This commit adds two types of simple DoS protection:
* Limit concurrent search requests per client IP address, regardless of
the searches being performed. This helps address issues of accidental
spamming from a malfunctioning OPAC workstation, or crawlers of various
types. The limit is controlled by a global flag called
"opac.max_concurrent_search.ip".
* Limit the global concurrent search requests for the same query. This
helps address both simple and distributed DoS that send the same search
request over and over. The limit is controlled by a global flag called
"opac.max_concurrent_search.query", and defaults to 20.
When the limit is exceeded in either case the client receives an HTTP
429 "Too many requests" response from the web server, and the connection
is ended.
Signed-off-by: Mike Rylander <email address hidden>
Signed-off-by: Jason Stephenson <email address hidden>
Signed-off-by: Galen Charlton <email address hidden>
