Differences in Using socket_clear_error Between UDP and TCP Sockets

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<p><?php<br>
// Main content: Differences in using socket_clear_error in UDP vs TCP sockets</p>
<p>/**</p>
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<p>Title: Differences in Using socket_clear_error Between UDP and TCP Sockets</p>
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<p>PHP provides the socket_clear_error() function to clear the error state on a given socket and return the error code before clearing.</p>
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<p>It is often used together with socket_last_error() for error handling and debugging.</p>
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<p>UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) differ significantly in their network communication models,</p>
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<p>so the usage scenarios and behavior of socket_clear_error() also differ.</p>
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<p>Characteristics of TCP sockets</p>
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<p>Connection-oriented: Requires establishing a connection before communication (three-way handshake).</p>
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<p>Reliable transmission: Lost packets are automatically retransmitted.</p>
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<p>Clear error feedback: Any send or receive error is usually reported immediately.</p>
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<p>For TCP sockets, if there is a write failure, connection interruption, or read timeout,</p>
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<p>socket_last_error() returns a specific error code. Using socket_clear_error() clears these error codes,</p>
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<p>providing a clean state for subsequent operations. Common uses include:</p>
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<p>Retrying after a connection exception</p>
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<p>Clearing socket state to avoid residual errors affecting the next communication</p>
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<p>Characteristics of UDP sockets</p>
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<p>Connectionless: No formal connection is established before sending data.</p>
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<p>Unreliable transmission: Packets may be lost or arrive out of order; the protocol does not guarantee delivery.</p>
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<p>Limited error feedback: In most cases, sending failures do not return specific errors immediately.</p>
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<p>For UDP sockets, even if sending fails (e.g., destination unreachable), many systems do not return an error immediately.</p>
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<p>Therefore, socket_last_error() often returns 0 or only in rare cases (such as local network interface errors) returns an error code.</p>
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<p>Calling socket_clear_error() on UDP sockets has limited effect and is mainly used to:</p>
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<p>Clear local socket state</p>
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<p>Ensure socket_last_error() returns a clean state for consistent error handling</p>
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<p>Usage examples<br>
*/</p>
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<p>$tcp_socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);<br>
$udp_socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);</p>
<p>// TCP connection example<br>
@socket_connect($tcp_socket, "127.0.0.1", 8080);<br>
$tcp_error_before = socket_last_error($tcp_socket);<br>
socket_clear_error($tcp_socket);<br>
$tcp_error_after = socket_last_error($tcp_socket);</p>
<p>// UDP send example<br>
@socket_sendto($udp_socket, "Test data", strlen("Test data"), 0, "127.0.0.1", 8081);<br>
$udp_error_before = socket_last_error($udp_socket);<br>
socket_clear_error($udp_socket);<br>
$udp_error_after = socket_last_error($udp_socket);</p>
<p>echo "TCP error code before clearing: $tcp_error_before, after clearing: $tcp_error_after\n";<br>
echo "UDP error code before clearing: $udp_error_before, after clearing: $udp_error_after\n";</p>
<p>/**</p>
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<p>Summary:</p>
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<p>TCP socket error states are usually directly related to connection reliability; socket_clear_error() effectively clears these errors.</p>
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<p>UDP socket error feedback is limited; socket_clear_error() mainly maintains a consistent error handling mechanism.</p>
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<p data-is-last-node="">In practical development, using socket_clear_error() for both TCP and UDP is meaningful, but its effect is more pronounced for TCP.<br>
*/<br>
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