Remembering all time samples makes nTimeOffset slow to respond to
system clock corrections. For instance, I start my node with a system
clock that's 30 minutes slow and run it for a few days. During that
time, I accumulate 10,000 offset samples with a median of 1800
seconds. Now I correct my system clock. Without this change, my node
must collect another 10,000 samples before nTimeOffset is correct
again. With this change, I must only accumulate 100 samples to
correct the offset.
Storing unlimited time samples also allows an attacker with many IP
addresses (ex, a large botnet) to perform a memory exhaustion attack
against Bitcoin nodes. The attacker sends a version message from each
IP to his target, consuming more of the target's memory each time.
Time samples are small, so this attack might be impractical under the
old code, but it's impossible with the new code.
The full list of time samples is rarely useful outside of debugging.
The node's time offset, however is useful for discovering local clock
drift, so it's displayed in all logging modes.
SecureString is identical to std::string except with secure_allocator
substituting for std::allocator. This makes casting between them
impossible, so converting between the two at API boundaries requires
calling ::c_str() for now.
This leads to the bitcoin core being shut down while the UI is accessing it, and generally results in a segmentation fault or crash. In case it is desirable to make it possible to shutdown the GUI from its RPC server, we'll need to implement a signal for it. For the mean time, this is a safe stopgap.
This RPC is exactly identical to getblockcount. This duplication
dates back to commit 22f721dbf2 when
Satoshi created the RPC interface.
There's no need to have both, so we standardize on "count" which
matches the naming convention in getconnectioncount.
Following the tradition established with previously deprecated APIs,
getblocknumber continues to work, but it's not listed in the help
system.
Wladimir J. van der Laan