base64 encode in JS

3 files changed, 110 insertions, 56 deletions

diff --git a/src/gleam/base.gleam b/src/gleam/base.gleam
index b589cb6..0995f1b 100644
--- a/src/gleam/base.gleam
+++ b/src/gleam/base.gleam
@@ -1,22 +1,29 @@
-if erlang {
-  import gleam/bit_string
-  import gleam/string
+import gleam/bit_string
+import gleam/string
+
+/// Encodes a BitString into a base 64 encoded string.
+pub fn encode64(input: BitString, padding: Bool) -> String {
+  let encoded = do_encode64(input)
+  case padding {
+    True -> encoded
+    False -> string.replace(encoded, "=", "")
+  }
+}
 
-  external fn erl_encode64(BitString) -> String =
+if erlang {
+  external fn do_encode64(BitString) -> String =
     "base64" "encode"
+}
+
+if javascript {
+  external fn do_encode64(BitString) -> String =
+    "../gleam_stdlib.js" "encode64"
+}
 
+if erlang {
   external fn erl_decode64(String) -> Result(BitString, Nil) =
     "gleam_stdlib" "base_decode64"
 
-  /// Encodes a BitString into a base 64 encoded string.
-  pub fn encode64(input: BitString, padding: Bool) -> String {
-    let encoded = erl_encode64(input)
-    case padding {
-      True -> encoded
-      False -> string.replace(encoded, "=", "")
-    }
-  }
-
   /// Decodes a base 64 encoded string into a BitString.
   pub fn decode64(encoded: String) -> Result(BitString, Nil) {
     let padded = case bit_string.byte_size(bit_string.from_string(encoded)) % 4 {
@@ -25,14 +32,16 @@ if erlang {
     }
     erl_decode64(padded)
   }
+}
 
-  /// Encodes a BitString into a base 64 encoded string with URL and filename safe alphabet.
-  pub fn url_encode64(input: BitString, padding: Bool) -> String {
-    encode64(input, padding)
-    |> string.replace("+", "-")
-    |> string.replace("/", "_")
-  }
+/// Encodes a BitString into a base 64 encoded string with URL and filename safe alphabet.
+pub fn url_encode64(input: BitString, padding: Bool) -> String {
+  encode64(input, padding)
+  |> string.replace("+", "-")
+  |> string.replace("/", "_")
+}
 
+if erlang {
   /// Decodes a base 64 encoded string with URL and filename safe alphabet into a BitString.
   pub fn url_decode64(encoded: String) -> Result(BitString, Nil) {
     encoded
diff --git a/src/gleam_stdlib.js b/src/gleam_stdlib.js
index 3658142..d26a4b6 100644
--- a/src/gleam_stdlib.js
+++ b/src/gleam_stdlib.js
@@ -382,3 +382,47 @@ export function parse_query(query) {
     return new Error(Nil);
   }
 }
+
+// From https://developer.mozilla.org/en-US/docs/Glossary/Base64#Solution_2_%E2%80%93_rewrite_the_DOMs_atob()_and_btoa()_using_JavaScript's_TypedArrays_and_UTF-8
+export function encode64(bit_string) {
+  let aBytes = bit_string.buffer;
+  let nMod3 = 2,
+    sB64Enc = "";
+
+  for (let nLen = aBytes.length, nUint24 = 0, nIdx = 0; nIdx < nLen; nIdx++) {
+    nMod3 = nIdx % 3;
+    if (nIdx > 0 && ((nIdx * 4) / 3) % 76 === 0) {
+      sB64Enc += "\r\n";
+    }
+    nUint24 |= aBytes[nIdx] << ((16 >>> nMod3) & 24);
+    if (nMod3 === 2 || aBytes.length - nIdx === 1) {
+      sB64Enc += String.fromCharCode(
+        uint6ToB64((nUint24 >>> 18) & 63),
+        uint6ToB64((nUint24 >>> 12) & 63),
+        uint6ToB64((nUint24 >>> 6) & 63),
+        uint6ToB64(nUint24 & 63)
+      );
+      nUint24 = 0;
+    }
+  }
+
+  return (
+    sB64Enc.substr(0, sB64Enc.length - 2 + nMod3) +
+    (nMod3 === 2 ? "" : nMod3 === 1 ? "=" : "==")
+  );
+}
+
+// From https://developer.mozilla.org/en-US/docs/Glossary/Base64#Solution_2_%E2%80%93_rewrite_the_DOMs_atob()_and_btoa()_using_JavaScript's_TypedArrays_and_UTF-8
+function uint6ToB64(nUint6) {
+  return nUint6 < 26
+    ? nUint6 + 65
+    : nUint6 < 52
+    ? nUint6 + 71
+    : nUint6 < 62
+    ? nUint6 - 4
+    : nUint6 === 62
+    ? 43
+    : nUint6 === 63
+    ? 47
+    : 65;
+}
diff --git a/test/gleam/base_test.gleam b/test/gleam/base_test.gleam
index dd59196..ade55c8 100644
--- a/test/gleam/base_test.gleam
+++ b/test/gleam/base_test.gleam
@@ -1,27 +1,26 @@
-if erlang {
-  import gleam/base
-  import gleam/io
-  import gleam/list
-  import gleam/should
-
-  pub fn encode64_test() {
-    <<255, 127, 254, 252>>
-    |> base.encode64(True)
-    |> should.equal("/3/+/A==")
-
-    <<255, 127, 254, 252>>
-    |> base.encode64(False)
-    |> should.equal("/3/+/A")
-
-    <<0, 0, 0>>
-    |> base.encode64(True)
-    |> should.equal("AAAA")
-
-    <<>>
-    |> base.encode64(True)
-    |> should.equal("")
-  }
+import gleam/base
+import gleam/list
+import gleam/should
+
+pub fn encode64_test() {
+  <<255, 127, 254, 252>>
+  |> base.encode64(True)
+  |> should.equal("/3/+/A==")
+
+  <<255, 127, 254, 252>>
+  |> base.encode64(False)
+  |> should.equal("/3/+/A")
+
+  <<0, 0, 0>>
+  |> base.encode64(True)
+  |> should.equal("AAAA")
+
+  <<>>
+  |> base.encode64(True)
+  |> should.equal("")
+}
 
+if erlang {
   pub fn decode64_test() {
     "/3/+/A=="
     |> base.decode64()
@@ -43,25 +42,27 @@ if erlang {
     |> base.decode64()
     |> should.equal(Error(Nil))
   }
+}
 
-  pub fn url_encode64_test() {
-    <<255, 127, 254, 252>>
-    |> base.url_encode64(True)
-    |> should.equal("_3_-_A==")
+pub fn url_encode64_test() {
+  <<255, 127, 254, 252>>
+  |> base.url_encode64(True)
+  |> should.equal("_3_-_A==")
 
-    <<255, 127, 254, 252>>
-    |> base.url_encode64(False)
-    |> should.equal("_3_-_A")
+  <<255, 127, 254, 252>>
+  |> base.url_encode64(False)
+  |> should.equal("_3_-_A")
 
-    <<0, 0, 0>>
-    |> base.url_encode64(True)
-    |> should.equal("AAAA")
+  <<0, 0, 0>>
+  |> base.url_encode64(True)
+  |> should.equal("AAAA")
 
-    <<>>
-    |> base.url_encode64(True)
-    |> should.equal("")
-  }
+  <<>>
+  |> base.url_encode64(True)
+  |> should.equal("")
+}
 
+if erlang {
   pub fn url_decode64_test() {
     "_3_-_A=="
     |> base.url_decode64()