A Beginner's Guide to PHP cURL Functions

cURL is a PHP library and a command-line tool that enables us to receive and transmit data utilizing URL syntax. It can transmit data in a wide range of forms, including HTTP posts, HTTP gets, FTP uploads and downloads, cookies, SOAP requests and responses, and so forth.

Engaging a web server with this  PHP extension may entail the most appropriate data which can be retrieved in the webpage database. An increasing proportion of the data included on webpages is acquired support from external sources, extensively across a Web application.

The data imparted by other internet services can be easily managed with cURL. Programmers can test their API requests and quickly receive performance results using cURL's versatile tool. Leveraging cURL's embedded libraries, you can also gather data from many other sites.

cURL has intuitive support for SSL, security management, certificate authentication, and HTTP cookie. It can be installed concurrently as a terminal framework or as a dynamic library (libcurl) which can be embedded across other applications.

Table Of Contents

1. The PHP cURL
2. Working of PHP cURL() extension
3. Basic PHP cURL Functions
4. Instances for PHP cURL
5. Multiple cURL requests in parallel
6. Additional Functions of PHP's cURL
7. Uses of PHP cURL function

The PHP cURL

Let's first look at what is cURL in PHP? The cURL library allows us to engage with other servers using a wide range of protocols. It empowers the user to transmit and receive data using URL syntax.  cURL may further improve security, send and receive cookies, import data to websites, and evaluate troubleshooting.

cURL strives as 'Client for URLs,' with "URL" transcribed in upper case letters to highlight how it interfaces with URLs. The PHP cURL model includes two options: libcurl and cURL. libcURL is a library that programmers can incorporate for a wide range of applications. cURL is a command-line data transmission tool.

cURL is a command-line feature for fetching and transmitting data through URL syntax. Since cURL is primarily focused on libcurl, it currently supports a wide range of frequently identified protocols, such as HTTP, HTTPS, FTP, FTPS, GOPHER, TELNET, DICT, and FILE.

The cURL library is employed to collaborate with most other servers using a range of protocols. And since cURL is intended to operate without user interaction, it can be employed in scripts or even cron jobs.

libcurl is a basic client-side URL transfer library that offers TTPS certificates, HTTP POST, HTTP PUT, FTP uploading, Kerberos, HTTP-based upload, proxies, cookies, user and password authentication,  HTTP proxy tunneling, and numerous other functionalities.

Working of PHP cURL() extension

In order to use PHP's cURL functions you need to install the libcurl package. cURL is enabled by default in PHP, but if not, you can enable it in your environment by following these steps:

1. Open the PHP configuration file php.ini.
2. Look for the line extension=php_curl.dll.
3. Remove the semicolon (;) from the beginning of the line.
4. Restart the Apache server.

To execute a basic PHP cURL request-response cycle, follow these steps:

i) Set up the cURL session

$curl = curl_init();

ii) The session can be configured with varied options

curl_setopt($handle, CURLOPT_URL, $url);

iii) Execution fetches/sends data from/to the server.

$response = curl_exec($handle);

iv) Terminate the session

curl_close($handle);

Here's a simple example of using cURL in PHP to make a GET request to a URL:

<?php
// Initialize cURL session
$curl = curl_init();

// Set the URL to be requested
curl_setopt($curl, CURLOPT_URL, "https://www.example.com");

// Return the response as a string instead of outputting it
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

// Execute the cURL request and get the response
$response = curl_exec($curl);

// Check if the cURL request was successful
if ($response === false) {
    echo "cURL Error: " . curl_error($curl);
} else {
    // Print the response
    echo $response;
}

// Close the cURL session
curl_close($curl);
?>

This example initializes a cURL session with curl_init(), sets the URL to be requested with curl_setopt($curl, CURLOPT_URL, "https://www.example.com"), tells cURL to return the response as a string with curl_setopt($curl, CURLOPT_RETURNTRANSFER, true), and executes the cURL request with curl_exec($curl).

The response is then checked for success, and if successful, printed. Finally, the cURL session is closed with curl_close($curl).

Basic PHP cURL Functions

Instances for PHP cURL

Here are some examples of how to use cURL in PHP for various purposes:

1. Making a GET request in PHP cURL

To make a GET request using cURL in PHP, you can use the following code:

<?php

$url = "https://api.example.com/endpoint?key1=value1&key2=value2";

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$response = curl_exec($ch);
curl_close($ch);

echo $response;

?>

This code will make a GET request to the API endpoint located at $url. The response from the API will be stored in the $response variable and can be output using echo.

2. Making a POST request using PHP cURL

Here's an example of using cURL in PHP to make a POST request with JSON data to an API endpoint:

<?php

$url = "https://api.example.com/endpoint";
$data = array("key1" => "value1", "key2" => "value2");

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($data));
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$response = curl_exec($ch);
curl_close($ch);

echo $response;

?>

This code will make a POST request to the API endpoint located at $url with the data $data encoded as JSON. The CURLOPT_HTTPHEADER option is set to specify the Content-Type header as application/json. The response from the API will be stored in the $response variable.

3. Downloading a file from the internet using PHP cURL

To download a file from the internet using cURL in PHP, you can use the following code:

<?php

$url = "https://www.example.com/file.zip";
$file = "file.zip";

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$data = curl_exec($ch);
curl_close($ch);

$fp = fopen($file, "w");
fwrite($fp, $data);
fclose($fp);

?>

The above code will download the file located at $url and save it to a file named $file in the current directory. The CURLOPT_SSL_VERIFYPEER option is set to false to skip SSL verification, but in a production environment you may want to keep this enabled for security reasons.

4. Handling redirects (HTTP 301,302) using cURL in PHP

To handle redirects (HTTP 301 and 302 status codes) using cURL in PHP, you can set the CURLOPT_FOLLOWLOCATION option to true in your cURL request.

Here's an example:

<?php

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, "https://www.example.com");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);

$result = curl_exec($ch);

curl_close($ch);

echo $result;

?>

This will cause cURL to automatically follow any redirects and return the final content of the target URL.

5. Logging cURL Errors with PHP cURL to a File

To log cURL errors into a file using cURL in PHP, you can add the following code to your cURL request:

<?php

$url = "https://api.example.com/endpoint";

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$response = curl_exec($ch);

if (curl_errno($ch)) {
    $error_message = curl_error($ch);
    $log_file = "curl_error.log";
    $log = fopen($log_file, "a");
    fwrite($log, "[" . date("Y-m-d H:i:s") . "] " . $error_message . "\n");
    fclose($log);
}

curl_close($ch);

echo $response;

?>

This code will write any cURL errors to a log file named curl_error.log in the same directory as your script. The error log will include the error message and the date and time of the error.

These examples demonstrate how you can use cURL to make HTTP requests in PHP, but there are many other options and settings available.

Multiple cURL requests in parallel

In PHP, you can make multiple cURL requests at the same time using the curl_multi_exec function. This allows you to increase the speed and efficiency of your scripts by reducing the wait time between requests.

Here is a simple example of how to use curl_multi_exec:

<?php

// Initialize multiple cURL requests
$mh = curl_multi_init();

// Add multiple cURL handles
$curl1 = curl_init();
curl_setopt($curl1, CURLOPT_URL, "http://example.com/api1");
curl_multi_add_handle($mh, $curl1);

$curl2 = curl_init();
curl_setopt($curl2, CURLOPT_URL, "http://example.com/api2");
curl_multi_add_handle($mh, $curl2);

// Execute multiple cURL requests

$running = null;
do {
    curl_multi_exec($mh, $running);
} while ($running);

// Get the results of each cURL request
$result1 = curl_multi_getcontent($curl1);
$result2 = curl_multi_getcontent($curl2);

// Clean up cURL resources
curl_multi_remove_handle($mh, $curl1);
curl_multi_remove_handle($mh, $curl2);
curl_multi_close($mh);
?>

In this Php curl example, we initialize multiple cURL requests using the curl_multi_init function, and then add two cURL handles using curl_multi_add_handle.

We execute the requests using curl_multi_exec, and wait for all the requests to finish by checking the value of the $running variable.

Once the requests are complete, we can retrieve the results of each request using curl_multi_getcontent, and clean up the resources using curl_multi_remove_handle and curl_multi_close.

Additional Functions of PHP's cURL

1. curl_reset  - Reconfigures all parameters of a libcurl session
2. curl_copy_handle - Duplicating a cURL Handle with its Preferences in PHP
3. curl_multi_init — Returns a new cURL multi handle
4. curl_multi_add_handle - Incorporating a Single cURL Handle into a cURL Multi Handle
5. curl_multi_select - Wait for activity on any curl_multi connection
6. curl_multi_setopt - Set an option for the cURL multi handle
7. curl_multi_exec - Execute the sub-components of the active cURL handle
8. curl_multi_getcontent - If CURLOPT_RETURNTRANSFER is set, returns the content of a cURL handle
9. curl_multi_close - Terminating Multiple cURL Handles
10. curl_multi_errno - Obtaining the Error Code of the Last cURL Multi Request
11. curl_multi_info_read - Get information about the current transfers
12. curl_multi_remove_handle - Remove a multi handle from a set of cURL handles
13. curl_multi_strerror - Return string describing error code
14. curl_version - Provides information about the version of cURL
15. curl_pause - The curl session can be paused and unpaused
16. curl_error - Returns the string representing the error encountered during the current session.
17. curl_file_create  - Creates a cURLFile object
18. curl_getinfo - Obtains information about a transfer

Uses of PHP cURL function

Here are some of the common uses of the PHP cURL library:

1. Sending HTTP requests: cURL can send HTTP requests to a server, including GET, POST, PUT, and DELETE requests. This can be used for various purposes, such as fetching data from an API, submitting form data, or uploading files to a server.
2. Scraping web pages: cURL can be used to scrape data from web pages, allowing you to extract information from websites and use it in your PHP code.
3. Downloading files: cURL can be used to download files from a server, such as images or documents, and save them on your local system.
4. Uploading files: cURL can be used to upload files to a server, such as images or documents, using methods like POST or PUT requests.
5. Checking URLs: cURL can be used to check the status of a URL and determine if it is accessible. This can be used to check if a website is down or not, for example.
6. Transferring data between servers: cURL can be used to transfer data between servers, such as sending data from one server to another for processing or storage.
7. Sending requests with different protocols: cURL supports various protocols, including HTTP, HTTPS, FTP, FTPS, and more, so it can be used for many network-related tasks.

These are just a few of the many uses of the PHP cURL library. Its versatility makes it a powerful tool for working with data and interacting with servers.

Final thoughts

cURL is an effective tool for automating repetitive tasks and testing APIs. libcurl is a prevalently used, open-source, cross-platform library that is compatible with several well languages.

You can enhance almost each attribute of cURL employing one of it's more than 380 flags. With cURL, developers can rapidly & firmly fetch data from the website, User interfaces, datasets, and others.

Collaborating with other webpages, notably those that have access to third party data, rapidly and effortlessly by using cURL in PHP extension. The extension is especially helpful because it makes it easier to get information from other websites.

Without having to manually write complicated code, it enables us to quickly and securely retrieve information. For many web developers who want to quickly access data from websites without having to worry about writing the code to do it manually, cURL has become a renowned extension.

For more information, you can refer to the cURL book provided in the PHP manual, accessible here.

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