feat: use ContentType to control HTML extension

cmd/goget/main.go

@@ -130,9 +130,12 @@ func runPostDownload(
 			fmt.Fprintf(os.Stderr, "Warning: failed to close writer: %v\n", cerr)
 		}
 
-		// Adjust extension: append .html to HTML files without extension
+		// Adjust extension: append .html to HTML files without extension.
+		// When ContentType is available (WebDAV, Gopher), only apply to
+		// text/html responses. When ContentType is empty (HTTP legacy
+		// path), preserve the existing wget-compatible behaviour.
 		if *f.AdjustExt && *f.Output != "" {
-			if filepath.Ext(*f.Output) == "" {
+			if filepath.Ext(*f.Output) == "" && isHTMLContentType(result.ContentType) {
 				newPath := *f.Output + ".html"
 				if err := os.Rename(*f.Output, newPath); err == nil {
 					*f.Output = newPath
@@ -289,6 +292,20 @@ func runPostDownload(
 	return 0
 }
 
+// isHTMLContentType returns true when ct indicates HTML content.
+// An empty string is treated as HTML for backward compatibility with
+// protocol handlers that do not populate ContentType (e.g. HTTP).
+func isHTMLContentType(ct string) bool {
+	if ct == "" {
+		return true
+	}
+	// Strip parameters (charset, boundary, …).
+	if i := strings.IndexByte(ct, ';'); i >= 0 {
+		ct = ct[:i]
+	}
+	return strings.TrimSpace(ct) == "text/html"
+}
+
 // splitCommand splits a shell-like command string into tokens respecting double quotes.
 // Used to parse --on-complete and --on-complete-url without invoking a shell.
 func splitCommand(raw string) []string {