add CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,107 @@
+# Contributing
+
+Thank you for your interest in contributing to sshpiper. 
+Make sure you have read [README.md](README.md) before starting.
+
+## Getting Started
+
+### Software Requirements
+ * Go <https://go.dev/>
+ * Docker <https://www.docker.com/>
+ * Docker Compose <https://docs.docker.com/compose/install/>
+ * Git <https://git-scm.com/>
+
+### Get the code
+
+rememeber to clone the submodules
+
+```
+git clone https://github.com/tg123/sshpiper
+cd sshpiper
+git submodule update --init --recursive
+```
+
+### Start Develop Environment
+
+```
+# in e2e folder, run:
+SSHPIPERD_DEBUG=1 docker-compose up --force-recreate
+```
+
+you will have two sshd:
+
+ * `host-password`: a password only sshd server (user: `user`, password: `pass`)
+ * `host-publickey`: a public key only sshd server (put your public key in `/sshconfig_publickey/.config/authorized_keys`)
+
+more settings: <https://github.com/linuxserver/docker-openssh-server>
+
+### Make some direct changes to source code
+
+after you have done, in e2e folder run:
+
+```
+go test
+```
+
+### Send PR with Github
+
+<https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request>
+
+## Understanding how sshpiper works
+
+### sshpiper seasoned cryto ssh lib
+
+The `crypto` folder contains the source code of the [sshpiper seasoned cryto ssh lib](./crypto/).
+It based on [crypto/ssh](https://golang.org/pkg/crypto/ssh/) and with a drop-in [sshpiper.go](./crypto/ssh/sshpiper.go) to expose all low level sshpiper required APIs.
+
+### sshpiperd
+
+[sshpiperd](./cmd/sshpiperd/) is the daemon wraps the `crypto/ssh` library to provide ssh connections management.
+It accepts ssh connections from `downstream` and routes them to `upstream`.
+The plugins are responsible to figure out how to authenticate `downstream` and map it to `upstream`
+
+### plugin
+
+The plugin is typically a grpc server that accepts requrests from `sshpiperd`. 
+The proto defines in [sshpiper.proto](./proto/sshpiper.proto).
+
+In most of the cases, the plugin connects with `sshpiperd` via `stdin/stdout`. The [ioconnn](./libplugin/ioconn/) wraps stdin/stdout to net.Conn for grpc use.
+`sshpiperd` also supports to create remote grpc connections to a plugin deploy in a different machine.
+
+## Your first plugin
+
+[fixed](./plugin/fixed/) and [simplematch](./plugin/simplematch/) are two good examples of plugins.
+They are very simple and just less than 50 lines of code.
+
+Take `fixed` as an example:
+
+```
+&libplugin.SshPiperPluginConfig{
+    PasswordCallback: func(conn libplugin.ConnMetadata, password []byte) (*libplugin.Upstream, error) {
+        return &libplugin.Upstream{
+            Host:          host,
+            Port:          int32(port),
+            IgnoreHostKey: true,
+            Auth:          libplugin.CreatePasswordAuth(password),
+        }, nil
+    },
+}
+```
+
+Here means the `downstream` is sending password to `sshpiperd`. Then `sshpiperd` will call plugin's `PasswordCallback` to get the `upstream` to connect to. 
+The `upstream` object contains host port and auth info about how to connect to the `upstream`. you can aslo return an error to deny the connection.
+
+### build and run the plugin
+
+simple build it with:
+
+```
+go build
+```
+
+you will get the executable in the current directory. say `myplugin`. start it with:
+
+```
+sshpiperd /path/to/myplugin
+```
+