LibTextCodec+LibURL: Implement utf-8 and euc-jp encoders

Implements the corresponding encoders, selects the appropriate one when
encoding URL search params. If an encoder for the given encoding could
not be found, fallback to utf-8.

Userland/Libraries/LibTextCodec/Encoder.cpp

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2024, Ben Jilks <benjyjilks@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Error.h>
+#include <AK/Utf8View.h>
+#include <LibTextCodec/Decoder.h>
+#include <LibTextCodec/Encoder.h>
+#include <LibTextCodec/LookupTables.h>
+
+namespace TextCodec {
+
+namespace {
+UTF8Encoder s_utf8_encoder;
+EUCJPEncoder s_euc_jp_encoder;
+}
+
+Optional<Encoder&> encoder_for_exact_name(StringView encoding)
+{
+    if (encoding.equals_ignoring_ascii_case("utf-8"sv))
+        return s_utf8_encoder;
+    if (encoding.equals_ignoring_ascii_case("euc-jp"sv))
+        return s_euc_jp_encoder;
+    dbgln("TextCodec: No encoder implemented for encoding '{}'", encoding);
+    return {};
+}
+
+Optional<Encoder&> encoder_for(StringView label)
+{
+    auto encoding = get_standardized_encoding(label);
+    return encoding.has_value() ? encoder_for_exact_name(encoding.value()) : Optional<Encoder&> {};
+}
+
+// https://encoding.spec.whatwg.org/#utf-8-encoder
+ErrorOr<void> UTF8Encoder::process(Utf8View input, Function<ErrorOr<void>(u8)> on_byte)
+{
+    ReadonlyBytes bytes { input.bytes(), input.byte_length() };
+    for (auto byte : bytes)
+        TRY(on_byte(byte));
+    return {};
+}
+
+// https://encoding.spec.whatwg.org/#euc-jp-encoder
+ErrorOr<void> EUCJPEncoder::process(Utf8View input, Function<ErrorOr<void>(u8)> on_byte)
+{
+    for (auto item : input) {
+        // 1. If code point is end-of-queue, return finished.
+
+        // 2. If code point is an ASCII code point, return a byte whose value is code point.
+        if (is_ascii(item)) {
+            TRY(on_byte(static_cast<u8>(item)));
+            continue;
+        }
+
+        // 3. If code point is U+00A5, return byte 0x5C.
+        if (item == 0x00A5) {
+            TRY(on_byte(static_cast<u8>(0x5C)));
+            continue;
+        }
+
+        // 4. If code point is U+203E, return byte 0x7E.
+        if (item == 0x203E) {
+            TRY(on_byte(static_cast<u8>(0x7E)));
+            continue;
+        }
+
+        // 5. If code point is in the range U+FF61 to U+FF9F, inclusive, return two bytes whose values are 0x8E and code point − 0xFF61 + 0xA1.
+        if (item >= 0xFF61 && item <= 0xFF9F) {
+            TRY(on_byte(0x8E));
+            TRY(on_byte(static_cast<u8>(item - 0xFF61 + 0xA1)));
+            continue;
+        }
+
+        // 6. If code point is U+2212, set it to U+FF0D.
+        if (item == 0x2212)
+            item = 0xFF0D;
+
+        // 7. Let pointer be the index pointer for code point in index jis0208.
+        auto pointer = code_point_jis0208_index(item);
+
+        // 8. If pointer is null, return error with code point.
+        if (!pointer.has_value()) {
+            // TODO: Report error.
+            continue;
+        }
+
+        // 9. Let lead be pointer / 94 + 0xA1.
+        auto lead = *pointer / 94 + 0xA1;
+
+        // 10. Let trail be pointer % 94 + 0xA1.
+        auto trail = *pointer % 94 + 0xA1;
+
+        // 11. Return two bytes whose values are lead and trail.
+        TRY(on_byte(static_cast<u8>(lead)));
+        TRY(on_byte(static_cast<u8>(trail)));
+    }
+
+    return {};
+}
+
+}