Failed when saving homework files

[keyunjie96]

1. It seems saving 3-byte file for any 'work' instance including 'work.answer' and 'work.file'
2. I tested the downloading url when downloading from a browser. It downloaded a correct homework file. However, request.get even wget (faking as browser) failed. It may be caused by js(not sure).
3. The content of 3-byte file: '\t\r\n'
4. How to reproduce it:

from thu_learn import *

login()
semester = Semester(current=False)
for i, course in semester.courses:
    base_path = os.path.join('file', course.name)
    os.makedirs(base_path, exist_ok=True)
    for work in course.works:
        print('%s\%s' % (course.name, work.title))
        work_path = os.path.join(base_path, work.title)
        os.makedirs(work_path, exist_ok=True)
        if work.file:
            work.file.save(work_path)
        if work.answer:
            work.answer.save(work_path)

[keyunjie96]

same as #3