Implemented memFS.WriteFile.

samples/memfs/fs.go

@@ -437,3 +437,21 @@ func (fs *memFS) ReadDir(
 
 	return
 }
+
+func (fs *memFS) WriteFile(
+	ctx context.Context,
+	req *fuse.WriteFileRequest) (resp *fuse.WriteFileResponse, err error) {
+	resp = &fuse.WriteFileResponse{}
+
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+
+	// Find the inode in question.
+	inode := fs.getInodeForModifyingOrDie(req.Inode)
+	defer inode.mu.Unlock()
+
+	// Serve the request.
+	_, err = inode.WriteAt(req.Data, req.Offset)
+
+	return
+}

samples/memfs/inode.go

@@ -279,3 +279,30 @@ func (inode *inode) ReadDir(offset int, size int) (data []byte, err error) {
 
 	return
 }
+
+// Write to the file's contents. See documentation for ioutil.WriterAt.
+//
+// REQUIRES: !inode.dir
+// EXCLUSIVE_LOCKS_REQUIRED(inode.mu)
+func (inode *inode) WriteAt(p []byte, off int64) (n int, err error) {
+	if inode.dir {
+		panic("WriteAt called on directory.")
+	}
+
+	// Ensure that the contents slice is long enough.
+	newLen := int(off) + len(p)
+	if len(inode.contents) < newLen {
+		padding := make([]byte, newLen-len(inode.contents))
+		inode.contents = append(inode.contents, padding...)
+	}
+
+	// Copy in the data.
+	n = copy(inode.contents[off:], p)
+
+	// Sanity check.
+	if n != len(p) {
+		panic(fmt.Sprintf("Unexpected short copy: %v", n))
+	}
+
+	return
+}