Add bit_array.pad_to_bytes. Pad bit arrays when encoding and in bytes_tree.

Author: richard-viney

CHANGELOG.md

@@ -4,6 +4,13 @@
 
 - The performance of `string.trim`, `string.trim_start`, and `string.trim_end`
   has been improved on JavaScript.
+- The `base64_encode`, `base64_url_encode`, and `base16_encode` functions in the
+  `bit_array` module no longer throw an exception when called with a bit array
+  which is not a whole number of bytes. Instead, the bit array is now padded
+  with zero bits prior to being encoded.
+- The `bit_array` module gains the `pad_to_bytes` function.
+- The `bytes_tree` module now pads unaligned bit arrays with zeros when they are
+  added to the tree.
 
 ## v0.44.0 - 2024-11-25
 

src/gleam/bit_array.gleam

@@ -23,6 +23,13 @@ pub fn bit_size(x: BitArray) -> Int {
 @external(javascript, "../gleam_stdlib.mjs", "length")
 pub fn byte_size(x: BitArray) -> Int
 
+/// Pads a bit array with zeros so that it is a whole number of bytes.
+///
+@external(erlang, "gleam_stdlib", "bit_array_pad_to_bytes")
+pub fn pad_to_bytes(x: BitArray) -> BitArray {
+  x
+}
+
 /// Creates a new bit array by joining two bit arrays.
 ///
 /// ## Examples
@@ -104,6 +111,9 @@ fn unsafe_to_string(a: BitArray) -> String
 pub fn concat(bit_arrays: List(BitArray)) -> BitArray
 
 /// Encodes a BitArray into a base 64 encoded string.
+/// 
+/// If the bit array does not contain a whole number of bytes then it is padded
+/// with zero bits prior to being encoded.
 ///
 @external(erlang, "gleam_stdlib", "bit_array_base64_encode")
 @external(javascript, "../gleam_stdlib.mjs", "encode64")
@@ -123,15 +133,20 @@ pub fn base64_decode(encoded: String) -> Result(BitArray, Nil) {
 @external(javascript, "../gleam_stdlib.mjs", "decode64")
 fn decode64(a: String) -> Result(BitArray, Nil)
 
-/// Encodes a `BitArray` into a base 64 encoded string with URL and filename safe alphabet.
+/// Encodes a `BitArray` into a base 64 encoded string with URL and filename
+/// safe alphabet.
+///
+/// If the bit array does not contain a whole number of bytes then it is padded
+/// with zero bits prior to being encoded.
 ///
 pub fn base64_url_encode(input: BitArray, padding: Bool) -> String {
   base64_encode(input, padding)
   |> string.replace("+", "-")
   |> string.replace("/", "_")
 }
 
-/// Decodes a base 64 encoded string with URL and filename safe alphabet into a `BitArray`.
+/// Decodes a base 64 encoded string with URL and filename safe alphabet into a
+/// `BitArray`.
 ///
 pub fn base64_url_decode(encoded: String) -> Result(BitArray, Nil) {
   encoded
@@ -140,10 +155,17 @@ pub fn base64_url_decode(encoded: String) -> Result(BitArray, Nil) {
   |> base64_decode()
 }
 
-@external(erlang, "binary", "encode_hex")
+/// Encodes a `BitArray` into a base 16 encoded string.
+///
+/// If the bit array does not contain a whole number of bytes then it is padded
+/// with zero bits prior to being encoded.
+///
+@external(erlang, "gleam_stdlib", "base16_encode")
 @external(javascript, "../gleam_stdlib.mjs", "base16_encode")
 pub fn base16_encode(input: BitArray) -> String
 
+/// Decodes a base 16 encoded string into a `BitArray`.
+///
 @external(erlang, "gleam_stdlib", "base16_decode")
 @external(javascript, "../gleam_stdlib.mjs", "base16_decode")
 pub fn base16_decode(input: String) -> Result(BitArray, Nil)

src/gleam/bytes_tree.gleam

@@ -19,7 +19,6 @@
 ////
 //// On Erlang this type is compatible with Erlang's iolists.
 
-// TODO: pad bit arrays to byte boundaries when adding to a tree.
 import gleam/bit_array
 import gleam/list
 import gleam/string_tree.{type StringTree}
@@ -104,7 +103,6 @@ pub fn concat(trees: List(BytesTree)) -> BytesTree {
 ///
 /// Runs in constant time.
 ///
-@external(erlang, "gleam_stdlib", "identity")
 pub fn concat_bit_arrays(bits: List(BitArray)) -> BytesTree {
   bits
   |> list.map(fn(b) { from_bit_array(b) })
@@ -135,8 +133,14 @@ pub fn from_string_tree(tree: string_tree.StringTree) -> BytesTree {
 ///
 /// Runs in constant time.
 ///
-@external(erlang, "gleam_stdlib", "wrap_list")
 pub fn from_bit_array(bits: BitArray) -> BytesTree {
+  bits
+  |> bit_array.pad_to_bytes
+  |> wrap_list
+}
+
+@external(erlang, "gleam_stdlib", "wrap_list")
+fn wrap_list(bits: BitArray) -> BytesTree {
   Bytes(bits)
 }
 

src/gleam_stdlib.erl

@@ -5,7 +5,7 @@
     decode_float/1, decode_list/1, decode_option/2, decode_field/2, parse_int/1,
     parse_float/1, less_than/2, string_pop_grapheme/1, string_pop_codeunit/1,
     string_starts_with/2, wrap_list/1, string_ends_with/2, string_pad/4,
-    decode_map/1, uri_parse/1, bit_array_int_to_u32/1, bit_array_int_from_u32/1,
+    decode_map/1, uri_parse/1,
     decode_result/1, bit_array_slice/3, decode_bit_array/1, compile_regex/2,
     regex_scan/2, percent_encode/1, percent_decode/1, regex_check/2,
     regex_split/2, base_decode64/1, parse_query/1, bit_array_concat/1,
@@ -14,8 +14,8 @@
     tuple_get/2, classify_dynamic/1, print/1, println/1, print_error/1,
     println_error/1, inspect/1, float_to_string/1, int_from_base_string/2,
     utf_codepoint_list_to_string/1, contains_string/2, crop_string/2,
-    base16_decode/1, string_replace/3, regex_replace/3, slice/3,
-    bit_array_to_int_and_size/1
+    base16_encode/1, base16_decode/1, string_replace/3, regex_replace/3,
+    slice/3, bit_array_to_int_and_size/1, bit_array_pad_to_bytes/1
 ]).
 
 %% Taken from OTP's uri_string module
@@ -207,12 +207,21 @@ string_pop_grapheme(String) ->
 string_pop_codeunit(<<Cp/integer, Rest/binary>>) -> {Cp, Rest};
 string_pop_codeunit(Binary) -> {0, Binary}.
 
+bit_array_pad_to_bytes(Bin) ->
+    case erlang:bit_size(Bin) rem 8 of
+        0 -> Bin;
+        TrailingBits ->
+            PaddingBits = 8 - TrailingBits,
+            <<Bin/bits, 0:PaddingBits>>
+    end.
+
 bit_array_concat(BitArrays) ->
     list_to_bitstring(BitArrays).
 
 -if(?OTP_RELEASE >= 26).
 bit_array_base64_encode(Bin, Padding) ->
-    base64:encode(Bin, #{padding => Padding}).
+    PaddedBin = bit_array_pad_to_bytes(Bin),
+    base64:encode(PaddedBin, #{padding => Padding}).
 -else.
 bit_array_base64_encode(_Bin, _Padding) ->
     erlang:error(<<"Erlang OTP/26 or higher is required to use base64:encode">>).
@@ -223,16 +232,6 @@ bit_array_slice(Bin, Pos, Len) ->
     catch error:badarg -> {error, nil}
     end.
 
-bit_array_int_to_u32(I) when 0 =< I, I < 4294967296 ->
-    {ok, <<I:32>>};
-bit_array_int_to_u32(_) ->
-    {error, nil}.
-
-bit_array_int_from_u32(<<I:32>>) ->
-    {ok, I};
-bit_array_int_from_u32(_) ->
-    {error, nil}.
-
 compile_regex(String, Options) ->
     {options, Caseless, Multiline} = Options,
     OptionsList = [
@@ -552,6 +551,10 @@ crop_string(String, Prefix) ->
 contains_string(String, Substring) ->
     is_bitstring(string:find(String, Substring)).
 
+base16_encode(Bin) ->
+    PaddedBin = bit_array_pad_to_bytes(Bin),
+    binary:encode_hex(PaddedBin).
+
 base16_decode(String) ->
     try
         {ok, binary:decode_hex(String)}

test/gleam/bit_array_test.gleam

@@ -36,11 +36,50 @@ pub fn bit_size_erlang_only_test() {
 }
 
 pub fn byte_size_test() {
-  bit_array.byte_size(bit_array.from_string("hello"))
+  bit_array.byte_size(<<>>)
+  |> should.equal(0)
+
+  bit_array.byte_size(<<0, 1, 2, 3, 4>>)
   |> should.equal(5)
+}
 
-  bit_array.byte_size(bit_array.from_string(""))
-  |> should.equal(0)
+// This test is target specific since it's using non byte-aligned BitArrays
+// and those are not supported on the JavaScript target.
+@target(erlang)
+pub fn byte_size_erlang_only_test() {
+  bit_array.byte_size(<<1, 2, 3:6>>)
+  |> should.equal(3)
+}
+
+pub fn pad_to_bytes_test() {
+  <<>>
+  |> bit_array.pad_to_bytes
+  |> should.equal(<<>>)
+
+  <<0xAB>>
+  |> bit_array.pad_to_bytes
+  |> should.equal(<<0xAB>>)
+
+  <<0xAB, 0x12>>
+  |> bit_array.pad_to_bytes
+  |> should.equal(<<0xAB, 0x12>>)
+}
+
+// This test is target specific since it's using non byte-aligned BitArrays
+// and those are not supported on the JavaScript target.
+@target(erlang)
+pub fn pad_to_bytes_erlang_only_test() {
+  <<1:1>>
+  |> bit_array.pad_to_bytes
+  |> should.equal(<<0x80>>)
+
+  <<-1:7>>
+  |> bit_array.pad_to_bytes
+  |> should.equal(<<0xFE>>)
+
+  <<0xAB, 0x12, 3:3>>
+  |> bit_array.pad_to_bytes
+  |> should.equal(<<0xAB, 0x12, 0x60>>)
 }
 
 pub fn not_equal_test() {
@@ -85,9 +124,25 @@ pub fn concat_test() {
 // and those are not supported on the JavaScript target.
 @target(erlang)
 pub fn concat_erlang_only_test() {
+  [<<-1:32>>, <<0:1>>, <<0:0>>]
+  |> bit_array.concat
+  |> should.equal(<<255, 255, 255, 255, 0:1>>)
+
+  [<<-20:6, 2>>, <<3:4>>, <<7:3>>, <<-1:64>>]
+  |> bit_array.concat
+  |> should.equal(<<176, 8, 255, 255, 255, 255, 255, 255, 255, 255, 31:size(5)>>)
+
   [<<1, 2:4>>, <<3>>]
   |> bit_array.concat
   |> should.equal(<<1, 2:4, 3>>)
+
+  [<<-1:32>>, <<0:1>>, <<0:0>>]
+  |> bit_array.concat
+  |> should.equal(<<255, 255, 255, 255, 0:1>>)
+
+  [<<-20:6, 2>>, <<3:4>>, <<7:3>>, <<-1:64>>]
+  |> bit_array.concat
+  |> should.equal(<<176, 8, 255, 255, 255, 255, 255, 255, 255, 255, 31:size(5)>>)
 }
 
 pub fn slice_test() {
@@ -133,6 +188,19 @@ pub fn slice_test() {
   |> should.equal(Ok(<<"b":utf8>>))
 }
 
+// This test is target specific since it's using non byte-aligned BitArrays
+// and those are not supported on the JavaScript target.
+@target(erlang)
+pub fn slice_erlang_onyl_test() {
+  <<0, 1, 2:7>>
+  |> bit_array.slice(0, 3)
+  |> should.equal(Error(Nil))
+
+  <<0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15>>
+  |> bit_array.slice(8, 12)
+  |> should.equal(Error(Nil))
+}
+
 pub fn to_string_test() {
   <<>>
   |> bit_array.to_string
@@ -155,6 +223,15 @@ pub fn to_string_test() {
   |> should.equal(Error(Nil))
 }
 
+// This test is target specific since it's using non byte-aligned BitArrays
+// and those are not supported on the JavaScript target.
+@target(erlang)
+pub fn to_string_erlang_only_test() {
+  <<"ø":utf8, 50:4>>
+  |> bit_array.to_string
+  |> should.equal(Error(Nil))
+}
+
 pub fn is_utf8_test() {
   <<>>
   |> bit_array.is_utf8
@@ -207,6 +284,23 @@ pub fn base64_encode_test() {
   ))
 }
 
+// This test is target specific since it's using non byte-aligned BitArrays
+// and those are not supported on the JavaScript target.
+@target(erlang)
+pub fn base64_erlang_only_encode_test() {
+  <<-1:7>>
+  |> bit_array.base64_encode(True)
+  |> should.equal("/g==")
+
+  <<0xFA, 5:3>>
+  |> bit_array.base64_encode(True)
+  |> should.equal("+qA=")
+
+  <<0xFA, 0xBC, 0x6D, 1:1>>
+  |> bit_array.base64_encode(True)
+  |> should.equal("+rxtgA==")
+}
+
 pub fn base64_decode_test() {
   "/3/+/A=="
   |> bit_array.base64_decode()
@@ -305,6 +399,27 @@ pub fn base16_test() {
   |> should.equal("A1B2C3D4E5F67891")
 }
 
+// This test is target specific since it's using non byte-aligned BitArrays
+// and those are not supported on the JavaScript target.
+@target(erlang)
+pub fn base16_encode_erlang_only_test() {
+  <<-1:7>>
+  |> bit_array.base16_encode()
+  |> should.equal("FE")
+
+  <<0xFA, 5:3>>
+  |> bit_array.base16_encode()
+  |> should.equal("FAA0")
+
+  <<0xFA, 5:4>>
+  |> bit_array.base16_encode()
+  |> should.equal("FA50")
+
+  <<0xFA, 0xBC, 0x6D, 1:1>>
+  |> bit_array.base16_encode()
+  |> should.equal("FABC6D80")
+}
+
 pub fn base16_decode_test() {
   bit_array.base16_decode("")
   |> should.equal(Ok(<<>>))
@@ -353,7 +468,7 @@ pub fn inspect_test() {
 // This test is target specific since it's using non byte-aligned BitArrays
 // and those are not supported on the JavaScript target.
 @target(erlang)
-pub fn inspect_partial_bytes_test() {
+pub fn inspect_erlang_only_test() {
   bit_array.inspect(<<4:5>>)
   |> should.equal("<<4:size(5)>>")
 
@@ -365,7 +480,7 @@ pub fn inspect_partial_bytes_test() {
 }
 
 @target(erlang)
-pub fn compare_different_sizes_test() {
+pub fn compare_test() {
   bit_array.compare(<<4:5>>, <<4:5>>)
   |> should.equal(order.Eq)
 
@@ -458,4 +573,10 @@ pub fn starts_with_erlang_only_test() {
 
   bit_array.starts_with(<<0:127>>, <<1:127>>)
   |> should.be_false
+
+  bit_array.starts_with(<<0xFF, 0x81>>, <<0xFF, 1:1>>)
+  |> should.be_true
+
+  bit_array.starts_with(<<0xFF, 0x81>>, <<0xFF, 0:1>>)
+  |> should.be_false
 }