Log4rs JsonEncoder using yaml based configuration

December 19, 2022

How do I specify when using a yaml based configuration for log4rs for the encoder to be the json instead of pattern?

For Example, let’s say my log4rs.yml file is the following, which logs stdout to the console and also to the log file log/requests.log

refresh_rate: 30 seconds

appenders:
  stdout:
    kind: console

  requests:
    kind: file
    path: "log/requests.log"
    encoder:
      pattern: "{d} - {m}{n}"

root:
  level: warn
  appenders:
    - stdout
    - requests

And then starting up within the main.rs with the following:

log4rs::init_file("log4rs.yml", Default::default()).unwrap();

Instead of the requests appender using the pattern format, how can I set it to output using json?

>Solution :

To specify the encoder for the requests appender to output using json, you can modify the encoder field as follows:

encoder:
  kind: json

This will tell Log4rs to use the json encoder for the requests appender. You can also specify additional options for the json encoder, such as the fields to include in the json output. For example:

encoder:
  kind: json
  fields:
    - { field: "level", value: "%l" }
    - { field: "timestamp", value: "%d" }
    - { field: "message", value: "%m" }

This will include the log level, timestamp, and message fields in the json output.

For more information on configuring the json encoder and other encoders in Log4rs, you can refer to the documentation:

https://docs.rs/log4rs/latest/log4rs/struct.JsonEncoder.html