Papyrus

Lightweight, modular JSON logger for Deno with support for external formatter and transports.

Features

• 5 logging levels: trace, debug, info, warn and error
• Debug features
• All logs output as JSON strings
• Decorate your logs with bindings
• Create child loggers inherit their parent’s bindings and settings
• Support for external formatters and transports

How to use

Basic usage:

import Papyrus from "https://deno.land/x/papyrus/mod.ts";

const logger = new Papyrus({
  useLabels: true,
});

logger.trace("Hello World!");
logger.debug("Hello World!");
logger.info("Hello World!");
logger.warn("Hello World!");
logger.error("Hello World!");

// Outputs:
//   {"level":"trace","time":1589371200000,"message":"Hello World!"}
//   {"level":"debug","time":1589371200000,"message":"Hello World!"}
//   {"level":"info","time":1589371200000,"message":"Hello World!"}
//   {"level":"warn","time":1589371200000,"message":"Hello World!"}
//   {"level":"error","time":1589371200000,"message":"Hello World!"}

Using child loggers

import Papyrus from "https://deno.land/x/papyrus/mod.ts";

const parent = new Papyrus({
  bindings: {pid: Deno.pid},
  name: "parentLogger",
  useLabels: true,
});

parent.info("Hello from parent!");

const child = parent.child({
  bindings: {host: "127.0.0.1"},
  name: "childLogger"
});

child.info("Hello from child!");
// Outputs:
//   {"level":"info","name":"parentLogger","time":1589371200000,"pid":6210,"message":"Hello from parent!"}
//   {"level":"info","name":"childLogger","time":1589371200000,"pid":6210,"host":"127.0.0.1","message":"Hello from child!"}

Table of contents

• How to use
• Table of contents
• Creating a logger
• Logging with bindings
• Child loggers
• Options
  • PapyrusOptions
  • ChildOptions
  • TransportOptions
• Logging
  • Level enum
  • Log methods and debug features
  • Logging with payload
• Output
  • Route of a log
  • Interfaces of a log
• Formatter
  • What’s a formatter?
  • How to create a formatter?
• Transport
  • What’s a transport?
  • How to create a transport?
• Plugins
• Contributions

Creating a logger

Import Papyrus from Deno.land:

import Papyrus from "https://deno.land/x/papyrus/mod.ts";
// Or
import { Papyrus } from "https://deno.land/x/papyrus/mod.ts";

Nameless logger with default options

A nameless logger will be created with the default options:

const logger = new Papyrus();

Named logger with default options

A named logger will be created with the default options:

const logger = new Papyrus("myLogger");

Customized logger

An object of type PapyrusOptions can be used to specify options:

const logger = new Papyrus({
  // options...
});

Logging with bindings

Bindings are properties that are bound to the logger. In other therms, any log output by the logger will contain it’s bindings. Bindings are typically found before the log’s message.

const logger = new Papyrus({
  bindings: {pid: Deno.pid}
});

logger.info("Hello World!");

// Outputs:
//   {"level":2,"time":1589371200000,"pid":3876,"message":"Hello World!"}

If the mergeBindings property is false, all bindings will be grouped in a plain object under the bindings property.

const logger = new Papyrus({
  bindings: {pid: Deno.pid},
  mergeBindings: false
});

logger.info("Hello World!");

// Outputs:
//   {"level":2,"time":1589371200000,"bindings":{"pid":4309},"message":"Hello World!"}

Child loggers

Child loggers can be created from a Papyrus logger by calling the child method. The child method requires options of type ChildOptions that contains at least a name property. A child logger inherits of all of its parent’s bindings.

const logger = new Papyrus({
  bindings: {pid: Deno.pid}
}).child({
    bindings: {host: "127.0.0.1"},
    name: "myChildLogger"
  });

logger.info("Hello World!");

// Outputs:
//   {"level":2,"name":"childLogger","time":1589371200000,"pid":4022,"host":"127.0.0.1","message":"Hello World!"}

Options

PapyrusOptions

Papyrus can be configured through an object that implements the interface PapyrusOptions. All properties are optional.

interface PapyrusOptions {
  bindings?: KeyValuePair;
  destination?: DestinationOptions | DestinationOptions[];
  enabled?: boolean;
  formatter?: Formatter;
  level?: Level | keyof typeof Level;
  mergeBindings?: boolean;
  mergePayload?: boolean;
  name?: string;
  time?: boolean;
  useLabels?: boolean;
}

ChildOptions

A ChildOptions configuration object must be provided when creating a child logger.

interface ChildOptions {
  bindings?: KeyValuePair;
  name: string;
}

TransportOptions

A TransportOptions configuration object is used when specifying a Transport.

interface TransportOptions {
  use?: Transport;
  formatter?: Formatter;
}

Logging

Level enum

All levels are defined in a numeric enum.

enum Level {
  trace,     // Value: 0
  debug,     // Value: 1
  info,      // Value: 2
  warn,      // Value: 3
  error,     // Value: 4
}

Log methods and debug features

Instances of Papyrus have five logging methods that one can use, each specific to a level. The methods are trace, debug, info, warn and error.

const logger = new Papyrus();

logger.trace("Level is trace");
logger.debug("Level is debug");
logger.info("Level is info");
logger.warn("Level is warn");
logger.error("Level is error");

// Outputs:
//   {"level":0,"time":1589371200000,"message":"Level is trace"}
//   {"level":1,"time":1589371200000,"message":"Level is debug"}
//   {"level":2,"time":1589371200000,"message":"Level is info"}
//   {"level":3,"time":1589371200000,"message":"Level is warn"}
//   {"level":4,"time":1589371200000,"message":"Level is error"}

It’s possible to configure your logger so that it doesn’t output logs below a given level. Let’s repeat the example of above with the level set to warn.

const logger = new Papyrus({level: Level.warn});

logger.trace("Level is trace");
logger.debug("Level is debug");
logger.info("Level is info");
logger.warn("Level is warn");
logger.error("Level is error");

// Outputs:
//   {"level":3,"time":1589371200000,"message":"Level is warn"}
//   {"level":4,"time":1589371200000,"message":"Level is error"}

Only the logs with a level of warn or above were output. Note that we imported the level directly from the enum in this example. The configurations {level: "warn"} and {level: 3} would have given the same result.

Logging with payload

A payload is like bindings, except that it’s log-specific. A payload is typically found after the log’s message.

const logger = new Papyrus();

logger.info("Hello World!", {a: "A"});

// Outputs:
//   {"level":2,"time":1589371200000,"message":"Hello World!","a":"A"}

If the mergePayload property is false, all properties from the payload will be grouped in a plain object under the payload property.

const logger = new Papyrus({mergePayload: false});

logger.info("Hello World!", {a: "A"});

// Outputs:
//   {"level":2,"time":1589371200000,"message":"Hello World!","payload":{"a":"A"}}

Output

Route of a log

Internally, Papyrus logs are defined as plain objects implementing Log. The log is then sent to the formatter, which may return the log as a modified Log object or as a JSON string. At this point, any log which is not already a string will be stringified using the JSON.stringify() function. The string is finally sent to the transport(s) which will consume the log.

Papyrus supports several transports, and each can have their own formatter.

Interfaces of a log

A log is transmitted to a formatter or a transport as an object implementing the Log interface, which is a generic interface for any type of log, or as a JSON string representing this object. In formatters and transports, it can be interesting to differentiate messages from errors. Which is why Papyrus is exporting the interfaces LogWithMessage and LogWithError.

All logs contain a level property.

interface Log {
  level: number | string;
  name?: string;
  time?: number | string;
  bindings?: KeyValuePair;
  message?: string | number | boolean;
  error?: {
    message: string;
    name: string;
    stack?: string;
  };
  payload?: KeyValuePair;
}

interface LogWithMessage {
  level: number | string;
  name?: string;
  time?: number | string;
  bindings?: KeyValuePair;
  message?: string | number | boolean;
  payload?: KeyValuePair;
}

interface LogWithError {
  level: number | string;
  name?: string;
  time?: number | string;
  bindings?: KeyValuePair;
  error: {
    message: string;
    name: string;
    stack?: string;
  }
  payload?: KeyValuePair;
}

Formatter

What’s a formatter?

A formatter is a class that implements the Formatter interface. It can modify an object of type Log, or convert it into a string. There are two kind of formatters:

• Editors: These formatters will alter, add or delete properties of Log. In principle, they should always return a object that implements Log, or a JSON representation of such object.
• Prettifiers: These formatters will convert Log to a string formatted to be easier to read than a JSON string.

interface Formatter {
  format: (data: string | Log, _v: number) => string | Log;
}

The _v property represents the version of the Log interface and will always be the same value for a given version of Papyrus. is hidden and defines the version of the Log interface. Should the Log interface be updated in the future, the value of _v will be incremented. For now, it is always 1.

How to create a formatter?

Here is an example of a formatter that returns the log it receives as a Log:

class IdentityFormatter implements Formatter {
  public format(log: Log | string): Log {
    if(typeof log === "string") return JSON.parse(log);
    else return log;
  }
}

Transport

What’s a transport?

A transport is a class that implements the Transport interface. It’s the final destination of the log. For example, it can:

• Send the log to the console
• Write the log into a file
• Save the log in a database

interface Transport {
  log: (data: string, _v: number) => void;
}

How to create a Transport?

Here is an example of a transport sends the log to the console as a string:

class ConsoleTransport implements Transport {
  public log(log: Log |string): void {
    if(typeof log === "string") console.log(log);
    else JSON.stringify(log);
  }
}

Plugins

• Papyrus-File: A transport for writing into files
• Papyrus-Pretty: A formatter that prettifies your logs

Contributions

PRs are welcome!