Support for setting userid/groupid for process execution

examples/setuserid/main.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+
+	"github.com/vladimirvivien/gexe"
+)
+
+// This examples demonstrates how to use gexe to run
+// subprocesses with different userid/groupid.
+// Note: setting userid/gid for subprocesses requires
+// elevated privilege such as using sudo.
+
+func main() {
+	p := gexe.NewProc(`echo "Hello World!`)
+	var uid string
+
+	switch runtime.GOOS {
+	case "windows":
+	case "darwin":
+		uid = gexe.Run(`id -u`)
+	case "linux":
+		uid = gexe.Run(`id -l`)
+	}
+
+	if uid != "" {
+		if err := p.SetUserid(uid).Err(); err != nil {
+			fmt.Println("Failed to set userid: ", err)
+			os.Exit(1)
+		}
+	}
+
+	result := p.Run()
+	if err := result.Err(); err != nil {
+		fmt.Println("Error: ", err)
+		os.Exit(1)
+	}
+
+	fmt.Println("Running process with userid:", uid)
+	fmt.Println(result.Result())
+}

exec/proc.go

@@ -6,7 +6,10 @@ import (
 	"io"
 	"os"
 	osexec "os/exec"
+	"os/user"
+	"strconv"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/vladimirvivien/gexe/vars"
@@ -16,6 +19,8 @@ import (
 type Proc struct {
 	id         int
 	err        error
+	userid     *int
+	groupid    *int
 	state      *os.ProcessState
 	result     *bytes.Buffer
 	outputPipe io.ReadCloser
@@ -36,6 +41,7 @@ func NewProc(cmdStr string) *Proc {
 	}
 
 	command := osexec.Command(words[0], words[1:]...)
+
 	return &Proc{
 		cmd:    command,
 		result: new(bytes.Buffer),
@@ -132,6 +138,26 @@ func (p *Proc) Start() *Proc {
 		p.cmd.Stderr = p.result
 	}
 
+	// apply user id and user grp
+	var procCred *syscall.Credential
+	if p.userid != nil {
+		procCred = &syscall.Credential{
+			Uid: uint32(*p.userid),
+		}
+	}
+	if p.groupid != nil {
+		if procCred == nil {
+			procCred = new(syscall.Credential)
+		}
+		procCred.Uid = uint32(*p.groupid)
+	}
+	if procCred != nil {
+		if p.cmd.SysProcAttr == nil {
+			p.cmd.SysProcAttr = new(syscall.SysProcAttr)
+		}
+		p.cmd.SysProcAttr.Credential = procCred
+	}
+
 	if err := p.cmd.Start(); err != nil {
 		p.err = err
 		return p
@@ -155,6 +181,41 @@ func (p *Proc) Command() *osexec.Cmd {
 	return p.cmd
 }
 
+// SetUserid looks up the user by a numerical id or
+// by a name to be used for the process when launched.
+func (p *Proc) SetUserid(user string) *Proc {
+	if p.err != nil {
+		return p
+	}
+	uid, err := lookupUserID(user)
+	if err != nil {
+		p.err = err
+		return p
+	}
+
+	p.userid = &uid
+
+	return p
+}
+
+// SetGroupid looks up the group by a numerical id or
+// by a name to be used for the process when launched.
+func (p *Proc) SetGroupid(grp string) *Proc {
+	if p.err != nil {
+		return p
+	}
+
+	gid, err := lookupGroupID(grp)
+	if err != nil {
+		p.err = err
+		return p
+	}
+
+	p.groupid = &gid
+
+	return p
+}
+
 // Peek attempts to read process state information
 func (p *Proc) Peek() *Proc {
 	p.state = p.cmd.ProcessState
@@ -338,3 +399,59 @@ func (p *Proc) hasStarted() bool {
 func Parse(cmd string) ([]string, error) {
 	return parse(cmd)
 }
+
+func lookupUserID(userid string) (int, error) {
+	var uid int
+	var usr *user.User
+	var err error
+
+	// assume userid is a valid numerical user id
+	usr, err = user.LookupId(userid)
+	if err == nil {
+		uid, _ = strconv.Atoi(usr.Uid)
+		return uid, nil
+	}
+
+	// if not numercal id, lookup by username
+	usr, err = user.Lookup(userid)
+	if err == nil {
+		uid, _ = strconv.Atoi(usr.Uid)
+		return uid, nil
+	}
+
+	return 0, err
+}
+
+func lookupGroupID(grpid string) (int, error) {
+	var gid int
+	var grp *user.Group
+	var err error
+
+	// assume grpid is a valid numerical group id
+	grp, err = user.LookupGroupId(grpid)
+	if err == nil {
+		gid, _ = strconv.Atoi(grp.Gid)
+		return gid, nil
+	}
+
+	// if not numercal id, lookup by groupname
+	grp, err = user.LookupGroup(grpid)
+	if err == nil {
+		gid, _ = strconv.Atoi(grp.Gid)
+		return gid, nil
+	}
+
+	return 0, err
+}
+
+func getDefaultUserIDs() (int, int, error) {
+	usr, err := user.Current()
+	if err != nil {
+		return 0, 0, err
+	}
+
+	uid, _ := strconv.Atoi(usr.Uid)
+	gid, _ := strconv.Atoi(usr.Gid)
+
+	return uid, gid, nil
+}