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master
Sven Slootweg 4 months ago
commit
d570e44ddc
  1. 3
      .eslintrc
  2. 1
      .gitignore
  3. 31
      example.js
  4. 58
      index.js
  5. 24
      package.json
  6. 1294
      yarn.lock

3
.eslintrc

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{
"extends": "@joepie91/eslint-config"
}

1
.gitignore

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node_modules

31
example.js

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"use strict";
const Promise = require("bluebird");
const derivedStream = require("./");
const pipe = require("@promistream/pipe");
const collect = require("@promistream/collect");
const rangeNumbers = require("@promistream/range-numbers");
return Promise.try(() => {
let producedStream = pipe([
rangeNumbers(0, 10),
derivedStream((source) => {
/* NOTE: This example doesn't actually do anything *useful*. It
only demonstrates the higher-order stream mechanism.
Real-world code implementing eg. load-balanced stream forks
would probably do something like producing an array of multiple
streams here (instead of a single pipeline), and do some
internal routing of source values across them. */
return pipe([
source,
collect()
]);
})
]).read();
return producedStream.read();
}).then((result) => {
console.log(result); // [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
});

58
index.js

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"use strict";
const Promise = require("bluebird");
const Aborted = require("@promistream/aborted");
const EndOfStream = require("@promistream/end-of-stream");
const errorChain = require("error-chain");
const { validateArguments } = require("@validatem/core");
const required = require("@validatem/required");
const isFunction = require("@validatem/is-function");
module.exports = function simpleSource(_deriver) {
let [ deriver ] = validateArguments(arguments, {
deriver: [ required, isFunction ]
});
let hasBeenDerived = false;
let errorReason = null;
return {
_promistreamVersion: 0,
description: `derived stream`,
peek: function peekValue_derivedStream(_source) {
// A derived-stream is guaranteed to produce a value; either a new stream, or an EndOfStream, or an Aborted marker
return true;
},
read: function produceValue_derivedStream(source) {
// TODO: Abstract out the abort handling here and in `abort`? The logic is almost entirely shared between `simple-source` and `derived-stream`.
if (errorReason != null) {
if (errorReason === true) {
throw new Aborted("Stream was aborted");
} else if (errorReason instanceof Error) {
throw new errorChain.chain(errorReason, Aborted, `Stream was aborted due to error: ${errorReason.message}`);
}
} else if (hasBeenDerived === true) {
throw new EndOfStream;
} else {
hasBeenDerived = true;
return deriver(source);
}
},
abort: function abort_simpleSource(reason, _source) {
// NOTE: Even though a `source` is provided, we don't do anything with it; higher-order stream producers should *not* propagate aborts upstream, as a read from such a producer would never constitute a read upstream.
return Promise.try(() => { // FIXME: Remove Promise.try here?
if (errorReason == null) {
if (reason === true || reason instanceof Error) {
errorReason = reason;
} else {
throw new Error("You must specify a reason (either `true` or an Error object) when aborting a stream");
}
} else {
// FIXME: Require this behaviour in the spec? Or is there a composability-related reason to permit/require quietly ignoring this, to make it idempotent? (Duplicate of simple-source)
throw new Error(`The stream is already aborted`);
}
});
}
};
};

24
package.json

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{
"name": "@promistream/derived-stream",
"version": "0.1.0",
"main": "index.js",
"repository": "http://git.cryto.net/promistream/derived-stream.git",
"author": "Sven Slootweg <admin@cryto.net>",
"license": "WTFPL OR CC0-1.0",
"dependencies": {
"@promistream/aborted": "^0.1.1",
"@promistream/end-of-stream": "^0.1.1",
"@validatem/core": "^0.3.12",
"@validatem/is-function": "^0.1.0",
"@validatem/required": "^0.1.1",
"bluebird": "^3.7.2",
"error-chain": "^0.1.0"
},
"devDependencies": {
"@joepie91/eslint-config": "^1.1.0",
"@promistream/collect": "^0.1.1",
"@promistream/pipe": "^0.1.0",
"@promistream/range-numbers": "^0.1.2",
"eslint": "^7.29.0"
}
}

1294
yarn.lock
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