Limit for logs filter.

[tomusdrw]

Similar to #2073

This time it allows to specify optional limit parameter to newFilter and then subsequent calls to getFilterLogs or getFilterChanges will return limited number of logs.

[coveralls]

Coverage decreased (-0.2%) to 85.131% when pulling 7c0831e on limit-filter into 48be609 on master.

[jacogr]

From a documentation and use perspective, is the API (where 25 indicates the limit) -

eth_newFilter({
  from: 'earliest',
  to: 'latest',
}, 25)

or

eth_newFilter({
  from: 'earliest',
  to: 'latest',
  limit: 25
})

[tomusdrw]

Hmm, currently it's the first option (additional parameter), I guess the latter one is much better though.
I'll update the PR.

[tomusdrw]

Fixed the API, limit is now part of the Filter object. Complete reference:

eth_getLogs({ from: 'earliest', limit: 10 }) // returns 10 last logs
let filterId = eth_newFilter({
  from: 'earliest',
  to: 'latest',
  limit: 25
})
eth_getFilterChanges(filterId) // returns changes, but at most 25 last logs
eth_getFilterLogs(filterId) // returns logs matching filter, but at most 25 last logs

[coveralls]

Coverage decreased (-0.1%) to 85.166% when pulling db43462 on limit-filter into 48be609 on master.

[rphmeier]

side note: seems that topics only has four members -- why bother allocating a Vec at all?

[tomusdrw]

Hmm, it can contain up to 4 entries - but that's true, we could substitute this with array of 4 Option. I will prepare a separate PR.