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+/*
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+ * Copyright (c) 2023, Valtteri Koskivuori <vkoskiv@gmail.com>
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+ *
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+ * SPDX-License-Identifier: BSD-2-Clause
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+ */
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+
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+#include "QuotedPrintable.h"
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+#include <AK/Base64.h>
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+#include <AK/GenericLexer.h>
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+#include <AK/StringBuilder.h>
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+#include <LibIMAP/MessageHeaderEncoding.h>
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+#include <LibTextCodec/Decoder.h>
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+
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+namespace IMAP {
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+
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+ErrorOr<ByteBuffer> decode_rfc2047_encoded_words(StringView input)
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+{
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+ GenericLexer lexer(input);
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+ StringBuilder output;
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+
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+ while (!lexer.is_eof()) {
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+ auto ascii_view = lexer.consume_until("=?"sv);
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+ DeprecatedString ascii = ascii_view.replace("\r"sv, " "sv, ReplaceMode::All);
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+ ascii = ascii.replace("\n"sv, " "sv, ReplaceMode::All);
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+ TRY(output.try_append(ascii));
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+ if (lexer.is_eof())
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+ break;
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+ lexer.consume_specific("=?"sv);
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+ auto charset = lexer.consume_until('?');
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+ lexer.consume();
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+ auto encoding = lexer.consume_until('?');
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+ lexer.consume();
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+ auto encoded_text = lexer.consume_until("?=");
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+ lexer.consume_specific("?="sv);
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+
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+ // RFC 2047 Section 6.2, "...any 'linear-white-space' that separates a pair of adjacent 'encoded-word's is ignored."
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+ // https://datatracker.ietf.org/doc/html/rfc2047#section-6.2
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+ bool found_next_start = false;
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+ int spaces = 0;
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+ for (size_t i = 0; i < lexer.tell_remaining(); ++i) {
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+ if (lexer.peek(i) == ' ' || lexer.peek(i) == '\r' || lexer.peek(i) == '\n') {
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+ spaces++;
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+ if (lexer.peek(i + 1) == '=' && lexer.peek(i + 2) == '?') {
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+ found_next_start = true;
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+ break;
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+ }
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+ } else {
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+ break;
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+ }
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+ }
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+ if (found_next_start) {
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+ for (int i = 0; i < spaces; i++) {
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+ lexer.consume();
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+ }
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+ }
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+
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+ ByteBuffer first_pass_decoded;
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+ if (encoding == 'Q' || encoding == 'q') {
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+ auto maybe_decoded_data = decode_quoted_printable(encoded_text);
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+ if (maybe_decoded_data.is_error()) {
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+ dbgln("Failed to decode quoted-printable rfc2047 text, skipping.");
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+ continue;
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+ }
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+ // RFC 2047 Section 4.2.2, https://datatracker.ietf.org/doc/html/rfc2047#section-4.2
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+ auto decoded_data = maybe_decoded_data.release_value();
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+ for (auto character : decoded_data.bytes()) {
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+ if (character == '_')
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+ first_pass_decoded.append(' ');
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+ else
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+ first_pass_decoded.append(character);
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+ }
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+ } else if (encoding == 'B' || encoding == 'b') {
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+ auto maybe_decoded_data = AK::decode_base64(encoded_text);
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+ if (maybe_decoded_data.is_error()) {
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+ dbgln("Failed to decode base64-encoded rfc2047 text, skipping.");
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+ continue;
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+ }
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+ first_pass_decoded = maybe_decoded_data.release_value();
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+ } else {
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+ dbgln("Unknown encoding \"{}\" found, skipping, original string: \"{}\"", encoding, input);
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+ continue;
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+ }
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+ if (first_pass_decoded.is_empty())
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+ continue;
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+ auto maybe_decoder = TextCodec::decoder_for(charset);
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+ if (!maybe_decoder.has_value()) {
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+ dbgln("No decoder found for charset \"{}\", skipping.", charset);
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+ continue;
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+ }
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+ auto decoded_text = TRY(maybe_decoder->to_utf8(first_pass_decoded));
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+ TRY(output.try_append(decoded_text));
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+ }
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+
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+ return output.to_byte_buffer();
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+}
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+
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+}
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