Is an API Always Necessary for Server-Client Communication?

fog37 said:

I conceptually understand what an API is: it is like an intermediary between two programs that makes integration easy.

fog37 said:

For example, we build app A and want to connect to app B. The connection may not be easy unless app B offers an API to which to connect...

fog37 said:

does it means that in every client/software communication there is an API, another program, seating between the client and server?

fog37 said:

is an API just another higher level protocol?

fog37 said:

TL;DR Summary: API and sever/client communication

It is clear that a server and a client are programs communicative iwth each other using one or more protocols (HTTP, TCP, etc.)
I conceptually understand what an API is: it is like an intermediary between two programs that makes integration easy.

fog37 said:

For example, we build app A and want to connect to app B. The connection may not be easy unless app B offers an API to which to connect...

That said, does it means that in every client/software communication there is an API, another program, seating between the client and server?

fog37 said:

Or is an API just another higher level protocol?

fog37 said:

I am confused about the relation between server, client, API...

For example, could we have a server and a client communicating with each other without an intermediary API?

fog37 said:

In a different post, I talked about writing simple client.py and server.py scripts in Python that represent a server and a client. There was no API discussion in that context....So API don't always need to be part of the server/client exchange?

fog37 said:

In a different post, I talked about writing simple client.py and server.py scripts in Python that represent a server and a client. There was no API discussion in that context....

PeterDonis said:

Obviously not. In your example, there is just app A and app B. There is no program C in between them.


Not really, because an API doesn't specify how app A connects to app B; the TCP protocol and the system of IP addresses and ports does that. An API specifies what kinds of content can be exchanged once the connection is made.

fog37 said:

Some people talk about building APIs which made me think that API are actual programs/code that developers write...

fog37 said:

My confusion stems from hearing people saying that they use this or that API, for example the API specific to a website server (ex: Youtube API, Twitter API)

fog37 said:

Some people talk about building APIs which made me think that API are actual programs/code that developers write...

fog37 said:

In essence, it seems that an API is really a protocol, like HTTP and TCP.

fog37 said:

the API as a protocol seems to run above the HTTP layer of communication

fog37 said:

making functions available to the code to get content from the server in a specific way, as a json file...

jack action said:

The term Application Programming Interface (API) is usually used in opposition to User Interface (UI) which is the space where interactions between humans and machines occur. The output of UI is formatted with graphics, sounds, and interactive components like forms, for example, the HTML format.

API is meant to serve the essential pieces of information to another program in a simplified format, for example, JSON, XML, etc.

So a server could respond with a highly formatted, human-readable, answer to an HTTP request and a simple JSON file to the same request but sent to its API instead.

fog37 said:

let's say I write a python script that performs some useful task....where would the API piece fit in?

fog37 said:

When people actually build APIs (instead of just using them), does it mean there is some website that does not have an API and we want to create one for it so we can request information from it via a program we write?

fog37 said:

In essence, it seems that an API is really a protocol,

fog37 said:

like HTTP and TCP.

fog37 said:

But the API as a protocol seems to run above the HTTP layer of communication making functions available to the code to get content from the server in a specific way, as a json file...

Bosko said:

HTTP and TCP are not at the same level of OSI

PeterDonis said:

HTTP itself isn't even confined to a single level of OSI; it contains elements of levels 5, 6, and 7.

Bosko said:

the difference between OSI levels is not so clear

fog37 said:

let's say I write a python script that performs some useful task....where would the API piece fit in?

def getJSONData():
    JSONstring = ""
    """
    fetch info from database and put it in the JSON formatted string JSONstring
    """
    return JSONstring
    

def getHTMLwebPage():
    JSONdata = getJSONdata()
    HTMLstring = ""
    """
    Insert the JSONdata into an HTML template then save in HTMLstring
    """
    return HTMLstring


def getData(url):
    HTMurl = "https://example.com/get-info"
    APIurl = "https://example.com/api/get-info"
    
    if url == HTMLurl:
        return getHTMLwebPage()
    elif url == APIurl:
        return getJSONdata()

jack action said:

Python:

def getJSONData():
    JSONstring = ""
    """
    fetch info from database and put it in the JSON formatted string JSONstring
    """
    return JSONstring
   

def getHTMLwebPage():
    JSONdata = getJSONdata()
    HTMLstring = ""
    """
    Insert the JSONdata into an HTML template then save in HTMLstring
    """
    return HTMLstring


def getData(url):
    HTMurl = "https://example.com/get-info"
    APIurl = "https://example.com/api/get-info"
   
    if url == HTMLurl:
        return getHTMLwebPage()
    elif url == APIurl:
        return getJSONdata()

fog37 said:

Can a single web server have multiple APIs at the same time?

{
  "messages": [
    {
      "id": string,
      "threadId": string
    },
    ...
  ],
  "nextPageToken": string,
  "resultSizeEstimate": integer
}

jack action said:

View attachment 340779​

• For example, the knobs on a radio are APIs....The power outlet is example of a physical outlet (we get electricity from it and don't care about all the details about the power plant and transmission lines). Inside a computer, I am sure some there are many software APIs that let components communicate with lower-level hardware. In programming, a library is sometimes called an API (ex: Keras is an API for Tensorflow, Seaborn is an API for matplotlib, etc. since they allow us to use those libraries/frameworks in a more convenient way...). Even a simple python function that converts a string from lowercase to uppercase is an API in a sense since we simply call the function ##upper()## and it does its job but we have no idea of how happens under the hood.

• However, as ubiquitous APIs are, I read that there are many scenarios in which they are not used (see this interesting quora reply: https://www.quora.com/Do-all-websites-use-an-API-I-believe-they-would-as-a-client-needs-to-communicate-data-and-requests-to-the-server-but-is-there-an-alternative-method#:~:text=Not%20all%20websites%20use%20an%20API%20(Application%20Programming%20Interface)%20in,to%20exchange%20data%20and%20requests.

• One ore two APIs? are there one or two APIs, one on the server side and one on the client side, or just one API? Does it depend on the API? Server APIs expose endpoints....How would a client-API work? For example, are Google Maps APIs client-APIs or server-APIs?
• Python script: the short python script in the attached figure represents an API call to the yelp server...An API has a URL (URI) that specifies both the IP address the API endpoint, and possibly other parameters. When working with the requests library, we can use the HTTP verbs like GET, PUT, DELETE, etc. Here we use GET to get some information back as a json file. We are essentially using a python library, requests, and its functions get to perform the communication. But this code snippet is NOT really the API itself...even if we described an API as a simple set of rules implemented by the functions of the library requests, correct?

fog37 said:

Analogy: finally, we know that an IP address identifies a specific host on the Internet and the port number identifies the specific service offered by the host. For example, port 80 is the door that a client knocks at to get web-like information from a server....The analogy is that the IP address identifies the house and the port identifies one of the house access doors to different rooms in the house where different resources are stored...Using this oversimplified analogy, what would an API and an API endpoint represent?

jack action said:

API is the language (English, German, Japanese) chosen to communicate between the client and the resource. What are the endpoints of the Japanese language? The one who talks and the ones who listen (or the one who writes and the ones who read), so the client and resource themselves.

The API specification would be the dictionary and grammar of the chosen language.

With Web API, we mean any URL that doesn't return an HTML document or a file stored on the server. But technically, HTTP and HTML are some sort of APIs.

fog37 said:

the remote web server program, and the API program

fog37 said:

What data format would be used for unstructured data?

fog37 said:

a browser could also request a pdf file, which not markup language...There is not API involved there, correct?

fog37 said:

URL are just IP addresses.

fog37 said:

Is the API's IP address the same IP for the remote web server?

fog37 said:

Do APIs also have ports?

fog37 said:

What if instead of asking a web API for structured data, which would be sent back to the client as json or XML file, the client was requesting unstructured data like images or audio files? How would the data be sent back? REST APIs provide the requested content in the form of json files...What data format would be used for unstructured data?

fog37 said:

URL are just IP addresses.