doc: add description for filehandle.write(string[, position[, encoding]]) #23224

darahayes · 2018-10-02T18:34:32Z

Hey folks, this PR adds missing docs for filehandle.write(string[, position[, encoding]]) in the fs.promises API.

As per #20406, only the buffer version of this API is documented right now.

One thing I wanted to ask. I believe the intention is to reconcile the Promise based API as much as possible with the callback based one. In the docs submitted with this PR, I described the encoding option has having the default value utf8. This is the behaviour in the callback based API.

Based off the code here. I don't think that's actually happening in the Promise based version.

I have two questions:

Should the behaviour be modified such that a default value of utf8 is used? I'd be delighted to provide a PR and some tests.
Or should I just remove any mention of it from this PR?

Cheers!

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
tests and/or benchmarks are included
documentation is changed or added
commit message follows commit guidelines

vsemozhetbyt · 2018-10-02T19:33:23Z

CI-lite: https://ci.nodejs.org/job/node-test-pull-request-lite-pipeline/1100/

vsemozhetbyt · 2018-10-02T19:34:23Z

cc @jasnell

thefourtheye · 2018-10-03T04:15:11Z

doc/api/fs.md

+the value will be coerced to one.
+
+`position` refers to the offset from the beginning of the file where this data
+should be written. If `typeof position !== 'number'` the data will be written at


Could this be simply written as, "If the type of position is not a number"?

So I basically copied the same wording used here: https://github.com/nodejs/node/pull/23224/files#diff-acabf706a8aa070a8796e3573f7e4678R3910

This style is used in the callback APIs too. I figured I would use the same wording that's used in those other places. I'd be happy to clarify those other places also if you think that's a good idea.

thefourtheye · 2018-10-03T04:19:55Z

Based off the code here. I don't think that's actually happening in the Promise based version.

Looks like you are correct. If possible, could you come up with a test case which will break because of this?

cc @nodejs/fs

darahayes · 2018-10-03T04:48:45Z

If possible, could you come up with a test case which will break because of this?

Sure thing. I'll look to see how it's tested in the callback based API and see if I can get some inspiration from there.

benjamingr · 2018-10-03T13:35:19Z

Should the behaviour be modified such that a default value of utf8 is used? I'd be delighted to provide a PR and some tests.

I believe so - yes, and work improving the promises fs API is always appreciated. (cc @jasnell )

Changes in this PR LGTM

benjamingr · 2018-10-03T13:36:12Z

doc/api/fs.md

+`encoding` is the expected string encoding.
+
+It is unsafe to use `filehandle.write()` multiple times on the same file
+without waiting for the `Promise` to be resolved (or rejected). For this


Nit: a rejected promise is still resolved (and so is a promise following another promise) - fulfilled instead of resolved or "settled" instead of either would work here.

Hey there, I've addressed some other feedback but I haven't addressed this one yet. I did that for two reasons.

This is the same wording used in other parts of the documentation. See the docs for the filehandle.write(buffer)

I would argue that explicitly using the words resolved and rejected make sense in this context. If you're familiar with Promises, this makes sense. I would argue the same cannot exactly be said about the word fulfilled because it's not as commonly used when referring to Promises. (at least as far as I can tell). In my opinion that potentially introduces some ambiguity.

All that being said: I am happy to make the suggested changes here, as well as in the other parts of the same doc to ensure consistency.

darahayes · 2018-10-08T11:56:57Z

Hey folks, sorry I was away for the past couple of days so I couldn't do any more work on this. I mentioned that I would try to come up with some test cases wrt to the encoding option. Still willing to do this, but I'm wondering should it be done as part of this PR or as a different one? Thanks!

thefourtheye · 2018-10-08T12:19:38Z

@darahayes I would say, you can add them as separate commits in this PR itself. Because without the code changes, this doc patch would not be correct.

doc/api/fs.md

darahayes · 2018-11-02T11:27:31Z

Hey folks, it's been so long but I was finally able to get some more time with this issue.

I've added a code change that ensures the same behaviour as the callback-based API. A default value of 'utf8' is used for the encoding when none is supplied.

All that being said, there was a request to come up with a test case for this and I'm struggling with that a little bit.

The callback based fs.write(filehandle, string) method only has a single test and it doesn't test the behaviour around defaulting to utf8.

I'm not 100% sure how to test that the string contents written to a file is indeed utf8 encoded. Anyone have any ideas? Thanks

darahayes · 2018-11-12T11:26:06Z

@thefourtheye Hey there. Sorry to bother you like this, I figured I would ping you as the original reviewer. I know you folks were probably really busy with all the PRs from the recent code and learn events 😃. Just wanted to bump for some visibility.

Just a quick summary of where I'm at - I believe I have made the necessary changes but I'm not 100% sure how write a good test case for this. I was hoping I could get some pointers if anyone has the time. Thanks!

thefourtheye · 2018-11-13T06:58:53Z

@darahayes No problem at all. I am sorry I couldn't get to this on time. Let me take a look at this today. Thanks for being patient.

thefourtheye · 2018-11-13T15:14:31Z

Okay, looks like I was wrong.

In the docs submitted with this PR, I described the encoding option has having the default value utf8. This is the behaviour in the callback based API.

Based off the code here. I don't think that's actually happening in the Promise based version.

I took a deeper look at the code and the default encoding value is actually set to UTF-8. Let me break this down.

node/lib/internal/fs/promises.js

Lines 255 to 256 in dde9b3a

    
           const bytesWritten = (await binding.writeString(handle.fd, buffer, offset, 
        
                                                           length, kUsePromises)) || 0;

which actually parses the encoding like this

node/src/node_file.cc

Line 1720 in 6ae6383

const auto enc = ParseEncoding(isolate, args[3], UTF8);

args[3] is actually the length. So, ParseEncoding does this

node/src/node_encoding.cc

Lines 89 to 100 in fcd7a72

    
           enum encoding ParseEncoding(Isolate* isolate, 
        
                                       Local<Value> encoding_v, 
        
                                       enum encoding default_encoding) { 
        
             CHECK(!encoding_v.IsEmpty()); 
        
             if (!encoding_v->IsString()) 
        
               return default_encoding; 
        
             Utf8Value encoding(isolate, encoding_v); 
        
             return ParseEncoding(*encoding, default_encoding); 
        
           }

If the length parameter is actually not a String then the default encoding (UTF8) will be used. Also, if the passed length value is not a valid encoding type, then

node/src/node_encoding.cc

Lines 79 to 85 in fcd7a72

    
           } else if (StringEqualNoCase(encoding, "buffer")) { 
        
             return BUFFER; 
        
           } else if (StringEqualNoCase(encoding, "hex")) { 
        
             return HEX; 
        
           } else { 
        
             return default_encoding; 
        
           }

will take care of it.

@darahayes Sorry, I misled you. Could you please drop the commit which introduces default value for encoding?

Add missing docs for filehandle.write(string[, position[, encoding]]) In the fs.promises API. fixes: nodejs#20406

darahayes · 2018-11-13T16:36:20Z

@thefourtheye thanks so much for your help! I'm kicking myself that I didn't figure that out sooner. I've dropped the commit you mentioned and I also addressed some of the feedback on the docs changes.

thefourtheye · 2018-11-14T17:03:35Z

Lite-CI: https://ci.nodejs.org/job/node-test-pull-request-lite-pipeline/1613/

thefourtheye · 2018-11-14T17:38:52Z

@nodejs/fs PTAL once.

Trott · 2018-11-20T03:11:15Z

Landed in 692b09f

Add missing docs for filehandle.write(string[, position[, encoding]]) In the fs.promises API. Fixes: nodejs#20406 PR-URL: nodejs#23224 Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

thefourtheye · 2018-11-20T04:24:23Z

Thanks @Trott. I am currently traveling, otherwise I would have landed this sooner.

@darahayes Thanks for your patience in getting this done.

Add missing docs for filehandle.write(string[, position[, encoding]]) In the fs.promises API. Fixes: #20406 PR-URL: #23224 Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

Add missing docs for filehandle.write(string[, position[, encoding]]) In the fs.promises API. Fixes: nodejs#20406 PR-URL: nodejs#23224 Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

Add missing docs for filehandle.write(string[, position[, encoding]]) In the fs.promises API. Fixes: #20406 PR-URL: #23224 Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

nodejs-github-bot added doc Issues and PRs related to the documentations. fs Issues and PRs related to the fs subsystem / file system. labels Oct 2, 2018

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doc: add filehandle.write(string[, position[, encoding]])

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Add missing docs for filehandle.write(string[, position[, encoding]]) In the fs.promises API. fixes: nodejs#20406

darahayes force-pushed the fs.promises.write branch from 30e241d to 8bc4de6 Compare November 13, 2018 16:28

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doc: add description for filehandle.write(string[, position[, encoding]]) #23224

doc: add description for filehandle.write(string[, position[, encoding]]) #23224

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doc: add description for filehandle.write(string[, position[, encoding]]) #23224

doc: add description for filehandle.write(string[, position[, encoding]]) #23224

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