Use unique identifiers for sockets

This commit modifies the plugin binary to accept a single argument as a socket
name which is generated upon calling `plugin.Use`. This now allows multiple instances
of a plugin to be used on one machine (if that's desirable) and avoids possible clashes
where plugins may not have gracefully exited.

Signed-off-by: David Bond <davidsbond93@gmail.com>

Author: davidsbond

README.md

@@ -19,9 +19,9 @@ via protocol buffers can be invoked.
 ```mermaid
 graph TD
 ;
-    Application["Your application"] <-->|Sends Commands| Socket["/tmp/plugin_example.sock"]
+    Application["Your application"] <-->|Sends Commands| Socket["/tmp/d1hf45ohpe2r63pr1bk.sock"]
     Plugin <-->|Handles Commands| Socket
-    Application -->|Executes| Plugin["/var/plugins/example"]
+    Application -->|Executes| Plugin["/var/plugins/example d1hf45ohpe2r63pr1bk"]
 ```
 
 ### Defining commands
@@ -56,6 +56,7 @@ import (
 	"log"
 
 	"github.com/davidsbond/plugin"
+	command "github.com/yourusername/path/to/protos"
 )
 
 func main() {
@@ -84,9 +85,7 @@ This `main.go` file should be compiled and placed on the same machine as the app
 ### Using plugins
 
 The `plugin.Use` function is used to execute the plugin binary, starting its gRPC server and creating a client that
-communicates with it via a UNIX domain socket. Only a single instance of the plugin should exist throughout your
-application as its lifecycle is managed via the `Use` and `Close` functions. Below is an example of how we start using
-our `add` command:
+communicates with it via a UNIX domain socket. Below is an example of how we start using our `add` command:
 
 ```go
 package main
@@ -96,16 +95,17 @@ import (
 	"fmt"
 
 	"github.com/davidsbond/plugin"
+	command "github.com/yourusername/path/to/protos"
 )
 
 func main() {
 	ctx := context.Background()
-	
+
 	p, err := plugin.Use(ctx, "./example")
 	if err != nil {
 		panic(err)
 	}
-	
+
 	// Remember the call Close() when you're done using the plugin!
 	defer p.Close()
 

go.mod

@@ -9,6 +9,7 @@ tool (
 )
 
 require (
+	github.com/rs/xid v1.6.0
 	github.com/stretchr/testify v1.10.0
 	golang.org/x/sync v0.15.0
 	google.golang.org/grpc v1.73.0

go.sum

@@ -158,6 +158,8 @@ github.com/rogpeppe/go-internal v1.13.1 h1:KvO1DLK/DRN07sQ1LQKScxyZJuNnedQ5/wKSR
 github.com/rogpeppe/go-internal v1.13.1/go.mod h1:uMEvuHeurkdAXX61udpOXGD/AzZDWNMNyH2VO9fmH0o=
 github.com/rs/cors v1.11.1 h1:eU3gRzXLRK57F5rKMGMZURNdIG4EoAmX8k94r9wXWHA=
 github.com/rs/cors v1.11.1/go.mod h1:XyqrcTp5zjWr1wsJ8PIRZssZ8b/WMcMf71DJnit4EMU=
+github.com/rs/xid v1.6.0 h1:fV591PaemRlL6JfRxGDEPl69wICngIQ3shQtzfy2gxU=
+github.com/rs/xid v1.6.0/go.mod h1:7XoLgs4eV+QndskICGsho+ADou8ySMSjJKDIan90Nz0=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/segmentio/asm v1.2.0 h1:9BQrFxC+YOHJlTlHGkTrFWf59nbL3XnCoFLTwDCI7ys=

internal/plugin/client.go

@@ -19,10 +19,9 @@ type (
 	}
 )
 
-// NewClient attempts to create a new connection to the plugin using the expected UNIX domain socket for the plugin
-// name.
-func NewClient(name string) (*Client, error) {
-	conn, err := grpc.NewClient("unix:///tmp/plugin_"+name+".sock",
+// NewClient attempts to create a new connection to the plugin using the provided UNIX domain socket.
+func NewClient(socket string) (*Client, error) {
+	conn, err := grpc.NewClient("unix:///tmp/"+socket+".sock",
 		grpc.WithTransportCredentials(insecure.NewCredentials()),
 	)
 	if err != nil {

plugin.go

@@ -5,9 +5,9 @@
 // the plugin interface.
 //
 // Plugins are external binaries that serve gRPC requests over a UNIX domain socket on the local machine. Each plugin
-// creates a socket using its name (which must be unique across all plugins used locally). Plugins make use of the
-// protobuf "Any" type in order to allow user-defined inputs and outputs to keep strong typing across application and
-// language boundaries.
+// creates a socket using a unique identifier passed as an argument from the host application to the plugin. Plugins
+// make use of the protobuf "Any" type in order to allow user-defined inputs and outputs to keep strong typing across
+// application and language boundaries.
 package plugin
 
 import (
@@ -23,6 +23,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/rs/xid"
 	"golang.org/x/sync/errgroup"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
@@ -102,6 +103,10 @@ func Run(config Config) error {
 	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM, syscall.SIGKILL)
 	defer cancel()
 
+	if len(os.Args) == 0 {
+		return errors.New("plugin expects at least one argument")
+	}
+
 	server := grpc.NewServer()
 
 	info := plugin.Info{
@@ -117,8 +122,8 @@ func Run(config Config) error {
 
 	plugin.NewAPI(info, handlers).Register(server)
 
-	socket := "/tmp/plugin_" + config.Name + ".sock"
-	listener, err := createPluginListener(socket)
+	socket := "/tmp/" + os.Args[0] + ".sock"
+	listener, err := net.Listen("unix", socket)
 	if err != nil {
 		return err
 	}
@@ -131,31 +136,12 @@ func Run(config Config) error {
 	group.Go(func() error {
 		<-ctx.Done()
 		server.GracefulStop()
-		return os.RemoveAll(socket)
+		return listener.Close()
 	})
 
 	return group.Wait()
 }
 
-func createPluginListener(socket string) (net.Listener, error) {
-	var errno syscall.Errno
-
-	listener, err := net.Listen("unix", socket)
-	switch {
-	case errors.As(err, &errno) && errors.Is(errno, syscall.EADDRINUSE):
-		// This socket should only ever be in use by us, so if it's already in use, we'll recreate it.
-		if err = os.Remove(socket); err != nil {
-			return nil, err
-		}
-
-		return net.Listen("unix", socket)
-	case err != nil:
-		return nil, err
-	default:
-		return listener, nil
-	}
-}
-
 func getPluginVersion() string {
 	if info, ok := debug.ReadBuildInfo(); ok {
 		return info.Main.Version
@@ -190,8 +176,13 @@ var (
 //
 // If successful, it is up to the caller to eventually call Plugin.Close when they no longer require use of the plugin.
 func Use(ctx context.Context, path string) (*Plugin, error) {
+	socket := xid.New().String()
+
 	cmd := &exec.Cmd{
 		Path: path,
+		Args: []string{
+			socket,
+		},
 	}
 
 	err := cmd.Start()
@@ -204,7 +195,7 @@ func Use(ctx context.Context, path string) (*Plugin, error) {
 	}
 
 	name := filepath.Base(path)
-	p.client, err = plugin.NewClient(name)
+	p.client, err = plugin.NewClient(socket)
 	if err != nil {
 		return nil, fmt.Errorf("failed to dial plugin %q: %w", name, err)
 	}