AK: Add a simple and inefficient Base64 decoder

1 files changed, 87 insertions, 0 deletions

diff --git a/AK/Base64.cpp b/AK/Base64.cpp
new file mode 100644
index 0000000000..72016f6dfa
--- /dev/null
+++ b/AK/Base64.cpp
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * 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/ByteBuffer.h>
+#include <AK/StringView.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+
+namespace AK {
+
+static constexpr u8 s_alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+static u8 s_table[256] = {};
+static bool s_initialized = false;
+
+static void build_lookup_table_if_needed()
+{
+    if (s_initialized)
+        return;
+    for (size_t i = 0; i < sizeof(s_alphabet) - 1; ++i)
+        s_table[s_alphabet[i]] = i;
+    s_initialized = true;
+}
+
+ByteBuffer decode_base64(const StringView& input)
+{
+    build_lookup_table_if_needed();
+
+    auto get = [&](size_t offset, bool* is_padding = nullptr) -> u8 {
+        if (offset >= input.length())
+            return 0;
+        if (input[offset] == '=') {
+            if (is_padding)
+                *is_padding = true;
+            return 0;
+        }
+        return s_table[(u8)input[offset]];
+    };
+
+    Vector<u8> output;
+
+    for (size_t i = 0; i < input.length(); i += 4) {
+        bool in2_is_padding = false;
+        bool in3_is_padding = false;
+
+        u8 in0 = get(i);
+        u8 in1 = get(i + 1);
+        u8 in2 = get(i + 2, &in2_is_padding);
+        u8 in3 = get(i + 3, &in3_is_padding);
+
+        u8 out0 = (in0 << 2) | ((in1 >> 4) & 3);
+        u8 out1 = ((in1 & 0xf) << 4) | ((in2 >> 2) & 0xf);
+        u8 out2 = ((in2 & 0x3) << 6) | in3;
+
+        output.append(out0);
+        if (!in2_is_padding)
+            output.append(out1);
+        if (!in3_is_padding)
+            output.append(out2);
+    }
+
+    return ByteBuffer::copy(output.data(), output.size());
+}
+
+}