Lognostic

Lognostic is a logger facade that provides decorators and context management.

WARNING: This module does not yet have any functionality.

Please do not install this module and expect it to work until you see v1.0.0.

Proposal

When designing an anostic logger, we have to keep in mind that some loggers:

• support custom log levels
• do not have the same builtin log levels (e.g. bunyan has fatal but winston does not)

Note: lognostic should work irrespective of log format (e.g. space separated vs json).

You should be able to pass in any logger like so:

// Assume logger is created according to logger facade:
const bunyan = new BunyanLogger();
const winston = new WinstonLogger();
const pino = new PinoLogger();

import { LogFactory, Log } from 'lognostic';

// Interface for setting/defining a logger change over time. This is just an example:
LogFactory.setLogger(winston);

class InvoiceService {
    // The idea is to have level override which log level to label the events as.
    @Log({ level: 'debug' })
    getUser(username: string) : Promise<User> {
        return wait this.dynamoDbClient.get(/*...parameters...*/).promise();
    }

    @Log({ level: 'debug' })
    generateInvoice(user: User, session: Session) : Invoice {
        return new Invoice(user, session);
    }

    @Log({ level: 'info' })
    submitInvoice(invoice: Invoice) : Promise<void> {
        return this.invoiceQueue.send(invoice);
    }
}

In this example, we invoke the class methods like so:

const service = new InvoiceService();
const user = await service.getUser('username123');
const invoice = await service.generateInvoice(user, session);
await service.submitInvoice(invoice);

Every function invocation with a decorator would pass events to the registered logger as a type:

{
    level: <LOG LEVEL>,
    logEvent: 'start',
    function: {
        name: 'getUser'
        args: [ 'username123' ]
    }
}
{
    level: 'error',
    logEvent: 'error',
    function: {
        name: 'getUser'
        args: [ 'username123' ]
    },
    error: {
        name: 'SomeError',
        message: 'some error message',
        stack: 'stack trace...'
    }
}
{
    level: <LOG LEVEL>,
    logEvent: 'end',
    function: {
        name: 'getUser'
        args: [ 'username123' ]
    }
}

In the future, the idea is to allow the creation and maintainence of contexts for each @Log decorator:

class InvoiceService {
    // The idea is to have level override which log level to label the events as.
    @Log({ level: 'debug', using: Contextual.get() })
    getUser(username: string) : Promise<User> {
        return wait this.dynamoDbClient.get(/*...parameters...*/).promise();
    }

    @Log({ level: 'debug', using: { ...Contextual.get(), /*...figure out how to create child context from a parent context...*/} })
    generateInvoice(user: User, session: Session) : Invoice {
        return new Invoice(user, session);
    }

    @Log({ level: 'info' })
    submitInvoice(invoice: Invoice) : Promise<void> {
        return this.invoiceQueue.send(invoice);
    }
}

import { initializeTraceContext } from 'b3trace';
const invoiceService = new InvoiceService();
function handler({headers}, ctx) {
    const traceId = headers['x-b3-traceid'];
    const spanId = headers['x-b3-spanid'];
    const trace = initializeTraceContext({ traceId, spanId });

    Contextual.using(traceId, { trace });
    try {
        const user = await service.getUser('username123');
        const invoice = await service.generateInvoice(user, session);
        await service.submitInvoice(invoice);
        return { statusCode: 200 };
    } catch(err) {
        return {
            // handle error states
        };
    } finally {
        Contextual.remove(traceId);
    }
}

export {
    handler
};

The exact details for preserving and resetting a context has not been fully defined.

The problem with the proposed design above is that there is no clear way to create & manage child Contexts:

/**
 * How do I construct a child trace from the parent?
 * Will other methods that want to create a child context point to the correct parent?
 * How will a context know if it's the child or the parent?
 * Can I guarantee the context tree integrity if the a method is called multiple times within a single context? Will this cause issues down the line?
 */
@Log({ level: 'debug', using: Contextual.get() })
getUser(username: string) : Promise<User> { /*...*/ }