windows: add command line escaping wrappers around EscapeArg and CommandLineToArgv

DecomposeCommandLine makes CommandLineToArgv usable in an ordinary way.
There's actually a pure-Go version of this available as the private
os.commandLineToArgv function, which we could copy, but given this is
x/sys/windows, it seems best to stick to the actual Windows primitives
which will always remain current. Then, ComposeCommandLine is just a
simple wrapper around EscapeArg (which has no native win32 substitute).

Change-Id: Ia2c7ca2ded9e5713b281dade34639dfeacf1171c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/319229
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

windows/exec_windows.go

@@ -78,6 +78,40 @@ func EscapeArg(s string) string {
 	return string(qs[:j])
 }
 
+// ComposeCommandLine escapes and joins the given arguments suitable for use as a Windows command line,
+// in CreateProcess's CommandLine argument, CreateService/ChangeServiceConfig's BinaryPathName argument,
+// or any program that uses CommandLineToArgv.
+func ComposeCommandLine(args []string) string {
+	var commandLine string
+	for i := range args {
+		if i > 0 {
+			commandLine += " "
+		}
+		commandLine += EscapeArg(args[i])
+	}
+	return commandLine
+}
+
+// DecomposeCommandLine breaks apart its argument command line into unescaped parts using CommandLineToArgv,
+// as gathered from GetCommandLine, QUERY_SERVICE_CONFIG's BinaryPathName argument, or elsewhere that
+// command lines are passed around.
+func DecomposeCommandLine(commandLine string) ([]string, error) {
+	if len(commandLine) == 0 {
+		return []string{}, nil
+	}
+	var argc int32
+	argv, err := CommandLineToArgv(StringToUTF16Ptr(commandLine), &argc)
+	if err != nil {
+		return nil, err
+	}
+	defer LocalFree(Handle(unsafe.Pointer(argv)))
+	var args []string
+	for _, v := range (*argv)[:argc] {
+		args = append(args, UTF16ToString((*v)[:]))
+	}
+	return args, nil
+}
+
 func CloseOnExec(fd Handle) {
 	SetHandleInformation(Handle(fd), HANDLE_FLAG_INHERIT, 0)
 }

windows/syscall_windows_test.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"math/rand"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -599,3 +600,61 @@ func TestResourceExtraction(t *testing.T) {
 		t.Errorf("did not find </assembly> in manifest")
 	}
 }
+
+func TestCommandLineRecomposition(t *testing.T) {
+	const (
+		maxCharsPerArg  = 35
+		maxArgsPerTrial = 80
+		doubleQuoteProb = 4
+		singleQuoteProb = 1
+		backSlashProb   = 3
+		spaceProb       = 1
+		trials          = 1000
+	)
+	randString := func(l int) []rune {
+		s := make([]rune, l)
+		for i := range s {
+			s[i] = rand.Int31()
+		}
+		return s
+	}
+	mungeString := func(s []rune, char rune, timesInTen int) {
+		if timesInTen < rand.Intn(10)+1 || len(s) == 0 {
+			return
+		}
+		s[rand.Intn(len(s))] = char
+	}
+	argStorage := make([]string, maxArgsPerTrial+1)
+	for i := 0; i < trials; i++ {
+		args := argStorage[:rand.Intn(maxArgsPerTrial)+2]
+		args[0] = "valid-filename-for-arg0"
+		for j := 1; j < len(args); j++ {
+			arg := randString(rand.Intn(maxCharsPerArg + 1))
+			mungeString(arg, '"', doubleQuoteProb)
+			mungeString(arg, '\'', singleQuoteProb)
+			mungeString(arg, '\\', backSlashProb)
+			mungeString(arg, ' ', spaceProb)
+			args[j] = string(arg)
+		}
+		commandLine := windows.ComposeCommandLine(args)
+		decomposedArgs, err := windows.DecomposeCommandLine(commandLine)
+		if err != nil {
+			t.Errorf("Unable to decompose %#q made from %v: %v", commandLine, args, err)
+			continue
+		}
+		if len(decomposedArgs) != len(args) {
+			t.Errorf("Incorrect decomposition length from %v to %#q to %v", args, commandLine, decomposedArgs)
+			continue
+		}
+		badMatches := make([]int, 0, len(args))
+		for i := range args {
+			if args[i] != decomposedArgs[i] {
+				badMatches = append(badMatches, i)
+			}
+		}
+		if len(badMatches) != 0 {
+			t.Errorf("Incorrect decomposition at indices %v from %v to %#q to %v", badMatches, args, commandLine, decomposedArgs)
+			continue
+		}
+	}
+}