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