pack() in php. Illegal hex digit warning

问题

i am having some problems using pack() in php

$currencypair = "EUR/USD";
$buy_sell = "buy";
$alert_device_token =array("a","a","b");
$message = "Your " . $currencypair . " " . $buy_sell . " alert price has been reached!";
$payload['aps'] = array (
  'alert' => $message,
  'badge' => 1,
  'sound' => 'default'
);
$payload = json_encode($payload);

foreach ($alert_device_token as $alert_device)
{
  $apnsMessage = chr(0) . chr(0) . chr(32) . 
                 pack('H*', str_replace(' ', '', $alert_device)) . 
                 chr(0) . chr(strlen($payload)) . $payload;
  echo $apnsMessage;
}

Now sometimes i get following warnings running the same code -

Warning: pack() [function.pack]: Type H: illegal hex digit g in /code/FR2BVl

the illegal hex digit keeps varying though. Any ideas about this warning and ways to remove it.

check it live here

回答1:

pack converts hexadecimal number to binary, e.g.:

  echo pack("H*", "2133")

produces !3, since ! has code 0x21 and 3 has code 0x33. Since g is not hex digit, warning is given. To be useful for pack's H format, the argument must be hex number. If $alert_device isn't - you should use something else, depending on what it is and what you expect as the result.

回答2:

One of the reason for the error is related to the checksums,

Because PHP's integer type is signed many crc32 checksums will result in negative integers on 32bit platforms. On 64bit installations all crc32() results will be positive integers though. So you need to use the "%u" formatter of sprintf() or printf() to get the string representation of the unsigned crc32() checksum in decimal format. http://www.php.net/crc32

To fix the error this might be sufficient,

sprintf('%u', CRC32($someString))

In this case,

pack('H*', str_replace(' ', '', sprintf('%u', CRC32($alert_device))))

Ref: https://github.com/bearsunday/BEAR.Package/issues/136

回答3:

I was having the same issue when developing a hybrid app using Ionic/Cordova/PhoneGap. As the same code is run in Android and iOS devices, I had made a mistake of storing Google FCM token as APNS token. The APNS token is purely hexadecimal but Google FCM token can have non-hexadecimal characters. So, packing a Google FCM token using PHP's pack() function will result in the illegal hex digit error.

回答4:

Use strtr(rtrim(base64_encode(pack('H*', sprintf('%u', $algo($data)))), '='), '+/', '-_') insted of using pack('H*', $value).

回答5:

In this case, $alert_device is an array.

For packing it needs a value.

Use pack('H*', str_replace(' ', '', $alert_device[0])) instead.

回答6:

You must change

pack('H*', $someString)

strtr(rtrim(base64_encode(pack('H*', sprintf('%u', CRC32($someString))))

回答7:

Try to save your file in utf-8 encoding.

来源：https://stackoverflow.com/questions/4732681/pack-in-php-illegal-hex-digit-warning

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