English
English
CURLOPT_RETURNTRANSFER is an option in the cURL library typically used to control how the response from a cURL request is returned. When this option is set to true, the result of the cURL request is not directly output to the browser or console but returned as a string. This enables developers to capture and further manipulate the response data through PHP code instead of having cURL output it directly.
Basic usage:
<span><span><span class="hljs-title function_ invoke__">curl_setopt</span></span><span>(</span><span><span class="hljs-variable">$ch</span></span><span>, CURLOPT_RETURNTRANSFER, </span><span><span class="hljs-literal">true</span></span><span>);
</span></span>When executing multiple cURL requests using curl_multi_exec, you generally need to set specific options for each request. You can use curl_multi_setopt to configure options for each cURL session, including CURLOPT_RETURNTRANSFER.
<span><span><span class="hljs-comment">// Initialize multiple cURL sessions</span></span>
</span><span><span class="hljs-variable">$ch1</span></span><span> = </span><span><span class="hljs-title function_ invoke__">curl_init</span></span><span>(</span><span>"http://example.com"</span></span><span>);
</span><span><span class="hljs-variable">$ch2</span></span><span> = </span><span><span class="hljs-title function_ invoke__">curl_init</span></span><span>(</span><span>"http://example.org"</span></span><span>);
<p></span>// Set options<br>
</span>curl_setopt($ch1, CURLOPT_RETURNTRANSFER, </span>true);<br>
curl_setopt($ch2, CURLOPT_RETURNTRANSFER, </span>true);</p>
<p>// Initialize multi cURL session<br>
</span>$mh = curl_multi_init();<br>
curl_multi_add_handle($mh, </span>$ch1);<br>
curl_multi_add_handle($mh, </span>$ch2);</p>
<p>// Execute requests<br>
</span>$running = </span>null;<br>
</span>do {<br>
curl_multi_exec($mh, </span>$running);<br>
} while ($running);</p>
<p>// Get results<br>
</span>$response1 = </span>curl_multi_getcontent($ch1);<br>
$response2 = </span>curl_multi_getcontent($ch2);</p>
<p>// Output results<br>
</span>echo $response1;<br>
</span>echo $response2;</p>
<p></span>// Close cURL sessions<br>
</span>curl_multi_remove_handle($mh, </span>$ch1);<br>
curl_multi_remove_handle($mh, </span>$ch2);<br>
curl_multi_close($mh);<br>
curl_close($ch1);<br>
curl_close($ch2);<br>
</span>In this example, we set CURLOPT_RETURNTRANSFER to true for each cURL session, making each request's response data returned as a string instead of directly outputting it to the browser or console. This way, you can collect the response content of each request when handling multiple requests.
CURLOPT_RETURNTRANSFER controls the output behavior of cURL requests:
Set to true: The returned content is delivered as a string, allowing developers to further process it (such as parsing, storing, or outputting). This is the recommended setting in most cases, especially when executing multiple requests where you need to handle each request's result.
Set to false: The cURL request will directly output the content to the browser or console. In this case, you cannot capture the response within your code. This setting is commonly used for simple GET requests or file downloads.
Each cURL handle must be set: When using curl_multi_setopt to handle multiple requests, every individual cURL handle must have CURLOPT_RETURNTRANSFER set. Even if some requests don’t need to return content, this option should still be set for them.
Handling response content: In multi-threaded requests, you typically need to retrieve each request’s response content using curl_multi_getcontent() after all requests have finished executing. Make sure to handle the returned results of each cURL session after completion.
Debugging: If some returned content from multi-threaded requests is unexpected, you can temporarily set CURLOPT_RETURNTRANSFER to false to check if the issue is caused by cURL configuration.
Fetching multiple API responses: By setting multiple API requests with curl_multi_setopt and executing them concurrently, efficiency can be greatly improved. Use CURLOPT_RETURNTRANSFER to capture each request’s response for further processing.
Batch file downloads: When downloading files in batches, you can use CURLOPT_RETURNTRANSFER to return file contents as strings or binary streams, avoiding direct output to the browser and facilitating subsequent save operations.
Web scraping: For crawler programs that need to fetch multiple webpages concurrently, CURLOPT_RETURNTRANSFER is a critical configuration. It helps capture the HTML content of each request for parsing and storage.
Properly setting the CURLOPT_RETURNTRANSFER parameter is essential for the smooth execution of multi-threaded cURL requests. By setting this parameter to true, you can effectively capture the response content of each request for further handling or storage in your program. When using curl_multi_setopt, ensure this option is correctly set for every cURL handle to enable efficient data processing.
In practical development, understanding and flexibly applying these options allows you to achieve better performance and control when dealing with concurrent requests.
