fs: make sure to write entire buffer #42434
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fs.write(v) is not guaranteed to write everything in a single call. Make sure we don't assume so.
lib/internal/fs/streams.js
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| retries = bytesWritten ? 0 : retries + 1 | ||
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| if (retries > 5) { | ||
| return cb(new Error('writev failed')); |
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What are we trying for 5 times here? Writing a non-zero number of bytes?
lib/internal/fs/streams.js
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| retries = bytesWritten ? 0 : retries + 1 | ||
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| if (retries > 5) { | ||
| return cb(new Error('writev failed')); |
lib/internal/fs/streams.js
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| } | ||
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| if (bytesWritten < size) { | ||
| writevAll([Buffer.concat(buffers).slice(bytesWritten)], pos + bytesWritten, cb, retries); |
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I would recommend being a bit more subtle here and avoid the massive slowdown. Worst case you are allocating 2x memory to pick one byte. I would recommend just concatenating the buffers that have not been completely written.
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This is a cold path though? It should almost never happen. Is it worth optimizing for?
| pos += bytesWritten; | ||
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| 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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Checked the existing codes, no idea either 😅
| if (retries > 5) { | ||
| cb(new Error('writev failed')); | ||
| } else if (size) { | ||
| writevAll([Buffer.concat(buffers).slice(bytesWritten)], size, pos, cb, retries); |
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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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or people have learned to handle retries on their own?
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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.
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Needs a test as well. |
| pos += bytesWritten; | ||
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| if (retries > 5) { | ||
| cb(new Error('writev failed')); |
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This needs to be a proper error with code?
Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>
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| 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?
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@nodejs/fs someone willing to help get this over the finish line? I still think it's a potential bug. |
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Maybe @rluvaton or @atlowChemi ? |
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What help is needed? |
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Linting and Tests |
@ronag Can you check the |
Hm. I don't know how to do that. Can you just push to a new branch/PR? |
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Superseded by #49211 |
fs.write(v) is not guaranteed to write everything in a single
call. Make sure we don't assume so.