Shutting down the HTTP server currently breaks off all current requests.
This can create a race condition with RPC `stop` command, where the calling
process never receives confirmation.
This change removes the listening sockets on shutdown so that no new
requests can come in, but no longer breaks off requests in progress.
Meant to fix bitcoin/#6717.
Zcash: cherry-picked from commit 5e0c22135600fe36811da3b78216efc61ba765fb
Corrections are to the median block times, which were generated by subtracting
CBlockIndex::nMedianTimeSpan / 2 from the block height and then multiplying by
the target spacing. GetMedianTimePast() takes an array sorted by std::sort() and
returns element CBlockIndex::nMedianTimeSpan / 2, meaning that if
CBlockIndex::nMedianTimeSpan is odd (which it is), there is an out-by-one error
in the subtraction.
Fixes#2480 where missing map entry would cause a segfault.
`wtxHeight = mapBlockIndex[wtx.hashBlock]->nHeight;` results in undefined behaviour when the block hash is not present in the map, returning a null value which is dereferenced via `->nHeight`. This error is triggered by a zero-conf wallet transaction which has not been mined yet. As discussed in #2480, on some systems there is a segfault whilst on others there is a silent exit. This makes it difficult to write a test, but the fix has been tested empirically to confirm an exception is thrown. This PR fixes the segfault and complements #2525 which prevents a user from sending from a zaddr with minconf 0.
Wladimir J. van der Laan