 -> Ok(<<1:3, 27:5, v:64>>)
-    v -> Error(EncodeError("Int value too large: " <> string.inspect(v)))
+    v -> {
+      let l = string.length(int.to_base16(v))
+      let l = l - { l / 2 }
+      case l < 0b100000 {
+        True -> Ok(<<6:3, 3:5, 2:3, l:5, v:size(l)-unit(8)>>)
+        False ->
+          Error(EncodeError(
+            "Absolute Int value too large: " <> string.inspect(v),
+          ))
+      }
+    }
   }
 }
 

test/round_trip_test.gleam

@@ -3,18 +3,18 @@
 //// Negative values
 //// Special values (Infinity, NaN)
 
+import gbor as g
+import gbor/decode as d
+import gbor/encode as e
 import gleam/bit_array
 import gleam/bool
 import gleam/dynamic/decode as gdd
 import gleam/list
 import gleam/result
 import gleam/string
+import gleam/time/timestamp
 import gleeunit
 
-import gbor as g
-import gbor/decode as d
-import gbor/encode as e
-
 pub fn main() {
   gleeunit.main()
 }
@@ -184,28 +184,27 @@ pub fn decode_simple_test() {
 }
 
 pub fn decode_taggded_test() {
-  let assert Ok(payload) = bit_array.base16_decode("010000000000000000")
   let assert Ok(_) =
-    round_trip(g.CBTagged(2, g.CBBinary(payload)), "c249010000000000000000")
+    round_trip(g.CBInt(18_446_744_073_709_551_616), "c249010000000000000000")
 
-  let assert Ok(payload) = bit_array.base16_decode("010000000000000000")
   let assert Ok(_) =
-    round_trip(g.CBTagged(3, g.CBBinary(payload)), "c349010000000000000000")
+    round_trip(g.CBInt(-18_446_744_073_709_551_617), "c349010000000000000000")
 
+  let assert Ok(timestamp) = timestamp.parse_rfc3339("2013-03-21T20:04:00Z")
   let assert Ok(_) =
     round_trip(
-      g.CBTagged(0, g.CBString("2013-03-21T20:04:00Z")),
+      g.CBTime(timestamp),
       "c074323031332d30332d32315432303a30343a30305a",
     )
 
-  let assert Ok(_) =
-    round_trip(g.CBTagged(1, g.CBInt(1_363_896_240)), "c11a514b67b0")
+  // CBTagged(1, CBInt(1363896240)) <=>
+  // "c11a514b67b0" <=>
+  // "2013-03-21T20:04:00Z"
+  let assert Ok(_) = round_trip(g.CBTime(timestamp), "c11a514b67b0")
 
-  let assert Ok(_) =
-    round_trip(
-      g.CBTagged(1, g.CBFloat(1_363_896_240.5)),
-      "c1fb41d452d9ec200000",
-    )
+  // CBTagged(1, CBFloat(1363896240.5)) <=> "c1fb41d452d9ec200000"
+  let assert Ok(timestamp) = timestamp.parse_rfc3339("2013-03-21T20:04:00.50Z")
+  let assert Ok(_) = round_trip(g.CBTime(timestamp), "c1fb41d452d9ec200000")
 
   let assert Ok(_) =
     round_trip(
@@ -283,8 +282,9 @@ fn round_trip(expected: g.CBOR, hex: String) -> Result(Nil, String) {
     ),
   )
 
+  // Time is always encoded to tag 0, so skip when decoded from tag 1
   let assert Ok(encoded) = e.to_bit_array(v)
-  case encoded == binary {
+  case encoded == binary || string.starts_with(string.lowercase(hex), "c1") {
     True -> Ok(Nil)
     False -> {
       let encoded_hex = bit_array.base16_encode(encoded)