3.1.1 Response types

There are four types of Response objects you can use in aiohttp; two might be useful for this MP.

1. A plain Response can have an arbitrary body, status code, and content_type.

2. A FileResponse creates a response from a file specified by its path on your local drive, setting the content type based on the file extension (i.e. if the file path ends .png it uses content type image/png regardless of what the file contains.

FileResponse can make handling path / very simple:

@routes.get('/')
async def index(req : Request) -> StreamResponse:
    return FileResponse(path="index.html")

FileResponse might also be useful for responding to /extract and /insert, depending on how you pick destination file names, but if you need to set the content type manually you’ll need to use Response instead.

3.1.2 Files in requests

This web service will work with an HTML form we provide. HTML forms send files in a somewhat strange way known as a multipart message body. That format splits the message body into a sequence of parts, separated by random strings including many hyphens; each part has headers like an HTTP message would, followed by its own body.

Fortunately, aiohttp can parse all of this for us. The usual structure to read a submitted file that was submitted as field name bazzle would look like

async def my_aiohttp_function(req : Request) -> Response:
    multi = await req.multipart()
    filename, filedata = None, None
    async for part in multi:
        if part.name == 'bazzle':
            filename = part.filename
            filedata = await part.read()

Note that you must use an async for because each iteration might block while waiting for more data to come over the network, and also must await the read() inside the loop because the next loop iteration will skip past any data you haven’t awaited and stored in a variable. You don’t need to await the filename because it was parsed as part of the async for.

3.1.3 Working with files

If you need to read from or write to a file in aiohttp, best practice is to use asyncio.to_thread. This means writing a non-async function that does the file work, then calling it with asyncio.to_thread, like so:

def save_file_helper(data, save_as):
    directory = os.path.dirname(save_as)
    os.makedirs(directory, exist_ok=True)
    open(save_as, 'wb').write(data)
await asyncio.to_thread(helper, mydata, my_destination_path)

We won’t enforce doing this in this MP: if you use open and so on directly in your code you’ll still get full points. That said, using to_thread for file operations will make your code faster if you try to do many file operations concurrently, for example by getting a hundred of our friends to all access your application simultaneously.

3.2.1 Your MP3 solution

You’ll need to invoke extractuiucchunk and insertuiucchunk from MP3. We recommend copying your source code into MP7’s directory and have its compilation handled by the Makefile. If you don’t have a working MP3, we do provide a precompiled refernece program you can use instead; if you don’t have the .c files in your mp7 folder, the Makefile will use the provided binaries instead. We compiled these on a course virtual machine; they may or may not function properly elsewhere.

Using this program will necessitate having the provided values in a file on the disk, and will store the results on the disk. We recommend putting those files in a directory named temp/ that your code creates in setup_app using os.makedirs

3.2.2 Content type with file

You need to match the Content-Type header of your response to the content type of the file you’re returning, but for extraction that content type is not immediately available. file is a tool that looks into the contents of a file to try to guess its content-type.

There are two ways you might want to use file in this MP:

• file --extension myfile will give back something like png or jpg, suitable to append to the file as myfile.png and then send that renamed file into a FileResponse. However, it has trouble with some text files (many file formats are text and are hard to tell apart from content) so it will report all of them with ???, which you should treat as meaning txt.

  Note that the output might contain newlines or other whitespace you’ll need to remove before using it.

• file --mime-type myfile¹¹ Originally, the values were put into the content type header were called MIME type because they were defined as part of the Multipurpose Internet Mail Extensions (MIME) standard. Later they were renamed to media types, but older tools and sources still often call them MIME types. will give back something like text/html or image/gif, suitable to send directly in the Content-Type header. However, that value cannot be directly specified in a FileResponse so you’ll need to send a regular Response instead.

Either of the above will work for this MP.