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fs: make sure to write entire buffer #42434

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fs: make sure to write entire buffer #42434

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fs: make sure to write entire buffer
ronag Mar 22, 2022
b6b9680
fixup
ronag Mar 22, 2022
a5bf600
fixup
ronag Mar 22, 2022
523314a
fixup
ronag Mar 22, 2022
d4c7a90
fixup
ronag Mar 22, 2022
d0afc94
fixuP
ronag Mar 22, 2022
43f2529
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ronag Mar 22, 2022
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ronag Mar 22, 2022
3869561
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ronag Mar 22, 2022
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ronag Mar 22, 2022
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ronag Mar 22, 2022
09b7994
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ronag Mar 22, 2022
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Update lib/internal/fs/promises.js
ronag Mar 23, 2022
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72 changes: 58 additions & 14 deletions lib/internal/fs/streams.js
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Original file line number Diff line number Diff line change
Expand Up @@ -386,22 +386,71 @@ WriteStream.prototype.open = openWriteFs;

WriteStream.prototype._construct = _construct;

function writeAll(data, size, pos, cb, retries = 0) {
this[kFs].write(this.fd, data, 0, size, pos, (er, bytesWritten, buffer) => {
if (er?.code === 'EAGAIN') {
er = null;
bytesWritten = 0;
}

if (this.destroyed || er) {
return cb(er);
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this.bytesWritten += bytesWritten;

retries = bytesWritten ? 0 : retries + 1;
size -= bytesWritten;
pos += bytesWritten;

if (retries > 5) {
cb(new Error('writev failed'));
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This needs to be a proper error with code?

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Suggestions?

} else if (size) {
writeAll(buffer.slice(bytesWritten), size, pos, cb, retries);
} else {
cb();
}
});
}

function writevAll(chunks, size, pos, cb, retries = 0) {
this[kFs].writev(this.fd, chunks, this.pos, (er, bytesWritten, buffers) => {
if (er?.code === 'EAGAIN') {
er = null;
bytesWritten = 0;
}

if (this.destroyed || er) {
return cb(er);
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will er here be something if this.destroyed is truthy? Otherwise, this could signal to the caller that the call succeeded?

}

this.bytesWritten += bytesWritten;

retries = bytesWritten ? 0 : retries + 1;
size -= bytesWritten;
pos += bytesWritten;

if (retries > 5) {
cb(new Error('writev failed'));
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I need a little help here... not sure what error to use

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Lemme check

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Checked the existing codes, no idea either 😅

} else if (size) {
writevAll([Buffer.concat(buffers).slice(bytesWritten)], size, pos, cb, retries);
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@mscdex mscdex Mar 22, 2022 •
edited
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If we're going to be concatenating, we may as well just do it once and call writeAll() with it instead. Otherwise like @mcollina said, we should handle this more efficiently.

Ideally it would be great if we didn't have to even keep recreating arrays on retry. That might be a nice addition to the fs.writev() API to make it more like fs.write() with its offset parameter, so we could just pass a starting index or something. With something like that all we'd have to do is possibly slice() a single buffer (or simply increasing the starting index) before retrying.

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This is a cold path though? It should almost never happen. Is it worth optimizing for?

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It should almost never happen

It think it would be useful to get an idea of how often it happens (I personally have no idea). How cold is it?

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Well, if it does happen often then we have a lot of seriously broken software out there... I guess we would have quite a bit of reports....

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@mscdex mscdex Mar 22, 2022 •
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or people have learned to handle retries on their own?

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@ronag ronag Mar 22, 2022 •
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I don’t think you can actually detect that in this interface… there is nothing a user can do… it will just be corrupt w/o any way to detect or recover… so no

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Well, if it does happen often then we have a lot of seriously broken software out there... I guess we would have quite a bit of reports....

makes sense, yeah sounds like a cold path to me.

} else {
cb();
}
});
}

WriteStream.prototype._write = function(data, encoding, cb) {
this[kIsPerformingIO] = true;
this[kFs].write(this.fd, data, 0, data.length, this.pos, (er, bytes) => {
writeAll.call(this, data.length, data, this.pos, (er) => {
this[kIsPerformingIO] = false;
if (this.destroyed) {
// Tell ._destroy() that it's safe to close the fd now.
cb(er);
return this.emit(kIoDone, er);
}

if (er) {
return cb(er);
}

this.bytesWritten += bytes;
cb();
cb(er);
});

if (this.pos !== undefined)
Expand All @@ -421,20 +470,15 @@ WriteStream.prototype._writev = function(data, cb) {
}

this[kIsPerformingIO] = true;
this[kFs].writev(this.fd, chunks, this.pos, (er, bytes) => {
writevAll.call(this, size, chunks, this.pos, (er) => {
this[kIsPerformingIO] = false;
if (this.destroyed) {
// Tell ._destroy() that it's safe to close the fd now.
cb(er);
return this.emit(kIoDone, er);
}

if (er) {
return cb(er);
}

this.bytesWritten += bytes;
cb();
cb(er);
});

if (this.pos !== undefined)
Expand Down