AK: Add a simple and inefficient Base64 encoder

The test cases are taken from RFC 4648.

AK/Base64.cpp

@@ -84,4 +84,44 @@ ByteBuffer decode_base64(const StringView& input)
     return ByteBuffer::copy(output.data(), output.size());
 }
 
+ByteBuffer encode_base64(const StringView& input)
+{
+    Vector<u8> output;
+
+    auto get = [&](size_t offset, bool* need_padding = nullptr) -> u8 {
+        if (offset >= input.length()) {
+            if (need_padding)
+                *need_padding = true;
+            return 0;
+        }
+        return (u8)input[offset];
+    };
+
+    for (size_t i = 0; i < input.length(); i += 3) {
+        bool is_8bit = false;
+        bool is_16bit = false;
+
+        u8 in0 = get(i);
+        u8 in1 = get(i + 1, &is_16bit);
+        u8 in2 = get(i + 2, &is_8bit);
+
+        u8 index0 = (in0 >> 2) & 0x3f;
+        u8 index1 = ((in0 << 4) | (in1 >> 4)) & 0x3f;
+        u8 index2 = ((in1 << 2) | (in2 >> 6)) & 0x3f;
+        u8 index3 = in2 & 0x3f;
+
+        u8 out0 = s_alphabet[index0];
+        u8 out1 = s_alphabet[index1];
+        u8 out2 = is_16bit ? '=' : s_alphabet[index2];
+        u8 out3 = is_8bit ? '=' : s_alphabet[index3];
+
+        output.append(out0);
+        output.append(out1);
+        output.append(out2);
+        output.append(out3);
+    }
+
+    return ByteBuffer::copy(output.data(), output.size());
+}
+
 }

AK/Base64.h

@@ -32,6 +32,9 @@ namespace AK {
 
 ByteBuffer decode_base64(const StringView&);
 
+ByteBuffer encode_base64(const StringView&);
+
 }
 
 using AK::decode_base64;
+using AK::encode_base64;

AK/Tests/TestBase64.cpp

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2020, Tom Lebreux <tomlebreux@hotmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/TestSuite.h>
+
+#include <AK/Base64.h>
+#include <AK/ByteBuffer.h>
+#include <AK/String.h>
+
+TEST_CASE(test_encode)
+{
+    auto encode_equal = [&](const char* input, const char* expected) {
+        auto encoded = encode_base64(StringView(input));
+        EXPECT(String::copy(encoded) == String(expected));
+    };
+
+    encode_equal("", "");
+    encode_equal("f", "Zg==");
+    encode_equal("fo", "Zm8=");
+    encode_equal("foo", "Zm9v");
+    encode_equal("foob", "Zm9vYg==");
+    encode_equal("fooba", "Zm9vYmE=");
+    encode_equal("foobar", "Zm9vYmFy");
+}
+
+TEST_MAIN(Base64)