How to generate short unique names for uploaded files in nodejs?

Question

I need to name uploaded files by short unique identifier like nYrnfYEv a4vhAoFG hwX6aOr7. How could I ensure uniqueness of files?

Answer 1

(Posting my comments as answer, with responses to your concerns)

You may want to check out the shortid NPM module, which generates short ids (shockingly, I know :) ) similar to the ones you were posting as example. The result is configurable, but by default it's a string between 7 and 14 characters (length is random too), all URL-friendly (A-Za-z0-9\_\- in a regex).

To answer your (and other posters') concerns:

• Unless your server has a true random number generator (highly unlikely), every solution will use a PRNG (Pseudo-Random Number Generator). shortid uses Node.js crypto module to generate PRNG numbers, however, which is a much better generator than Math.random()
• shortid's are not sequential, which makes it even harder to guess them
• While shortid's are not guaranteed to be unique, the likelihood of a collision is extremely small. Unless you generate billions of entries per year, you could safely assume that a collision will never happen.
• For most cases, relying on probability to trust that collisions won't happen is enough. If your data is too important to risk even that tiny amount, you could make the shortid basically 100% unique by just prepending a timestamp to it. As an additional benefit, the file names will be harder to guess too. (Note: I wrote "basically 100% unique" because you could still, in theory, have a collision if two items are generated in the same timestamp, i.e. the same second. However, I would never be concerned of this. To have a real 100% certainty your only option is to run a check against a database or the filesystem, but that requires more resources.)
• The reason why shortid doesn't do that by itself is because for most applications the likelihood of a collision is too small to be a concern, and it's more important to have the shortest possible ids.