Expand paths with tilde

Currently, if you pass a path with a tilde to nats.UserCredentials it fails
because it doesn't expand the tilde to mean the user's home directory.

This change adds support to expand paths with a tilde, such as "~/.nkeys".

nats.go

@@ -28,6 +28,8 @@ import (
 	"math/rand"
 	"net"
 	"net/url"
+	"os"
+	"path/filepath"
 	"runtime"
 	"strconv"
 	"strings"
@@ -4016,14 +4018,59 @@ func wipeSlice(buf []byte) {
 }
 
 func userFromFile(userFile string) (string, error) {
-	contents, err := ioutil.ReadFile(userFile)
+	path, err := expandPath(userFile)
+	if err != nil {
+		return _EMPTY_, fmt.Errorf("nats: %v", err)
+	}
+
+	contents, err := ioutil.ReadFile(path)
 	if err != nil {
 		return _EMPTY_, fmt.Errorf("nats: %v", err)
 	}
 	defer wipeSlice(contents)
 	return jwt.ParseDecoratedJWT(contents)
 }
 
+func homeDir() (string, error) {
+	if runtime.GOOS == "windows" {
+		homeDrive, homePath := os.Getenv("HOMEDRIVE"), os.Getenv("HOMEPATH")
+		userProfile := os.Getenv("USERPROFILE")
+
+		var home string
+		if homeDrive == "" || homePath == "" {
+			if userProfile == "" {
+				return _EMPTY_, errors.New("nats: failed to get home dir, require %HOMEDRIVE% and %HOMEPATH% or %USERPROFILE%")
+			}
+			home = userProfile
+		} else {
+			home = filepath.Join(homeDrive, homePath)
+		}
+
+		return home, nil
+	}
+
+	home := os.Getenv("HOME")
+	if home == "" {
+		return _EMPTY_, errors.New("nats: failed to get home dir, require $HOME")
+	}
+	return home, nil
+}
+
+func expandPath(p string) (string, error) {
+	p = os.ExpandEnv(p)
+
+	if !strings.HasPrefix(p, "~") {
+		return p, nil
+	}
+
+	home, err := homeDir()
+	if err != nil {
+		return _EMPTY_, err
+	}
+
+	return filepath.Join(home, p[1:]), nil
+}
+
 func nkeyPairFromSeedFile(seedFile string) (nkeys.KeyPair, error) {
 	contents, err := ioutil.ReadFile(seedFile)
 	if err != nil {

nats_test.go

@@ -98,6 +98,103 @@ func TestVersionMatchesTag(t *testing.T) {
 	}
 }
 
+func TestExpandPath(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		origUserProfile := os.Getenv("USERPROFILE")
+		origHomeDrive, origHomePath := os.Getenv("HOMEDRIVE"), os.Getenv("HOMEPATH")
+		defer func() {
+			os.Setenv("USERPROFILE", origUserProfile)
+			os.Setenv("HOMEDRIVE", origHomeDrive)
+			os.Setenv("HOMEPATH", origHomePath)
+		}()
+
+		cases := []struct {
+			path        string
+			userProfile string
+			homeDrive   string
+			homePath    string
+
+			wantPath string
+			wantErr  bool
+		}{
+			// Missing HOMEDRIVE and HOMEPATH.
+			{path: "/Foo/Bar", userProfile: `C:\Foo\Bar`, wantPath: "/Foo/Bar"},
+			{path: "Foo/Bar", userProfile: `C:\Foo\Bar`, wantPath: "Foo/Bar"},
+			{path: "~/Fizz", userProfile: `C:\Foo\Bar`, wantPath: `C:\Foo\Bar\Fizz`},
+			{path: `${HOMEDRIVE}${HOMEPATH}\Fizz`, userProfile: `C:\Foo\Bar`, wantPath: `C:\Foo\Bar\Fizz`},
+
+			// Missing USERPROFILE.
+			{path: "~/Fizz", homeDrive: "X:", homePath: `\Foo\Bar`, wantPath: `X:\Foo\Bar\Fizz`},
+
+			// Set all environment variables. HOMEDRIVE and HOMEPATH take
+			// precedence.
+			{path: "~/Fizz", userProfile: `C:\Foo\Bar`,
+				homeDrive: "X:", homePath: `\Foo\Bar`, wantPath: `X:\Foo\Bar\Fizz`},
+
+			// Missing all environment variables.
+			{path: "~/Fizz", wantErr: true},
+		}
+		for i, c := range cases {
+			t.Run(fmt.Sprintf("windows case %d", i), func(t *testing.T) {
+				os.Setenv("USERPROFILE", c.userProfile)
+				os.Setenv("HOMEDRIVE", c.homeDrive)
+				os.Setenv("HOMEPATH", c.homePath)
+
+				gotPath, err := expandPath(c.path)
+				if !c.wantErr && err != nil {
+					t.Fatalf("unexpected error: got=%v; want=%v", err, nil)
+				} else if c.wantErr && err == nil {
+					t.Fatalf("unexpected success: got=%v; want=%v", nil, "err")
+				}
+
+				if gotPath != c.wantPath {
+					t.Fatalf("unexpected path: got=%v; want=%v", gotPath, c.wantPath)
+				}
+			})
+		}
+
+		return
+	}
+
+	// Unix tests
+
+	origHome := os.Getenv("HOME")
+	defer os.Setenv("HOME", origHome)
+
+	cases := []struct {
+		path    string
+		home    string
+		testEnv string
+
+		wantPath string
+		wantErr  bool
+	}{
+		{path: "/foo/bar", home: "/fizz/buzz", wantPath: "/foo/bar"},
+		{path: "foo/bar", home: "/fizz/buzz", wantPath: "foo/bar"},
+		{path: "~/fizz", home: "/foo/bar", wantPath: "/foo/bar/fizz"},
+		{path: "$HOME/fizz", home: "/foo/bar", wantPath: "/foo/bar/fizz"},
+
+		// missing HOME env var
+		{path: "~/fizz", wantErr: true},
+	}
+	for i, c := range cases {
+		t.Run(fmt.Sprintf("unix case %d", i), func(t *testing.T) {
+			os.Setenv("HOME", c.home)
+
+			gotPath, err := expandPath(c.path)
+			if !c.wantErr && err != nil {
+				t.Fatalf("unexpected error: got=%v; want=%v", err, nil)
+			} else if c.wantErr && err == nil {
+				t.Fatalf("unexpected success: got=%v; want=%v", nil, "err")
+			}
+
+			if gotPath != c.wantPath {
+				t.Fatalf("unexpected path: got=%v; want=%v", gotPath, c.wantPath)
+			}
+		})
+	}
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Reconnect tests
 ////////////////////////////////////////////////////////////////////////////////