simple-sink/index.js

"use strict";

const Promise = require("bluebird");
const propagateAbort = require("@ppstreams/propagate-abort");
const propagatePeek = require("@ppstreams/propagate-peek");
const { isEndOfStream } = require("@ppstreams/end-of-stream-marker");
const { isAborted } = require("@ppstreams/aborted-marker");

const { validateOptions } = require("@validatem/core");
const required = require("@validatem/required");
const isFunction = require("@validatem/is-function");
const defaultTo = require("@validatem/default-to");

// FIXME: Update other stream implementations to new API
module.exports = function simpleSinkStream(_options) {
	let { onResult, onEnd, onAbort } = validateOptions(arguments, {
		onResult: [ required, isFunction ],
		onEnd: [ isFunction, defaultTo.literal(defaultOnEnd) ],
		onAbort: [ isFunction, defaultTo.literal(defaultOnAbort) ]
	});

	let lastResult;
	let onEndCalled = false;
	let onEndResult;
	let abortHandled = false;

	function defaultOnEnd() {
		// We return whatever value we got last from the specified onResult callback.
		return lastResult;
	}

	function defaultOnAbort() {
		// no-op
	}

	return {
		description: `simple sink stream`,
		abort: propagateAbort,
		peek: propagatePeek,
		read: function produceValue_simpleSinkStream(source) {
			function attemptRead() {
				return Promise.try(() => {
					return source.read();
				}).then((value) => {
					// FIXME: Document that you can pause the sink from the onResult callback, by returning a Promise that resolves when it should be resumed
					return onResult(value);
				}).then((result) => {
					lastResult = result;

					return attemptRead();
				}).catch(isEndOfStream, () => {
					/* Don't attempt to do another read, we're done.  */
					if (onEndCalled) {
						return onEndResult;
					} else {
						return Promise.try(() => {
							return onEnd();
						}).then((result) => {
							onEndResult = result;
							return result;
						});
					}
				}).catch((error) => !isAborted(error), (error) => {
					return Promise.try(() => {
						return source.abort(error);
					}).catch((abortError) => {
						let message = [
							`Tried to abort stream due to encountering an error, but the aborting itself failed`,
							`Original error message: ${error.message}`,
							`Abort failure message: ${abortError.message}`
						].join("\n");

						// FIXME: Make this some sort of chained error
						let combinedError = new Error(message);
						combinedError.stack = abortError.stack; // HACK
						throw combinedError;
					}).then(() => {
						// Pass through the original error to the user
						throw error;
					});
				}).catch(isAborted, (marker) => {
					if (abortHandled === false) {
						abortHandled = true;

						return Promise.try(() => {
							return onAbort();
						}).then(() => {
							if (marker.reason instanceof Error) {
								// NOTE: This ensures that the original error causing the abort is thrown exactly once
								throw marker.reason;
							} else {
								throw marker;
							}
						});
					} else {
						// Don't interfere, we only need special behaviour on the first occurrence
						throw marker;
					}
				});
			}

			return attemptRead();
		}
	};
};