feat: b64urlDecode() Decode URL-safe base64 to original string

Author: waitingsong

src/lib/helper.ts

@@ -170,16 +170,26 @@ export function b64toURLSafe(base64: string): string {
 export function b64fromURLSafe(base64: string): string {
   validateB64URL(base64)
   const str = base64.replace(/-/g, '+').replace(/_/g, '/')
+  return b64PadSuffix(str)
+}
+
+
+export function b64PadSuffix(input: string): string {
   let num = 0
-  const mo = str.length % 4
+  const mo = input.length % 4
   switch (mo) {
     case 3:
       num = 1
       break
     case 2:
       num = 2
       break
+    case 0:
+      num = 0
+      break
+    default:
+      throw new Error(ErrMsg.notValidB64URLLength)
   }
 
-  return str + '='.repeat(num)
+  return input + '='.repeat(num)
 }

src/lib/index.ts

@@ -4,7 +4,7 @@ import {
   fromBuffer as browserFromBuffer,
 } from './browser'
 import { defaultConfig } from './config'
-import { b64toURLSafe, isRunningInNodejs } from './helper'
+import { b64toURLSafe, b64PadSuffix, isRunningInNodejs } from './helper'
 import { TextDecoderFn, TextEncoderFn } from './model'
 import {
   fromBuffer as nodeFromBuffer,
@@ -79,3 +79,21 @@ export function b64urlEncode(
   const b64 = b64encode(input, textEncoder)
   return b64toURLSafe(b64)
 }
+
+
+/**
+ * Decode URL-safe base64 to original string.
+ *
+ * Note: using b64fromURLSafe() for converting URL-safe base64 string to base64 string
+ *
+ * @see https://en.wikipedia.org/wiki/Base64#URL_applications
+ */
+export function b64urlDecode(
+  input: string,
+  outputEncoding: string = 'utf-8',
+  textDecoder?: TextDecoderFn,
+): string {
+
+  const str = b64PadSuffix(input) // for URL-safe
+  return b64decode(str, outputEncoding, textDecoder)
+}

test/10_index.test.ts

@@ -9,7 +9,7 @@ import * as assert from 'power-assert'
 import rewire = require('rewire')
 import { TextDecoder, TextEncoder } from 'util'
 
-import { b64decode, b64encode, b64fromBuffer, b64urlEncode } from '../src/index'
+import { b64decode, b64encode, b64fromBuffer, b64urlDecode, b64urlEncode } from '../src/index'
 import { defaultConfig, ErrMsg } from '../src/lib/config'
 
 import { input1, input2, input3, input4, input44, input5, input8, inputURLSafe, inputURLSafe2 } from './config'
@@ -115,4 +115,30 @@ describe(filename, () => {
     })
   })
 
+
+  describe('Should b64urlDecode() works', () => {
+    it('with valid input', () => {
+      inputURLSafe.forEach(([input, b64, b64url]) => {
+        const ret1 = b64urlDecode(b64, 'utf8', TextDecoder)
+        const ret2 = b64urlDecode(b64url, (void 0), TextDecoder)
+
+        assert(ret1 === ret2, `0: "${ret1}" !== "${ret2}"`)
+        assert(ret1 === input, `1: "${ret1}" !== "${input}"`)
+      })
+    })
+
+    it('with invalid input', () => {
+      inputURLSafe2.forEach(b64 => {
+        try {
+          b64urlDecode(b64, 'utf8', TextDecoder)
+          assert(false, 'Should throw error, but NOT')
+        }
+        catch (ex) {
+          assert(true)
+        }
+      })
+    })
+  })
+
+
 })