问题
How do you create multiple HTTPDownloader instance with partial download asynchronously? and does it assemble the file automatically after all download is done?
回答1:
You must use Range HTTP header:
Range. Request only part of an entity. Bytes are numbered from 0. Range: bytes=500-999
Ie. If you want download 1000 file in 4 parts, you will starts 4 downloads:
- 0-2499
- 2500-4999
- 5000-7499
- 7500-9999
And then simply join data from responses.
To check file size you can use HEAD method:
HEAD Asks for the response identical to the one that would correspond to a GET request, but without the response body. This is useful for retrieving meta-information written in response headers, without having to transport the entire content.
来源：https://stackoverflow.com/questions/3328059/how-to-create-partial-download-in-twisted