Fix dup'd streams so that point to the same offset/etc (#17184)

Author: hoodmane

src/library_fs.js

@@ -403,29 +403,39 @@ FS.staticInit();` +
         FS.FSStream = /** @constructor */ function() {
           this.shared = { };
         };
-        FS.FSStream.prototype = {
+        FS.FSStream.prototype = {};
+        Object.defineProperties(FS.FSStream.prototype, {
           object: {
+            /** @this {FS.FSStream} */
             get: function() { return this.node; },
+            /** @this {FS.FSStream} */
             set: function(val) { this.node = val; }
           },
           isRead: {
+            /** @this {FS.FSStream} */
             get: function() { return (this.flags & {{{ cDefine('O_ACCMODE') }}}) !== {{{ cDefine('O_WRONLY') }}}; }
           },
           isWrite: {
+            /** @this {FS.FSStream} */
             get: function() { return (this.flags & {{{ cDefine('O_ACCMODE') }}}) !== {{{ cDefine('O_RDONLY') }}}; }
           },
           isAppend: {
+            /** @this {FS.FSStream} */
             get: function() { return (this.flags & {{{ cDefine('O_APPEND') }}}); }
           },
           flags: {
+            /** @this {FS.FSStream} */
             get: function() { return this.shared.flags; },
+            /** @this {FS.FSStream} */
             set: function(val) { this.shared.flags = val; },
           },
           position : {
-            get function() { return this.shared.position; },
+            /** @this {FS.FSStream} */
+            get: function() { return this.shared.position; },
+            /** @this {FS.FSStream} */
             set: function(val) { this.shared.position = val; },
           },
-        };
+        });
       }
       // clone it, so we can return an instance of FSStream
       stream = Object.assign(new FS.FSStream(), stream);

tests/unistd/dup.c

@@ -10,6 +10,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <emscripten.h>
+#include <assert.h>
 
 
 int main() {
@@ -59,5 +60,14 @@ int main() {
   read(g, buf, 5);
   // should print "buf: abc\n"
   printf("buf: %s\n", buf);
+
+
+  int fd1 = open("./blah.txt", O_RDWR | O_CREAT | O_EXCL, 0600);
+  int fd2 = dup(fd1);
+  int n = write(fd1, "abcabc\n", 7);
+  assert(n == 7);
+  assert(lseek(fd1, 0, SEEK_CUR) == 7);
+  assert(lseek(fd2, 0, SEEK_CUR) == 7);
+
   return 0;
 }