I’m interested in calculating IPFS hashes for various files and directories, somewhat similar to ipfs add -n. I’ve searched around, but wasn’t able to find any solid documentation on how this is calculated exactly. I’ve had a quick look through code and tried figuring it out from experimentation, a…

Could you clarify the question? ‘ipfs add -n’ does exactly what you’re asking – it calculates the hashes of whatever you’re adding. The ‘-n’ flag tells ipfs to just calculate the hashes without actually adding the files. Are you asking how to do this in code rather than from the command line? is …

I don’t know the specifics of how the current default behavior of ipfs add -n is implemented, but depending on your use case it might be worth noting that the hashes generated by go-ipfs’s add command for a given file/directory are dependent on a variety of factors (where the defaults might change).…

Oh, so a file could have many possible hashes? And how hashes are calculated isn’t yet standardised/stable? That was something I was unaware of, so thank you very much for the information! I realised that the multi-hash system could allow the same file to have different hashes, but I was under the …

As I understand it, the IPFS hash is a self-describing hash, i.e. a node will know from the format which algorithm was used, at which length etc. As long as you have the latest version installed, you should be fine. The latter was a problem for me, when I tried accessing the Turkish Wikipedia mirror…

yeah… as I understand it the first two letters(“Qm” most commonly found in IPFS hashes) state how a file is going to be hashed. https://github.com/ipfs/faq/issues/22 So if you used a different hash function the first two letters would be different which should be recognized automatically…

Thanks for the responses, but from what leerspace is saying, this isn’t the only issue. The multi-hash format only provides a wrapper around the hash algorithm, so you can change from SHA256 to BLAKE2b, and the prefix will differ. HOWEVER, the hash is also affected by the chunking algorithm, DAG fo…

yes… what you are saying could happen. However, if this happens most likely the user is forcing the duplication, as knowing how to change the hash algorithm, chunking algorithm, DAG format and CID version is more complicated and time consuming than most users would have time to do it, without substa…

Sidenote: I’ve installed the prebuilt multihash binary here , and it’s giving me an IPFS hash different from running ipfs add -n /path/to/FileOrDir, both in default setting (i.e. sha2-256). I assume this has to do with the changes made to hashing at one of the earlier ipfs updates—I believe it was 0.…

Multihash just hashes the file and prints out it hash in multihash format. ipfs add creates merkeldag and wraps the file in needed format, that is why the hash is different.

How to calculate file/directory hash?

Help

Nyan July 16, 2017, 12:40am 3

Yes, sorry for not making that clear. To put it another way, is there some specification/guide on how I would write a program to basically do the same thing as ipfs add -n ?

Thank you for the response by the way.

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How to calculate file/directory hash?

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