To run this:

go install github.com/btc/bget
bget

To specify the number of chunks to download in parallel:

bget -n 1000

To override the URL:

bget -url MY_URL

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The implementation is split into these parts:

main.go handles flags, calls MultiSourceGet, and saves the downloaded file to PWD.

multisource_get.go implements MultiSourceGet which sets up the download and delegates work.

worker.go implements HTTP range requests.

file_download.go is home to FileDownload, which encapsulates the shared state of the download, storing chunks and tracking the completion of ranges.

main_test.go contains a variety of tests. Some tests are exploratory: probing various file servers to reveal how responses can differ across implementations in the wild. These ones hit the network. Other tests are unit tests intended to mitigate risk.

notes.txt contains some notes I took during the process of learning the domain.