Differentiate between file pointers and file descriptors.

1 files changed, 19 insertions, 3 deletions

diff --git a/src/library_fs.js b/src/library_fs.js
index 8d83048e..e97ba588 100644
--- a/src/library_fs.js
+++ b/src/library_fs.js
@@ -414,6 +414,22 @@ mergeInto(LibraryManager.library, {
     },
 
     //
+    // file pointers
+    //
+    // instead of maintaining a separate mapping from FILE* to file descriptors,
+    // we employ a simple trick: the pointer to a stream is its fd plus 1.  This
+    // means that all valid streams have a valid non-zero pointer while allowing
+    // the fs for stdin to be the standard value of zero.
+    // 
+    //
+    getStreamFromPtr: function(ptr) {
+      return FS.streams[ptr - 1];
+    },
+    getPtrForStream: function(stream) {
+      return stream ? stream.fd + 1 : 0;
+    },
+
+    //
     // devices
     //
     // each character device consists of a device id + stream operations.
@@ -1166,15 +1182,15 @@ mergeInto(LibraryManager.library, {
 
       // open default streams for the stdin, stdout and stderr devices
       var stdin = FS.open('/dev/stdin', 'r');
-      {{{ makeSetValue(makeGlobalUse('_stdin'), 0, 'stdin.fd', 'void*') }}};
+      {{{ makeSetValue(makeGlobalUse('_stdin'), 0, 'FS.getPtrForStream(stdin)', 'void*') }}};
       assert(stdin.fd === 0, 'invalid handle for stdin (' + stdin.fd + ')');
 
       var stdout = FS.open('/dev/stdout', 'w');
-      {{{ makeSetValue(makeGlobalUse('_stdout'), 0, 'stdout.fd', 'void*') }}};
+      {{{ makeSetValue(makeGlobalUse('_stdout'), 0, 'FS.getPtrForStream(stdout)', 'void*') }}};
       assert(stdout.fd === 1, 'invalid handle for stdout (' + stdout.fd + ')');
 
       var stderr = FS.open('/dev/stderr', 'w');
-      {{{ makeSetValue(makeGlobalUse('_stderr'), 0, 'stderr.fd', 'void*') }}};
+      {{{ makeSetValue(makeGlobalUse('_stderr'), 0, 'FS.getPtrForStream(stderr)', 'void*') }}};
       assert(stderr.fd === 2, 'invalid handle for stderr (' + stderr.fd + ')');
     },
     ensureErrnoError: function() {