POSIX implementation of ExpandPath

pkg/utils/path.go

@@ -1,20 +1,67 @@
 package utils
 
 import (
+	"fmt"
 	"os"
+	"os/user"
 	"path/filepath"
 	"strings"
 )
 
 func ExpandPath(path string) (string, error) {
-	if strings.HasPrefix(path, "~") {
+	if len(path) == 0 {
+		return path, nil
+	}
+
+	if !strings.HasPrefix(path, "~") {
+		return filepath.Abs(os.ExpandEnv(path))
+	}
+
+	// [...] the characters in the tilde-prefix following the <tilde> are treated
+	// as a possible login name from the user database. [...].
+
+	parts := pathSegments(path)
+	if len(parts[0]) == 1 {
+		// If the login name is null (that is, the tilde-prefix contains only the tilde),
+		// the tilde-prefix is replaced by the value of the variable HOME. If HOME is
+		// unset, the results are unspecified. [continue]
 		home, err := os.UserHomeDir()
 		if err != nil {
-			return "", err
+			return path, err
 		}
+
 		path = strings.Replace(path, "~", home, 1)
+
+		return filepath.Abs(os.ExpandEnv(path))
+	}
+
+	// Otherwise, the tilde-prefix shall be replaced
+	// by a pathname of the initial working directory associated with the login name
+	// obtained using the getpwnam() function as defined in the System Interfaces volume
+	// of POSIX.1-2017. If the system does not recognize the login name, the results are
+	// undefined.
+
+	// treat what follows the tilde as a potentially valid username
+
+	usr, err := user.Lookup(strings.TrimPrefix(parts[0], "~"))
+	if err == nil {
+		// replace the tilde-prefix with the user's home directory
+		return filepath.Abs(os.ExpandEnv(strings.Replace(path, parts[0], usr.HomeDir, 1)))
+	}
+
+	switch terr := err.(type) {
+	case user.UnknownUserError: // non existing user, move on
+	default: // unexpected error
+		return path, fmt.Errorf("ExpandPath: got unexpected error %v", terr)
 	}
 
-	path = os.ExpandEnv(path)
-	return filepath.Abs(path)
+	return os.ExpandEnv(path), nil
+}
+
+func pathSegments(path string) []string {
+	dir, last := filepath.Split(path)
+	if dir == "" {
+		return []string{last}
+	}
+	return append(pathSegments(filepath.Clean(dir)), last)
 }

pkg/utils/path_test.go

@@ -0,0 +1,63 @@
+package utils
+
+import (
+	"fmt"
+	"log"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestExpandPath(t *testing.T) {
+	tests := []struct {
+		name    string
+		path    string
+		want    string
+		wantErr bool
+	}{
+		{"empty", "", "", false},
+		{"non existing user", "~NONEXISTING/", "~NONEXISTING/", false},
+		{"any path", "/patgh/to/file", "/patgh/to/file", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ExpandPath(tt.path)
+			if tt.wantErr {
+				assert.NotNil(t, err)
+				return
+			}
+
+			assert.Nil(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func ExampleExpandPath() {
+	p, err := ExpandPath("~/test")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	_, last := filepath.Split(p)
+	fmt.Println(last)
+
+	p, _ = ExpandPath("~NONEXISTINGUSER/path/to/file")
+	fmt.Println(p)
+
+	p, _ = ExpandPath("/path/to/file/tilde/~")
+	fmt.Println(p)
+
+	p, _ = ExpandPath("")
+	fmt.Println(p)
+
+	p, _ = ExpandPath("")
+	fmt.Println(p)
+
+	// Output:
+	// test
+	// ~NONEXISTINGUSER/path/to/file
+	// /path/to/file/tilde/~
+	//
+}