Add process info (#59)

Example output:

$ gops <pid>
parent PID:	5985
threads:	27
memory usage:	0.199%
cpu usage:	0.139%
username:	jbd
cmd+args:	/Applications/Splice.app/Contents/Resources/Splice Helper.app/Contents/MacOS/Splice Helper -pid 5985
local/remote:	127.0.0.1:56765 <-> :0 (LISTEN)
local/remote:	127.0.0.1:56765 <-> 127.0.0.1:50955 (ESTABLISHED)
local/remote:	100.76.175.164:52353 <-> 54.241.191.232:443 (ESTABLISHED)

Fixes #58.

main.go

@@ -8,19 +8,20 @@ package main
 import (
 	"bytes"
 	"fmt"
+	"log"
 	"os"
 	"regexp"
 	"strconv"
 	"strings"
 
 	"github.com/google/gops/goprocess"
+	"github.com/shirou/gopsutil/process"
 )
 
 const helpText = `gops is a tool to list and diagnose Go processes.
 
-Usage:
-
-    gops [command [pid|address:port]]
+	gops <cmd> <pid|addr> ...
+	gops <pid> # displays process info
 
 Commands:
     stack       	Prints the stack trace.
@@ -49,12 +50,17 @@ func main() {
 	}
 
 	cmd := os.Args[1]
+
+	// See if it is a PID.
+	pid, err := strconv.Atoi(cmd)
+	if err == nil {
+		processInfo(pid)
+		return
+	}
+
 	if cmd == "help" {
 		usage("")
 	}
-	if len(os.Args) < 3 {
-		usage("missing PID or address")
-	}
 	fn, ok := cmds[cmd]
 	if !ok {
 		usage("unknown subcommand")
@@ -110,6 +116,39 @@ func processes() {
 	}
 }
 
+func processInfo(pid int) {
+	p, err := process.NewProcess(int32(pid))
+	if err != nil {
+		log.Fatalf("Cannot read process info: %v", err)
+	}
+	if v, err := p.Parent(); err == nil {
+		fmt.Printf("parent PID:\t%v\n", v.Pid)
+	}
+	if v, err := p.NumThreads(); err == nil {
+		fmt.Printf("threads:\t%v\n", v)
+	}
+	if v, err := p.MemoryPercent(); err == nil {
+		fmt.Printf("memory usage:\t%.3f%%\n", v)
+	}
+	if v, err := p.CPUPercent(); err == nil {
+		fmt.Printf("cpu usage:\t%.3f%%\n", v)
+	}
+	if v, err := p.Username(); err == nil {
+		fmt.Printf("username:\t%v\n", v)
+	}
+	if v, err := p.Cmdline(); err == nil {
+		fmt.Printf("cmd+args:\t%v\n", v)
+	}
+	if v, err := p.Connections(); err == nil {
+		if len(v) > 0 {
+			for _, conn := range v {
+				fmt.Printf("local/remote:\t%v:%v <-> %v:%v (%v)\n",
+					conn.Laddr.IP, conn.Laddr.Port, conn.Raddr.IP, conn.Raddr.Port, conn.Status)
+			}
+		}
+	}
+}
+
 var develRe = regexp.MustCompile(`devel\s+\+\w+`)
 
 func shortenVersion(v string) string {