Oops, preserve the size invariant.

samples/memfs/inode.go

@@ -377,14 +377,19 @@ func (inode *inode) SetAttributes(size *uint64) {
 	// Update the modification time.
 	inode.attributes.Mtime = inode.clock.Now()
 
-	// Do we need to truncate?
+	// Truncate?
 	if size != nil {
 		intSize := int(*size)
+
+		// Update contents.
 		if intSize <= len(inode.contents) {
 			inode.contents = inode.contents[:intSize]
 		} else {
 			padding := make([]byte, intSize-len(inode.contents))
 			inode.contents = append(inode.contents, padding...)
 		}
+
+		// Update attributes.
+		inode.attributes.Size = *size
 	}
 }

samples/memfs/memfs_test.go

@@ -875,6 +875,11 @@ func (t *MemFSTest) Truncate_Smaller() {
 	err = f.Truncate(2)
 	AssertEq(nil, err)
 
+	// Stat it.
+	fi, err := f.Stat()
+	AssertEq(nil, err)
+	ExpectEq(2, fi.Size())
+
 	// Read the contents.
 	contents, err := ioutil.ReadFile(fileName)
 	AssertEq(nil, err)