feat: Implement base64decode

Author: hyperupcall

README.md

@@ -7,7 +7,7 @@ All algorithms use _only_ builtins and create _no subshells_
 ## Algorithms
 
 - [x] base64 encode
-- [ ] base64 decode
+- [x] base64 decode
 - [ ] md5
 - [ ] sha1
 - [ ] sha256

pkg/lib/public/bash-algo.sh

@@ -42,3 +42,53 @@ algo.base64encode() {
 		REPLY+="${output_byte_one}${output_byte_two}${output_byte_three}${output_byte_four}"
 	done
 }
+
+algo.base64decode() {
+	unset REPLY; REPLY=
+	local input="$1"
+
+	local input_byte_{one,two,three,four}=
+	local index_{one,two,three,four}=
+	local char_str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+	for ((i=0; i<${#input}; i=i+4)); do
+		printf -v input_byte_one '%c' "${input:$i:1}"
+		printf -v input_byte_two '%c' "${input:$i+1:1}"
+		printf -v input_byte_three '%c' "${input:$i+2:1}"
+		printf -v input_byte_four '%c' "${input:$i+3:1}"
+
+		# TODO: `set -o nocasematch` likely affects this
+		# Equivalent to char_str.indexOf(input)
+		index_one="${char_str%$input_byte_one*}"; index_one=${#index_one}
+		index_two="${char_str%$input_byte_two*}"; index_two=${#index_two}
+		index_three="${char_str%$input_byte_three*}"; index_three=${#index_three}
+		index_four="${char_str%$input_byte_four*}"; index_four=${#index_four}
+
+		# Output byte one
+		bits_one=$(( ((index_one & 2#00111111) << 2) | ((index_two >> 4) & 2#00000011) ))
+		printf -v output_byte_one '%03o' "$bits_one"
+		printf -v output_byte_one "\\$output_byte_one"
+
+		# An index of '64' means char_str.`indexOf(input)` could not find the substring
+		# i.e. `-1` in traditional languages. This occurs when an `=` is found
+
+		# Output byte two
+		if ((index_three == 64)); then
+			output_byte_two=
+		else
+			bits_two=$(( ((index_two & 2#00001111) << 4) | ((index_three >> 2) & 2#00001111) ))
+			printf -v output_byte_two '%03o' "$bits_two"
+			printf -v output_byte_two "\\$output_byte_two"
+		fi
+
+		# Output byte three
+		if ((index_four == 64)); then
+			output_byte_three=
+		else
+			bits_three=$(( ((index_three & 2#00000011) << 6) | (index_four & 2#00111111) ))
+			printf -v output_byte_three '%03o' "$bits_three"
+			printf -v output_byte_three "\\$output_byte_three"
+		fi
+
+		REPLY+="${output_byte_one}${output_byte_two}${output_byte_three}"
+	done
+}

tests/all.bats

@@ -3,7 +3,7 @@
 load './util/init.sh'
 
 @test "base64encode" {
-	algo.base64encode "paraguay-uruguay"
+	algo.base64encode 'paraguay-uruguay'
 	assert [ "$REPLY" = 'cGFyYWd1YXktdXJ1Z3VheQ==' ]
 
 	test_util.base64encode 'A'
@@ -14,3 +14,16 @@ load './util/init.sh'
 	test_util.base64encode 'kafka38quebec'
 	test_util.base64encode 'EcHo##8(0}}'
 }
+
+@test "base64decode" {
+	algo.base64decode 'cGFyYWd1YXktdXJ1Z3VheQ=='
+	assert [ "$REPLY" = 'paraguay-uruguay' ]
+
+	test_util.base64decode 'QQ=='
+	test_util.base64decode 'QUI='
+	test_util.base64decode 'QUJD'
+	test_util.base64decode 'QUJDRA=='
+	test_util.base64decode 'V09PRg=='
+	test_util.base64decode 'a2Fma2EzOHF1ZWJlYw=='
+	test_util.base64decode 'RWNIbyMjOCgwfX0='
+}

tests/util/test_util.sh

@@ -4,3 +4,8 @@ test_util.base64encode() {
 	algo.base64encode "$1"
 	assert [ "$REPLY" = "$(printf '%s' "$1" | base64)" ]
 }
+
+test_util.base64decode() {
+	algo.base64decode "$1"
+	assert [ "$REPLY" = "$(printf '%s' "$1" | base64 --decode)" ]
+}