PHP getprotobynumber Function

last modified April 4, 2025

The PHP getprotobynumber function looks up protocol names by number. It’s useful for network programming and protocol analysis.

Basic Definition

getprotobynumber returns the protocol name associated with a number. It checks the system’s protocol database (/etc/protocols on Unix-like systems).

Syntax: getprotobynumber(int $number): string|false. Returns protocol name or false if not found. Requires network support.

Basic Protocol Lookup

This example demonstrates looking up a protocol name by its standard number.

basic_lookup.php

<?php

declare(strict_types=1);

$protocolNumber = 6; $protocolName = getprotobynumber($protocolNumber);

if ($protocolName !== false) { echo “Protocol number $protocolNumber is $protocolName”; } else { echo “Protocol number $protocolNumber not found”; }

This looks up protocol number 6, which is TCP. The function returns the name if found in the system’s protocol database.

Checking Common Protocols

This example checks several common protocol numbers and displays their names.

common_protocols.php

<?php

declare(strict_types=1);

$protocols = [ 1 => “ICMP”, 6 => “TCP”, 17 => “UDP”, 58 => “ICMPv6” ];

foreach ($protocols as $number => $expected) { $name = getprotobynumber($number); echo “$number: " . ($name === $expected ? “OK” : “Mismatch”) . “\n”; }

This verifies standard protocol numbers against expected names. It’s useful for validating system protocol database contents.

Handling Unknown Protocols

This example shows how to handle cases where a protocol number isn’t recognized.

unknown_protocol.php

<?php

declare(strict_types=1);

$unknownNumber = 255; $protocolName = getprotobynumber($unknownNumber);

if ($protocolName === false) { echo “Protocol number $unknownNumber is unknown”; } else { echo “Protocol number $unknownNumber is $protocolName”; }

The function returns false for unknown protocol numbers. This example demonstrates proper error handling for such cases.

Protocol Analysis Function

This shows a complete function for analyzing protocol numbers in network data.

protocol_analyzer.php

<?php

declare(strict_types=1);

function analyzeProtocol(int $number): string { $name = getprotobynumber($number);

if ($name === false) {
    return "Unknown protocol ($number)";
}

return "$name ($number)";

}

echo analyzeProtocol(17); // UDP echo “\n”; echo analyzeProtocol(99); // Unknown

This function provides a standardized way to display protocol information. It handles both known and unknown protocol numbers gracefully.

Building a Protocol Reference

This example builds a reference table of protocol numbers and names.

protocol_reference.php

<?php

declare(strict_types=1);

$protocolNumbers = range(0, 30); echo “Protocol Number Reference:\n”;

foreach ($protocolNumbers as $number) { $name = getprotobynumber($number); echo sprintf("%3d: %s\n”, $number, $name ?? “Not assigned”); }

This generates a reference table for protocol numbers 0 through 30. It shows how to systematically examine protocol number assignments.

Best Practices

• Error Handling: Always check for false return values

• Caching: Cache results if repeatedly looking up same numbers

• Validation: Validate protocol numbers before lookup

• Documentation: Refer to IANA protocol number assignments

Source

PHP getprotobynumber Documentation

This tutorial covered the PHP getprotobynumber function with practical examples for protocol number lookups in network programming.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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