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test: ensure stream preprocessing order
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Sometimes it is necessary to preprocess some initial bit
of a stream data before giving the entire stream
to the main processing function. Sometimes this bit should be extracted
from the stream before the main processing; sometimes it should be
returned to the stream. This test checks an order of stream
modes, methods and events for a possible preprocessing algorithm.
Stream BOM stripping is selected as a use case.

See nodejs/help#221 as the prehistory.

PR-URL: #7741
Reviewed-By: Anna Henningsen <anna@addaleax.net>
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vsemozhetbyt authored and addaleax committed Jul 27, 2016
1 parent 1d83013 commit ea725ed
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3 changes: 3 additions & 0 deletions test/fixtures/file-to-read-with-bom.txt
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3 changes: 3 additions & 0 deletions test/fixtures/file-to-read-without-bom.txt
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67 changes: 67 additions & 0 deletions test/parallel/test-stream-preprocess.js
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'use strict';
const common = require('../common');
const assert = require('assert');

const fs = require('fs');
const path = require('path');
const rl = require('readline');

const BOM = '\uFEFF';

// Get the data using a non-stream way to compare with the streamed data.
const modelData = fs.readFileSync(
path.join(common.fixturesDir, 'file-to-read-without-bom.txt'), 'utf8'
);
const modelDataFirstCharacter = modelData[0];

// Detect the number of forthcoming 'line' events for mustCall() 'expected' arg.
const lineCount = modelData.match(/\n/g).length;

// Ensure both without-bom and with-bom test files are textwise equal.
assert.strictEqual(
fs.readFileSync(
path.join(common.fixturesDir, 'file-to-read-with-bom.txt'), 'utf8'
),
`${BOM}${modelData}`
);

// An unjustified BOM stripping with a non-BOM character unshifted to a stream.
const inputWithoutBOM = fs.createReadStream(
path.join(common.fixturesDir, 'file-to-read-without-bom.txt'), 'utf8'
);

inputWithoutBOM.once('readable', common.mustCall(() => {
const maybeBOM = inputWithoutBOM.read(1);
assert.strictEqual(maybeBOM, modelDataFirstCharacter);
assert.notStrictEqual(maybeBOM, BOM);

inputWithoutBOM.unshift(maybeBOM);

let streamedData = '';
rl.createInterface({
input: inputWithoutBOM,
}).on('line', common.mustCall((line) => {
streamedData += `${line}\n`;
}, lineCount)).on('close', common.mustCall(() => {
assert.strictEqual(streamedData, modelData);
}));
}));

// A justified BOM stripping.
const inputWithBOM = fs.createReadStream(
path.join(common.fixturesDir, 'file-to-read-with-bom.txt'), 'utf8'
);

inputWithBOM.once('readable', common.mustCall(() => {
const maybeBOM = inputWithBOM.read(1);
assert.strictEqual(maybeBOM, BOM);

let streamedData = '';
rl.createInterface({
input: inputWithBOM,
}).on('line', common.mustCall((line) => {
streamedData += `${line}\n`;
}, lineCount)).on('close', common.mustCall(() => {
assert.strictEqual(streamedData, modelData);
}));
}));

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