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diff --git a/doc/message-structure.md b/doc/message-structure.md new file mode 100644 index 0000000..093a10c --- /dev/null +++ b/doc/message-structure.md @@ -0,0 +1,18 @@ +# Log message structure + +Within monolog log messages are passed around as arrays, for example to processors or handlers. +The table below describes which keys are always available for every log message. + +key | type | description +-----------|---------------------------|------------------------------------------------------------------------------- +message | string | The log message. When the `PsrLogMessageProcessor` is used this string may contain placeholders that will be replaced by variables from the context, e.g., "User %username% logged in" with `['username' => 'John']` as context will be written as "User John logged in". +level | int | Severity of the log message. See log levels described in [01-usage.md](01-usage.md). +level_name | string | String representation of log level. +context | array | Arbitrary data passed with the construction of the message. For example the username of the current user or their IP address. +channel | string | The channel this message was logged to. This is the name that was passed when the logger was created with `new Logger($channel)`. +datetime | Monolog\DateTimeImmutable | Date and time when the message was logged. Class extends `\DateTimeImmutable`. +extra | array | A placeholder array where processors can put additional data. Always available, but empty if there are no processors registered. + +At first glance `context` and `extra` look very similar, and they are in the sense that they both carry arbitrary data that is related to the log message somehow. +The main difference is that `context` can be supplied in user land (it is the 3rd parameter to `Logger::addRecord()`) whereas `extra` is internal only and can be filled by processors. +The reason processors write to `extra` and not to `context` is to prevent overriding any user provided data in `context`. |