fs: add `FileHandle.prototype.readLines` #42590

aduh95 · 2022-04-03T14:45:26Z

It seems to be a frequent enough use case that it makes sense to have a shortcut method.

aduh95 · 2022-04-03T15:08:04Z

//cc @nodejs/fs @nodejs/readline

RaisinTen

I think convenience methods like this one which isn't strictly necessary for the API to be fully functional should belong to userland modules like https://github.com/jprichardson/node-fs-extra.

aduh95 · 2022-04-29T14:56:20Z

@RaisinTen I disagree, I think it would be a shame to have to use a third party module for something like this.

Other languages have this feature built-in:

Additionally, it's very little code to maintain on out end, and saves our users a good chunk of boilerplate.

targos · 2022-04-29T15:07:37Z

doc/api/fs.md

+    console.log(line);
+  }
+} finally {
+  await file?.close();


Could this be handled automatically by the async iterator?

Oh it is indeed, autoClose defaults to true so that explicit close call is superfluous.

RaisinTen · 2022-04-29T15:13:26Z

@RaisinTen I disagree, I think it would be a shame to have to use a third party module for something like this.

Other languages have this feature built-in:

Python: file.readlines()

I think python is the only language in this list that has an equivalent API for what we are doing in this PR.

Rust: BufReader::lines()

Java: java.util.Scanner

Aren't both of these like our 'readline' module? These deal with streams not files specifically which is a kind of a stream.

Additionally, it's very little code to maintain on out end, and saves our users a good chunk of boilerplate.

But what's wrong with using an npm module? Those have loads of utilities already to reduce boilerplate code.

aduh95 · 2022-04-29T15:31:00Z

But what's wrong with using an npm module? Those have loads of utilities already to reduce boilerplate code.

I'm not saying using an npm package is wrong, and I don't think adding this utility would change anything to the download stats of e.g. node-fs-extra. What I'm saying is I don't want to have to download an external package (that I have to audit now?) for something like this.

aduh95 · 2022-04-29T15:41:51Z

Aren't both of these like our 'readline' module? These deal with streams not files specifically which is a kind of a stream.

To be clear, I'm totally OK to move this to the node:readline module (or node:readline/promises) if you think it's a better place, what I'm looking for is an util to easily iterate over the lines of an open file handle.

RaisinTen · 2022-04-29T16:00:49Z

What I'm saying is I don't want to have to download an external package (that I have to audit now?) for something like this.

If we don't want to audit an external package, I think it's okay if we use the boilerplate code. I don't think the core repo is supposed to solve the use case of reducing boilerplate code.

To be clear, I'm totally OK to move this to the node:readline module (or node:readline/promises) if you think it's a better place, what I'm looking for is an util to easily iterate over the lines of an open file handle.

I still don't think that would be a good idea because readline is supposed to be an interface - a wrapper around any sort of readable stream we want to read lines from. If we allow folks to use it in a way that's not like using an interface, I feel it kinda goes against the principles of that module.

aduh95 · 2022-04-29T16:11:49Z

My use case is the following:

I want to read the content of an open file handle line by line.
I don't want to use npm.
I don't want to learn by hearth the boilerplate.

Is your response to this: "just use Python"? I don't really get how this util being part of core is detrimental to you or anyone (and if it's not detrimental, why do you block it?).
If you're OK with this feature landing, but not in the current form, what would you like me to change?

RaisinTen · 2022-04-30T06:28:23Z

My use case is the following:

I want to read the content of an open file handle line by line.

I don't want to use npm.

I don't want to learn by hearth the boilerplate.

Why don't you want to use npm? It would be really helpful to reduce a lot of boilerplate code throughout your application. Even if you are against using npm, you could create a utility function in your application and use that wherever you need to read lines from a file. That way, you could write the boilerplate code just once and forget it and use the more approachable utility function everywhere you need it - no need to learn anything by heart. Maybe you could put that into a private package repo if you don't want that utility to be there in your main application source?

Is your response to this: "just use Python"?

That's a very valid solution.

I don't really get how this util being part of core is detrimental to you or anyone (and if it's not detrimental, why do you block it?).

It's not detrimental, it's very helpful. It just doesn't look like something that should belong to core because of the reasons I stated above.

If you're OK with this feature landing, but not in the current form, what would you like me to change?

If we absolutely do have to add this functionality to core, I would start off by adding it to readable streams, so that all sorts of readable streams can benefit from this (readline accepts a readable stream as the input object for that purpose). If it gets accepted there then I'm okay with adding it to fs if the createReadStream() part looks too much.

aduh95 · 2022-04-30T09:06:13Z

It just doesn't look like something that should belong to core because of the reasons I stated above.

Sorry, but what reasons? The only reason I'm reading is that you don't think it belongs in core.

@RaisinTen Let's assume that:

We both know what npm is and how it works.
We both are knowledgable enough to chose for ourselves if npm fits our usecase.
We both know what is a utility function and know how to set it up.
We both know how to make a (private or not) package when something's too niche for our use case.

And now with all that, I'm telling you: I still want this in core, I think it belongs there.

I working with Node.js because I find it fun, and on Node.js core development because it let me overcome the frustrations I have with it sometimes. If you are not going to let me fix them when I found one, well that's not cool. Node.js is a community-owned project, refusing a feature on the basis that you don't like it is not acceptable IMHO, so if you agree that it's a useful feature and would not be detrimental as far as you know, then please remove your block.

I would start off by adding it to readable streams, so that all sorts of readable streams can benefit from this (readline accepts a readable stream as the input object for that purpose).

TBF that's already a one-liner:

import { createInterface as readLines } from 'node:readline'

for await(const line of readLines(myStream)) console.log(line)

But that's not really my use-case anyway, mine is specifically about open file handles.

RaisinTen · 2022-04-30T13:51:12Z

It just doesn't look like something that should belong to core because of the reasons I stated above.

Sorry, but what reasons? The only reason I'm reading is that you don't think it belongs in core.

This is my reasoning:

This function is purely for utility purposes and what it does can already be achieved in userland using the already exposed file system primitive operations. Exposing this from fs would add a non-primitive fs operation and make the API inconsistent, so IMO it doesn't belong to fs.
And I don't think it belongs to the readline module either because readline is supposed to be a wrapper around a readable stream object and it is used to read lines from it. If we bind the interface to a specific object, it doesn't remain purely an interface anymore.

I would start off by adding it to readable streams, so that all sorts of readable streams can benefit from this (readline accepts a readable stream as the input object for that purpose).

TBF that's already a one-liner:
import { createInterface as readLines } from 'node:readline'

for await(const line of readLines(myStream)) console.log(line)
But that's not really my use-case anyway, mine is specifically about open file handles.

Well, there is a one-liner for this too

for await(const line of readLines(openFileHandle.createReadStream())) console.log(line)

I'll let others from @nodejs/fs and @nodejs/readline decide if we should add this

RaisinTen · 2022-04-30T14:04:05Z

Actually, please disregard my second point. Could you please share what the API would look like if we expose this from readline?

aduh95 · 2022-04-30T15:02:00Z

Exposing this from fs would add a non-primitive fs operation and make the API inconsistent, so IMO it doesn't belong to fs.

Thanks for clarifying, I didn't get that point, I think it's reasonable (although I don't agree 😅).

Well, there is a one-liner for this too

for await(const line of readLines(openFileHandle.createReadStream())) console.log(line)

That's the gotcha: you need to provide crlfDelay option if you don't want to see weird behaviour.

for await(const line of readLines({ input: openFileHandle.createReadStream(), crlfDelay: Infinity })) console.log(line)

Could you please share what the API would look like if we expose this from readline?

Well I suppose the easiest would be to add support for FileHandle as input for the readline Interface:

import { createInterface as readLines } from 'node:readline';
import { open } from 'node:fs/promises';

const fh = await open('path/to/file', 'r');
for await(const line of readLines(fh)) console.log(line);

RaisinTen · 2022-04-30T15:29:54Z

That's the gotcha: you need to provide crlfDelay option if you don't want to see weird behaviour.

Does it sound reasonable to change the crlfDelay default to Infinity? Not sure if the one-liner would satisfy your needs then.

aduh95 · 2022-05-20T14:26:15Z

@nodejs/fs @nodejs/readline can I get some more reviews please?

RaisinTen · 2022-05-20T15:06:11Z

For anyone else following along, the other half of the discussion regarding the inclusion of this functionality in core took place in #43102.

LiviaMedeiros

+1 on having this method in fs; I think that importance of builtin utility functions is underestimated: their absence might be an invisible obstacle for the whole language to become a convenient utility tool for daily routine.

It doesn't create inconsistency between low- and high-level API here, since we already have .readFile .writeFile anyway.

doc/api/fs.md

RaisinTen · 2022-05-22T14:20:05Z

I think that importance of builtin utility functions is underestimated: their absence might be an invisible obstacle for the whole language to become a convenient utility tool for daily routine.

Well, the whole readline module is a builtin utility API. I don't see why we should create additional APIs on fs which internally just calls a single public API of readline given that it can be done very easily in userland, which is why we never got so many complaints about fs.readline not being a thing in Node.js.

I feel that landing this change would have some consequences:

more functions that internally just forwards calls to other public APIs which could very well be done in userland
a lot of churn in the ecosystem that would turn code like https://nodejs.org/api/readline.html#example-read-file-stream-line-by-line into fs.readLines, without much gain

I think it's only fair to add a builtin utility function to core if it's tedious to implement in userland using public APIs of Node.js.

It doesn't create inconsistency between low- and high-level API here, since we already have .readFile .writeFile anyway.

.readFile and .writeFile is exposed from fs., fsPromises. and filehandle.. If we don't expose the readline function from all of these 3, I get the signal that we aren't supporting fs. and fsPromises.. I think we should add this feature to those too in the same PR that's adding this feature.

tniessen · 2022-05-27T18:30:21Z

I agree that a utility to read a stream of lines from an arbitrary data source, whether it's a node stream or a web stream or a file handle, is desirable -- the lack thereof might be why I often switch to Python whenever I have to process line-based input data.

The readline module has always felt a bit hacky to me -- its design clearly goes way beyond simply reading lines. For example, I don't think the result of file.readLines() should have a question() function. As long as it does, this probably does not belong in fs but rather in readline.

aduh95 · 2022-09-15T12:24:34Z

@tniessen do you think it's ok to land this now that .question has been removed on main?

nodejs-github-bot · 2022-09-15T13:20:09Z

CI: https://ci.nodejs.org/job/node-test-pull-request/46603/

nodejs-github-bot · 2022-09-16T17:06:02Z

CI: https://ci.nodejs.org/job/node-test-pull-request/46628/

PR-URL: #42590 Reviewed-By: LiviaMedeiros <livia@cirno.name>

Notable changes: * cli: * (SEMVER-MINOR) add `--watch` (Moshe Atlow) #44366 * fs: * (SEMVER-MINOR) add `FileHandle.prototype.readLines` (Antoine du Hamel) #42590 * http: * (SEMVER-MINOR) add writeEarlyHints function to ServerResponse (Wing) #44180 * http2: * (SEMVER-MINOR) make early hints generic (Yagiz Nizipli) #44820 * src: * (SEMVER-MINOR) add detailed embedder process initialization API (Anna Henningsen) #44121 * util: * (SEMVER-MINOR) add default value option to parsearg (Manuel Spigolon) #44631

Notable changes: * cli: * (SEMVER-MINOR) add `--watch` (Moshe Atlow) #44366 * fs: * (SEMVER-MINOR) add `FileHandle.prototype.readLines` (Antoine du Hamel) #42590 * http: * (SEMVER-MINOR) add writeEarlyHints function to ServerResponse (Wing) #44180 * http2: * (SEMVER-MINOR) make early hints generic (Yagiz Nizipli) #44820 * src: * (SEMVER-MINOR) add detailed embedder process initialization API (Anna Henningsen) #44121 * util: * (SEMVER-MINOR) add default value option to parsearg (Manuel Spigolon) #44631 PR-URL: #44968

Notable changes: * cli: * (SEMVER-MINOR) add `--watch` (Moshe Atlow) #44366 * fs: * (SEMVER-MINOR) add `FileHandle.prototype.readLines` (Antoine du Hamel) #42590 * http: * (SEMVER-MINOR) add writeEarlyHints function to ServerResponse (Wing) #44180 * http2: * (SEMVER-MINOR) make early hints generic (Yagiz Nizipli) #44820 * lib: * (SEMVER-MINOR) refactor transferable AbortSignal (flakey5) #44048 * src: * (SEMVER-MINOR) add detailed embedder process initialization API (Anna Henningsen) #44121 * util: * (SEMVER-MINOR) add default value option to parsearg (Manuel Spigolon) #44631 PR-URL: #44968

watch mode (experimental): Running in 'watch' mode using `node --watch` restarts the process when an imported file is changed. Contributed by Moshe Atlow in [#44366](#44366) Other notable changes: * fs: * (SEMVER-MINOR) add `FileHandle.prototype.readLines` (Antoine du Hamel) #42590 * http: * (SEMVER-MINOR) add writeEarlyHints function to ServerResponse (Wing) #44180 * http2: * (SEMVER-MINOR) make early hints generic (Yagiz Nizipli) #44820 * lib: * (SEMVER-MINOR) refactor transferable AbortSignal (flakey5) #44048 * src: * (SEMVER-MINOR) add detailed embedder process initialization API (Anna Henningsen) #44121 * util: * (SEMVER-MINOR) add default value option to parsearg (Manuel Spigolon) #44631 PR-URL: #44968

watch mode (experimental): Running in 'watch' mode using `node --watch` restarts the process when an imported file is changed. Contributed by Moshe Atlow in #44366 Other notable changes: * fs: * (SEMVER-MINOR) add `FileHandle.prototype.readLines` (Antoine du Hamel) #42590 * http: * (SEMVER-MINOR) add writeEarlyHints function to ServerResponse (Wing) #44180 * http2: * (SEMVER-MINOR) make early hints generic (Yagiz Nizipli) #44820 * lib: * (SEMVER-MINOR) refactor transferable AbortSignal (flakey5) #44048 * src: * (SEMVER-MINOR) add detailed embedder process initialization API (Anna Henningsen) #44121 * util: * (SEMVER-MINOR) add default value option to parsearg (Manuel Spigolon) #44631 PR-URL: #44968

kamatil-dev · 2023-12-16T18:34:49Z

is there a way to use zlib in this function? or i must use the readline package?

tniessen · 2023-12-16T18:47:29Z

@kamatil-dev As you can see from the implementation, this is just a thin wrapper around readline and doesn't work for arbitrary streams. I'd suggest using readline.

kamatil-dev · 2023-12-16T21:02:04Z

@tniessen thank you ❤, but as i can see in my end, the new readLines() function performs better than the actual seperated package

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readline: add support for FileHandle #43102

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fs: add FileHandle.prototype.readLines

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fs: add `FileHandle.prototype.readLines` #42590

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