Implement Base64

mirai-core-utils/src/nativeMain/kotlin/Base64.kt

@@ -9,10 +9,107 @@
 
 package net.mamoe.mirai.utils
 
+import io.ktor.utils.io.core.*
+
 actual fun String.decodeBase64(): ByteArray {
-    TODO("Not yet implemented")
+    return Base64Impl.decode(this)
 }
 
 actual fun ByteArray.encodeBase64(): String {
-    TODO("Not yet implemented")
+    return Base64Impl.encode(this)
+}
+
+/**
+ * From <https://gist.github.com/EmilHernvall/953733>.
+ * @author EmilHernvall
+ */
+private object Base64Impl {
+    fun encode(data: ByteArray): String {
+        val tbl = charArrayOf(
+            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
+            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
+            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
+            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
+        )
+        val buffer = StringBuilder()
+        var pad = 0
+        var i = 0
+        while (i < data.size) {
+            var b = data[i].toInt() and 0xFF shl 16 and 0xFFFFFF
+            if (i + 1 < data.size) {
+                b = b or (data[i + 1].toInt() and 0xFF shl 8)
+            } else {
+                pad++
+            }
+            if (i + 2 < data.size) {
+                b = b or (data[i + 2].toInt() and 0xFF)
+            } else {
+                pad++
+            }
+            for (j in 0 until 4 - pad) {
+                val c = b and 0xFC0000 shr 18
+                buffer.append(tbl[c])
+                b = b shl 6
+            }
+            i += 3
+        }
+        for (j in 0 until pad) {
+            buffer.append("=")
+        }
+        return buffer.toString()
+    }
+
+    fun decode(data: String): ByteArray {
+        val tbl = intArrayOf(
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54,
+            55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2,
+            3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
+            20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30,
+            31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
+            48, 49, 50, 51, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
+        )
+        val bytes: ByteArray = data.toByteArray()
+        return buildPacket {
+            var i = 0
+            while (i < bytes.size) {
+                var b: Int
+                b = if (tbl[bytes[i].toInt()] != -1) {
+                    tbl[bytes[i].toInt()] and 0xFF shl 18
+                } else {
+                    i++
+                    continue
+                }
+                var num = 0
+                if (i + 1 < bytes.size && tbl[bytes[i + 1].toInt()] != -1) {
+                    b = b or (tbl[bytes[i + 1].toInt()] and 0xFF shl 12)
+                    num++
+                }
+                if (i + 2 < bytes.size && tbl[bytes[i + 2].toInt()] != -1) {
+                    b = b or (tbl[bytes[i + 2].toInt()] and 0xFF shl 6)
+                    num++
+                }
+                if (i + 3 < bytes.size && tbl[bytes[i + 3].toInt()] != -1) {
+                    b = b or (tbl[bytes[i + 3].toInt()] and 0xFF)
+                    num++
+                }
+                while (num > 0) {
+                    val c = b and 0xFF0000 shr 16
+                    writeByte(c.toByte())
+                    b = b shl 8
+                    num--
+                }
+                i += 4
+            }
+        }.readBytes()
+    }
+
 }