as3 之 Base64 共享

import flash.utils.ByteArray;
	
	public class Base64 {
		
		private static const BASE64_CHARS:String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

		public static const version:String = "1.0.0";

		public static function encode(data:String):String {
			// Convert string to ByteArray
			var bytes:ByteArray = new ByteArray();
			bytes.writeUTFBytes(data);
			
			// Return encoded ByteArray
			return encodeByteArray(bytes);
		}
		
		public static function encodeByteArray(data:ByteArray):String {
			// Initialise output
			var output:String = "";
			
			// Create data and output buffers
			var dataBuffer:Array;
			var outputBuffer:Array = new Array(4);
			
			// Rewind ByteArray
			data.position = 0;
			
			// while there are still bytes to be processed
			while (data.bytesAvailable > 0) {
				// Create new data buffer and populate next 3 bytes from data
				dataBuffer = new Array();
				for (var i:uint = 0; i < 3 && data.bytesAvailable > 0; i++) {
					dataBuffer[i] = data.readUnsignedByte();
				}
				
				// Convert to data buffer Base64 character positions and 
				// store in output buffer
				outputBuffer[0] = (dataBuffer[0] & 0xfc) >> 2;
				outputBuffer[1] = ((dataBuffer[0] & 0x03) << 4) | ((dataBuffer[1]) >> 4);
				outputBuffer[2] = ((dataBuffer[1] & 0x0f) << 2) | ((dataBuffer[2]) >> 6);
				outputBuffer[3] = dataBuffer[2] & 0x3f;
				
				// If data buffer was short (i.e not 3 characters) then set
				// end character indexes in data buffer to index of '=' symbol.
				// This is necessary because Base64 data is always a multiple of
				// 4 bytes and is basses with '=' symbols.
				for (var j:uint = dataBuffer.length; j < 3; j++) {
					outputBuffer[j + 1] = 64;
				}
				
				// Loop through output buffer and add Base64 characters to 
				// encoded data string for each character.
				for (var k:uint = 0; k < outputBuffer.length; k++) {
					output += BASE64_CHARS.charAt(outputBuffer[k]);
				}
			}
			
			// Return encoded data
			return output;
		}
		
		public static function decode(data:String):String {
			// Decode data to ByteArray
			var bytes:ByteArray = decodeToByteArray(data);
			
			// Convert to string and return
			return bytes.readUTFBytes(bytes.length);
		}
		
		public static function decodeToByteArray(data:String):ByteArray {
			// Initialise output ByteArray for decoded data
			var output:ByteArray = new ByteArray();
			
			// Create data and output buffers
			var dataBuffer:Array = new Array(4);
			var outputBuffer:Array = new Array(3);

			// While there are data bytes left to be processed
			for (var i:uint = 0; i < data.length; i += 4) {
				// Populate data buffer with position of Base64 characters for
				// next 4 bytes from encoded data
				for (var j:uint = 0; j < 4 && i + j < data.length; j++) {
					dataBuffer[j] = BASE64_CHARS.indexOf(data.charAt(i + j));
				}
      			
      			// Decode data buffer back into bytes
				outputBuffer[0] = (dataBuffer[0] << 2) + ((dataBuffer[1] & 0x30) >> 4);
				outputBuffer[1] = ((dataBuffer[1] & 0x0f) << 4) + ((dataBuffer[2] & 0x3c) >> 2);		
				outputBuffer[2] = ((dataBuffer[2] & 0x03) << 6) + dataBuffer[3];
				
				// Add all non-padded bytes in output buffer to decoded data
				for (var k:uint = 0; k < outputBuffer.length; k++) {
					if (dataBuffer[k+1] == 64) break;
					output.writeByte(outputBuffer[k]);
				}
			}
			
			// Rewind decoded data ByteArray
			output.position = 0;
			
			// Return decoded data
			return output;
		}
		
		public function Base64() {
			throw new Error("Base64 class is static container only");
		}
	}

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