Exists & IsNotExist

[icholy]

Added a simpler way of checking if keys exist.

[peterbourgon]

Thanks for the idea! I implemented it slightly differently.

[icholy]

is there ever a time when Read returns an error that isn't a result of the key not existing?

[peterbourgon]

Sure,

• if the key is cached, and you're using compression, and there's any problem constructing the Compression reader over the cached data (link)
• same scenario, and there's any problem reading the data from memory (link)
• if the underlying file entry is somehow broken, e.g. missing (link)
• if the underlying file resolves to a directory (link)
• if the file exists but cannot be opened, e.g. due to permission issues (link)
• if you're using compression, and there's any problem constructing the Compression reader over the non-cached data (link)
• if there's any problem draining the ReadCloser returned by read into a byte slice (link)

[peterbourgon]

And, nicely: Go's unambiguous error idioms make constructing this list of 100% of the failure cases in Read trivial.