Refactor procstat input (#2540)

fixes #1636 
fixes #2315

plugins/inputs/procstat/pgrep.go

@@ -0,0 +1,91 @@
+package procstat
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+type PIDFinder interface {
+	PidFile(path string) ([]PID, error)
+	Pattern(pattern string) ([]PID, error)
+	Uid(user string) ([]PID, error)
+	FullPattern(path string) ([]PID, error)
+}
+
+// Implemention of PIDGatherer that execs pgrep to find processes
+type Pgrep struct {
+	path string
+}
+
+func NewPgrep() (PIDFinder, error) {
+	path, err := exec.LookPath("pgrep")
+	if err != nil {
+		return nil, fmt.Errorf("Could not find pgrep binary: %s", err)
+	}
+	return &Pgrep{path}, nil
+}
+
+func (pg *Pgrep) PidFile(path string) ([]PID, error) {
+	var pids []PID
+	pidString, err := ioutil.ReadFile(path)
+	if err != nil {
+		return pids, fmt.Errorf("Failed to read pidfile '%s'. Error: '%s'",
+			path, err)
+	}
+	pid, err := strconv.Atoi(strings.TrimSpace(string(pidString)))
+	if err != nil {
+		return pids, err
+	}
+	pids = append(pids, PID(pid))
+	return pids, nil
+}
+
+func (pg *Pgrep) Pattern(pattern string) ([]PID, error) {
+	args := []string{pattern}
+	return find(pg.path, args)
+}
+
+func (pg *Pgrep) Uid(user string) ([]PID, error) {
+	args := []string{"-u", user}
+	return find(pg.path, args)
+}
+
+func (pg *Pgrep) FullPattern(pattern string) ([]PID, error) {
+	args := []string{"-f", pattern}
+	return find(pg.path, args)
+}
+
+func find(path string, args []string) ([]PID, error) {
+	out, err := run(path, args)
+	if err != nil {
+		return nil, err
+	}
+
+	return parseOutput(out)
+}
+
+func run(path string, args []string) (string, error) {
+	out, err := exec.Command(path, args...).Output()
+	if err != nil {
+		return "", fmt.Errorf("Error running %s: %s", path, err)
+	}
+	return string(out), err
+}
+
+func parseOutput(out string) ([]PID, error) {
+	pids := []PID{}
+	fields := strings.Fields(out)
+	for _, field := range fields {
+		pid, err := strconv.Atoi(field)
+		if err != nil {
+			return nil, err
+		}
+		if err == nil {
+			pids = append(pids, PID(pid))
+		}
+	}
+	return pids, nil
+}