我可以尝试/捕捉警告吗？

Question

I need to catch some warnings being thrown from some php native functions and then handle them.

Specifically:

array dns_get_record  ( string $hostname  [, int $type= DNS_ANY  [, array &$authns  [, array &$addtl  ]]] )

It throws a warning when the DNS query fails.

try / catch doesn't work because a warning is not an exception.

I now have 2 options:

1. set_error_handler seems like overkill because I have to use it to filter every warning in the page (is this true?);

2. Adjust error reporting/display so these warnings don't get echoed to screen, then check the return value; if it's false , no records is found for hostname.

What's the best practice here?

Answer 1

Set and restore error handler

One possibility is to set your own error handler before the call and restore the previous error handler later with restore_error_handler() .

set_error_handler(function() { /* ignore errors */ });
dns_get_record();
restore_error_handler();

You could build on this idea and write a re-usable error handler that logs the errors for you.

set_error_handler([$logger, 'onSilencedError']);
dns_get_record();
restore_error_handler();

Turning errors into exceptions

You can use set_error_handler() and the ErrorException class to turn all php errors into exceptions.

set_error_handler(function($errno, $errstr, $errfile, $errline) {
    // error was suppressed with the @-operator
    if (0 === error_reporting()) {
        return false;
    }
    
    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
});

try {
    dns_get_record();
} catch (ErrorException $e) {
    // ...
}

The important thing to note when using your own error handler is that it will bypass the error_reporting setting and pass all errors (notices, warnings, etc.) to your error handler. You can set a second argument on set_error_handler() to define which error types you want to receive, or access the current setting using ... = error_reporting() inside the error handler.

Suppressing the warning

Another possibility is to suppress the call with the @ operator and check the return value of dns_get_record() afterwards. But I'd advise against this as errors/warnings are triggered to be handled, not to be suppressed.

Answer 2

The solution that really works turned out to be setting simple error handler with E_WARNING parameter, like so:

set_error_handler("warning_handler", E_WARNING);
dns_get_record(...)
restore_error_handler();

function warning_handler($errno, $errstr) { 
// do something
}

Answer 3

Be careful with the @ operator - while it suppresses warnings it also suppresses fatal errors. I spent a lot of time debugging a problem in a system where someone had written @mysql_query( '...' ) and the problem was that mysql support was not loaded into PHP and it threw a silent fatal error. It will be safe for those things that are part of the PHP core but please use it with care.

bob@mypc:~$ php -a
Interactive shell

php > echo @something(); // this will just silently die...

No further output - good luck debugging this!

bob@mypc:~$ php -a
Interactive shell

php > echo something(); // lets try it again but don't suppress the error
PHP Fatal error:  Call to undefined function something() in php shell code on line 1
PHP Stack trace:
PHP   1. {main}() php shell code:0
bob@mypc:~$ 

This time we can see why it failed.

Answer 4

I wanted to try/catch a warning, but at the same time keep the usual warning/error logging (eg in /var/log/apache2/error.log ); for which the handler has to return false . However, since the "throw new..." statement basically interrupts the execution, one then has to do the "wrap in function" trick, also discussed in:

Is there a static way to throw exception in php

Or, in brief:

  function throwErrorException($errstr = null,$code = null, $errno = null, $errfile = null, $errline = null) {
    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
  }
  function warning_handler($errno, $errstr, $errfile, $errline, array $errcontext) {
    return false && throwErrorException($errstr, 0, $errno, $errfile, $errline);
    # error_log("AAA"); # will never run after throw
    /* Do execute PHP internal error handler */
    # return false; # will never run after throw
  }
  ...
  set_error_handler('warning_handler', E_WARNING);
  ...
  try {
    mkdir($path, 0777, true);
  } catch (Exception $e) {
    echo $e->getMessage();
    // ...
  }

---

EDIT: after closer inspection, it turns out it doesn't work: the " return false && throwErrorException ... " will, basically, not throw the exception, and just log in the error log; removing the " false && " part, as in " return throwErrorException ... ", will make the exception throwing work, but will then not log in the error_log... I'd still keep this posted, though, as I haven't seen this behavior documented elsewhere.

Answer 5

Combining these lines of code around a file_get_contents() call to an external url helped me handle warnings like " failed to open stream: Connection timed out " much better:

set_error_handler(function ($err_severity, $err_msg, $err_file, $err_line, array $err_context)
{
    throw new ErrorException( $err_msg, 0, $err_severity, $err_file, $err_line );
}, E_WARNING);
try {
    $iResult = file_get_contents($sUrl);
} catch (Exception $e) {
    $this->sErrorMsg = $e->getMessage();
}
restore_error_handler();

This solution works within object context, too. You could use it in a function:

public function myContentGetter($sUrl)
{
  ... code above ...
  return $iResult;
}

Answer 6

Normaly you should never use @ unless this is the only solution. In that specific case the function dns_check_record should be use first to know if the record exists.

Answer 7

您可能应该尝试完全摆脱警告，但如果这不可能，您可以在调用前加上@（即@dns_get_record(...)），然后使用您可以获得的任何信息来确定警告是否发生或不。

Answer 8

如果dns_get_record()失败，它应该返回FALSE ，因此您可以使用@抑制警告，然后检查返回值。

Answer 9

try checking whether it returns some boolean value then you can simply put it as a condition. I encountered this with the oci_execute(...) which was returning some violation with my unique keys.

ex.
oci_parse($res, "[oracle pl/sql]");
if(oci_execute){
...do something
}

Answer 10

As of PHP8, you can do the following instead of setting error handlers to catch Errors and Warnings. I Believe in PHP 7.something you could catch some Errors.

try {
    call_user_func('sprintf', array_merge([$string], $args));
} catch (Throwable $e) {
    $logger->info('mesage...');
}

You should generally be somewhere that you can pass or access a logger if you bulkhead in this way, as it can obfuscate coder errors, such as passing incorrectly typed parameters to a method, and mask a variety of other problems.

https://php.watch/versions/8.0/internal-function-exceptions

Not sure if notices are caught (likely not), but you can likely solve around examples like this one, by thinking a little more about what you are looking to do.

Both builder pattern, and options patterns provide solutions for this where prior to the site of call, which can be a private function or just after validity checks, you can throw a real custom exception that is attributable only to your code. That will make even built-in functions very safe to use.

One other nice practice is to use either debug_backtrace , with DEBUG_BACKTRACE_IGNORE_ARGS or use the getTrace or getTraceAsString methods on the Throwable so that some of the context is preseved.

Answer 11

FolderStructure

index.php //Script File
logs //Folder for log Every warning and Errors
CustomException.php //Custom exception File

CustomException.php

/**
* Custom error handler
*/
function handleError($code, $description, $file = null, $line = null, $context = null) {
    $displayErrors = ini_get("display_errors");;
    $displayErrors = strtolower($displayErrors);
    if (error_reporting() === 0 || $displayErrors === "on") {
        return false;
    }
    list($error, $log) = mapErrorCode($code);
    $data = array(
        'timestamp' => date("Y-m-d H:i:s:u", time()),
        'level' => $log,
        'code' => $code,
        'type' => $error,
        'description' => $description,
        'file' => $file,
        'line' => $line,
        'context' => $context,
        'path' => $file,
        'message' => $error . ' (' . $code . '): ' . $description . ' in [' . $file . ', line ' . $line . ']'
    );
    $data = array_map('htmlentities',$data);
    return fileLog(json_encode($data));
}

/**
* This method is used to write data in file
* @param mixed $logData
* @param string $fileName
* @return boolean
*/
function fileLog($logData, $fileName = ERROR_LOG_FILE) {
    $fh = fopen($fileName, 'a+');
    if (is_array($logData)) {
        $logData = print_r($logData, 1);
    }
    $status = fwrite($fh, $logData . "\n");
    fclose($fh);
//    $file = file_get_contents($filename);
//    $content = '[' . $file .']';
//    file_put_contents($content); 
    return ($status) ? true : false;
}

/**
* Map an error code into an Error word, and log location.
*
* @param int $code Error code to map
* @return array Array of error word, and log location.
*/
function mapErrorCode($code) {
    $error = $log = null;
    switch ($code) {
        case E_PARSE:
        case E_ERROR:
        case E_CORE_ERROR:
        case E_COMPILE_ERROR:
        case E_USER_ERROR:
            $error = 'Fatal Error';
            $log = LOG_ERR;
            break;
        case E_WARNING:
        case E_USER_WARNING:
        case E_COMPILE_WARNING:
        case E_RECOVERABLE_ERROR:
            $error = 'Warning';
            $log = LOG_WARNING;
            break;
        case E_NOTICE:
        case E_USER_NOTICE:
            $error = 'Notice';
            $log = LOG_NOTICE;
            break;
        case E_STRICT:
            $error = 'Strict';
            $log = LOG_NOTICE;
            break;
        case E_DEPRECATED:
        case E_USER_DEPRECATED:
            $error = 'Deprecated';
            $log = LOG_NOTICE;
            break;
        default :
            break;
    }
    return array($error, $log);
}
//calling custom error handler
set_error_handler("handleError");

just include above file into your script file like this

index.php

error_reporting(E_ALL);
ini_set('display_errors', 'off');
define('ERROR_LOG_FILE', 'logs/app_errors.log');

include_once 'CustomException.php';
echo $a; // here undefined variable warning will be logged into logs/app_errors.log

Answer 12

Since PHP7 you can catch most errors and warnings like so:

try {
    whatever();
} catch (Throwable $e) {
}

More: https://www.php.net/manual/en/language.errors.php7.php

Answer 13

I would only recommend using @ to suppress warnings when it's a straight forward operation (eg $prop = @($high/($width - $depth)); to skip division by zero warnings). However in most cases it's better to handle.