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diff --git a/guide/rest_principles.md b/guide/rest_principles.md deleted file mode 100644 index 922f158..0000000 --- a/guide/rest_principles.md +++ /dev/null @@ -1,165 +0,0 @@ -REST principles -=============== - -This chapter will attempt to define the concepts behind REST -and explain what makes a service RESTful. - -REST is often confused with performing a distinct operation -depending on the HTTP method, while using more than the GET -and POST methods. That's highly misguided at best. - -We will first attempt to define REST and will look at what -it means in the context of HTTP and the Web. -For a more in-depth explanation of REST, you can read -[Roy T. Fielding's dissertation](http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm) -as it does a great job explaining where it comes from and -what it achieves. - -REST architecture ------------------ - -REST is a *client-server* architecture. The client and the server -both have a different set of concerns. The server stores and/or -manipulates information and makes it available to the user in -an efficient manner. The client takes that information and -displays it to the user and/or uses it to perform subsequent -requests for information. This separation of concerns allows both -the client and the server to evolve independently as it only -requires that the interface stays the same. - -REST is *stateless*. That means the communication between the -client and the server always contains all the information needed -to perform the request. There is no session state in the server, -it is kept entirely on the client's side. If access to a resource -requires authentication, then the client needs to authenticate -itself with every request. - -REST is *cacheable*. The client, the server and any intermediary -components can all cache resources in order to improve performance. - -REST provides a *uniform interface* between components. This -simplifies the architecture, as all components follow the same -rules to speak to one another. It also makes it easier to understand -the interactions between the different components of the system. -A number of constraints are required to achieve this. They are -covered in the rest of the chapter. - -REST is a *layered system*. Individual components cannot see -beyond the immediate layer with which they are interacting. This -means that a client connecting to an intermediate component, like -a proxy, has no knowledge of what lies beyond. This allows -components to be independent and thus easily replaceable or -extendable. - -REST optionally provides *code on demand*. Code may be downloaded -to extend client functionality. This is optional however because -the client may not be able to download or run this code, and so -a REST component cannot rely on it being executed. - -Resources and resource identifiers ----------------------------------- - -A resource is an abstract concept. In a REST system, any information -that can be named may be a resource. This includes documents, images, -a collection of resources and any other information. Any information -that can be the target of an hypertext link can be a resource. - -A resource is a conceptual mapping to a set of entities. The set of -entities evolves over time; a resource doesn't. For example a resource -can map to "users who have logged in this past month" and another -to "all users". At some point in time they may map to the same set of -entities, because all users logged in this past month. But they are -still different resources. Similarly, if nobody logged in recently, -then the first resource may map to the empty set. This resource exists -regardless of the information it maps to. - -Resources are identified by uniform resource identifiers, also known -as URIs. Sometimes internationalized resource identifiers, or IRIs, -may also be used, but these can be directly translated into a URI. - -In practice we will identify two kinds of resources. Individual -resources map to a set of one element, for example "user Joe". -Collection of resources map to a set of 0 to N elements, -for example "all users". - -Resource representations ------------------------- - -The representation of a resource is a sequence of bytes associated -with metadata. - -The metadata comes as a list of key-value pairs, where the name -corresponds to a standard that defines the value's structure and -semantics. With HTTP, the metadata comes in the form of request -or response headers. The headers' structure and semantics are well -defined in the HTTP standard. Metadata includes representation -metadata, resource metadata and control data. - -The representation metadata gives information about the -representation, such as its media type, the date of last -modification, or even a checksum. - -Resource metadata could be link to related resources or -information about additional representations of the resource. - -Control data allows parameterizing the request or response. -For example, we may only want the representation returned if -it is more recent than the one we have in cache. Similarly, -we may want to instruct the client about how it should cache -the representation. This isn't restricted to caching. We may -for example want to store a new representation of a resource -only if it wasn't modified since we first retrieved it. - -The data format of a representation is also known as the media -type. Some media types are intended for direct rendering to the -user, while others are intended for automated processing. The -media type is a key component of the REST architecture. - -Self-descriptive messages -------------------------- - -Messages must be self-descriptive. That means that the data -format of a representation must always come with its media -type (and similarly requesting a resource involves choosing -the media type of the representation returned). If you are -sending HTML, then you must say it is HTML by sending the -media type with the representation. In HTTP this is done -using the content-type header. - -The media type is often an IANA registered media type, like -`text/html` or `image/png`, but does not need to be. Exactly -two things are important for respecting this constraint: that -the media type is well specified, and that the sender and -recipient agree about what the media type refers to. - -This means that you can create your own media types, like -`application/x-mine`, and that as long as you write the -specifications for it and that both endpoints agree about -it then the constraint is respected. - -Hypermedia as the engine of application state ---------------------------------------------- - -The last constraint is generally where services that claim -to be RESTful fail. Interactions with a server must be -entirely driven by hypermedia. The client does not need -any prior knowledge of the service in order to use it, -other than an entry point and of course basic understanding -of the media type of the representations, at the very least -enough to find and identify hyperlinks and link relations. - -To give a simple example, if your service only works with -the `application/json` media type then this constraint -cannot be respected (as there are no concept of links in -JSON) and thus your service isn't RESTful. This is the case -for the majority of self-proclaimed REST services. - -On the other hand if you create a JSON based media type -that has a concept of links and link relations, then -your service might be RESTful. - -Respecting this constraint means that the entirety of the -service becomes self-discoverable, not only the resources -in it, but also the operations you can perform on it. This -makes clients very thin as there is no need to implement -anything specific to the service to operate on it. |