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Caminho

Tool for creating efficient data pipelines in a JavaScript environment.
The motivation behind Caminho is from an increased demand for data processing systems in combination with the mainstream usage of NodeJS for IO tasks. The JavaScript Ecosystem urges for a tool that offers Concurrency, Batching, Parallelism and Backpressure in a simple and efficient manner.

Features

• Concurrency
• Batching
• Parallelism
• Backpressure
• Filtering
• Reduce
• Logging

Usage Instructions

Installation

npm install caminho
# or
deno add @pedrokehl/caminho

Basic Usage

fromGenerator() is the starting point of Caminho, which returns a Caminho instance based on the provided AsyncGenerator.

A Caminho instance contains the following methods to define the flow:

pipe receives a StepFunction definition, the provided function will receive a ValueBag, which contains the cumulative values from the previous steps, including the generator, if the step has provides, the value will be added to the ValueBag accordingly.
parallel receives StepFunction[], and it will execute the steps in parallel, it has the same abilities as pipe.
filter Filter items emitted by the previous step by only emitting those that satisfy the specified predicate, so the subsequent steps won't receive it.
reduce Allows to reduce through all records of the flow and produce an aggregated property.

After the steps definition, execute your Caminho flow by calling .run().

run: Returns a Promise which is fulfilled when the Generator has finished providing values and all the items have been processed by all the defined steps in the Caminho flow.
The function takes an initial valueBag as parameter, which is passed to the child steps, and the returned value from the promise is an object that contains the context of the last execution of the flow.

Simple flow:

import { fromGenerator } from 'caminho'

const caminho = fromGenerator({ fn: generateCars, provides: 'carId' })
  .parallel([
    { fn: fetchPrice, maxConcurrency: 100, provides: 'price' },
    { fn: fetchSpecs, maxConcurrency: 20, provides: 'specs' },
  ])
  .pipe({ fn: mapCar, provides: 'mappedCar' })
  .pipe({ fn: saveCar, batch: { maxSize: 50, timeoutMs: 100 } })

await caminho.run({ manufacturer: 'subaru' })

Generator

from receives an AsyncGenerator that provides any amount of items to the subsequent steps.
Use maxItemsFlowing for lossless backpressure, it limits the amount of data concurrently in the flow, useful to avoid memory overflow.

import { fromGenerator, ValueBag } from 'caminho'

async function* generateCars(valueBag: ValueBag) {
  const limit = 50
  let page = 1
  while(true) {
    const cars = await getCarsByManufacturer(valueBag.manufacturer, { page, limit })
    for (carId of cars) yield carId
    if (cars.length < limit) {
      break
    }
    page++
  }
}

await fromGenerator({ fn: generateCars, provides: 'carId' }, { maxItemsFlowing: 1_000 })
  .pipe( fn: doSomething })
  .run({ manufacturer: 'nissan' })

Concurrency

Concurrency is unlimited by default, which means a step function can be dispatched concurrently as many times as the number of items the generator provides.
You can limit the concurrency by providing maxConcurrency option on a step definition, this is useful when you use an API that can't handle too many concurrent requests.

await fromGenerator(generator)
  .pipe({ fn: (valueBag: ValueBag) => {}, maxConcurrency: 5 })
  .run()

Batching

Batching can be achieved by providing the batch option on a StepFunction, it works in combination with concurrency, and can be used both in the pipe or parallel methods.

A batch configuration consists of two parameters:
maxSize: Defines the maximum number of items that a batch can contain.
timeoutMs: Time for a batch to be dispatched if the maxSize is not achieved before.

Your batch step can also provide values to the ValueBag, but keep in mind that the order of the returned values must be the same order you received the ValueBag, so it gets merged and is properly assigned to the next pipe.

async function saveCars(valueBags: ValueBag[]): string[] {
  const cars = valueBags.map((valueBag) => valueBag.car)
  const response = await saveManyCars(cars)
  return response.ids
}

await fromGenerator({ fn: generateCars, provides: 'car' })
  .pipe({ fn: saveCars, batch: { maxSize: 50, timeoutMs: 500 }, provides: 'id' })
  .pipe({ fn: doSomethingWithCarId })
  .run()

Parallelism

parallel() receives an array of StepFunctions and each provided step has the same parameters and behavior as a pipe.
Useful only for Asynchronous operations.

Comparable to Promise.all

await fromGenerator({ fn: generateCars, provides: 'car' })
  .parallel([
    { fn: fetchPrice, provides: 'price', maxConcurrency: 100 },
    { fn: fetchSpecs, provides: 'specs', maxConcurrency: 5, batch: { maxSize: 20, timeoutMs: 100 } },
  ])
  .run()

Filtering

filter() receives a predicate, to test item of the Flow, the predicate should return a value that coerces to true to keep the element, or to false otherwise.

Comparable to Array.filter

await fromGenerator({ fn: generateCars, provides: 'car' })
  .filter({ fn: ({ car }: { car: Car }) => car.price >= 100_000 })
  .pipe({ fn: processCarsThatCosts100kOrMore })
  .run()

Reduce

Caminho features a reduce implementation in its flows, it allows to reduce through all records of the flow and produce an aggregated property.
To use it, call reduce() with the following properties:

• fn: (acc: A, value: ValueBag, index: number) => A, Similar to a callback provided to Array.reduce.
• seed: A: Defines the initial acc value received on your aggregator function.
• provides: string: The property name to be appended to the valueBag with the value returned from the reducer.
• keep: string[]: Optional list of the properties that you want to keep the last known value in the valueBag for following steps, by default it keeps only the reduce result.

function sumPrice(acc: number, item: ValueBag) {
  return acc + item.price
}

const result = await fromGenerator({ fn: generateCars, provides: 'carId' })
  .pipe({ fn: fetchPrice, provides: 'price' })
  .reduce({ fn: sumPrice, seed: 0, provides: 'sum', keep: ['manufacturer'] })
  .pipe( { fn: saveTotalForManufacturer })
  .run({ manufacturer: 'Mazda' })

console.log('result', result)
// result { "sum": 1_532_600, "manufacturer": "Mazda" }

Nested Caminhos

You can combine multiple instances of Caminho in the same execution for nested generators.
This approach works with Parallelism, Concurrency and Batching, since the run function will be treated as a normal step.

const childCaminho = fromGenerator({ fn: generateItemsByCarId, provides: 'carItem' })
  .pipe({ fn: saveItem })

await fromGenerator({ fn: generateCars, provides: 'carId' })
  .pipe({ fn: childCaminho.run })
  .run()

Logging

Caminho features a simple log mechanism which executes a syncronous callback function on every step start and finish.
The functions can be defined with the onStepStart and onStepFinished parameter on one of the from flow initializers.

The onStepStart provides the callback with the following information:

• name: string - The name provided on the step definition, fallback to the name of the step function.
• valueBags: ValueBag[] - Array of value bags at the moment this was executed.
• received: number - Time of items received (this will only be greater than 1 in case it's a batch).

The onStepFinished provides the callback with the following information:

• name: string - The name provided on the step definition, fallback to the name of the step function.
• valueBags: ValueBag[] - Array of value bags at the moment this was executed.
• emitted: number - Number of items processed (this will only be greater than 1 in case it's a batch).
• tookMs: number - Time for the step to execute.

Example:

await fromGenerator(
    { fn: generateCars, provides: 'carId' },
    {
      onStepStarted: (log) => console.log('stepStarted', log),
      onStepFinished: (log) => console.log('stepFinished', log),
    }
  )
  // stepStarted { name: 'generateCars', received: 1, valueBags: [{}}] }
  // stepFinished { name: 'generateCars', tookMs: number, emitted: 1, valueBags: [{ carId: "1" }] }
  // stepStarted { name: 'generateCars', received: 1, valueBags: [{}] }
  // stepFinished { name: 'generateCars', tookMs: number, emitted: 1, valueBags: [{ carId: "2" }] }
  .pipe({ fn: fetchPrice, provides: 'price', name: 'customName' })
  // stepStarted { name: 'customName', received: 1, valueBags: [{ carId: "1" }] }
  // stepFinished { name: 'customName', tookMs: number, emitted: 1, valueBags: [{ carId: "1", customName: "car-1" }] }
  // stepStarted { name: 'customName', received: 1, valueBags: [{ carId: "2" }] }
  // stepFinished { name: 'customName', tookMs: number, emitted: 1, valueBags: [{ carId: "2", customName: "car-2" }] }
  .pipe({ fn: fetchSpecs, provides: 'specs', batch: { maxSize: 50, timeoutMs: 500 } })
  // stepStarted { name: 'fetchSpecs', received: 2, valueBags: [{ carId: "1", customName: "car-1" }, { carId: "2", customName: "car-2" } }] }
  // stepFinished { name: 'fetchSpecs', tookMs: number, emitted: 2, valueBags: [{ carId: "1", customName: "car-1", specs: { engineSize: 1600 } }, { carId: "2", customName: "car-2", specs: { engineSize: 2000 } }] }
  .run()

Contributing

Setup

git clone https://github.com/pedrokehl/caminho
cd caminho
npm install

Testing changes

npm test
or
npm run test:watch