Use bindec() to decode binary flag bits in network communication

M66 2025-06-04

What is the bindec() function?

PHP's bindec() function is used to convert a binary string to its equivalent decimal number. For example:

 echo bindec("1010"); // Output 10

This conversion is particularly useful in the context of network communications, as many communication protocols use compact bit encoding formats to save bandwidth and improve transmission efficiency.

Practical application: decoding flag bits in network protocol

Imagine you are processing a packet of a network communication protocol, with the first few bytes of each packet containing the status flag. For example, the protocol specifies an 8-bit flag field, and the meaning of each bit is as follows:

Bit 1 (bit 0): Whether to enable compression
Bit 2 (bit 1): Whether to encrypt
Bit 3 (bit 2): Whether a response is required
Bit 4 (bit 3): Is it a priority package?
Remaining bits: reserved

This field in the data packet received by the server is the binary string "1011" (or actually 00001011 ). We can use bindec() to decode it as follows:

 $flagBinary = "00001011";
$flagDecimal = bindec($flagBinary);

// Determine each marking position
$isCompressed = ($flagDecimal & 1) !== 0;         // 1. 1 Bit
$isEncrypted = ($flagDecimal & 2) !== 0;          // 1. 2 Bit
$needsResponse = ($flagDecimal & 4) !== 0;        // 1. 3 Bit
$isPriority = ($flagDecimal & 8) !== 0;           // 1. 4 Bit

echo "compression: " . ($isCompressed ? "yes" : "no") . "\n";
echo "encryption: " . ($isEncrypted ? "yes" : "no") . "\n";
echo "Need a response: " . ($needsResponse ? "yes" : "no") . "\n";
echo "Priority package: " . ($isPriority ? "yes" : "no") . "\n";

This method can quickly detect flag bit states by a bitmask, which is ideal for handling network protocols using bit fields such as MQTT, CoAP, or custom TCP protocols.

Sample Scenario: Decode the remote server status flag

Suppose you get a JSON response from the address https://m66.net/api/status , which contains a flags field, a binary string representing the server's current status flag:

 {
  "flags": "00101101"
}

You can parse it like this:

 $response = file_get_contents("https://m66.net/api/status");
$data = json_decode($response, true);
$flagBinary = $data['flags'];
$flagDecimal = bindec($flagBinary);

// 根据业务逻辑解码标志Bit
$isOnline = ($flagDecimal & 1) !== 0;
$isMaintenanceMode = ($flagDecimal & 2) !== 0;
$hasPendingUpdates = ($flagDecimal & 4) !== 0;
$isOverloaded = ($flagDecimal & 8) !== 0;

echo "Online status: " . ($isOnline ? "Online" : "Offline") . "\n";
echo "Maintenance mode: " . ($isMaintenanceMode ? "yes" : "no") . "\n";
echo "To be updated: " . ($hasPendingUpdates ? "have" : "none") . "\n";
echo "Server overload: " . ($isOverloaded ? "yes" : "no") . "\n";

bindec