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cURL is a very common and powerful tool when performing network data transfers in PHP. Whether uploading files to a remote server or downloading files from a remote server, cURL offers flexible control. In some scenarios, such as temporarily interrupting the network, waiting for certain verification mechanisms to complete, or responding to specific security events, we may want to pause file uploads or downloads. PHP's curl_pause() function provides this capability.
The curl_pause() function is used to temporarily pause or resume the upload or download data flow during a cURL session. This is useful for controlling the data transfer process, saving resources, and responding to asynchronous events.
The function is defined as follows:
curl_pause(CurlHandle $handle, int $bitmask): int
Here, $handle is the cURL session resource, and $bitmask is the control flag for pausing/resuming.
Common $bitmask constants include:
CURLPAUSE_RECV: Pauses receiving (downloading) data
CURLPAUSE_SEND: Pauses sending (uploading) data
CURLPAUSE_ALL: Pauses both uploading and downloading
CURLPAUSE_CONT: Resumes uploading and downloading
The following example demonstrates how to pause a download during the process and resume it after a certain time.
<?php
$ch = curl_init();
<p>// Set the URL of the file to be downloaded<br>
curl_setopt($ch, CURLOPT_URL, "<a rel="noopener" target="_new" class="" href="https://m66.net/files/testfile.zip">https://m66.net/files/testfile.zip</a>");<br>
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);</p>
<p>// Set the callback function for receiving data<br>
curl_setopt($ch, CURLOPT_WRITEFUNCTION, function ($ch, $data) {<br>
static $totalReceived = 0;</p>
echo "Received " . $totalReceived . " bytes\n";
if ($totalReceived > 1024 * 100) { // Pause after receiving more than 100KB
echo "Pausing download...\n";
curl_pause($ch, CURLPAUSE_RECV);
sleep(5); // Simulate waiting for security verification or event response
echo "Resuming download...\n";
curl_pause($ch, CURLPAUSE_CONT);
}
return strlen($data);
});
curl_exec($ch);
curl_close($ch);
?>
In this example, we use CURLOPT_WRITEFUNCTION to customize the data receiving logic. After the cumulative download exceeds 100KB, we call curl_pause($ch, CURLPAUSE_RECV) to pause receiving, and after a 5-second delay, we resume using curl_pause($ch, CURLPAUSE_CONT).
If we upload a file using POST, we can also pause the upload at a certain point, just like in the previous example.
<?php
$ch = curl_init();
<p>curl_setopt($ch, CURLOPT_URL, "<a rel="noopener" target="_new" class="" href="https://m66.net/upload">https://m66.net/upload</a>");<br>
curl_setopt($ch, CURLOPT_POST, true);</p>
<p>// Open the file and set the upload field<br>
$file = fopen("testfile.zip", "r");<br>
curl_setopt($ch, CURLOPT_INFILE, $file);<br>
curl_setopt($ch, CURLOPT_INFILESIZE, filesize("testfile.zip"));</p>
<p>// Set the callback function for uploading data<br>
curl_setopt($ch, CURLOPT_READFUNCTION, function ($ch, $fd, $length) {<br>
static $uploaded = 0;<br>
$chunk = fread($fd, $length);<br>
$uploaded += strlen($chunk);</p>
echo "Pausing upload...\n";
curl_pause($ch, CURLPAUSE_SEND);
sleep(3); // Simulate a delay for security mechanisms or authentication
echo "Resuming upload...\n";
curl_pause($ch, CURLPAUSE_CONT);
}
return $chunk;
});
curl_exec($ch);
fclose($file);
curl_close($ch);
?>
This example demonstrates the ability to dynamically control the upload progress during the file upload process. After a certain amount of data is uploaded, the upload is temporarily interrupted to allow for response time from a security mechanism or external system, before continuing the upload.
By combining the curl_pause() function, we can better manage the data transfer process securely:
With authentication processes: Pause the data flow before authentication results are returned to prevent unauthorized data transfers.
Handling abnormal traffic: Pause the data flow when abnormal behaviors or traffic patterns are detected to reduce resource wastage.
Progressive transmission: Break large files into chunks and pause, transmit, and verify each chunk to improve stability and fault tolerance.
curl_pause() provides finer control, which is especially important when building high-availability, controllable data transfer systems. By flexibly combining pausing and resuming operations, we can not only achieve safer transmission control but also optimize resource usage and enhance system robustness. Mastering this feature allows PHP programs to handle various challenges more smoothly in complex network environments.
