HTTP allows you to specify byte ranges for requests. This allows the implementation of resumable downloads and skippable audio and video streams alike. The following example uses a text file to make the range request process easier.

shell> cat file.txt
My hovercraft is full of eels!

Uploading this as an attachment to a text database using curl:

shell> curl -X PUT http://127.0.0.1:5984/test/doc/file.txt \
    -H "Content-Type: application/octet-stream" -d@file.txt
{"ok":true,"id":"doc","rev":"1-287a28fa680ae0c7fb4729bf0c6e0cf2"}

Requesting the whole file works as normal:

shell> curl -X GET http://127.0.0.1:5984/test/doc/file.txt
My hovercraft is full of eels!

But to retrieve only the first 13 bytes using curl:

shell> curl -X GET http://127.0.0.1:5984/test/doc/file.txt -H "Range: bytes=0-12"
My hovercraft

HTTP supports many ways to specify single and even multiple byte rangers. See RFC 2616.