THE BRIEF ON APIs
APPLICATION PROGRAMMING INTERFACE
Application Programming Interface(API) can be best understood as software that grants two applications the ability to talk to each other, an API is a messenger or a middleman that delivers your request to a server that you are requesting from and delivers the response back to you. API is built to integrate into applications for different functions, for example, google maps and bolt app, bolt app has an API that integrates google maps into it so the bolt application can tell where you are on the map or where other places are.
APIs can be used between apps and websites, like the weather application on your phone, the API can get information from a website on the current or past weather conditions and sends the information to the app on your phone then the app displays it to you. This is the way applications and websites communicate with each other on the internet by using APIs to connect to apps and webs to enhance apps and webs made by programmers/developers.
OPEN APIs
- OPEN APIs: They are also known as External or Public APIs. The Open API Specifications(OAS) defines a standard, language-agnostic interface to RESTful APIs which allow both humans and computers to discover and understand the capabilities of the service without access to the source code, it is a file specifications that outline how to describe a REST API and what an API can do by using YAML, JSON, etc.
Other examples of API includes COMPOSITE APIs, WEB APIs, INTERNAL APIs, PARTNER APIs,
JSON(JavaScript Object Notation) is a standard text-based format for representing structured data based on JavaScript object syntax. It is commonly used for transmitting data in web applications.
Open API is used to:
- Describes the REST API's: RESOURCES, ENDPOINTS, OPERATIONS, PARAMETERS, AUTHORIZATIONS.
- It allows a user to understand/use the service API.
Allows you to extend your REST API with tooling. ATTRIBUTES OF A GOOD OPEN API(s):
- Does not leak private information
- Performs prudently
- Free of software bugs
- Good security
EXAMPLES OF OPEN API(s):
REST(REPRESENTATIONAL STATE TRANSFER) APIs
It is a set of protocols that guides the creation of web services, it allows a client and server to communicate with each other using HTTP/HTTPS protocols. This API defines how a web should behave and web services that obey its protocols are described as RESTful. A REST API provides its web resources to the user and allows the user to read, modify with a stateless protocol and a predefined set of operations. The textual representation of a REST API consists of the REST API information ( version, URL, etc), Description of the API request, description of API response, example response.
HTTP VERBS
We use HTTP protocol principles to provide support to CREATE, READ, UPDATE, DELETE, and DATA this operation is referred to as CRUD operations. Let's say we have a company named BLUX which offers car rentals, the company would have an OPEN API that manages the list of customers. That server can be accessed using a link blux.com/api/customers as an end-point, the address starts with "http" if you want the data to be exchanged on a secured channel you would use "https", after that we have the domain of the application, "blux.com", next is "/api" it can be kept before the domain name after that "/customers" refers to the collection of customers it could be "/cars" this is known as a resource, accessing this resource is done by sending an https request, the type of HTTP request determines the kind of operation, every HTTP has a what we call a verb or method they include:
- GET, for getting data(GET/api/customers)
- POST, for creating data(POST/api/customers/1)
- PUT, for updating data(PUT/api/customers/1)
DELETE, for deleting data(DELETE/api/customers)
RESPONSE CODE
When a request is made to a server a three-digit HTTP response status code is returned, it is a means of the server communicating back to the client's response these codes indicate what is about to happen on a website.
Types Of Response Codes
Information Codes :
100 "Continue": This interim response indicates that everything so far is OK and that the client should continue the request, or ignore the response if the request is already finished.
101 "Switching Protocol": This code is sent in response to an Upgrade request header from the client, and indicates the protocol the server is switching to.
- 102 "Processing" (WebDAV): This code indicates that the server has received and is processing the request, but no response is available yet.
- 103 "Early Hints": This status code is primarily intended to be used with the Link header, letting the user agent start preloading resources while the server prepares a response.
- Successful codes :
200 "OK": The request has succeeded. The meaning of the success depends on the HTTP method:
GET: The resource has been fetched and is transmitted in the message body.
HEAD: The representation headers are included in the response without any message body.
PUT or POST: The resource describing the result of the action is transmitted in the message body.
TRACE: The message body contains the request message as received by the server.
201 "Created": The request has succeeded and a new resource has been created as a result. This is typically the response sent after POST requests or some PUT requests.
- 202 "Accepted": The request has been received but not yet acted upon. It is noncommittal since there is no way in HTTP to later send an asynchronous response indicating the outcome of the request. It is intended for cases where another process or server handles the request, or for batch processing.
- 203 "Non-Authoritative Information" : This response code means the returned meta-information is not exactly the same as is available from the origin server but is collected from a local or a third-party copy. This is mostly used for mirrors or backups of another resource. Except for that specific case, the "200 OK" response is preferred to this status.
- 204 "No Content" : There is no content to send for this request, but the headers may be useful. The user-agent may update its cached headers for this resource with the new ones.
- 205 Reset Content: Tells the user-agent to reset the document which sent this request.
- 206 "Partial Content" : This response code is used when the Range header is sent from the client to request only part of a resource.
- 207 "Multi-Status" (WebDAV): Conveys information about multiple resources, for situations where multiple status codes might be appropriate.
- 208 "Already Reported" (WebDAV): Used inside a response element to avoid repeatedly enumerating the internal members of multiple bindings to the same collection.
- 226 "IM Used" (HTTP Delta encoding): The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance manipulations applied to the current instance.
- Redirection Messages :
- 300 "Multiple Choice" : The request has more than one possible response. The user-agent or user should choose one of them. (There is no standardized way of choosing one of the responses, but HTML links to the possibilities are recommended so the user can pick.)
301 "Moved Permanently": The URL of the requested resource has been changed permanently. The new URL is given in the response.
302 "Found" : This response code means that the URI of the requested resource has been changed temporarily. Further changes in the URI might be made in the future. Therefore, this same URI should be used by the client in future requests.
- 303 "See Other": The server sent this response to direct the client to get the requested resource at another URI with a GET request.
- 304 "Not Modified" : This is used for caching purposes. It tells the client that the response has not been modified, so the client can continue to use the same cached version of the response.
- 305 "Use Proxy" : Defined in a previous version of the HTTP specification to indicate that a requested response must be accessed by a proxy. It has been deprecated due to security concerns regarding the in-band configuration of a proxy.
- 306 "unused": This response code is no longer used; it is just reserved. It was used in a previous version of the HTTP/1.1 specification.
- 307 "Temporary Redirect": The server sends this response to direct the client to get the requested resource at another URI with the same method that was used in the prior request. This has the same semantics as the 302 Found HTTP response code, with the exception that the user agent must not change the HTTP method used: If a POST was used in the first request, a POST must be used in the second request.
- 308 "Permanent Redirect": This means that the resource is now permanently located at another URI, specified by the Location: HTTP Response header. This has the same semantics as the 301 Moved Permanently HTTP response code, with the exception that the user agent must not change the HTTP method used: If a POST was used in the first request, a POST must be used in the second request.
- Client Error Response :
400 "Bad Request": The server could not understand the request due to invalid syntax.
401 "Unauthorized": Although the HTTP standard specifies "unauthorized", semantically this response means "unauthenticated". That is, the client must authenticate itself to get the requested response.
- 402 "Payment Required": This response code is reserved for future use. The initial aim for creating this code was using it for digital payment systems, however, this status code is used very rarely and no standard convention exists.
- 403 "Forbidden": The client does not have access rights to the content; that is, it is unauthorized, so the server is refusing to give the requested resource. Unlike 401, the client's identity is known to the server.
- 404 "Not Found": The server can not find the requested resource. In the browser, this means the URL is not recognized. In an API, this can also mean that the endpoint is valid but the resource itself does not exist. Servers may also send this response instead of 403 to hide the existence of a resource from an unauthorized client. This response code is probably the most famous one due to its frequent occurrence on the web.
- 405 "Method Not Allowed" : The request method is known by the server but is not supported by the target resource. For example, an API may forbid DELETE-ing a resource.
- 406 "Not Acceptable" : This response is sent when the webserver, after performing server-driven content negotiation, doesn't find any content that conforms to the criteria given by the user agent.
- 407 "Proxy Authentication Required" : This is similar to 401 but authentication is needed to be done by a proxy.
- 408 "Request Timeout" : This response is sent on an idle connection by some servers, even without any previous request by the client. It means that the server would like to shut down this unused connection. This response is used much more since some browsers, like Chrome, Firefox 27+, or IE9, use HTTP pre-connection mechanisms to speed up surfing. Also, note that some servers merely shut down the connection without sending this message.
- 409 "Conflict": This response is sent when a request conflicts with the current state of the server.
- 410 "Gone": This response is sent when the requested content has been permanently deleted from the server, with no forwarding address. Clients are expected to remove their caches and links to the resource. The HTTP specification intends this status code to be used for "limited-time, promotional services". APIs should not feel compelled to indicate resources that have been deleted with this status code.
- 411 "Length Required": The server rejected the request because the Content-Length header field is not defined and the server requires it.
- 412 "Precondition Failed": The client has indicated preconditions in its headers which the server does not meet.
- 413 "Payload Too Large": Request entity is larger than limits defined by server; the server might close the connection or return a Retry-After header field.
- 414 "URI Too Long": The URI requested by the client is longer than the server is willing to interpret.
- 415 "Unsupported Media Type": The media format of the requested data is not supported by the server, so the server is rejecting the request.
- 416 "Range Not Satisfiable": The range specified by the Range header field in the request can't be fulfilled; the range may be outside the size of the target URI's data.
- 417 "Expectation Failed": This response code means the expectation indicated by the Expect request-header field can't be met by the server.
- 418 "I'm a teapot": The server refuses the attempt to brew coffee with a teapot.
- 421 "Misdirected Request": The request was directed at a server that is not able to produce a response. This can be sent by a server that is not configured to produce responses for the combination of scheme and authority that are included in the request URI.
- 422 "Unprocessable Entity" (WebDAV): The request was well-formed but was unable to be followed due to semantic errors.
- 423 "Locked" (WebDAV): The resource that is being accessed is locked.
- 424 "Failed Dependency" (WebDAV): The request failed due to the failure of a previous request.
- 425 "Too Early": This indicates that the server is unwilling to risk processing a request that might be replayed.
- 426 "Upgrade Required": The server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server sends an Upgrade header in a 426 response to indicate the required protocol(s).
- 428 "Precondition Required" : The origin server requires the request to be conditional. This response is intended to prevent the 'lost update' problem, where a client GETs a resource's state, modifies it, and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.
- 429 "Too Many Requests": The user has sent too many requests in a given amount of time ("rate limiting").
- 431 "Request Header Fields Too Large": The server is unwilling to process the request because its header fields are too large. The request may be resubmitted after reducing the size of the request header fields.
- 451 "Unavailable For Legal Reasons": The user-agent requested a resource that cannot legally be provided, such as a web page censored by a government.
Server Error Response:
500 "Internal Server Error": The server has encountered a situation it doesn't know how to handle.
501 "Not Implemented": The request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are GET and HEAD.
- 502 "Bad Gateway": This error response means that the server while working as a gateway to get a response needed to handle the request, got an invalid response.
- 503 "Service Unavailable": The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent. This response should be used for temporary conditions and the Retry-After: HTTP header should, if possible, contain the estimated time before the recovery of the service. The webmaster must also take care of the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.
- 504 "Gateway Timeout": This error response is given when the server is acting as a gateway and cannot get a response in time.
- 505 "HTTP Version Not Supported": The HTTP version used in the request is not supported by the server.
- 506 "Variant Also Negotiates": The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself and is therefore not a proper endpoint in the negotiation process.
- 507 "Insufficient Storage" (WebDAV): The method could not be performed on the resource because the server is unable to store the representation needed to complete the request.
- 508 "Loop Detected" (WebDAV): The server detected an infinite loop while processing the request.
- 510 "Not Extended": Further extensions to the request are required for the server to fulfill it.
- 511 "Network Authentication Required":
The 511 status code indicates that the client needs to authenticate to gain network access.
HOW TO USE AN API(EXAMPLE)
To get access to an application or company API the first step is to send an HTTP request, lets say we want to view youtube's facebook profile we use
if we want access to Facebook graph API we use
graph.facebook.com/youtube as an endpoint,
then a JSON structured data is displayed there you can see youtube's data if we want access to just the likes and names we use parameters
the parameter will filter the data to only the name of the profiles and likes.