fix: correctly resolve executable path on windows

- closes: #51

Signed-off-by: Liam Stanley <liam@liam.sh>

command_others.go

@@ -7,10 +7,15 @@
 package ytdlp
 
 import (
+	"os"
 	"os/exec"
 )
 
 // applySyscall applies any OS-specific syscall attributes to the command.
 func (c *Command) applySyscall(_ *exec.Cmd) {
 	// No-op by default.
 }
+
+func isExecutable(_ string, stat os.FileInfo) bool {
+	return true // no-op.
+}

command_unix.go

@@ -7,6 +7,7 @@
 package ytdlp
 
 import (
+	"os"
 	"os/exec"
 	"syscall"
 )
@@ -17,3 +18,8 @@ func (c *Command) applySyscall(cmd *exec.Cmd) {
 		Setpgid: c.separateProcessGroup,
 	}
 }
+
+func isExecutable(_ string, stat os.FileInfo) bool {
+	// On Unix systems, check if executable bit is set (user, group, or others).
+	return stat.Mode().Perm()&0o100 != 0 || stat.Mode().Perm()&0o010 != 0 || stat.Mode().Perm()&0o001 != 0
+}

command_windows.go

@@ -7,6 +7,8 @@
 package ytdlp
 
 import (
+	"debug/pe"
+	"os"
 	"os/exec"
 	"syscall"
 )
@@ -21,3 +23,13 @@ func (c *Command) applySyscall(cmd *exec.Cmd) {
 		cmd.SysProcAttr.CreationFlags |= syscall.CREATE_NEW_PROCESS_GROUP
 	}
 }
+
+func isExecutable(path string, _ os.FileInfo) bool {
+	// Try to parse as PE (Portable Executable) format.
+	f, err := pe.Open(path)
+	if err != nil {
+		return false
+	}
+	f.Close()
+	return true
+}

install.go

@@ -368,7 +368,7 @@ func resolveExecutable(fromCache, calleeIsDownloader bool) (r *ResolvedInstall,
 				continue
 			}
 
-			if !stat.IsDir() && (stat.Mode().Perm()&0o100 != 0 || stat.Mode().Perm()&0o010 != 0 || stat.Mode().Perm()&0o001 != 0) {
+			if !stat.IsDir() && isExecutable(bin, stat) {
 				r = &ResolvedInstall{
 					Executable: bin,
 					FromCache:  true,