# ja-netfilter 2022.2.0

### A Java Instrumentation Framework

## Usage

* download from the [releases page](https://gitee.com/ja-netfilter/ja-netfilter/releases)
* add `-javaagent:/absolute/path/to/ja-netfilter.jar` argument (**Change to your actual path**)
    * add as an argument of the `java` command. eg: `java -javaagent:/absolute/path/to/ja-netfilter.jar -jar executable_jar_file.jar`
    * some apps support the `JVM Options file`, you can add as a line of the `JVM Options file`.
    * **WARNING: DO NOT put some unnecessary whitespace characters!**
* or execute `java -jar /path/to/ja-netfilter.jar` to use `attach mode`.
* for **Java 17** you have to add at least these `JVM Options`:

  ```
  --add-opens=java.base/jdk.internal.org.objectweb.asm=ALL-UNNAMED
  --add-opens=java.base/jdk.internal.org.objectweb.asm.tree=ALL-UNNAMED
  ```

* edit your plugin config files: `${lower plugin name}.conf` file in the `config` dir where `ja-netfilter.jar` is located.
* the `config`, `logs` and `plugins` directories can be specified through **the javaagent args**.
  * eg: `-javaagent:/path/to/ja-netfilter.jar=appName`, your config, logs and plugins directories will be `config-appname`, `logs-appname` and `plugins-appname`.
  * if no javaagent args, they default to `config`, `logs` and `plugins`.
  * this mechanism will avoid extraneous and bloated `config`, `logs` and `plugins`.

* run your java application and enjoy~

## Config file format

```
[ABC]
# for the specified section name

# for example
[URL]
EQUAL,https://someurl

[DNS]
EQUAL,somedomain

# EQUAL       Use `equals` to compare
# EQUAL_IC    Use `equals` to compare, ignore case
# KEYWORD     Use `contains` to compare
# KEYWORD_IC  Use `contains` to compare, ignore case
# PREFIX      Use `startsWith` to compare
# PREFIX_IC   Use `startsWith` to compare, ignore case
# SUFFIX      Use `endsWith` to compare
# SUFFIX_IC   Use `endsWith` to compare, ignore case
# REGEXP      Use regular expressions to match
```


## Debug info

* the `ja-netfilter` will **NOT** output debugging information by default
* add environment variable `JANF_DEBUG=1` (log level) and start to enable it
* or add system property `-Djanf.debug=1` (log level) to enable it
* log level: `NONE=0`, `DEBUG=1`, `INFO=2`, `WARN=3`, `ERROR=4`

## Debug output

* the `ja-netfilter` will output debugging information to the `console` by default
* add environment variable `JANF_OUTPUT=value` and start to change output medium
* or add system property `-Djanf.output=value` to change output medium
* output medium value: [`NONE=0`, `CONSOLE=1`, `FILE=2`, `CONSOLE+FILE=3`, `WITH_PID=4`]
* eg: `console` + `file` + `pid file name` = 1 + 2 + 4 = 7, so the `-Djanf.output=7`

## Plugin system

* for developer:
    * view the [scaffold project](https://gitee.com/ja-netfilter/ja-netfilter-sample-plugin) written for the plugin system
    * compile your plugin and publish it
    * just use your imagination~

* for user:
    * download the jar file of the plugin
    * put it in the subdirectory called `plugins` where the ja-netfilter.jar file is located
    * enjoy the new capabilities brought by the plugin
    * if the file suffix is `.disabled.jar`, the plugin will be disabled