Pure PHP, basic IMAP implementation

imap.php

<?php

/*
 * Copyright (c) 2018, brian
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * * 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.
 */

require_once "$_SERVER[DOCUMENT_ROOT]/superheader.php";

class imap {

	private $Socket;
	public $Debug;
	public $Folder;
	public $Log = '';
	private $Passwords = [];
	private $ConnectionInformation;

	public function __construct(string $Host, int $Port, bool $SSL, string $Username, string $Password, string $Folder = null, bool $Debug = null) {
		$this->ConnectionInformation = func_get_args();
		$this->Debug = $this->Debug ?? $Debug ?? false;

		$this->Folder = $Folder;

		$HasSSL = strtolower(substr($Host, 0, 6)) === 'ssl://';
		if ($SSL && !$HasSSL) {
			$Host = "ssl://$Host";
		} else if (!$SSL && $HasSSL) {
			$Host = substr($Host, 6);
		}

		$this->Passwords[] = $Password;

		Retry(function() use($Host, $Port, $SSL, $Username, $Password, $Folder) {
			if (!($this->Socket = fsockopen($Host, $Port, $ErrorCode, $ErrorString, 60))) {
				throw new Exception("Failed to connect to the IMAP server {$ErrorString}", $ErrorCode);
			}
			if (!stream_set_timeout($this->Socket, 600)) {
				throw new Exception("Could not set IMAP timeout");
			}

			$this->LogEntry("Opened connection with $Host:$Port\n");

			$this->exec('LOGIN "' . addcslashes($Username, '\"') . '" "' . addcslashes($Password, '\"') . '"', null, false);
		}, 20, [$this, 'LogError'], null, [$this, 'close'], null, false);

		if (!strempty($Folder)) {
			$this->SelectFolder($Folder);
		}
	}

	public function SelectFolder(string $Folder): void {
		$this->Folder = $Folder;
		$this->exec('EXAMINE "' . addcslashes($Folder, '\"') . '"');
	}

	public function GetUIDs(string $Search = 'ALL'): array {
		return Retry(function() use($Search): array {
			$UIDs = null;
			$this->exec("UID SEARCH $Search", function($Line) use(&$UIDs) {
				if (!is_array($UIDs) && strtok($Line, $t = " \r\n") === '*' && strtok($t) === 'SEARCH') {
					$UIDs = [];
					while (($UID = strtok($t)) !== false) {
						$UID = (int) $UID;
						if ($UID !== 0) {
							$UIDs[] = (int) $UID;
						} else {
							throw new Exception('UID cannot be less than or equal to zero');
						}
					}
				}

				unset($Line);
				strtok('', '');
				return true;
			}, false);

			if (is_array($UIDs)) {
				return $UIDs;
			} else {
				throw new Exception('UID result is empty');
			}
		}, 3, [$this, 'LogError'], null, [$this, 'reconnect'], [$this, 'close'], false);
	}

	public function GetOverviews($UIDs = '1:*'): array {
		return Retry(function() use($UIDs): array {
			$Overviews = [];

			if (is_array_or_alike($UIDs)) {
				$UIDs = implode(',', array_map('trim', $UIDs));
			} else if (!can_be_string($UIDs)) {
				throw new Exception('UIDs must be type string or array');
			}

			if (strempty($UIDs)) {
				return [];
			}

			$Records = $this->ParseFetchResponse($this->exec("UID FETCH $UIDs ALL"));

			foreach ($Records as $Record) {
				if (!isset($Record['UID'])) {
					throw new Exception('UID missing from record');
				}
				$Overviews[$Record['UID']] = $Record;
			}

			return $Overviews;
		}, 3, [$this, 'LogError'], null, [$this, 'reconnect'], [$this, 'close'], false);
	}

	public function GetBodies($UIDs = '1:*'): array {
		return Retry(function() use($UIDs): array {
			$Bodies = [];

			if (is_array_or_alike($UIDs)) {
				$UIDs = implode(',', array_map('trim', $UIDs));
			} else if (!can_be_string($UIDs)) {
				throw new Exception('UIDs must be type string or array');
			}

			if (strempty($UIDs)) {
				return [];
			}

			$Records = $this->ParseFetchResponse($this->exec("UID FETCH $UIDs BODY.PEEK[]"));

			foreach ($Records as $Record) {
				if (!isset($Record['UID']) || !isset($Record['BODY[]'])) {
					throw new Exception('UID/Body missing from record');
				}
				$Bodies[$Record['UID']] = $Record['BODY[]'];
			}

			return $Bodies;
		}, 3, [$this, 'LogError'], null, [$this, 'reconnect'], [$this, 'close'], false);
	}

	public function exec(string $Command, callable $ProcessLine = null, bool $Retry = true): ?string {
		$Execute = function() use($Command, $ProcessLine): ?string {
			global $IMAP_EXEC_DISABLE_ENDLINE_CHECK;

			$IMAP_EXEC_DISABLE_ENDLINE_CHECK = $IMAP_EXEC_DISABLE_ENDLINE_CHECK ?? false;
			$Tag = strtoupper(bin2hex(bid2())) . ' ';
			$Length = strlen($Tag);
			$Response = '';
			$Skip = 0;
			$Success = false;
			$Command = "$Tag$Command\r\n";
			$this->LogEntry($Command);

			if (is_resource($this->Socket)) {
				fwrite($this->Socket, $Command);
				while ($Line = fgets($this->Socket)) {
					$this->LogEntry($Line);

					if ($Skip > 0) {
						$Skip--;
						continue;
					} else if ($Skip < 0) {
						$Skip = 0;
					}

					if (!$IMAP_EXEC_DISABLE_ENDLINE_CHECK && substr($Line, 0, $Length) === $Tag) {
						if (substr($Line, $Length, 3) === 'OK ') {
							$Success = true;
							break;
						} else {
							throw new Exception("IMAP command failed");
						}
					}

					if ($ProcessLine !== null) {
						$Returned = $ProcessLine($Line, $Response, $Skip);
						if ($Returned === true) {
							continue;
						} else if ($Returned === false) {
							break;
						}
					}

					$Response .= $Line;
				}
			}

			if (!$Success) {
				throw new Exception("IMAP unexpected end of response");
			}

			return $Response;
		};

		if ($Retry) {
			return Retry($Execute, 3, [$this, 'LogError'], null, [$this, 'reconnect'], [$this, 'close'], false);
		} else {
			return $Execute();
		}
	}

	public static function ParseFetchResponse(string $s): array {
		$c = str_split($s);
		$l = count($c);
		$Records = [];
		for ($i = 0; $i < $l; $i++) {
			if ($c === "\r" || $c === "\n") {
				continue;
			}

			$Line = substr($s, $i, min(strpos($s, "\r", $i + 1), strpos($s, "\n", $i + 1)) - $i);

			if (strtok($Line, $t = " \r\n") === '*' && ctype_digit(strtok($t)) && strtok($t) === 'FETCH') {
				$i += strpos($Line, '(') + 1;

				$Record = [];

				$Pointers[$d = 0] = &$Record;

				for (; $i < $l; $i++) {
					unset($t);

					switch (true) {
						case $c[$i] === '"':
							$b = $i++;
							while ($i < $l && $c[$i] !== '"') {
								if ($c[$i] === '\\') {
									$i++;
								}
								$i++;
							}
							$t = substr($s, $b, $i + 1 - $b);
							break;
						case $c[$i] === '{':
							$b = $i++;
							while ($i < $l && $s[$i] !== '}') {
								if (!ctype_digit($s[$i])) {
									throw new Exception("Unexpected character '$c[$i]' in size token");
								}
								$i++;
							}
							$Size = substr($s, $b + 1, $i++ - 1 - $b);
							$i++;

							if ($c[$i] === "\r" || $c[$i] === "\n") {
								$i++;
							}

							$t = substr($s, $i, $Size);
							$i += $Size - 1;

							break;
						case $c[$i] === '\\' || ctype_alnum($c[$i]):
							$b = $i++;
							while ($i < $l && (ctype_alnum($c[$i]) || $c[$i] === '.' || $c[$i] === '[' || $c[$i] === ']')) {
								$i++;
							}
							$t = substr($s, $b, $i-- - $b);
							break;
						case $c[$i] === '(':
							$Pointers[++$d] = &$Pointers[$d - 1][];
							break;
						case $c[$i] === ')':
							unset($Pointers[$d--]);
							break;
						case ctype_space($c[$i]):
							break;
						default:
							throw new Exception("IMAP fetch parse failed; unexpected '$c[$i]'");
					}

					if ($d < 0) {
						$Records[] = self::AssociateValues($Record);
						break;
					} else if (isset($t)) {
						if (substr($t, 0, 1) === '"') {
							$t = stripslashes(substr($t, 1, -1));
						} else if ($t === 'NIL') {
							$t = null;
						}
						$Pointers[$d][] = $t;
					}
				}
			} else {
				$i += strlen($Line);
			}
		}

		return $Records;
	}

	public static function AssociateValues(array $Array): array {
		if (($Count = count($Array)) & 1 === 1) {
			throw new Exception("Array must be even to associate its values\n\n" . DebugArray($Array, 2));
		}

		$NewArray = [];
		$ArrayKeys = array_keys($Array);

		for ($i = 0; $i < $Count - 1; $i += 2) {
			$NewArray[$Array[$ArrayKeys[$i]]] = $Array[$ArrayKeys[$i + 1]];
		}

		return $NewArray;
	}

	public function LogError(string $Message, int $Code): void {
		global $argv;
		LogAction('<h4>Request</h4><pre>' . DebugArray($_REQUEST ?? [], 3) . '</pre><h4>Arguments</h4><pre>' . DebugArray($argv ?? [], 3) . '</pre>' . nl2br(html("$Code: $Message\n\n")) . '<pre>' . html($this->Log) . '</pre>', 3, rtrim(strtok($Message, "\n")));
		exit();
	}

	public function LogEntry(string $Entry): void {
		$Entry = str_replace($this->Passwords, '***', $Entry);
		$this->Log .= $Entry;
		if ($this->Debug) {
			echo $Entry;
		}
	}

	public function reconnect(): void {
		$this->close();
		$this->ConnectionInformation = array_slice($this->ConnectionInformation, 0, 5);
		$this->ConnectionInformation[] = $this->Folder ?? null;
		$this->__construct(...$this->ConnectionInformation);
	}

	public function close(): void {
		if (is_resource($this->Socket)) {
			fclose($this->Socket);
			$this->LogEntry("Closed connection\n" . str_repeat('-', 80) . "\n");
		}
	}

}