LibIMAP: Add a new IMAP client and support NOOP

A large commit, but sets up the framework for how the IMAP library will
work. Right now only the NOOP command and response is supported.

Userland/Libraries/LibIMAP/Parser.cpp

@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2021, Kyle Pereira <hey@xylepereira.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/CharacterTypes.h>
+#include <LibIMAP/Parser.h>
+
+namespace IMAP {
+
+ParseStatus Parser::parse(ByteBuffer&& buffer, bool expecting_tag)
+{
+    if (m_incomplete) {
+        m_buffer += buffer;
+        m_incomplete = false;
+    } else {
+        m_buffer = move(buffer);
+        position = 0;
+        m_response = SolidResponse();
+    }
+
+    if (try_consume("+")) {
+        consume(" ");
+        auto data = parse_while([](u8 x) { return x != '\r'; });
+        consume("\r\n");
+        return { true, { ContinueRequest { data } } };
+    }
+
+    if (expecting_tag) {
+        if (at_end()) {
+            m_incomplete = true;
+            return { true, {} };
+        }
+        parse_response_done();
+    }
+
+    if (m_parsing_failed) {
+        return { false, {} };
+    } else {
+        return { true, { { move(m_response) } } };
+    }
+}
+
+bool Parser::try_consume(StringView x)
+{
+    size_t i = 0;
+    auto previous_position = position;
+    while (i < x.length() && !at_end() && to_ascii_lowercase(x[i]) == to_ascii_lowercase(m_buffer[position])) {
+        i++;
+        position++;
+    }
+    if (i != x.length()) {
+        // We didn't match the full string.
+        position = previous_position;
+        return false;
+    }
+
+    return true;
+}
+
+void Parser::parse_response_done()
+{
+    consume("A");
+    auto tag = parse_number();
+    consume(" ");
+
+    ResponseStatus status = parse_status();
+    consume(" ");
+
+    m_response.m_tag = tag;
+    m_response.m_status = status;
+
+    StringBuilder response_data;
+
+    while (!at_end() && m_buffer[position] != '\r') {
+        response_data.append((char)m_buffer[position]);
+        position += 1;
+    }
+
+    consume("\r\n");
+    m_response.m_response_text = response_data.build();
+}
+
+void Parser::consume(StringView x)
+{
+    if (!try_consume(x)) {
+        dbgln("{} not matched at {}, buffer: {}", x, position, StringView(m_buffer.data(), m_buffer.size()));
+
+        m_parsing_failed = true;
+    }
+}
+
+Optional<unsigned> Parser::try_parse_number()
+{
+    auto number_matched = 0;
+    while (!at_end() && 0 <= m_buffer[position] - '0' && m_buffer[position] - '0' <= 9) {
+        number_matched++;
+        position++;
+    }
+    if (number_matched == 0)
+        return {};
+
+    auto number = StringView(m_buffer.data() + position - number_matched, number_matched);
+
+    return number.to_uint();
+}
+
+unsigned Parser::parse_number()
+{
+    auto number = try_parse_number();
+    if (!number.has_value()) {
+        m_parsing_failed = true;
+        return -1;
+    }
+
+    return number.value();
+}
+
+StringView Parser::parse_atom()
+{
+    auto is_non_atom_char = [](u8 x) {
+        auto non_atom_chars = { '(', ')', '{', ' ', '%', '*', '"', '\\', ']' };
+        return AK::find(non_atom_chars.begin(), non_atom_chars.end(), x) != non_atom_chars.end();
+    };
+
+    auto start = position;
+    auto count = 0;
+    while (!at_end() && !is_ascii_control(m_buffer[position]) && !is_non_atom_char(m_buffer[position])) {
+        count++;
+        position++;
+    }
+
+    return StringView(m_buffer.data() + start, count);
+}
+
+ResponseStatus Parser::parse_status()
+{
+    auto atom = parse_atom();
+
+    if (atom.matches("OK")) {
+        return ResponseStatus::OK;
+    } else if (atom.matches("BAD")) {
+        return ResponseStatus::Bad;
+    } else if (atom.matches("NO")) {
+        return ResponseStatus::No;
+    }
+
+    m_parsing_failed = true;
+    return ResponseStatus::Bad;
+}
+
+StringView Parser::parse_while(Function<bool(u8)> should_consume)
+{
+    int chars = 0;
+    while (!at_end() && should_consume(m_buffer[position])) {
+        position++;
+        chars++;
+    }
+    return StringView(m_buffer.data() + position - chars, chars);
+}
+
+}