Support for loading .so plugin files

closes #1717

circle.yml

@@ -4,9 +4,9 @@ machine:
   post:
     - sudo service zookeeper stop
     - go version
-    - go version | grep 1.7.5 || sudo rm -rf /usr/local/go
-    - wget https://storage.googleapis.com/golang/go1.7.5.linux-amd64.tar.gz
-    - sudo tar -C /usr/local -xzf go1.7.5.linux-amd64.tar.gz
+    - sudo rm -rf /usr/local/go
+    - wget https://storage.googleapis.com/golang/go1.8rc3.linux-amd64.tar.gz
+    - sudo tar -C /usr/local -xzf go1.8rc3.linux-amd64.tar.gz
     - go version
 
 dependencies:

cmd/telegraf/telegraf.go

@@ -6,6 +6,9 @@ import (
 	"log"
 	"os"
 	"os/signal"
+	"path"
+	"path/filepath"
+	"plugin"
 	"runtime"
 	"strings"
 	"syscall"
@@ -13,12 +16,14 @@ import (
 	"github.com/influxdata/telegraf/agent"
 	"github.com/influxdata/telegraf/internal/config"
 	"github.com/influxdata/telegraf/logger"
+
 	_ "github.com/influxdata/telegraf/plugins/aggregators/all"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	_ "github.com/influxdata/telegraf/plugins/inputs/all"
 	"github.com/influxdata/telegraf/plugins/outputs"
 	_ "github.com/influxdata/telegraf/plugins/outputs/all"
 	_ "github.com/influxdata/telegraf/plugins/processors/all"
+
 	"github.com/kardianos/service"
 )
 
@@ -50,6 +55,8 @@ var fUsage = flag.String("usage", "",
 	"print usage for a plugin, ie, 'telegraf -usage mysql'")
 var fService = flag.String("service", "",
 	"operate on the service")
+var fPlugins = flag.String("plugins", "",
+	"path to directory containing external plugins")
 
 // Telegraf version, populated linker.
 //   ie, -ldflags "-X main.version=`git describe --always --tags`"
@@ -246,11 +253,53 @@ func (p *program) Stop(s service.Service) error {
 	return nil
 }
 
+// loadExternalPlugins loads external plugins from shared libraries (.so, .dll, etc.)
+// in the specified directory.
+func loadExternalPlugins(rootDir string) error {
+	return filepath.Walk(rootDir, func(pth string, info os.FileInfo, err error) error {
+		// Stop if there was an error.
+		if err != nil {
+			return err
+		}
+
+		// Ignore directories.
+		if info.IsDir() {
+			return nil
+		}
+
+		// Ignore files that aren't shared libraries.
+		ext := strings.ToLower(path.Ext(pth))
+		if ext != ".so" && ext != ".dll" {
+			return nil
+		}
+
+		// Load plugin.
+		_, err = plugin.Open(pth)
+		if err != nil {
+			return fmt.Errorf("error loading [%s]: %s", pth, err)
+		}
+
+		return nil
+	})
+}
+
 func main() {
 	flag.Usage = func() { usageExit(0) }
 	flag.Parse()
 	args := flag.Args()
 
+	// Load external plugins, if requested.
+	if *fPlugins != "" {
+		pluginsDir, err := filepath.Abs(*fPlugins)
+		if err != nil {
+			log.Fatal("E! " + err.Error())
+		}
+		log.Printf("I! Loading external plugins from: %s\n", pluginsDir)
+		if err := loadExternalPlugins(*fPlugins); err != nil {
+			log.Fatal("E! " + err.Error())
+		}
+	}
+
 	inputFilters, outputFilters := []string{}, []string{}
 	if *fInputFilters != "" {
 		inputFilters = strings.Split(":"+strings.TrimSpace(*fInputFilters)+":", ":")