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111 lines
4.5 KiB
Markdown
111 lines
4.5 KiB
Markdown
# Adding a new protocol?
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Every once in a while someone comes up with the idea of adding support for yet
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another protocol to curl. After all, curl already supports 25 something
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protocols and it is the Internet transfer machine for the world.
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In the curl project we love protocols and we love supporting many protocols
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and do it well.
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So how do you proceed to add a new protocol and what are the requirements?
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## No fixed set of requirements
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This document is an attempt to describe things to consider. There is no
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checklist of the twenty-seven things you need to cross off. We view the entire
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effort as a whole and then judge if it seems to be the right thing - for
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now. The more things that look right, fit our patterns and are done in ways
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that align with our thinking, the better are the chances that we will agree
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that supporting this protocol is a grand idea.
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## Mutual benefit is preferred
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curl is not here for your protocol. Your protocol is not here for curl. The
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best cooperation and end result occur when all involved parties mutually see
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and agree that supporting this protocol in curl would be good for everyone.
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Heck, for the world!
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Consider "selling us" the idea that we need an implementation merged in curl,
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to be fairly important. *Why* do we want curl to support this new protocol?
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## Protocol requirements
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### Client-side
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The protocol implementation is for a client's side of a "communication
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session".
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### Transfer oriented
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The protocol itself should be focused on *transfers*. Be it uploads or
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downloads or both. I should at least be possible to view the transfers as
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such, like we can view reading emails over POP3 as a downloading and sending
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emails over SMTP as an upload.
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If you cannot even shoehorn the protocol into a transfer focused view, then
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you are up for a tough argument.
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### URL
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There should be a documented URL format. If there is an RFC for it there is no
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question about it but the syntax doesn't have to be a published RFC. It could
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be enough if it is already in use by other implementations.
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If you make up the syntax just in order to be able to propose it to curl, then
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you are in a bad place. URLs are designed and defined for interoperability.
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There should at least be a good chance that other clients and servers can be
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implemented supporting the same URL syntax and work the same or similar way.
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URLs work on registered 'schemes'. There is a register of [all officially
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recognized
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schemes](https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml). If
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your protocol is not in there, is it really a protocol we want?
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### Wide and public use
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The protocol shall already be used or have an expectation of getting used
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widely. Experimental protocols are better off worked on in experiments first,
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to prove themselves before they are adopted by curl.
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## Code
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Of course the code needs to be written, provided, licensed agreeably and it
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should follow our code guidelines and review comments have to be dealt with.
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If the implementation needs third party code, that third party code should not
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have noticeably lesser standards than the curl project itself.
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## Tests
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As much of the protocol implementation as possible needs to be verified by
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curl test cases. We must have the implementation get tested by CI jobs,
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torture tests and more.
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We've experienced many times in the past how new implementations were brought
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to curl and immediately once the code had been merged, the originator vanished
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from the face of the earth. That is fine, but we need to take the necessary
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precautions so when it happens we are still fine.
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Our test infrastructure is powerful enough to test just about every possible
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protocol - but it might require a bit of an effort to make it happen.
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## Documentation
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We cannot assume that users are particularly familiar with specific details
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and peculiarities of the protocol. It needs documentation.
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Maybe it even needs some internal documentation so that the developers who
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will try to debug something five years from now can figure out functionality a
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little easier!
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The protocol specification itself should be freely available without requiring
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any NDA or similar.
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## Don't compare
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We are constantly raising the bar and we are constantly improving the
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project. A lot of things we did in the past would not be acceptable if done
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today. Therefore, you might be tempted to use shortcuts or "hacks" you can
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spot other - existing - protocol implementations have used, but there is
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nothing to gain from that. The bar has been raised. Former "cheats" won't be
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tolerated anymore.
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