rw-stream
v0.3.3
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A simple stream that allows reading and writing to the same file at the same time.[H[C[F
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rw-stream
A stream that can substitute contents of a file in streaming fashion.
The aim of this module is to expose a readable and writable stream connected to a single file at the same time. It works similarily to fs.createReadStream
and fs.createWriteStream
, but allows writing and reading simultanously, without creating a new file or move operations.
This is achieved by disallowing any write operations to advance further than the current reading index. This module will then make sure that a byte of the file will be read before it's overwritten.
Note: In any case, the file will be accessed and it's contents may be overwritten even if there's no actual read operation done (due to node.js streams buffering mechanisms).
Usage:
const rw = require("../");
const {fd, readStream, writeStream} = await rw(path, options);
Arguments:
- path
string
- the path of the file to access. - options
object
- options, currently none.
Returns an object
with the following properties:
- fd
int
- file descriptor number (fromfs.open
) - writeStream
Writable
- Writable stream for new file contents. - readStream
Readable
- Readable stream containing previous contents.
Samples
A simple module that replaces the contents of a file while keeping a backup:
const replaceAndBackup = async (newContentStream) => {
const {readStream, writeStream} = await rw(path);
readStream.pipe(fs.createWriteStream(`${path}.bak`));
newContentStream.pipe(writeStream);
return new Promise((res, rej) => writeStream.on('finish', res).on('error', rej));
}
Testing
For now there's just:
$ node test
Two tests will be executed:
- one for file that's being grown.
- one for file that's being shrinked.
We're working on more and proper tests.