unpack: do not mutate cwd when extract strip empties a path

README.md

@@ -524,9 +524,11 @@ The following options are supported:
   symlink that would affect the location of an extracted file. [Alias:
   `U`]
 - `strip` Remove the specified number of leading path elements.
-  Pathnames with fewer elements will be silently skipped. Note that
-  the pathname is edited after applying the filter, but before
-  security checks. [Alias: `strip-components`, `stripComponents`]
+  Pathnames with fewer elements, or whose names become empty after
+  stripping, are silently skipped and do not change the extraction
+  directory. Note that the pathname is edited after applying the
+  filter, but before security checks. [Alias: `strip-components`,
+  `stripComponents`]
 - `preserveOwner` If true, tar will set the `uid` and `gid` of
   extracted entries to the `uid` and `gid` fields in the archive.
   This defaults to true when run as root, and false otherwise. If
@@ -856,9 +858,10 @@ Most unpack errors will cause a `warn` event to be emitted. If the
   With this option, existing hardlinks will be broken, as will any
   symlink that would affect the location of an extracted file.
 - `strip` Remove the specified number of leading path elements.
-  Pathnames with fewer elements will be silently skipped. Note that
-  the pathname is edited after applying the filter, but before
-  security checks.
+  Pathnames with fewer elements, or whose names become empty after
+  stripping, are silently skipped and do not change the extraction
+  directory. Note that the pathname is edited after applying the
+  filter, but before security checks.
 - `umask` Filter the modes of entries like `process.umask()`.
 - `dmode` Default mode for directories
 - `fmode` Default mode for files

src/options.ts

@@ -178,7 +178,8 @@ export interface TarOptions {
    * entry path. For example, with `{strip: 2}`, the entry `a/b/c/d` would be
    * extracted to `{cwd}/c/d`.
    *
-   * Any entry whose entire path is stripped will be excluded.
+   * Any entry whose entire path is stripped will be excluded, and will
+   * not change ownership, mode, or mtime of the extraction directory.
    */
   strip?: number
 

src/unpack.ts

@@ -336,6 +336,12 @@ export class Unpack extends Parser {
         }
       }
       parts.splice(0, this.strip)
+      // GNU tar --strip-components skips members whose names become
+      // empty. Applying those entries would mutate cwd ownership,
+      // mode, and mtime (#294).
+      if (parts.every(part => part === '' || part === '.')) {
+        return false
+      }
       entry.path = parts.join('/')
     }
 
@@ -383,6 +389,8 @@ export class Unpack extends Parser {
 
     // an archive can set properties on the extraction directory, but it
     // may not replace the cwd with a different kind of thing entirely.
+    // Fully-stripped directory entries never reach here; they are
+    // skipped above so strip does not mutate cwd (#294).
     if (
       entry.absolute === this.cwd &&
       entry.type !== 'Directory' &&