error[E0623]: lifetime mismatch
  --> $DIR/signature-mismatch.rs:79:10
   |
LL |         &'a self,
   |         -------- this parameter and the return type are declared with different lifetimes...
...
LL |     ) -> impl Future<Output = Vec<u8>> {
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |          |
   |          ...but data from `buff` is returned here

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0623`.