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Nope, the current state of affairs is an indictment of the "standards". It should be easy and obvious to implement something according to the standards, but it's not. I'm a relatively smart guy, and I've tried. You very quickly reach the point where you ask, "why the fuck am I doing this?" and just do what makes sense.

Let's take RFC8288 as an example since you've brought it up. Where in that RFC does it discuss _why the fuck_ I would want to put an API link in the headers instead of the body?

The fact is that this RFC isn't "the standard". The standard thing is to put API links in the body with other attributes, and it's the standard because that's what everyone does, and because that's what makes sense. This RFC is a hammer for HTTP pedants to hit people over the head with.

The web is based on linking

And where to we expect those links to appear? In the header?




FWIW, RFC 8288 was preceded [1] by RFC 5988, and RFC 5988 [2] says in its section '1. Introduction':

"A means of indicating the relationships between resources on the Web, as well as indicating the type of those relationships, has been available for some time in HTML [W3C.REC-html401-19991224], and more recently in Atom [RFC4287]. These mechanisms, although conceptually similar, are separately specified. However, links between resources need not be format specific; it can be useful to have typed links that are independent of their serialisation, especially when a resource has representations in multiple formats."

"To this end, this document defines a framework for typed links that isn't specific to a particular serialisation or application. It does so by redefining the link relation registry established by Atom to have a broader domain, and adding to it the relations that are defined by HTML."

[1] https://tools.ietf.org/html/rfc8288 [2] https://tools.ietf.org/html/rfc5988


it can be useful

Such as in which situations? It's not obvious at all, so a reader (that is, an API designer) is on their own to try and divine whether there's any real reason to follow this "standard" instead of doing things in the more natural and standard way.

This is my point. Not that it's hard to read these RFCs... but that they're often so vague, and is so often hard to know whether there's any benefit at all to following them in one's specific situation.

That doesn't stop self-appointed standards cops from smacking people down.


I might be missing the obvious, but I don't see in your quote the answer to the question:

> Where in that RFC does it discuss _why the fuck_ I would want to put an API link in the headers instead of the body?


The answer is in the part that says "it can be useful to have typed links that are independent of their serialisation, especially when a resource has representations in multiple formats".

In HTTP, URLs locate a 'resource'. Then you and the server do content negotiation, implicit and/or explicit, to select a 'resource representation'. Think of these as different formats for the same conceptual thing identified by the URL. Some formats like HTML can support hypermedia that can have embedded links. Some, like 'text/plain' or 'image/gif', can't.

Link headers allow links from the current resource to other resources to be communicated even if the chosen representation can't communicate links in its body.


Got it, thanks. How do you define 'the chosen representation can't communicate links in its body'?


You as the client try to GET /my-receipts/20190512-1 from Fancy Receipt Scanning Service, and content-negotiate with an Accept header to "text/plain" or "image/gif" (e.g. to get a plain copy or a scan). There's no agreed-upon way of communicating links in plain text or GIF, so Fancy Receipt Scanning Service can't serve you a GIF scan of your receipt that links to a product page for every item you bought.

If you accepted "text/html", it could have served HTML that embedded these links within the response body, but you didn't accept "text/html".

It can choose to send links as headers, if it still wishes to communicate links.


That's fair, but if I'm defining an API that serves, say, JSON, I can define a schema for it and tell my clients what things mean in the schema, including which things are links.


> Nope, the current state of affairs is an indictment of the "standards".

That's not true at all. Those "standards" are not taken into account at all. I mean, there are currently about half a dozen HATEOAS standards and specifications that repeatedly implement the same concept, and they have existed for quite a few years. Yet, how many of those standards and specifications were taken into account in this particular blog post? Zero. Instead of taking into account any prior work already done on the issue of web linking, the problem is for some reason presented as a novel idea that, for some reason, no one in the world would have ever thought about.

How is that a reasonable starting point?

> It should be easy and obvious to implement something according to the standards, but it's not.

You got to be kidding.

Let's consider RFC8288. RFC8288 in essence specifies a single HTTP header and a format to represent link relations. You want to link your resource to any other resources? Well, just add the link relations. You want to check what resources are related to the resource you've just requested? Well, just check the Links headers.

Let's consider Hypertext Application Language (HAL). HAL in essence specifies a wrapper document type that extends the resource with a "_links" name:object pair. You want to link your resource to any other resources? Well, just add the link relations to the "_links" object. You want to check what resources are related to the resource you've just requested? Well, just check the object referred by the "_links" name.

Let's consider the Ion Hypermedia Type. Ion in essence specifies a wrapper object type that includes all link relations as JSON name:value pairs and contains the resource as the value of the "value" name:value pair. You want to link your resource to any other resource? Well, just add the link relation as a name:value pair. You want to check what resources are related to the resource you've requested? Well, just check the name:value pairs of the response object.

And the same applies to other HATEOAS standards and specifications such as JSON-LD, Hydra, Collection+JSON, Siren, etc etc etc...

Where's the rocket science?

> Where in that RFC does it discuss _why the fuck_ I would want to put an API link in the headers instead of the body?

You can't be serious.


As someone who is wholly unfamiliar with this, why should relationships be treated any differently than any other attribute of some object returned by a web api?

If data-attributes have to be parsed out of some json-body, but link-attributes have to be parsed out of the header, that's weird. It becomes even weirder if I decide to switch from using a key-in-the-body to a link-in-the-header.

That doesn't sound easy or obvious. As is, as someone dealing with a REST API, I rarely, if ever, have to think of headers. When I do, they're related to things like CORS, and transport layer semantics, not application level semantics. But now you're saying that, actually, some of my application semantics should be in the header, but most should be in the body.

How is that easy or obvious? Why is that better?

I'm dead serious, I'm not kidding, I'm not the user you just responded to.


> As someone who is wholly unfamiliar with this, why should relationships be treated any differently than any other attribute of some object returned by a web api?

Because links are resource metadata, not the resource itself let alone entities represented by a resource. The relationships between resources are independent of the resources themselves.

> If data-attributes have to be parsed out of some json-body, but link-attributes have to be parsed out of the header, that's weird.

It really isn't. In fact, it's the other way around. Link relations depend on the request, not the resource, just like the particular version of the resource (see ETag header) or the date and time at which the origin server believes the resource was last modified (see Last-Modified header).

Considering the petstore example, it would be weird if the pet would include a version/hash or the last time it was modified. A pet is a pet. It has a name, a species, a breed, and an owner. The pet resource is the pet information that you received as a response to the request you've made in a specific moment in time.


> Link relations depend on the request, not the resource, just like the particular version of the resource (see ETag header) or the date and time at which the origin server believes the resource was last modified (see Last-Modified header).

Not really. Since it's mother's day, the fact that I'm related to my mother is an attribute of me, not an attribute of the request you make for information about me. I am related to my mom.

In a conventional database, link relations are defined on the tables themselves, but versioning information and last-modified information is normally defined in metadata tables. So I don't see any prior art for this. It just doesn't match how most people normally represent objects.

> and the pet resource is the pet information that you received as a response to the request you've made in a specific moment in time.

And at version X, the pet has a specific owner, defined as a relation on the pet itself. The request provides versioning information, but the owner is keyed on the pet, just like it would be in the server's database.


> Not really. Since it's mother's day, the fact that I'm related to my mother is an attribute of me, not an attribute of the request you make for information about me. I am related to my mom.

You are related to your mother, but that relationship is represented through link relations. You are represented by your resource, and your mother is represented through her resource. Where and how those resources are represented or found is an entirely different concern that has absolutely no relation with the relationship between you and your mother.

> In a conventional database, link relations are defined on the tables themselves

Actually, they are not. I mean, there are entity tables (the resources) and then there are the relationship tables (the... relations). Although some techniques involve using non-normalized databases, that does not mean that entities and entity metadata, such as relations, are or should be conflated.

Now, imagine that the database tables weren't fixed properties of the system, which is a basic design issue in resource-oriented architectures. Would it make any sense to hard-code references to other tables if they could change at any point in time, specially if you're operating a system that could cache table rows?

> And at version X, the pet has a specific owner, defined as a relation on the pet itself.

Yes, and that's also the wrong way to go about specifying the relationship between resources. The correct way would be to express the relationship between resources as a link relation. The identity of neither the pet or the owner depend on each other.


> Actually, they are not. I mean, there are entity tables (the resources) and then there are the relationship tables (the... relations)

Foreign keys are put in entity tables in normalized databases.

> The identity of neither the pet or the owner depend on each other

So then the only thing that belongs on the pet itself is an arbitrary id? Because the identity of the pet doesn't depend on it's age or when it was born, and a timestamp is just a timestamp, so putting "time of birth" could just be a link relationship to another entity.

Same for breed. Location too, that's not a tool for identifying the pet. Heck, even the name is often defined by the pet-owner relationship but not the pet itself.

So we're left with a pet object that has only a uuid, and a set of link relations in the headers.

Why is that better? You've said my way is "wrong", but you haven't actually explained what your way does to improve the situation. I just demonstrated that any arbitrary piece of info can be represented as a link relationship, so the whole thing is arbitrary anyway.

So the simple question, the only question is, as a designer or user of an API, how does sticking some relationships in headers make my life easier? How do I decide which relationships those should be?

You clearly have opinions on how this should be done, but neither you nor the RFC explains what I gain from your way of doing things. So again, I'm not asking what I should do, I'm asking why?


> As is, as someone dealing with a REST API, I rarely, if ever, have to think of headers.

Really?

Headers contain information about the content and the caller which are used in business logic. Authentication and authorization information is often passed in headers, for example.




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