nsqd: malicious client can (easily) crash server

[mreiferson]

nsqd can be easily crashed. Steps to reproduce:

• nsq and run nsqd (using the default settings)
• Telnet to the port it is running on
• Type ' V2IDENTIFY', press enter and then type 'ctrl-c'
• The server will panic.
  panic: runtime error: makeslice: len out of range

I am running v0.2.27 on OS X if that make any difference.

[mreiferson]

I'll take a look at this, thanks for the report @prio!

[mreiferson]

with the attached commit I now get:

$ ./nsqd
[nsqd] 2014/10/05 23:32:58.890088 nsqd v0.3.0-alpha (built w/go1.3.1)
[nsqd] 2014/10/05 23:32:58.891999 ID: 292
[nsqd] 2014/10/05 23:32:58.892030 NSQ: persisting topic/channel metadata to nsqd.292.dat
[nsqd] 2014/10/05 23:32:58.894088 TCP: listening on [::]:4150
[nsqd] 2014/10/05 23:32:58.894118 HTTP: listening on [::]:4151
[nsqd] 2014/10/05 23:33:01.902695 TCP: new client(127.0.0.1:63139)
[nsqd] 2014/10/05 23:33:05.892995 CLIENT(127.0.0.1:63139): desired protocol magic '  V2'
[nsqd] 2014/10/05 23:33:07.236588 ERROR: [127.0.0.1:63139] - E_BAD_BODY IDENTIFY invalid body size -720899

RFR @jehiah