Add std.base64 for encoding and decoding base64

Changelog: added

std/src/std/base64.inko

@@ -0,0 +1,259 @@
+# Base64 encoding and decoding.
+#
+# This module provides types and methods for encoding and decoding base64 data.
+# Data is encoded using the `Encoder` type, while decoding is done using the
+# `Decoder` type.
+
+let ENCODE_STD0 = [
+  0x41, 0x41, 0x41, 0x41, 0x42, 0x42, 0x42, 0x42, 0x43, 0x43, 0x43, 0x43, 0x44,
+  0x44, 0x44, 0x44, 0x45, 0x45, 0x45, 0x45, 0x46, 0x46, 0x46, 0x46, 0x47, 0x47,
+  0x47, 0x47, 0x48, 0x48, 0x48, 0x48, 0x49, 0x49, 0x49, 0x49, 0x4a, 0x4a, 0x4a,
+  0x4a, 0x4b, 0x4b, 0x4b, 0x4b, 0x4c, 0x4c, 0x4c, 0x4c, 0x4d, 0x4d, 0x4d, 0x4d,
+  0x4e, 0x4e, 0x4e, 0x4e, 0x4f, 0x4f, 0x4f, 0x4f, 0x50, 0x50, 0x50, 0x50, 0x51,
+  0x51, 0x51, 0x51, 0x52, 0x52, 0x52, 0x52, 0x53, 0x53, 0x53, 0x53, 0x54, 0x54,
+  0x54, 0x54, 0x55, 0x55, 0x55, 0x55, 0x56, 0x56, 0x56, 0x56, 0x57, 0x57, 0x57,
+  0x57, 0x58, 0x58, 0x58, 0x58, 0x59, 0x59, 0x59, 0x59, 0x5a, 0x5a, 0x5a, 0x5a,
+  0x61, 0x61, 0x61, 0x61, 0x62, 0x62, 0x62, 0x62, 0x63, 0x63, 0x63, 0x63, 0x64,
+  0x64, 0x64, 0x64, 0x65, 0x65, 0x65, 0x65, 0x66, 0x66, 0x66, 0x66, 0x67, 0x67,
+  0x67, 0x67, 0x68, 0x68, 0x68, 0x68, 0x69, 0x69, 0x69, 0x69, 0x6a, 0x6a, 0x6a,
+  0x6a, 0x6b, 0x6b, 0x6b, 0x6b, 0x6c, 0x6c, 0x6c, 0x6c, 0x6d, 0x6d, 0x6d, 0x6d,
+  0x6e, 0x6e, 0x6e, 0x6e, 0x6f, 0x6f, 0x6f, 0x6f, 0x70, 0x70, 0x70, 0x70, 0x71,
+  0x71, 0x71, 0x71, 0x72, 0x72, 0x72, 0x72, 0x73, 0x73, 0x73, 0x73, 0x74, 0x74,
+  0x74, 0x74, 0x75, 0x75, 0x75, 0x75, 0x76, 0x76, 0x76, 0x76, 0x77, 0x77, 0x77,
+  0x77, 0x78, 0x78, 0x78, 0x78, 0x79, 0x79, 0x79, 0x79, 0x7a, 0x7a, 0x7a, 0x7a,
+  0x30, 0x30, 0x30, 0x30, 0x31, 0x31, 0x31, 0x31, 0x32, 0x32, 0x32, 0x32, 0x33,
+  0x33, 0x33, 0x33, 0x34, 0x34, 0x34, 0x34, 0x35, 0x35, 0x35, 0x35, 0x36, 0x36,
+  0x36, 0x36, 0x37, 0x37, 0x37, 0x37, 0x38, 0x38, 0x38, 0x38, 0x39, 0x39, 0x39,
+  0x39, 0x2b, 0x2b, 0x2b, 0x2b, 0x2f, 0x2f, 0x2f, 0x2f,
+]
+let ENCODE_STD1 = [
+  0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d,
+  0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
+  0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
+  0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
+  0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f, 0x41,
+  0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
+  0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61,
+  0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e,
+  0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30,
+  0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f, 0x41, 0x42,
+  0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+  0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62,
+  0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+  0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31,
+  0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f, 0x41, 0x42, 0x43,
+  0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+  0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62, 0x63,
+  0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70,
+  0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31, 0x32,
+  0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f,
+]
+let ENCODE_STD2 = [
+  0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d,
+  0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
+  0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
+  0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
+  0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f, 0x41,
+  0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
+  0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61,
+  0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e,
+  0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30,
+  0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f, 0x41, 0x42,
+  0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+  0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62,
+  0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+  0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31,
+  0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f, 0x41, 0x42, 0x43,
+  0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+  0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62, 0x63,
+  0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70,
+  0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31, 0x32,
+  0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f,
+]
+let ENCODE_URL0 = [
+  0x41, 0x41, 0x41, 0x41, 0x42, 0x42, 0x42, 0x42, 0x43, 0x43, 0x43, 0x43, 0x44,
+  0x44, 0x44, 0x44, 0x45, 0x45, 0x45, 0x45, 0x46, 0x46, 0x46, 0x46, 0x47, 0x47,
+  0x47, 0x47, 0x48, 0x48, 0x48, 0x48, 0x49, 0x49, 0x49, 0x49, 0x4a, 0x4a, 0x4a,
+  0x4a, 0x4b, 0x4b, 0x4b, 0x4b, 0x4c, 0x4c, 0x4c, 0x4c, 0x4d, 0x4d, 0x4d, 0x4d,
+  0x4e, 0x4e, 0x4e, 0x4e, 0x4f, 0x4f, 0x4f, 0x4f, 0x50, 0x50, 0x50, 0x50, 0x51,
+  0x51, 0x51, 0x51, 0x52, 0x52, 0x52, 0x52, 0x53, 0x53, 0x53, 0x53, 0x54, 0x54,
+  0x54, 0x54, 0x55, 0x55, 0x55, 0x55, 0x56, 0x56, 0x56, 0x56, 0x57, 0x57, 0x57,
+  0x57, 0x58, 0x58, 0x58, 0x58, 0x59, 0x59, 0x59, 0x59, 0x5a, 0x5a, 0x5a, 0x5a,
+  0x61, 0x61, 0x61, 0x61, 0x62, 0x62, 0x62, 0x62, 0x63, 0x63, 0x63, 0x63, 0x64,
+  0x64, 0x64, 0x64, 0x65, 0x65, 0x65, 0x65, 0x66, 0x66, 0x66, 0x66, 0x67, 0x67,
+  0x67, 0x67, 0x68, 0x68, 0x68, 0x68, 0x69, 0x69, 0x69, 0x69, 0x6a, 0x6a, 0x6a,
+  0x6a, 0x6b, 0x6b, 0x6b, 0x6b, 0x6c, 0x6c, 0x6c, 0x6c, 0x6d, 0x6d, 0x6d, 0x6d,
+  0x6e, 0x6e, 0x6e, 0x6e, 0x6f, 0x6f, 0x6f, 0x6f, 0x70, 0x70, 0x70, 0x70, 0x71,
+  0x71, 0x71, 0x71, 0x72, 0x72, 0x72, 0x72, 0x73, 0x73, 0x73, 0x73, 0x74, 0x74,
+  0x74, 0x74, 0x75, 0x75, 0x75, 0x75, 0x76, 0x76, 0x76, 0x76, 0x77, 0x77, 0x77,
+  0x77, 0x78, 0x78, 0x78, 0x78, 0x79, 0x79, 0x79, 0x79, 0x7a, 0x7a, 0x7a, 0x7a,
+  0x30, 0x30, 0x30, 0x30, 0x31, 0x31, 0x31, 0x31, 0x32, 0x32, 0x32, 0x32, 0x33,
+  0x33, 0x33, 0x33, 0x34, 0x34, 0x34, 0x34, 0x35, 0x35, 0x35, 0x35, 0x36, 0x36,
+  0x36, 0x36, 0x37, 0x37, 0x37, 0x37, 0x38, 0x38, 0x38, 0x38, 0x39, 0x39, 0x39,
+  0x39, 0x2d, 0x2d, 0x2d, 0x2d, 0x5f, 0x5f, 0x5f, 0x5f,
+]
+let ENCODE_URL1 = [
+  0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d,
+  0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
+  0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
+  0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
+  0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f, 0x41,
+  0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
+  0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61,
+  0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e,
+  0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30,
+  0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f, 0x41, 0x42,
+  0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+  0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62,
+  0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+  0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31,
+  0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f, 0x41, 0x42, 0x43,
+  0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+  0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62, 0x63,
+  0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70,
+  0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31, 0x32,
+  0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f,
+]
+let ENCODE_URL2 = [
+  0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d,
+  0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
+  0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
+  0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
+  0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f, 0x41,
+  0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
+  0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61,
+  0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e,
+  0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30,
+  0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f, 0x41, 0x42,
+  0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+  0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62,
+  0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+  0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31,
+  0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f, 0x41, 0x42, 0x43,
+  0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+  0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62, 0x63,
+  0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70,
+  0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x30, 0x31, 0x32,
+  0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2d, 0x5f,
+]
+let PAD = 0x3d
+
+# A type for encoding raw input as a base64 sequence of bytes.
+#
+# # Examples
+#
+# Encoding input using the standard alphabet from RFC 4648:
+#
+# ```inko
+# import std.base64 (Encoder)
+#
+# let in = 'abcdefghijklmnopqrstuvwxyz0123456789|@{}/&#[]\\!?()<>=+*;\'"`:^%$~'.to_byte_array
+# let out = ByteArray.new
+#
+# Encoder.new.encode(in, out)
+# out.into_string #=> 'YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXowMTIzNDU2Nzg5fEB7fS8mI1tdXCE/KCk8Pj0rKjsnImA6XiUkfg=='
+# ```
+#
+# Encoding input using the URL safe alphabet from RFC 4648:
+#
+# ```inko
+# import std.base64 (Encoder)
+#
+# let in = 'abcdefghijklmnopqrstuvwxyz0123456789|@{}/&#[]\\!?()<>=+*;\'"`:^%$~'.to_byte_array
+# let out = ByteArray.new
+#
+# Encoder.url_safe.encode(in, out)
+# out.into_string #=> 'YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXowMTIzNDU2Nzg5fEB7fS8mI1tdXCE_KCk8Pj0rKjsnImA6XiUkfg=='
+# ```
+class pub Encoder {
+  let @table0: ref Array[Int]
+  let @table1: ref Array[Int]
+  let @table2: ref Array[Int]
+
+  # Returns an `Encoder` that uses the standard base64 alphabet.
+  fn static new -> Encoder {
+    Encoder(table0: ENCODE_STD0, table1: ENCODE_STD1, table2: ENCODE_STD2)
+  }
+
+  # Returns an `Encoder` that uses the URL safe base64 alphabet.
+  fn static url_safe -> Encoder {
+    Encoder(table0: ENCODE_URL0, table1: ENCODE_URL1, table2: ENCODE_URL2)
+  }
+
+  # Encodes the `input` `ByteArray` into a sequence of base64 encoded bytes,
+  # appending the sequence to `output.`
+  #
+  # # Encoding large inputs
+  #
+  # This method encodes `input` as a whole. For large inputs, you can perform
+  # incremental encoding by passing the data as a `ByteArray` chunk of which the
+  # size is a multiple of three. This ensures that padding is only applied to
+  # the last chunk, resulting in output identical to encoding the entire input
+  # as a whole.
+  #
+  # # Examples
+  #
+  # ```inko
+  # import std.base64 (Encoder)
+  #
+  # let out = ByteArray.new
+  #
+  # Encoder.new.encode('hello world'.to_byte_array, out)
+  # out.into_string #=> 'aGVsbG8gd29ybGQ='
+  # ```
+  fn pub encode(input: ref ByteArray, output: mut ByteArray) {
+    # The implementation here is based on the base64 encoder found in Google
+    # Chrome (https://github.com/chromium/chromium/blob/fd8a8914ca0183f0add65ae55f04e287543c7d4a/third_party/modp_b64/modp_b64.cc).
+    let mut e0 = @table0
+    let mut e1 = @table1
+    let mut e2 = @table2
+    let size = input.size
+    let mut i = 0
+
+    if size > 2 {
+      let max = size - 2
+
+      while i < max {
+        let t1 = input.get(i)
+        let t2 = input.get(i + 1)
+        let t3 = input.get(i + 2)
+
+        output.push(e0.get(t1))
+        output.push(e1.get((t1 & 0x03 << 4) | (t2 >> 4 & 0x0f)))
+        output.push(e1.get((t2 & 0x0f << 2) | (t3 >> 6 & 0x03)))
+        output.push(e2.get(t3))
+
+        i += 3
+      }
+    }
+
+    match size - i {
+      case 0 -> {}
+      case 1 -> {
+        let t1 = input.get(i)
+
+        output.push(e0.get(t1))
+        output.push(e1.get(t1 & 0x03 << 4))
+        output.push(PAD)
+        output.push(PAD)
+      }
+      case _ -> {
+        let t1 = input.get(i)
+        let t2 = input.get(i + 1)
+
+        output.push(e0.get(t1))
+        output.push(e1.get((t1 & 0x03 << 4) | (t2 >> 4 & 0x0f)))
+        output.push(e2.get(t2 & 0x0f << 2))
+        output.push(PAD)
+      }
+    }
+  }
+}
+
+# A type for decoding a base64 encoded sequence of bytes into a raw sequence of
+# bytes.
+class pub Decoder {
+  fn pub decode(input: ref ByteArray, output: mut ByteArray) {
+    panic('TODO')
+  }
+}

std/test/std/test_base64.inko

@@ -0,0 +1,84 @@
+import std.base64 (Encoder)
+import std.test (Tests)
+
+fn std(input: ref String) -> String {
+  let output = ByteArray.new
+
+  Encoder.new.encode(input.to_byte_array, output)
+  output.into_string
+}
+
+fn url(input: ref String) -> String {
+  let output = ByteArray.new
+
+  Encoder.url_safe.encode(input.to_byte_array, output)
+  output.into_string
+}
+
+fn pub tests(t: mut Tests) {
+  t.test('Encoder.encode using the standard encoding', fn (t) {
+    t.equal(std(''), '')
+    t.equal(std(' '), 'IA==')
+    t.equal(std('f'), 'Zg==')
+    t.equal(std('fo'), 'Zm8=')
+    t.equal(std('foo'), 'Zm9v')
+    t.equal(std('foob'), 'Zm9vYg==')
+    t.equal(std('fooba'), 'Zm9vYmE=')
+    t.equal(std('foobar'), 'Zm9vYmFy')
+    t.equal(std('0'), 'MA==')
+    t.equal(std('aa'), 'YWE=')
+    t.equal(std('hello'), 'aGVsbG8=')
+    t.equal(std('😃'), '8J+Ygw==')
+    t.equal(
+      std("We've Been Trying To Reach You About Your Car's Extended Warranty"),
+      'V2UndmUgQmVlbiBUcnlpbmcgVG8gUmVhY2ggWW91IEFib3V0IFlvdXIgQ2FyJ3MgRXh0ZW5kZWQgV2FycmFudHk=',
+    )
+    t.equal(
+      std('abcdefghijklmnopqrstuvwxyz0123456789|@{}/&#[]\\!?()<>=+*;\'"`:^%$~'),
+      'YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXowMTIzNDU2Nzg5fEB7fS8mI1tdXCE/KCk8Pj0rKjsnImA6XiUkfg==',
+    )
+
+    let out = ByteArray.new
+
+    Encoder.new.encode(ByteArray.from_array([250]), out)
+    t.equal(out.into_string, '+g==')
+  })
+
+  t.test('Encoder.encode using the URL safe encoding', fn (t) {
+    t.equal(url(''), '')
+    t.equal(url(' '), 'IA==')
+    t.equal(url('f'), 'Zg==')
+    t.equal(url('fo'), 'Zm8=')
+    t.equal(url('foo'), 'Zm9v')
+    t.equal(url('foob'), 'Zm9vYg==')
+    t.equal(url('fooba'), 'Zm9vYmE=')
+    t.equal(url('foobar'), 'Zm9vYmFy')
+    t.equal(url('0'), 'MA==')
+    t.equal(url('aa'), 'YWE=')
+    t.equal(url('hello'), 'aGVsbG8=')
+    t.equal(url('😃'), '8J-Ygw==')
+    t.equal(
+      url("We've Been Trying To Reach You About Your Car's Extended Warranty"),
+      'V2UndmUgQmVlbiBUcnlpbmcgVG8gUmVhY2ggWW91IEFib3V0IFlvdXIgQ2FyJ3MgRXh0ZW5kZWQgV2FycmFudHk=',
+    )
+    t.equal(
+      url('abcdefghijklmnopqrstuvwxyz0123456789|@{}/&#[]\\!?()<>=+*;\'"`:^%$~'),
+      'YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXowMTIzNDU2Nzg5fEB7fS8mI1tdXCE_KCk8Pj0rKjsnImA6XiUkfg==',
+    )
+
+    let out = ByteArray.new
+
+    Encoder.new.encode(ByteArray.from_array([250]), out)
+    t.equal(out.into_string, '+g==')
+  })
+
+  t.test('Encoding input in chunks', fn (t) {
+    let enc = Encoder.new
+    let out = ByteArray.new
+
+    # If the input size is a multiple of 3, there shouldn't be any padding.
+    enc.encode('abc'.to_byte_array, out)
+    enc.encode('def'.to_byte_array, out)
+    t.equal(out.into_string, std('abcdef'))
+  })
+}