IPFS hash verification in nodejs

Help Coding
1

I want to develop a nodejs app in which a user stores a file on IPFS and gives the hash to the app.
What I would like to do is to verify that the contents under this given hash produce the same hash, something similar to verifying the checksum.
Is there a way to do it using the ipfs-api module?

For example:

A user writes a “Hello world” string in the “data.txt” file, adds the file on IPFS and gets the hash: QmWpXFXgii2CfYMBXj9jihPcokpFhwCjGQqOipZ1LVGgTU

Then he runs my app with the IPFS hash:
node myapp.js QmWpXFXgii2CfYMBXj9jihPcokpFhwCjGQqOipZ1LVGgTU

I would like to verify that the contents under this hash are “Hello world” and he didn’t provide another hash.

2

I’m not sure I really understand what you are after.

Does your app know “Hello world” and you would like to know that hash of it? If yes you could try the “onlyHash” option.

3

Basically I want to read from an IPFS hash and get the contents of the file stored under this address, then I want to verify that the contents of the file produce actually the given hash.

In other words, a user claims that a file with “Hello world” gives this hash: QmWpXFXgii2CfYMBXj9jihPcokpFhwCjGQqOipZ1LVGgTU but when I read under this hash there is another file with “Hello”.
Actually I want to make sure that the hash that the user gives me is what he claims to be.

PS. In ipfs-api npm package I didn’t find an “onlyHash” option…

4

So it sounds like you want the “only hash” option. You would take the file and then add with onlyHash: true and you’ll get the hash of the file back. Then you can verify if it’s the same.

Though that shouldn’t actually be needed as if you retrieve a file with a certain hash from IPFS it’s guaranteed that the contents hashes to that hash.

If you run jsipfs add --help you’ll see the --only-hash option which maps to onlyHash when you use the module.