Fix dup in nodefs by refcounting nodefs file descriptors

src/library_fs.js

@@ -471,6 +471,11 @@ FS.staticInit();` +
     closeStream(fd) {
       FS.streams[fd] = null;
     },
+    dupStream(origStream, fd = -1) {
+      var stream = FS.createStream(origStream, fd);
+      stream.stream_ops?.dup?.(stream);
+      return stream;
+    },
 
     //
     // devices

src/library_nodefs.js

@@ -251,6 +251,7 @@ addToLibrary({
         var path = NODEFS.realPath(stream.node);
         try {
           if (FS.isFile(stream.node.mode)) {
+            stream.shared.refcount = 1;
             stream.nfd = fs.openSync(path, NODEFS.flagsForNode(stream.flags));
           }
         } catch (e) {
@@ -260,14 +261,17 @@ addToLibrary({
       },
       close(stream) {
         try {
-          if (FS.isFile(stream.node.mode) && stream.nfd) {
+          if (FS.isFile(stream.node.mode) && stream.nfd && --stream.shared.refcount === 0) {
             fs.closeSync(stream.nfd);
           }
         } catch (e) {
           if (!e.code) throw e;
           throw new FS.ErrnoError(NODEFS.convertNodeCode(e));
         }
       },
+      dup(stream) {
+        stream.shared.refcount++;
+      },
       read(stream, buffer, offset, length, position) {
         // Node.js < 6 compatibility: node errors on 0 length reads
         if (length === 0) return 0;

src/library_syscall.js

@@ -183,7 +183,7 @@ var SyscallsLibrary = {
   },
   __syscall_dup: (fd) => {
     var old = SYSCALLS.getStreamFromFD(fd);
-    return FS.createStream(old).fd;
+    return FS.dupStream(old).fd;
   },
   __syscall_pipe__deps: ['$PIPEFS'],
   __syscall_pipe: (fdPtr) => {
@@ -760,7 +760,7 @@ var SyscallsLibrary = {
           arg++;
         }
         var newStream;
-        newStream = FS.createStream(stream, arg);
+        newStream = FS.dupStream(stream, arg);
         return newStream.fd;
       }
       case {{{ cDefs.F_GETFD }}}:
@@ -1007,7 +1007,7 @@ var SyscallsLibrary = {
     if (old.fd === newfd) return -{{{ cDefs.EINVAL }}};
     var existing = FS.getStream(newfd);
     if (existing) FS.close(existing);
-    return FS.createStream(old, newfd).fd;
+    return FS.dupStream(old, newfd).fd;
   },
 };
 

test/fs/test_nodefs_dup.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2018 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+#include <emscripten.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#ifdef NODERAWFS
+#define CWD ""
+#else
+#define CWD "/working/"
+#endif
+
+int main(void)
+{
+    EM_ASM(
+#ifdef NODERAWFS
+        FS.close(FS.open('test.txt', 'w'));
+#else
+        FS.mkdir('/working');
+        FS.mount(NODEFS, {root: '.'}, '/working');
+        FS.close(FS.open('/working/test.txt', 'w'));
+#endif
+    );
+    int fd1 = open(CWD "test.txt", O_WRONLY);
+    int fd2 = dup(fd1);
+    int fd3 = fcntl(fd1, F_DUPFD_CLOEXEC, 0);
+
+    assert(fd1 == 3);
+    assert(fd2 == 4);
+    assert(fd3 == 5);
+    assert(close(fd1) == 0);
+    assert(write(fd2, "abcdef", 6) == 6);
+    assert(close(fd2) == 0);
+    assert(write(fd3, "ghijkl", 6) == 6);
+    assert(close(fd3) == 0);
+    printf("success\n");
+    return 0;
+}

test/test_core.py

@@ -5749,6 +5749,14 @@ def test_fs_nodefs_cloexec(self):
     self.emcc_args += ['-lnodefs.js']
     self.do_runf('fs/test_nodefs_cloexec.c', 'success')
 
+  @also_with_noderawfs
+  @requires_node
+  def test_fs_nodefs_dup(self):
+    if self.get_setting('WASMFS'):
+      self.set_setting('FORCE_FILESYSTEM')
+    self.emcc_args += ['-lnodefs.js']
+    self.do_runf('fs/test_nodefs_dup.c', 'success')
+
   @requires_node
   def test_fs_nodefs_home(self):
     self.set_setting('FORCE_FILESYSTEM')