DAG reader: seeking to the end of the file leaves the offset at zero

[schomatis]

Seeking to an offset equal to the size of the file (or a bigger) leaves the linkPosition (unmodified) at the start of the file (where subsequent read operations will pick up from).

https://github.com/ipfs/go-ipfs/blob/9bad5fe6fef11fc5d923e7ebecbe6f53deb044fe/unixfs/io/pbdagreader.go#L275-L286

I'm working on some modifications to the DAG reader and I'm not sure if this is a bug or it is an intended behavior (I don't know what happens in the Unix API when doing something like this) as some of the current tests (like TestLargeWriteChunks) depend on it.

[schomatis]

/cc @Stebalien

[Stebalien]

This should follow POSIX and seek past the end of the file. Reading should return zero bytes and an EOF.

[schomatis]

Ok, this is a bug then, thanks.

[schomatis]

Fixed in ipfs/go-unixfs#60.