翻译：【美国白宫网站的AP规范：WhiteHouse/api-standards】

White House Web API Standards

• Guidelines
• Pragmatic REST
• RESTful URLs
• HTTP Verbs
• Responses
• Error handling
• Versions
• Record limits
• Request & Response Examples
• Mock Responses
• JSONP

Guidelines【指导原则】

This document provides guidelines and examples for White House Web APIs, encouraging consistency, maintainability, and best practices across applications. White House APIs aim to balance a truly RESTful API interface with a positive developer experience (DX).

这篇文档为白宫的web api提供了一些（准则）和例子，鼓励一致、可维护、最好的实践经过应用。白宫的接口是为了提供一个真实的RESTful API，让开发者有更好的体验

This document borrows heavily from:（该文档大量参考了如下文章：）

• Designing HTTP Interfaces and RESTful Web Services
• API Facade Pattern, by Brian Mulloy, Apigee
• Web API Design, by Brian Mulloy, Apigee
• Fieldings Dissertation on REST

Pragmatic REST【实用的REST】

These guidelines aim to support a truly RESTful API. Here are a few exceptions:

这些规则意在支持一个真实的RESTfull API，下面是一些例外：

• Put the version number of the API in the URL (see examples below). Don’t accept any requests that do not specify a version number.
• 把版本号放到URL里（下面有例子），不接受任何没有明确API版本的请求
• Allow users to request formats like JSON or XML like this:
• 容许用户用json或xml两种请求格式，以下面：
• • http://example.gov/api/v1/magazines.json
  • http://example.gov/api/v1/magazines.xml

RESTful URLs

General guidelines for RESTful URLs　　[RESTful URLs一般的原则]

• A URL identifies a resource.
• 一个URL标识一个资源
• URLs should include nouns, not verbs.
• URLS应该包含名词，不含动词
• Use plural nouns only for consistency (no singular nouns).
• 用复数名词为了连贯性
• Use HTTP verbs (GET, POST, PUT, DELETE) to operate on the collections and elements.
• 用HTTP的请求方法（GET、POST、PUT、DELETE）进行资源上的操做
• You shouldn’t need to go deeper than resource/identifier/resource.
• 不须要比 resource/identifier/resource 层级更深
• Put the version number at the base of your URL, for example http://example.com/v1/path/to/resource.
• 在你的url中加进版本号，如：
• URL v. header:
  • If it changes the logic you write to handle the response, put it in the URL.
  • 若是你处理相应的逻辑变了，把版本号放到URL里
  • If it doesn’t change the logic for each response, like OAuth info, put it in the header.
  • 若是任何响应的逻辑都没有变，像认证信息，把版本号放进头信息里
• Specify optional fields in a comma separated list.
• 明确可选的字段信息用逗号分隔开
• Formats should be in the form of api/v2/resource/{id}.json
• 格式应该像这样 api/v2/resource/{id}.json

Good URL examples 　　[好的url例子]

• List of magazines:
  • http://www.example.gov/api/v1/magazines.json
• Filtering is a query:
  • http://www.example.gov/api/v1/magazines.json?year=2011&sort=desc
  • http://www.example.gov/api/v1/magazines.json?topic=economy&year=2011
• A single magazine in JSON format:
  • http://www.example.gov/api/v1/magazines/1234.json
• All articles in (or belonging to) this magazine:
  • http://www.example.gov/api/v1/magazines/1234/articles.json
• All articles in this magazine in XML format:
  • GET http://example.gov/api/v1/magazines/1234/articles.xml
• Specify optional fields in a comma separated list:
  • http://www.example.gov/api/v1/magazines/1234.json?fields=title,subtitle,date
• Add a new article to a particular magazine:
  • POST http://example.gov/api/v1/magazines/1234/articles

Bad URL examples

• Non-plural noun:
  • http://www.example.gov/magazine
  • http://www.example.gov/magazine/1234
  • http://www.example.gov/publisher/magazine/1234
• Verb in URL:
  • http://www.example.gov/magazine/1234/create
• Filter outside of query string
  • http://www.example.gov/magazines/2011/desc

HTTP Verbs

HTTP METHOD	POST	GET	PUT	DELETE
CRUD OP	CREATE	READ	UPDATE	DELETE
/dogs	Create new dogs	List dogs	Bulk update	Delete all dogs
/dogs/1234	Error	Show Bo	If exists, update Bo; If not, error	Delete Bo

(Example from Web API Design, by Brian Mulloy, Apigee.)

Responses

• No values in keys
• 在对应的名称中没有值
• No internal-specific names (e.g. "node" and "taxonomy term")
• 在内部没有明确的命名
• Metadata should only contain direct properties of the response set, not properties of the members of the response set
• 元数据应该只包括相应集合的资源，而不是相应集合的成员的资源

Good examples

No values in keys:

"tags": [
  {"id": "125", "name": "Environment"},
  {"id": "834", "name": "Water Quality"}
],

Bad examples

Values in keys:

"tags": [
  {"125": "Environment"},
  {"834": "Water Quality"}
],

Error handling

Error responses should include a common HTTP status code, message for the developer, message for the end-user (when appropriate), internal error code (corresponding to some specific internally determined error number), links where developers can find more info. For example:

错误的响应应该包含一个经常使用的http状态码、给开发者的错误信息、给最终用户的信息、内部的错误码、和给开发者的连接让他们查阅更多的信息：

{
  "status" : "400",
  "developerMessage" : "Verbose, plain language description of the problem. Provide developers
   suggestions about how to solve their problems here",
  "userMessage" : "This is a message that can be passed along to end-users, if needed.",
  "errorCode" : "444444",
  "more info" : "http://www.example.gov/developer/path/to/help/for/444444,
   http://drupal.org/node/444444",
}

Use three simple, common response codes indicating (1) success, (2) failure due to client-side problem, (3) failure due to server-side problem:

用3个简单、常见的响应码标识（1）成功（2）失败的缘由是客户端问题（3）失败的缘由是服务器端问题

• 200 - OK
• 400 - Bad Request
• 500 - Internal Server Error

Versions

• Never release an API without a version number.
• 决不开放没有版本号的api
• Versions should be integers, not decimal numbers, prefixed with ‘v’. For example:
• 版本应该是带‘v’前缀的整型，不该该是小数，如：
• • Good: v1, v2, v3
  • Bad: v-1.1, v1.2, 1.3
• Maintain APIs at least one version back.
• 维持APIS至少有一个回退版本

Record limits

• If no limit is specified, return results with a default limit.
• 若是没有limit值，将使用默认的limit值返回结果
• To get records 50 through 75 do this:
  • http://example.gov/magazines?limit=25&offset=50
  • offset=50 means, ‘begin with record number fifty’
  • limit=25 means, ‘return 25 records’

Information about record limits should also be included in the Example resonse. Example:

在响应的信息中应该包括limits信息

{
    "metadata": {
        "resultset": {
            "count": 50,
            "offset": 25,
            "limit": 25
        }
    },
    "results": [
        { .. }
    ]
}

Request & Response Examples

API Resources

• GET /magazines
• GET /magazines/[id]
• POST /magazines/[id]/articles

GET /magazines

Example: http://example.gov/api/v1/magazines.json

{
    "metadata": {
        "resultset": {
            "count": 123,
            "offset": 0,
            "limit": 10
        }
    },
    "results": [
        {
            "id": "1234",
            "type": "magazine",
            "title": "Public Water Systems",
            "tags": [
                {"id": "125", "name": "Environment"},
                {"id": "834", "name": "Water Quality"}
            ],
            "created": "1231621302"
        },
        {
            "id": 2351,
            "type": "magazine",
            "title": "Public Schools",
            "tags": [
                {"id": "125", "name": "Elementary"},
                {"id": "834", "name": "Charter Schools"}
            ],
            "created": "126251302"
        }
        {
            "id": 2351,
            "type": "magazine",
            "title": "Public Schools",
            "tags": [
                {"id": "125", "name": "Pre-school"},
            ],
            "created": "126251302"
        }
    ]
}

GET /magazines/[id]

Example: http://example.gov/api/v1/magazines/[id].json

{
    "id": "1234",
    "type": "magazine",
    "title": "Public Water Systems",
    "tags": [
        {"id": "125", "name": "Environment"},
        {"id": "834", "name": "Water Quality"}
    ],
    "created": "1231621302"
}

POST /magazines/[id]/articles

Example: Create – POST http://example.gov/api/v1/magazines/[id]/articles

{
    "title": "Raising Revenue",
    "author_first_name": "Jane",
    "author_last_name": "Smith",
    "author_email": "jane.smith@example.gov",
    "year": "2012"
    "month": "August"
    "day": "18"
    "text": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam eget ante ut augue scelerisque ornare. Aliquam tempus rhoncus quam vel luctus. Sed scelerisque fermentum fringilla. Suspendisse tincidunt nisl a metus feugiat vitae vestibulum enim vulputate. Quisque vehicula dictum elit, vitae cursus libero auctor sed. Vestibulum fermentum elementum nunc. Proin aliquam erat in turpis vehicula sit amet tristique lorem blandit. Nam augue est, bibendum et ultrices non, interdum in est. Quisque gravida orci lobortis... "

}

Mock Responses　　【模拟响应】

It is suggested that each resource accept a 'mock' parameter on the testing server. Passing this parameter should return a mock data response (bypassing the backend).

建议在测试机上每一个api接受一个‘模拟’的参数，经过这个参数返回一个模拟的响应

Implementing this feature early in development ensures that the API will exhibit consistent behavior, supporting a test driven development methodology.

较早在线上环境实现这个特征，确保api显示一致的行为，支持测试驱动开发的方法

Note: If the mock parameter is included in a request to the production environment, an error should be raised.

注意：在线上环境，若是请求带有模拟的参数，应该返回错误

JSONP

JSONP is easiest explained with an example. Here's a one from StackOverflow:

Say you're on domain abc.com, and you want to make a request to domain xyz.com. To do so, you need to cross domain boundaries, a no-no in most of browserland.

The one item that bypasses this limitation is <script> tags. When you use a script tag, the domain limitation is ignored, but under normal circumstances, you can't really DO anything with the results, the script just gets evaluated.

Enter JSONP. When you make your request to a server that is JSONP enabled, you pass a special parameter that tells the server a little bit about your page. That way, the server is able to nicely wrap up its response in a way that your page can handle.

For example, say the server expects a parameter called "callback" to enable its JSONP capabilities. Then your request would look like:

http://www.xyz.com/sample.aspx?callback=mycallback

Without JSONP, this might return some basic javascript object, like so:

{ foo: 'bar' }

However, with JSONP, when the server receives the "callback" parameter, it wraps up the result a little differently, returning something like this:

mycallback({ foo: 'bar' });

As you can see, it will now invoke the method you specified. So, in your page, you define the callback function:

mycallback = function(data){
        alert(data.foo);
    };

http://stackoverflow.com/questions/2067472/what-is-jsonp-all-about?answertab=votes#tab-top