[PROPOSAL] policy: Enable to define policy as go plugin

api/gobgp.proto

@@ -1076,6 +1076,7 @@ message Statement {
 message Policy {
   string name = 1;
   repeated Statement statements = 2;
+  string plugin_path = 3;
 }
 
 enum PolicyType {

api/grpc_server.go

@@ -2142,6 +2142,7 @@ func toPolicyApi(p *config.PolicyDefinition) *Policy {
 			}
 			return l
 		}(),
+		PluginPath: p.PluginPath,
 	}
 }
 
@@ -2187,6 +2188,10 @@ func NewPolicyFromApiStruct(a *Policy) (*table.Policy, error) {
 	if a.Name == "" {
 		return nil, fmt.Errorf("empty policy name")
 	}
+	applyFunc, err := table.ExtractApplyFuncFromPolicyPlugin(a.PluginPath)
+	if err != nil {
+		return nil, err
+	}
 	stmts := make([]*table.Statement, 0, len(a.Statements))
 	for idx, x := range a.Statements {
 		if x.Name == "" {
@@ -2199,8 +2204,10 @@ func NewPolicyFromApiStruct(a *Policy) (*table.Policy, error) {
 		stmts = append(stmts, y)
 	}
 	return &table.Policy{
-		Name:       a.Name,
-		Statements: stmts,
+		Name:            a.Name,
+		Statements:      stmts,
+		PluginPath:      a.PluginPath,
+		PluginApplyFunc: applyFunc,
 	}, nil
 }
 

config/bgp_configs.go

@@ -5824,6 +5824,9 @@ type PolicyDefinition struct {
 	// original -> rpol:statements
 	// Enclosing container for policy statements.
 	Statements []Statement `mapstructure:"statements" json:"statements,omitempty"`
+	// original -> gobgp:plugin-path
+	// Path to policy plugin which must be an shared object.
+	PluginPath string `mapstructure:"plugin-path" json:"plugin-path,omitempty"`
 }
 
 func (lhs *PolicyDefinition) Equal(rhs *PolicyDefinition) bool {
@@ -5849,6 +5852,9 @@ func (lhs *PolicyDefinition) Equal(rhs *PolicyDefinition) bool {
 			}
 		}
 	}
+	if lhs.PluginPath != rhs.PluginPath {
+		return false
+	}
 	return true
 }
 

docs/sources/cli-command-syntax.md

@@ -479,7 +479,7 @@ If you want to remove one element(extended community) of ExtCommunitySet, to spe
 
 ```shell
 # mod policy
-% gobgp policy { add | del | set } <policy name> [<statement name>...]
+% gobgp policy { add | del | set } <policy name> [<statement name>...] [plugin-path <plugin-path>]
 # show all policies
 % gobgp policy
 # show a specific policy

docs/sources/policy-plugin.md

@@ -0,0 +1,223 @@
+# Policy Plugin
+
+This page explains how to implement your own policy plugin and how to configure
+it.
+
+The policy plugin enables to apply policy rules flexibly which are difficult
+to define with the [OpenConfig](http://www.openconfig.net/) policy model, just
+logging received paths and complex attributes manipulation for example.
+
+## Prerequisites
+
+The following assumes you finished [Getting Started](getting-started.md) and
+bases of [GoBGP Policy Model](policy.md).
+
+Also, the policy plugin feature uses ["plugin"](https://golang.org/pkg/plugin/)
+package of Golang, which requires to use Golang version 1.8 or later.
+
+## Contents
+
+- [Implementation of Policy Plugin](#implementation-of-policy-plugin)
+- [Build Policy Plugin](#build-policy-plugin)
+- [Configuration](#configuration)
+- [Verification](#verification)
+
+## Implementation of Policy Plugin
+
+A policy plugin must have an `Apply` function which receives `path *table.Path`
+and `options *table.PolicyOptions` arguments, then returns `*table.Path` and
+`error`.
+
+```go
+package main
+
+import (
+    "github.com/osrg/gobgp/table"
+)
+
+func Apply(path *table.Path, options *table.PolicyOptions) (*table.Path, error) {
+    // Do some manipulation of "path".
+    // Or "return nil, nil" to reject "path".
+    return path, nil
+}
+```
+
+`path *table.Path` includes the incoming path information and
+`options *table.PolicyOptions` provides the additional information about sender
+router for example.
+
+The return value of `*table.Path` should be the updated path if successfully
+manipulated (also with nothing to update) and `error` describes errors during
+manipulation process. Also, to reject the given path, please `return nil, nil`.
+
+Example: `policy_a.go`
+
+```go
+package main
+
+import (
+    "fmt"
+
+    "github.com/osrg/gobgp/table"
+)
+
+func Apply(path *table.Path, options *table.PolicyOptions) (*table.Path, error) {
+    // Just do logging
+    fmt.Printf("Apply policy to %+v\n", path)
+    return path, nil
+}
+```
+
+## Build Policy Plugin
+
+To generate a loadable policy plugin, execute `go build` command with
+`-buildmode=plugin` option.
+
+```bash
+go build -buildmode=plugin -o <plugin name>.so <plugin name>.go
+```
+
+Example: Build `policy_a.so` with `policy_a.go`
+
+```bash
+go build -buildmode=plugin -o policy_a.so policy_a.go
+```
+
+## Configuration
+
+To attach the policy plugin to global RIB or neighbor's local RIB (only when
+the neighbor is configured as a "route-server client"), specify path to the
+generated policy plugin (`.so` file) with `plugin-path` in
+`[[policy-definitions]]` section.
+
+Example: Attach `policy_a.so` to global RIB as "import policy"
+
+```toml
+[global.apply-policy.config]
+  import-policy-list = ["policy_a"]
+  default-import-policy = "accept-route"
+  default-export-policy = "accept-route"
+
+[[policy-definitions]]
+  name = "policy_a"
+  plugin-path = "/path/to/policy_a.so"
+```
+
+Example: Attach `policy_a.so` to global RIB as "export policy"
+
+```toml
+[[neighbors]]
+  # ...(snip)...
+  [neighbors.route-server.config]
+    route-server-client = true
+  [neighbors.apply-policy.config]
+    export-policy-list = ["policy_a"]
+    default-import-policy = "accept-route"
+    default-export-policy = "accept-route"
+    default-in-policy = "accept-route"
+
+[[policy-definitions]]
+  name = "policy_a"
+  plugin-path = "/path/to/policy_a.so"
+```
+
+**NOTE:** When reloading the confirmation file, GoBGP will determine whether
+the configured values are updated or not before calling the reloading policy
+API. So if the configured value (`plugin-path`) is not changed, even if the
+plugin is updated, GoBGP can't detect the change of the plugin's
+implementation. Then for reloading the policy plugin, please also update the
+value of `plugin-path`, for example, `/path/to/policy_a.1.0.so` to
+`/path/to/policy_a.1.1.so` or appending the timestamp.
+
+## Verification
+
+Let's verify the example policy plugin `policy_a.so` attached to global RIB can
+output log messages when `Apply` function is called.
+
+Topology:
+
+```text
++----------+              +----------+
+| r1       |              | r2       |
+| 10.0.0.1 +----(iBGP)----+ 10.0.0.2 |
+| AS 65000 |              | AS 65000 |
++----------+              +----------+
+```
+
+`gobgpd.toml` on r1:
+
+```toml
+[global.config]
+  as = 65000
+  router-id = "1.1.1.1"
+
+[[neighbors]]
+  [neighbors.config]
+    neighbor-address = "10.0.0.2"
+    peer-as = 65000
+  [[neighbors.afi-safis]]
+    [neighbors.afi-safis.config]
+      afi-safi-name = "ipv4-unicast"
+
+[global.apply-policy.config]
+  import-policy-list = ["policy_a"]
+  default-import-policy = "accept-route"
+  default-export-policy = "accept-route"
+
+[[policy-definitions]]
+  name = "policy_a"
+  plugin-path = "/path/to/policy_a.so"
+```
+
+`gobgpd.toml` on r2:
+
+```toml
+[global.config]
+  as = 65000
+  router-id = "2.2.2.2"
+
+[[neighbors]]
+  [neighbors.config]
+    neighbor-address = "10.0.0.1"
+    peer-as = 65000
+  [[neighbors.afi-safis]]
+    [neighbors.afi-safis.config]
+      afi-safi-name = "ipv4-unicast"
+```
+
+Start GoBGP on r1 and r2.
+
+```bash
+r1> gobgpd -f gobgpd.toml
+{"level":"info","msg":"gobgpd started","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"Topic":"Config","level":"info","msg":"Finished reading the config file","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"level":"info","msg":"Peer 10.0.0.2 is added","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"Topic":"Peer","level":"info","msg":"Add a peer configuration for:10.0.0.2","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"Key":"10.0.0.2","State":"BGP_FSM_OPENCONFIRM","Topic":"Peer","level":"info","msg":"Peer Up","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+...(snip)...
+
+r2> gobgpd -f gobgpd.toml
+{"level":"info","msg":"gobgpd started","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"Topic":"Config","level":"info","msg":"Finished reading the config file","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"level":"info","msg":"Peer 10.0.0.1 is added","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"Topic":"Peer","level":"info","msg":"Add a peer configuration for:10.0.0.1","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+{"Key":"10.0.0.1","State":"BGP_FSM_OPENCONFIRM","Topic":"Peer","level":"info","msg":"Peer Up","time":"YYYY-MM-DDThh:mm:ss+09:00"}
+...(snip)...
+```
+
+Add a route on r2.
+
+```bash
+r2> gobgp global rib -a ipv4 add 10.2.1.0/24
+r2> gobgp global rib -a ipv4
+   Network              Next Hop             AS_PATH              Age        Attrs
+*> 10.2.1.0/24          0.0.0.0                                   00:00:00   [{Origin: ?}]
+```
+
+Then, GoBGP on r1 should output like;
+
+```bash
+r1> gobgpd -f r1_gobgpd.toml
+...(snip)...
+Apply policy to { 10.2.1.0/24 | src: { 10.0.0.2 | as: 65000, id: 2.2.2.2 }, nh: 10.0.0.2 }
+```

gobgp/cmd/policy.go

@@ -379,6 +379,7 @@ func printPolicy(indent int, pd *table.Policy) {
 	for _, s := range pd.Statements {
 		printStatement(indent, s)
 	}
+	fmt.Printf("%sPluginPath: %s\n", strings.Repeat(" ", indent), pd.PluginPath)
 }
 
 func showPolicy(args []string) error {
@@ -777,17 +778,26 @@ func modAction(name, op string, args []string) error {
 
 func modPolicy(modtype string, args []string) error {
 	if len(args) < 1 {
-		return fmt.Errorf("usage: gobgp policy %s <name> [<statement name>...]", modtype)
+		return fmt.Errorf("usage: gobgp policy %s <name> [<statement name>...] [plugin-path <plugin-path>]", modtype)
 	}
 	name := args[0]
 	args = args[1:]
 	stmts := make([]config.Statement, 0, len(args))
-	for _, n := range args {
-		stmts = append(stmts, config.Statement{Name: n})
+	pluginPath := ""
+	for idx, arg := range args {
+		if arg == "plugin-path" {
+			if len(args) <= idx+1 {
+				return fmt.Errorf("specify plugin-path argument")
+			}
+			pluginPath = args[idx+1]
+			break
+		}
+		stmts = append(stmts, config.Statement{Name: arg})
 	}
 	policy, err := table.NewPolicy(config.PolicyDefinition{
 		Name:       name,
 		Statements: stmts,
+		PluginPath: pluginPath,
 	})
 	if err != nil {
 		return err