The logger interface defines a common interface for logging system messages from an application or library.
This metadocument was written post-hoc, as PSR-3 was originally passed before meta-documents were standard practice.
It is the intent of this specification that the message passed to a logging method always be a static value. Any context-specific variability (such as a username, timestamp, or other information) should be provided via the $context array only, and the string should use a placeholder to reference it.
The intent of this design is twofold. One, the message is then readily available to translation systems to create localized versions of log messages. Two, context-specific data may contain user input, and thus requires escaping. That escaping will be necessarily different if the log message is stored in a database for later rendering in HTML, serialized to JSON, serialized to a syslog message string, etc. It is the responsibility of the logging implementation to ensure that $context data that is shown to the user is appropriately escaped.
The 2.0 release of the psr/log package includes scalar parameter types. The 3.0 release of the package includes return types. This structure leverages PHP 7.2 covariance support to allow for a gradual upgrade process, but requires PHP 8.0 for type compatibility.
Implementers MAY add return types to their own packages at their discretion, provided that:
Implementers MAY add parameter types to their own packages in a new major release, either at the same time as adding return types or in a subsequent release, provided that:
"psr/log": "^2.0 || ^3.0" so as to exclude the untyped 1.0 version.Implementers are encouraged but not required to transition their packages toward the 3.0 version of the package at their earliest convenience.