Reverse HTTP proxy to filter requests by different rules. Can be used between production webserver and the application server to prevent abuse of the application backend.
The original purpose of this program was to defend
searx , but it can be used to guard any web application.
$ go get github.com/asciimoo/filtron
$ "$GOPATH/bin/filtron" --help
Rules A rule has two required attributes:
name and
actions A rule can contain all of the following attributes:
-
limit integer - Defines how many matching requests allowed to access the application within interval seconds. (Can be omitted if 0 ) -
interval integer - Time range in seconds to reset rule numbers (Can be omitted if limit is 0 ) -
filters list of selectors -
aggregations list of selectors (if filters specified it activates only in case of the filter matches) -
subrules list of rules (if filters specified it activates only in case of the filter matches) -
disabled bool - Disable a rule (default is false ) -
stop bool - Finish request validation immediately and skip remaining rules (default is false )
JSON representation of a rule:
{
"name": "example rule",
"interval": 60,
"limit": 10,
"filters": ["GET:q", "Header:User-Agent=^curl"],
"actions": [
{"name": "log",
"params": {"destination": "stderr"}},
{"name": "block",
"params": {"message": "Not allowed"}}
]
}
Explanation: Allow only 10 requests a minute where
q represented as GET parameter and the user agent header starts with
curl . Request is logged to STDERR and blocked with a custom error message if limit is exceeded. See more examples
here .
actions Rule's actions are sequentially activated if a request exceeds rule's limit
Note: Only the rule's first action will be executed that serves custom response
Currently implemented actions log Log the request
block Serve HTTP 429 response instead of passing the request to the application
shell Execute a shell command.
cmd (string) and
args (list of selectors) are required params (Example:
{"name": "shell", "params": {"cmd": "echo %v is the IP", "args": ["IP"]}} )
filters If all the selectors found, it increments a counter. Rule blocks the request if counter reaches
limit aggregations Counts the values returned by selectors. Rule blocks the request if any value's number reaches
limit subrules Each rule can contain any number of subrules. Activates on parent rule's filter match.
Selectors Request's different parts can be extracted using selector expressions.
Selectors are strings that can match any attribute of a HTTP request with the following syntax:
[!]RequestAttribute[:SubAttribute][=Regex]
-
! can negate the selector -
RequestAttribute (required) selects specific part of a request - possible values: - Single value
- Multiple values
-
GET -
POST -
Param - it is an alias for both GET and POST -
Cookie -
Header
-
SubAttribute if RequestAttribute is not a single value, this can specify the inner attribute -
Regex regular expression to filter the selected attributes value
Examples IP returns the client's IP address
GET:x returns the
x GET parameter if exists
!Header:Accept-Language returns true if there is no
Accept-Language HTTP header
Path=^/(x|y)$ matches if the path is
/x or
/y API Filtron can be configured through its REST API which listens on
127.0.0.1:4005 by default.
API endpoints /rules Loaded rules in JSON format
/rules/reload Reload the rule file specified at startup
