1. We no longer use a fake client but just rewriting.
2. We group all the inserts into a single ZADD dispatch (big speed win).
3. As a side effect of the correct implementation, replication works.
4. The return value of the command is now correct.

limit.

When we fail to setup the write handler it does not make sense to take
the client around, it is missing writes: whatever is a client or a slave
anyway the connection should terminated ASAP.

Moreover what the function does exactly with its return value, and in
which case the write handler is installed on the socket, was not clear,
so the functions comment are improved to make the goals of the function
more obvious.

Also related to #2485.

master was closing the connection if the RDB transfer took long time.
and also sent PINGs to the slave before it got the initial ACK, in which case the slave wouldn't be able to find the EOF marker.

Change done in order to remove a warning and improve code robustness. No
actual bug here.

1. No need to set btype in processUnblockedClients(), since clients
   flagged REDIS_UNBLOCKED should have it already cleared.
2. When putting clients in the unblocked clients list, clientsArePaused()
   should flag them with REDIS_UNBLOCKED. Not strictly needed with the
   current code but is more coherent.

When the list of unblocked clients were processed, btype was set to
blocking type none, but the client remained flagged with REDIS_BLOCKED.
When timeout is reached (or when the client disconnects), unblocking it
will trigger an assertion.

There is no need to process pending requests from blocked clients, so
now clientsArePaused() just avoid touching blocked clients.

Close #2467.

Still many things to convert inside config.c in the next commits.
Some const safety in String objects creation and addReply() family
functions.

Thanks to @codeslinger (Toby DiPasquale) for identifying the issue.

Related to issue #2409.

This is safe since bufpos is small, inside the range of the local
client buffer.

read() and write() return ssize_t (signed long), not int.

For other offsets, we can use the unsigned size_t type instead
of a signed offset (since our replication offsets and buffer
positions are never negative).

Refactor a common pattern into one function so we don't
end up with copy/paste programming.

Specialized single-use function. Not the best match for sds.c btw.
Also genClientPeerId() is no longer static: we need symbols.

Instead of manually checking for strchr(n,':') everywhere,
we can use our new centralized IP formatting functions.

Track bandwidth used by clients and replication (but diskless
replication is not tracked since the actual transfer happens in the
child process).

This includes a refactoring that makes tracking new instantaneous
metrics simpler.

zmalloc(0) cauesd to actually trigger a non-zero allocation since with
standard libc malloc we have our own zmalloc header for memory tracking,
but at the same time the returned pointer is at the end of the block and
not in the middle. This triggers a false positive when testing with
valgrind.

When the inline protocol args count is 0, we now avoid reallocating
c->argv, preventing the issue to happen.

RDB EOF detection was relying on the final part of the RDB transfer to
be a magic 40 bytes EOF marker. However as the slave is put online
immediately, and because of sockets timeouts, the replication stream is
actually contiguous with the RDB file.

This means that to detect the EOF correctly we should either:

1) Scan all the stream searching for the mark. Sucks CPU-wise.
2) Start to send the replication stream only after an acknowledge.
3) Implement a proper chunked encoding.

For now solution "2" was picked, so the master does not start to send
ASAP the stream of commands in the case of diskless replication. We wait
for the first REPLCONF ACK command from the slave, that certifies us
that the slave correctly loaded the RDB file and is ready to get more
data.

Closes #2002

The code tested many times if a client had active Pub/Sub subscriptions
by checking the length of a list and dictionary where the patterns and
channels are stored. This was substituted with a client flag called
REDIS_PUBSUB that is simpler to test for. Moreover in order to manage
this flag some code was refactored.

This commit is believed to have no effects in the behavior of the
server.

Technically the problem is due to the client type API that does not
return a special value for the master, however fixing it locally in the
CLIENT KILL command is better currently because otherwise we would
introduce a new output buffer limit class as a side effect.

Added a new SKIPME option that is true by default, that prevents the
client sending the command to be killed, unless SKIPME NO is sent.

This will be used by CLIENT KILL and is also a good way to ensure a
given client is still the same across CLIENT LIST calls.

The output of CLIENT LIST was modified to include the new ID, but this
change is considered to be backward compatible as the API does not imply
you can do positional parsing, since each filed as a different name.

Because of output buffer limits Redis internals had this idea of type of
clients: normal, pubsub, slave. It is possible to set different output
buffer limits for the three kinds of clients.

However all the macros and API were named after output buffer limit
classes, while the idea of a client type is a generic one that can be
reused.

This commit does two things:

1) Rename the API and defines with more general names.
2) Change the class of clients executing the MONITOR command from "slave"
   to "normal".

"2" is a good idea because you want to have very special settings for
slaves, that are not a good idea for MONITOR clients that are instead
normal clients even if they are conceptually slave-alike (since it is a
push protocol).

The backward-compatibility breakage resulting from "2" is considered to
be minimal to care, since MONITOR is a debugging command, and because
anyway this change is not going to break the format or the behavior, but
just when a connection is closed on big output buffer issues.