The ioutil functions are deprecated since Go 1.17 and only wrap another
library function. Thus directly call the underlying function.
This commit only mechanically replaces the function calls.
if x { return true } return false => return x
fmt.Sprintf("%v", x) => fmt.Sprint(x) or x.String()
The fmt.Sprintf idiom is still used in the SecretString tests, where it
serves security hardening.
Accessing beyond the end of the file now removes the file from the cache
because it is assumed to be truncated. Usually, this means that the data
is fetched directly from the backend instead.
This commits adds rudimentary support for a cache directory, enabled by
default. The cache directory is created if it does not exist. The cache
is used if there's anything in it, newly created snapshot and index
files are written to the cache automatically.
