If Roy Fielding wanted developers to fully grasp whatever he was talking about with REST, he should have written a normative spec, not a dissertation, he didn't.
Roy Fielding isn't a deity. The version would be encoded in the 'Accepts' content type header. There is little distinction, one is in-band (in the path) and one is out-of-band (in the header), but the information is still represented.
I don’t think you have this right. First, both the URL and the headers are in-band. Out-of-band would be you knowing that the version is v2.3.7, because you just know. In-band is anything in the request and response – headers and all – anything else is an assumption and as such out-of-band.
Moreover, if I understand Roy’s argument correctly, he’s arguing against versioning URLs, because they are meant to be opaque identifiers that doesn’t convey any universal meaning. If you know the second segment of a URL path to be a version, it’s because you have out-of-band knowledge that it is, not because there’s anything in the request to say it is.
If however you have a header that tells what version you wish then that is in-band information that allows you to negotiate the content appropriately with the server. It also means you don’t have to change URLs whenever you make a change to your API, breaking or not. Of course the server and client needs to understand this header (to my knowledge there’s Accept-Version header) and if it’s non-standard then it can be argued that it’s just as bad as versioned URLs. Perhaps, but unless you get very granular with your versions (and most don’t, let’s just be honest) your still at the mercy of what the server chooses to present you at any given time. In fact, REST gives you no guarantees about what you’ll receive at any given point – you may just as well be given a picture of a cat. REST says you should be able to gracefully deal with this. Most clients (that aren’t web browsers or curl) don’t.
Well, I think from Roy's point of view REST is only HATEOAS. So URL's are irrelevant; you can put version numbers in there if you want but no client should realize it.
What you should be versioning is your media types (e.g. HTML4 vs HTML5).
He is not a deity, of course, he's "just" the one that invented REST. I guess what you mean is that he's not right about everything he says.
Well, what he exactly says is that URLs should not include versioning, because URLs are the interfaces names and REST estates that interface names should not be versioned, as that implies a breaking change in the API. It's just the wrong place for versioning in the REST way.
But he is not against versioning, as you say, you can use the Accept header. You could also use a custom header if you might, but the canonical way would be the Accept header.
nostalgeek|8 years ago
If Roy Fielding wanted developers to fully grasp whatever he was talking about with REST, he should have written a normative spec, not a dissertation, he didn't.
sitkack|8 years ago
mstade|8 years ago
Moreover, if I understand Roy’s argument correctly, he’s arguing against versioning URLs, because they are meant to be opaque identifiers that doesn’t convey any universal meaning. If you know the second segment of a URL path to be a version, it’s because you have out-of-band knowledge that it is, not because there’s anything in the request to say it is.
If however you have a header that tells what version you wish then that is in-band information that allows you to negotiate the content appropriately with the server. It also means you don’t have to change URLs whenever you make a change to your API, breaking or not. Of course the server and client needs to understand this header (to my knowledge there’s Accept-Version header) and if it’s non-standard then it can be argued that it’s just as bad as versioned URLs. Perhaps, but unless you get very granular with your versions (and most don’t, let’s just be honest) your still at the mercy of what the server chooses to present you at any given time. In fact, REST gives you no guarantees about what you’ll receive at any given point – you may just as well be given a picture of a cat. REST says you should be able to gracefully deal with this. Most clients (that aren’t web browsers or curl) don’t.
alien_at_work|8 years ago
What you should be versioning is your media types (e.g. HTML4 vs HTML5).
dordoka|8 years ago
Well, what he exactly says is that URLs should not include versioning, because URLs are the interfaces names and REST estates that interface names should not be versioned, as that implies a breaking change in the API. It's just the wrong place for versioning in the REST way.
But he is not against versioning, as you say, you can use the Accept header. You could also use a custom header if you might, but the canonical way would be the Accept header.
phlakaton|8 years ago