feat: support ascii encoding (#2)

For better or for worse, sometimes you want to covert between a Uint8Array and a string where each character of the string is created from the character code of the corresponding byte from the array.

Adds an `ascii` encoding which is similar to `binary` as used by node buffers.

It's not called `binary` as people confuse this with `base2`.

README.md

@@ -93,6 +93,7 @@ const fromString = require('uint8arrays/from-string')
 console.info(fromString('hello world')) // Uint8Array[104, 101 ...
 console.info(fromString('00010203aabbcc', 'base16')) // Uint8Array[0, 1 ...
 console.info(fromString('AAECA6q7zA', 'base64')) // Uint8Array[0, 1 ...
+console.info(fromString('01234', 'ascii')) // Uint8Array[48, 49 ...
 ```
 
 ### toString(array, encoding = 'utf8')
@@ -109,4 +110,5 @@ const fromString = require('uint8arrays/from-string')
 console.info(toString(Uint8Array.from([104, 101...]))) // 'hello world'
 console.info(toString(Uint8Array.from([0, 1, 2...]), 'base16')) // '00010203aabbcc'
 console.info(toString(Uint8Array.from([0, 1, 2...]), 'base64')) // 'AAECA6q7zA'
+console.info(toString(Uint8Array.from([48, 49, 50...]), 'ascii')) // '01234'
 ```

from-string.js

@@ -4,9 +4,30 @@ const { names } = require('multibase/src/constants')
 const { TextEncoder } = require('web-encoding')
 const utf8Encoder = new TextEncoder()
 
+/**
+ * Interperets each character in a string as a byte and
+ * returns a Uint8Array of those bytes.
+ *
+ * @param {String} string The string to turn into an array
+ * @returns {Uint8Array}
+ */
+function asciiStringToUint8Array (string) {
+  const array = new Uint8Array(string.length)
+
+  for (let i = 0; i < string.length; i++) {
+    array[i] = string.charCodeAt(i)
+  }
+
+  return array
+}
+
 /**
  * Create a `Uint8Array` from the passed string
  *
+ * Supports `utf8`, `utf-8` and any encoding supported by the multibase module.
+ *
+ * Also `ascii` which is similar to node's 'binary' encoding.
+ *
  * @param {String} string
  * @param {String} [encoding=utf8] utf8, base16, base64, base64urlpad, etc
  * @returns {Uint8Array}
@@ -17,6 +38,10 @@ function fromString (string, encoding = 'utf8') {
     return utf8Encoder.encode(string)
   }
 
+  if (encoding === 'ascii') {
+    return asciiStringToUint8Array(string)
+  }
+
   const codec = names[encoding]
 
   if (!codec) {

test/from-string.spec.js

@@ -27,6 +27,19 @@ describe('Uint8Array fromString', () => {
     expect(fromString(str, 'base64')).to.deep.equal(arr)
   })
 
+  it('creates a Uint8Array from an ascii string', () => {
+    const str = [
+      String.fromCharCode(0),
+      String.fromCharCode(1),
+      String.fromCharCode(2),
+      String.fromCharCode(3),
+      String.fromCharCode(4)
+    ].join('')
+    const arr = Uint8Array.from([0, 1, 2, 3, 4])
+
+    expect(fromString(str, 'ascii')).to.deep.equal(arr)
+  })
+
   it('throws when an unknown base is passed', () => {
     const str = 'hello world'
 

test/to-string.spec.js

@@ -27,6 +27,19 @@ describe('Uint8Array toString', () => {
     expect(toString(arr, 'base64')).to.deep.equal(str)
   })
 
+  it('creates an ascii string from a Uint8Array', () => {
+    const str = [
+      String.fromCharCode(0),
+      String.fromCharCode(1),
+      String.fromCharCode(2),
+      String.fromCharCode(3),
+      String.fromCharCode(4)
+    ].join('')
+    const arr = Uint8Array.from([0, 1, 2, 3, 4])
+
+    expect(toString(arr, 'ascii')).to.deep.equal(str)
+  })
+
   it('throws when an unknown base is passed', () => {
     const arr = Uint8Array.from([0, 1, 2, 3, 170, 187, 204])
 

to-string.js

@@ -4,19 +4,41 @@ const { names } = require('multibase/src/constants')
 const { TextDecoder } = require('web-encoding')
 const utf8Decoder = new TextDecoder('utf8')
 
+/**
+ * Turns a Uint8Array of bytes into a string with each
+ * character being the char code of the corresponding byte
+ *
+ * @param {Uint8Array} array The array to turn into a string
+ * @returns {String}
+ */
+function uint8ArrayToAsciiString (array) {
+  let string = ''
+
+  for (let i = 0; i < array.length; i++) {
+    string += String.fromCharCode(array[i])
+  }
+  return string
+}
+
 /**
  * Turns a `Uint8Array` into a string.
  *
- * Supports `utf8` and any encoding supported by the multibase module
+ * Supports `utf8`, `utf-8` and any encoding supported by the multibase module.
+ *
+ * Also `ascii` which is similar to node's 'binary' encoding.
  *
- * @param {Uint8Array} buf The array to turn into a string
+ * @param {Uint8Array} array The array to turn into a string
  * @param {String} [encoding=utf8] The encoding to use
  * @returns {String}
  * @see {@link https://www.npmjs.com/package/multibase|multibase} for supported encodings other than `utf8`
  */
-function toString (buf, encoding = 'utf8') {
+function toString (array, encoding = 'utf8') {
   if (encoding === 'utf8' || encoding === 'utf-8') {
-    return utf8Decoder.decode(buf)
+    return utf8Decoder.decode(array)
+  }
+
+  if (encoding === 'ascii') {
+    return uint8ArrayToAsciiString(array)
   }
 
   const codec = names[encoding]
@@ -25,7 +47,7 @@ function toString (buf, encoding = 'utf8') {
     throw new Error('Unknown base')
   }
 
-  return codec.encode(buf)
+  return codec.encode(array)
 }
 
 module.exports = toString