fix: print actual length in bytes in trimmed_hex

[kcsongor]

Motivation

The trimmed_hex function turns a slice of bytes into a hex string, trimming the output if the slice is longer than 32 bytes. If longer, an ellipsis is inserted in the middle, and the number of bytes is rendered into the output. Currently, this number actually corresponds to the length of the hex string, i.e. it's twice the number of bytes.

Solution

Render the length of the original slice instead of the hex string. I also slightly changed the code so only the visible parts of the slice are encoded as hex, which saves a bit of allocation.

[mattsse]

defer to @DaniPopes here

[mattsse]

hmm, not instantly obvious to me what the difference is

this now operates on the input and not the hex encoded input while also using 32 bytes instead of 64, but the slicing operations are the same?

so this is now only encodes the necessary slices? is that the change?

[kcsongor]

the key change is that s.len() (the third argument of the format! invocation) now operates on the input slice, so it will print the correct length (where previously a shadowing binding for s was introduced so s.len() operated on the hex string, doubling the length).

the original bug is fixable with a smaller diff (just putting s.len() / 2 in the 3rd argument), I'm happy to do that instead if that's preferred

[kcsongor]

so this is now only encodes the necessary slices? is that the change?

but yes, also only encodes the necessary slices -- technically that's an orthogonal change, but I thought the code looked a bit funny when all the operations were scaled back by 2

[DaniPopes]

it was less calls to hex::encode, but it doesn't matter

[mattsse]

got it now thanks @kcsongor

pending @DaniPopes