add linux ServerPath, dynamically find scsynth executable

Author: Brian Sorahan

server.go

@@ -1,15 +1,22 @@
 package sc
 
 import (
+	"errors"
 	"fmt"
+	"os"
 	"os/exec"
 	"strconv"
+	"strings"
 	"time"
 )
 
 // DefaultServerPort is the default listening port for scsynth.
 const DefaultServerPort = 57120
 
+// ErrNoScsynth happens when you try to start a SuperCollider
+// server but do not have an scsynth executable in your PATH.
+var ErrNoScsynth = errors.New("Please install scsynth somewhere in your PATH.")
+
 // Server represents a running instance of scsynth.
 type Server struct {
 	*exec.Cmd
@@ -19,6 +26,46 @@ type Server struct {
 	StartTimeout time.Duration
 }
 
+// getServerPath gets the path to the scsynth executable.
+func (s *Server) getServerPath() (string, error) {
+	for _, file := range strings.Split(ServerPath, ":") {
+		ok, err := isExecutable(file)
+		if err != nil {
+			return "", err
+		}
+		if ok {
+			return file, nil
+		}
+	}
+
+	path, hasPath := os.LookupEnv("PATH")
+	if !hasPath {
+		return "", ErrNoScsynth
+	}
+
+	for _, file := range strings.Split(path, ":") {
+		ok, err := isExecutable(file)
+		if err != nil {
+			return "", err
+		}
+		if ok {
+			return file, nil
+		}
+	}
+	return "", ErrNoScsynth
+}
+
+// isExecutable returns true if the provided file is executable, false otherwise.
+// It also returns any error that occurs while trying to read the file.
+func isExecutable(filename string) (bool, error) {
+	info, err := os.Stat(filename)
+	if err != nil {
+		return false, err
+	}
+	mode := info.Mode()
+	return ((mode & 0x01) | (mode & 0x08) | (mode & 0x40)) != 0, nil
+}
+
 // args gets the command line args to scsynth
 func (s *Server) args() ([]string, error) {
 	// Get the port.
@@ -48,7 +95,13 @@ func (s *Server) Start() error {
 	if err != nil {
 		return err
 	}
-	s.Cmd = exec.Command(ServerPath, args...)
+
+	serverPath, err := s.getServerPath()
+	if err != nil {
+		return err
+	}
+
+	s.Cmd = exec.Command(serverPath, args...)
 	if err := s.Cmd.Start(); err != nil {
 		return err
 	}

server_linux.go

@@ -0,0 +1,5 @@
+// +build linux
+package sc
+
+// ServerPath is the path the scsynth executable on linux systems.
+const ServerPath = "/usr/bin/scsynth:/usr/local/bin/scsynth"