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Add filter() and merge() methods

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This commit is contained in:
Sami Turcotte 2018-11-30 01:31:09 -05:00
parent d6660e7204
commit 46597f3185
4 changed files with 264 additions and 28 deletions
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1
.gitignore vendored
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@ -3,3 +3,4 @@ node_modules
dist
sample_output
yarn-error.log
TODO.md

7
package.json
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@ -1,7 +1,7 @@
{
"name": "mhysa",
"version": "0.5.0",
"description": "Promise, Stream and EventEmitter utils for Node.js",
"version": "0.6.0-beta.0",
"description": "Streams and event emitter utils for Node.js",
"keywords": [
"promise",
"stream",
@ -9,8 +9,7 @@
"utils"
],
"author": {
"name": "Sami Turcotte",
"email": "samiturcotte@gmail.com"
"name": "Wenzil"
},
"license": "MIT",
"main": "dist/index.js",

194
src/index.spec.ts
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@ -1,7 +1,17 @@
import test from "ava";
import { expect } from "chai";
import { Readable } from "stream";
import { fromArray, map, flatMap, split, join, collect, concat } from "./";
import {
fromArray,
map,
flatMap,
split,
join,
collect,
concat,
filter,
merge,
} from ".";
test.cb("fromArray() streams array elements in flowing mode", t => {
t.plan(3);
@ -9,7 +19,7 @@ test.cb("fromArray() streams array elements in flowing mode", t => {
const stream = fromArray(elements);
let i = 0;
stream
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.equal(elements[i]);
t.pass();
i++;
@ -52,7 +62,7 @@ test.cb("map() maps elements synchronously", t => {
let i = 0;
source
.pipe(map((element: string) => element.toUpperCase()))
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
@ -78,7 +88,7 @@ test.cb("map() maps elements asynchronously", t => {
return element.toUpperCase();
}),
)
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
@ -239,6 +249,104 @@ test.cb("flatMap() emits errors during asynchronous mapping", t => {
source.push(null);
});
test.cb("filter() filters elements synchronously", t => {
t.plan(2);
const source = new Readable({ objectMode: true });
const expectedElements = ["a", "c"];
let i = 0;
source
.pipe(filter((element: string) => element !== "b"))
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
})
.on("error", t.end)
.on("end", t.end);
source.push("a");
source.push("b");
source.push("c");
source.push(null);
});
test.cb("filter() filters elements asynchronously", t => {
t.plan(2);
const source = new Readable({ objectMode: true });
const expectedElements = ["a", "c"];
let i = 0;
source
.pipe(
filter(async (element: string) => {
await Promise.resolve();
return element !== "b";
}),
)
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
})
.on("error", t.end)
.on("end", t.end);
source.push("a");
source.push("b");
source.push("c");
source.push(null);
});
test.cb("filter() emits errors during synchronous filtering", t => {
t.plan(2);
const source = new Readable({ objectMode: true });
source
.pipe(
filter((element: string) => {
if (element !== "a") {
throw new Error("Failed filtering");
}
return true;
}),
)
.resume()
.on("error", err => {
expect(err.message).to.equal("Failed filtering");
t.pass();
})
.on("end", t.end);
source.push("a");
source.push("b");
source.push("c");
source.push(null);
});
test.cb("filter() emits errors during asynchronous filtering", t => {
t.plan(2);
const source = new Readable({ objectMode: true });
source
.pipe(
filter(async (element: string) => {
await Promise.resolve();
if (element !== "a") {
throw new Error("Failed filtering");
}
return true;
}),
)
.resume()
.on("error", err => {
expect(err.message).to.equal("Failed filtering");
t.pass();
})
.on("end", t.end);
source.push("a");
source.push("b");
source.push("c");
source.push(null);
});
test.cb("split() splits chunks using the default separator (\\n)", t => {
t.plan(5);
const source = new Readable({ objectMode: true });
@ -445,7 +553,7 @@ test.cb(
const expectedElements = ["a", "b", "c", "d", "e", "f"];
let i = 0;
concat(source1, source2)
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
@ -505,7 +613,7 @@ test.cb(
const expectedElements = ["a", "b", "c", "d", "e", "f"];
let i = 0;
concat(source1, source2)
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.deep.equal(Buffer.from(expectedElements[i]));
t.pass();
i++;
@ -548,13 +656,13 @@ test.cb(
.on("end", t.end);
source1.push("a");
source2.push("d");
source1.push("b");
source2.push("e");
source1.push("c");
source2.push("f");
source2.push(null);
source1.push(null);
setTimeout(() => source2.push("d"), 10);
setTimeout(() => source1.push("b"), 20);
setTimeout(() => source2.push("e"), 30);
setTimeout(() => source1.push("c"), 40);
setTimeout(() => source2.push("f"), 50);
setTimeout(() => source2.push(null), 60);
setTimeout(() => source1.push(null), 70);
},
);
@ -564,7 +672,7 @@ test.cb("concat() concatenates a single readable stream (object mode)", t => {
const expectedElements = ["a", "b", "c", "d", "e", "f"];
let i = 0;
concat(source)
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
@ -586,7 +694,7 @@ test.cb(
const expectedElements = ["a", "b", "c", "d", "e", "f"];
let i = 0;
concat(source)
.on("data", element => {
.on("data", (element: string) => {
expect(element).to.deep.equal(Buffer.from(expectedElements[i]));
t.pass();
i++;
@ -611,3 +719,59 @@ test.cb("concat() concatenates empty list of readable streams", t => {
.on("error", t.end)
.on("end", t.end);
});
test.cb.only(
"merge() merges multiple readable streams in chunk arrival order",
t => {
t.plan(6);
const source1 = new Readable({ objectMode: true, read: () => ({}) });
const source2 = new Readable({ objectMode: true, read: () => ({}) });
const expectedElements = ["a", "d", "b", "e", "c", "f"];
let i = 0;
merge(source1, source2)
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
})
.on("error", t.end)
.on("end", t.end);
source1.push("a");
setTimeout(() => source2.push("d"), 10);
setTimeout(() => source1.push("b"), 20);
setTimeout(() => source2.push("e"), 30);
setTimeout(() => source1.push("c"), 40);
setTimeout(() => source2.push("f"), 50);
setTimeout(() => source2.push(null), 60);
setTimeout(() => source1.push(null), 70);
},
);
test.cb("merge() merges a readable stream", t => {
t.plan(3);
const source = new Readable({ objectMode: true, read: () => ({}) });
const expectedElements = ["a", "b", "c"];
let i = 0;
merge(source)
.on("data", (element: string) => {
expect(element).to.equal(expectedElements[i]);
t.pass();
i++;
})
.on("error", t.end)
.on("end", t.end);
source.push("a");
source.push("b");
source.push("c");
source.push(null);
});
test.cb("merge() merges an empty list of readable streams", t => {
t.plan(0);
merge()
.on("data", () => t.pass())
.on("error", t.end)
.on("end", t.end);
});

88
src/index.ts
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@ -2,10 +2,10 @@ import { Transform, Readable } from "stream";
import * as _utils from "./utils";
export const utils = _utils;
export interface ReadableOptions {
export interface ThroughOptions {
objectMode?: boolean;
}
export interface ThroughOptions {
export interface TransformOptions {
readableObjectMode?: boolean;
writableObjectMode?: boolean;
}
@ -38,14 +38,14 @@ export function fromArray(array: any[]): NodeJS.ReadableStream {
*/
export function map<T, R>(
mapper: (chunk: T, encoding: string) => R,
options: ThroughOptions = {
options: TransformOptions = {
readableObjectMode: true,
writableObjectMode: true,
},
): NodeJS.ReadWriteStream {
return new Transform({
...options,
async transform(chunk, encoding, callback) {
async transform(chunk: T, encoding, callback) {
let isPromise = false;
try {
const mapped = mapper(chunk, encoding);
@ -75,14 +75,14 @@ export function flatMap<T, R>(
mapper:
| ((chunk: T, encoding: string) => R[])
| ((chunk: T, encoding: string) => Promise<R[]>),
options: ThroughOptions = {
options: TransformOptions = {
readableObjectMode: true,
writableObjectMode: true,
},
): NodeJS.ReadWriteStream {
return new Transform({
...options,
async transform(chunk, encoding, callback) {
async transform(chunk: T, encoding, callback) {
let isPromise = false;
try {
const mapped = mapper(chunk, encoding);
@ -102,6 +102,40 @@ export function flatMap<T, R>(
});
}
export function filter<T>(
predicate:
| ((chunk: T, encoding: string) => boolean)
| ((chunk: T, encoding: string) => Promise<boolean>),
options: ThroughOptions = {
objectMode: true,
},
) {
return new Transform({
readableObjectMode: options.objectMode,
writableObjectMode: options.objectMode,
async transform(chunk: T, encoding, callback) {
let isPromise = false;
try {
const result = predicate(chunk, encoding);
isPromise = result instanceof Promise;
if (!!(await result)) {
callback(undefined, chunk);
} else {
callback();
}
} catch (err) {
if (isPromise) {
// Calling the callback asynchronously with an error wouldn't emit the error, so emit directly
this.emit("error", err);
callback();
} else {
callback(err);
}
}
},
});
}
/**
* Return a ReadWrite stream that splits streamed chunks using the given separator
* @param separator The separator to split by, defaulting to "\n"
@ -138,7 +172,7 @@ export function join(separator: string): NodeJS.ReadWriteStream {
return new Transform({
readableObjectMode: true,
writableObjectMode: true,
async transform(chunk, encoding, callback) {
async transform(chunk: string, encoding, callback) {
if (!isFirstChunk) {
this.push(separator);
}
@ -155,7 +189,7 @@ export function join(separator: string): NodeJS.ReadWriteStream {
* @param options.objectMode Whether this stream should behave as a stream of objects
*/
export function collect(
options: ReadableOptions = { objectMode: false },
options: ThroughOptions = { objectMode: false },
): NodeJS.ReadWriteStream {
const collected: any[] = [];
return new Transform({
@ -215,3 +249,41 @@ export function concat(
});
return wrapper;
}
/**
* Return a stream of readable streams merged together in chunk arrival order
* @param streams The readable streams to merge
*/
export function merge(
...streams: NodeJS.ReadableStream[]
): NodeJS.ReadableStream {
let isStarted = false;
let streamEndedCount = 0;
return new Readable({
objectMode: true,
read() {
if (streamEndedCount >= streams.length) {
this.push(null);
} else if (!isStarted) {
isStarted = true;
streams.forEach(stream =>
stream
.on("data", chunk => {
if (!this.push(chunk)) {
streams.forEach(s => s.pause());
}
})
.on("error", err => this.emit("error", err))
.on("end", () => {
streamEndedCount++;
if (streamEndedCount === streams.length) {
this.push(null);
}
}),
);
} else {
streams.forEach(s => s.resume());
}
},
});
}