What are the differences between Guzzle 6 and Guzzle 7?

Guzzle is a PHP HTTP client that makes it easy to send HTTP requests and trivial to integrate with web services. Over time, Guzzle has evolved, with Guzzle 7 being the latest major release at the time of this writing. Guzzle 7 introduced several new features and improvements over Guzzle 6, as well as some backward compatibility breaks. Below are some of the key differences between Guzzle 6 and Guzzle 7:

1. PHP Version Requirement

• Guzzle 6: Requires PHP >= 5.5 but will work with PHP 5.4 if you don't use the use keyword to import functions.
• Guzzle 7: Requires PHP >= 7.2.5.

2. Type Hinting and Return Types

• Guzzle 6: Lacks type declarations for parameters and return types in methods.
• Guzzle 7: Adds type declarations and return types to methods, making the codebase more robust and self-documenting.

3. Promises/A+ Compliance

• Guzzle 6: Uses thenable promises but did not fully comply with the Promises/A+ specification.
• Guzzle 7: More closely follows the Promises/A+ specification, which aligns Guzzle promises with other promise implementations.

4. Curl Multi-Handling

• Guzzle 6: Uses the curl_multi_exec() function for concurrent HTTP requests.
• Guzzle 7: Introduces support for curl_multi_poll() and curl_multi_wait() which are more efficient and could lead to performance improvements when doing concurrent requests.

5. Middleware System

• Guzzle 6: Has a middleware system, but it's less flexible in terms of the handler stack manipulation.
• Guzzle 7: Improves the middleware system, providing more flexibility in how handlers can be injected and manipulated within the stack.

6. Exception Hierarchy

• Guzzle 6: Has a set of exception classes but does not differentiate between server and client errors.
• Guzzle 7: Introduces new exception classes, GuzzleHttp\Exception\ClientException and GuzzleHttp\Exception\ServerException, to better differentiate between 4xx client errors and 5xx server errors.

7. Base URI Handling

• Guzzle 6: Allows setting a base URI when creating a client.
• Guzzle 7: Improves the handling of the base URI, making it easier to combine base URIs with relative URIs when making requests.

8. Streaming Requests

• Guzzle 6: Supports streaming requests but with fewer options for customization.
• Guzzle 7: Enhances the streaming requests feature, providing more options for customization and better performance.

9. Debugging

• Guzzle 6: Offers debugging options that are less intuitive and harder to use.
• Guzzle 7: Improves the debugging experience by providing better tools and options to debug HTTP requests and responses.

10. PSR-7 and PSR-18 Compliance

• Guzzle 6: Follows PSR-7 standards but does not implement PSR-18.
• Guzzle 7: Fully implements PSR-18 (HTTP Client), making it compatible with other libraries that use this standard.

Backward Compatibility Breaks

Upgrading from Guzzle 6 to Guzzle 7 may require some code changes due to backward compatibility breaks. These include changes in method signatures, exception handling, and the behavior of certain features. It is important to review the Guzzle upgrade guide and test your application thoroughly when updating the Guzzle version.

When considering an upgrade from Guzzle 6 to Guzzle 7, you should review the official Guzzle CHANGELOG and migration guide for detailed information on changes and how to address them.