Add a checkOpExists helper for common code pattern. NFC (#23305)

We frequently check if a node op is present, if not raise a specific
error, if it is present call it. This factors out this common pattern.

Author: hoodmane

src/library_fs.js

@@ -433,6 +433,12 @@ FS.staticInit();
       }
       return FS.nodePermissions(node, FS.flagsToPermissionString(flags));
     },
+    checkOpExists(op, err) {
+      if (!op) {
+        throw new FS.ErrnoError(err);
+      }
+      return op;
+    },
 
     //
     // streams
@@ -895,10 +901,8 @@ FS.staticInit();
     readdir(path) {
       var lookup = FS.lookupPath(path, { follow: true });
       var node = lookup.node;
-      if (!node.node_ops.readdir) {
-        throw new FS.ErrnoError({{{ cDefs.ENOTDIR }}});
-      }
-      return node.node_ops.readdir(node);
+      var readdir = FS.checkOpExists(node.node_ops.readdir, {{{ cDefs.ENOTDIR }}});
+      return readdir(node);
     },
     unlink(path) {
       var lookup = FS.lookupPath(path, { parent: true });
@@ -951,10 +955,8 @@ FS.staticInit();
       if (!node) {
         throw new FS.ErrnoError({{{ cDefs.ENOENT }}});
       }
-      if (!node.node_ops.getattr) {
-        throw new FS.ErrnoError({{{ cDefs.EPERM }}});
-      }
-      return node.node_ops.getattr(node);
+      var getattr = FS.checkOpExists(node.node_ops.getattr, {{{ cDefs.EPERM }}});
+      return getattr(node);
     },
     lstat(path) {
       return FS.stat(path, true);
@@ -967,10 +969,8 @@ FS.staticInit();
       } else {
         node = path;
       }
-      if (!node.node_ops.setattr) {
-        throw new FS.ErrnoError({{{ cDefs.EPERM }}});
-      }
-      node.node_ops.setattr(node, {
+      var setattr = FS.checkOpExists(node.node_ops.setattr, {{{ cDefs.EPERM }}});
+      setattr(node, {
         mode: (mode & {{{ cDefs.S_IALLUGO }}}) | (node.mode & ~{{{ cDefs.S_IALLUGO }}}),
         ctime: Date.now(),
         dontFollow
@@ -991,10 +991,8 @@ FS.staticInit();
       } else {
         node = path;
       }
-      if (!node.node_ops.setattr) {
-        throw new FS.ErrnoError({{{ cDefs.EPERM }}});
-      }
-      node.node_ops.setattr(node, {
+      var setattr = FS.checkOpExists(node.node_ops.setattr, {{{ cDefs.EPERM }}});
+      setattr(node, {
         timestamp: Date.now(),
         dontFollow
         // we ignore the uid / gid for now
@@ -1018,9 +1016,6 @@ FS.staticInit();
       } else {
         node = path;
       }
-      if (!node.node_ops.setattr) {
-        throw new FS.ErrnoError({{{ cDefs.EPERM }}});
-      }
       if (FS.isDir(node.mode)) {
         throw new FS.ErrnoError({{{ cDefs.EISDIR }}});
       }
@@ -1031,7 +1026,8 @@ FS.staticInit();
       if (errCode) {
         throw new FS.ErrnoError(errCode);
       }
-      node.node_ops.setattr(node, {
+      var setattr = FS.checkOpExists(node.node_ops.setattr, {{{ cDefs.EPERM }}});
+      setattr(node, {
         size: len,
         timestamp: Date.now()
       });
@@ -1046,7 +1042,8 @@ FS.staticInit();
     utime(path, atime, mtime) {
       var lookup = FS.lookupPath(path, { follow: true });
       var node = lookup.node;
-      node.node_ops.setattr(node, {
+      var setattr = FS.checkOpExists(node.node_ops.setattr, {{{ cDefs.EPERM }}});
+      setattr(node, {
         atime: atime,
         mtime: mtime
       });

test/other/codesize/test_codesize_cxx_ctors1.gzsize

@@ -1 +1 @@
-8343
+8350

test/other/codesize/test_codesize_cxx_ctors1.jssize

@@ -1 +1 @@
-20271
+20272

test/other/codesize/test_codesize_cxx_ctors2.gzsize

@@ -1 +1 @@
-8325
+8334

test/other/codesize/test_codesize_cxx_ctors2.jssize

@@ -1 +1 @@
-20239
+20240

test/other/codesize/test_codesize_cxx_except.gzsize

@@ -1 +1 @@
-9346
+9349

test/other/codesize/test_codesize_cxx_except.jssize

@@ -1 +1 @@
-24039
+24040

test/other/codesize/test_codesize_cxx_except_wasm.gzsize

@@ -1 +1 @@
-8288
+8296

test/other/codesize/test_codesize_cxx_except_wasm.jssize

@@ -1 +1 @@
-20164
+20165

test/other/codesize/test_codesize_cxx_except_wasm_exnref.gzsize

@@ -1 +1 @@
-8288
+8296