short: flushing the bufio buffer is not enough to ensure data
consistency.
long:
Saving an entry to the WAL calls writeLine to append data to the
autofile group backing the WAL, then calls group.Flush() to flush that
data to persistent storage. group.Flush() in turn proxies to
headBuf.flush(), flushing the active bufio.BufferedWriter. However,
BufferedWriter wraps a Writer, not another BufferedWriter, and the way
it flushes is by calling io.Writer.Write() to clear the BufferedWriter's
buffer. The io.Writer we're wrapping here is AutoFile, whose Write
method calls os.File.Write(), performing an unbuffered write to the
operating system, where, I assume, it sits in the OS buffers awaiting
sync. This means that Wal.Save does not, in fact, ensure the saved
operation is synced to disk before returning.
Prior to this change, a custom Signer would have no knowledge of the private
key stored in the configuration file. This changes introduces a generator
function, which creates a Signer based on the private key. This provides an
opportunity for customer Signers to adjust behaviour based on the key
contents. (E.g. imagine key contents are a key label, rather than the key
itself).
By exporting all of the commands, we allow users to setup their own
tendermint node cli. This enables users to provide a different
pivValidator without the need to fork tendermint.
This example shows how a user of the tendermint library can build their
own node and supply it with its own commands. It includes two todos in
order to make it easier for library users to use tendermint.
