This commit implements pruning for the block nodes that form the memory
chain which are no longer needed. The validation of a block only requires
information from a set number of previous nodes. The initial code did not
prune old nodes as they were no longer needed, but the vast majority of
the infrastructure to support it was already in place as that was always
the goal. This commit finishes implementing the missing bits to make it
a reality.
Previously, the code was using big rational numbers for work values which
resulted in carrying way too much precision around (and ultimately a lot
of extra memory and computation to carry that precision). This commit
converts the work values to big integers and calculates them with integer
division. This is acceptable because the numerator is multiplied by 2^256
which is higher than the maximum possible proof of work. Therefore
anything after the decimal is superfluous precision for the purposes of
chain selection.
Also, add a check for negative difficulty values when calculating the work
value. Negative values won't occur in practice with valid blocks, but
it's possible an invalid block could trigger the code path, so be safe and
check for it.
This commit adds info level log statements when a block causes a chain
fork, extends a side chain (fork), or causes a reorganize. When a reorg
happens, the new and old chain heads along with the fork point are logged.
In addition to returning errors to the caller, log the error with a prefix
in a few key places that helps identify the origin for errors. In some
cases, the underlying error comes from a different subsystem such as the
SQL database driver and the error messages can be fairly generic.
This commit modifies the code to use params based on the active network
which paves the way for supporting the special rules and different genesis
blocks used by the test networks.
