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A more complex API

After seeing a simple example of an API let's take a look at a more complex example.

One List

The One List API is an API for managing a list of todo items.

Let's review the style of API access we've already seen. The first URL pattern will retrieve the full list of TODO items.

/items?access_token={access_token}

Each URL we investigate will have an access_token and this will allow us to maintain different lists for different users.

The examples below are based on the online documention of the One List API.

GET /items?access_token={access_token}

This API URL will get the list of all todo items. If we run http to fetch data from the API like:

http "https://one-list-api.herokuapp.com/items?access_token=illustriousvoyage"

We would see output similar to:

[
{
"id": 6,
"text": "Finish Assignment",
"complete": true,
"user_id": 4,
"created_at": "2016-08-17T20:06:34.874Z",
"updated_at": "2018-10-02T16:10:59.754Z"
},
{
"id": 20,
"text": "eat breakfast",
"complete": true,
"user_id": 4,
"created_at": "2016-08-17T20:42:59.666Z",
"updated_at": "2018-10-02T16:11:59.553Z"
}
]

We see that each item has six fields, id, text, complete, user_id, created_at, and updated_at.

fielddescription
idThe unique identifier for this column. It will be an increasing value.
textThe description of the todo
completeA boolean indicating if we consider the todo complete
user_idIdentifies the user/list and should be the same for any access_token
created_atThe timestamp when the item was created
updated_atThe timestamp when the item was last updated

Get a specific item

Use the URL GET /items/{id}?access_token={access_token} to retrieve a specific token. Notice that in the URL we put the specific TODO item's id while also providing the access token.

http "https://one-list-api.herokuapp.com/items/20?access_token=illustriousvoyage"

This will return the details on only item with id of 20.

{
"id": 20,
"text": "eat breakfast",
"complete": true,
"user_id": 4,
"created_at": "2016-08-17T20:42:59.666Z",
"updated_at": "2018-10-02T16:11:59.553Z"
}

Create a new item

We are now going to see our first API usage where we send data to the API to be stored/updated/deleted.

We use the URL POST /items?access_token={access_token} to CREATE an item. Notice for the first time we are using a different verb, the POST. The POST verb cannot be generated from the URL bar, but can from a web form, which makes sense since we often use forms to create data, as well as from code or the command line.

The JSON we will send to the server should look like this:

{
"item": {
"text": "New text here",
"complete": false
}
}

We can specify this on the command line with httpie by writing: item:='{ "text": "New text here", "complete": false }'. We can also specify the POST verb.

http POST "https://one-list-api.herokuapp.com/items?access_token=illustriousvoyage" item:='{ "text": "New text here", "complete": false }'

The response from this request will be the JSON representation of the newly created todo item. If you are also trying this, your IDs and timestamps will be different.

{
"id": 1588,
"text": "New text here",
"complete": false,
"user_id": 4,
"created_at": "2020-04-23T00:56:05.709Z",
"updated_at": "2020-04-23T00:56:05.709Z"
}

If you keep repeating the same command you will see new items being created and returned to you, each with new id values.

Update an item

To update an item with this API we use a very similar structure as the POST used to create, but this time we change the VERB to PUT and include the id in the URL:

PUT /items/{id}?access_token={access_token}

The body of the method has the same structure as the POST, that is the JSON object containing text and complete keys.

http PUT "https://one-list-api.herokuapp.com/items/1588?access_token=illustriousvoyage" item:='{ "text": "New text here. Updated", "complete": true }'

The JSON response from this will be similar to:

{
"id": 1588,
"text": "New text here. Updated",
"complete": true,
"user_id": 4,
"created_at": "2020-04-23T00:56:05.709Z",
"updated_at": "2020-04-23T01:03:16.815Z"
}

Notice that the text and complete are updated, but the server has also updated the updated_at time.

Deleting items

To delete an item we switch to using the DELETE verb and specify the item in the URL.

DELETE /items/{id}?access_token={access_token}

However we do not specify a body since no additional information is needed to find the item and remove it.

http DELETE "https://one-list-api.herokuapp.com/items/1588?access_token=illustriousvoyage"

And this will return an empty response.

But what would happen if we were to try to delete the item again? We need to also consider the response code that the server sends us in addition to the body of the response. The response code is a number that represents a status of what the server did in response to our request. If we run that http command to delete that item again, you will see that this will return a 404 response code which means not found.

Review our API questions

If you review the API documentation at: https://one-list-api.herokuapp.com/ you will see that each API URL (known as an end point) has different answers to our API questions

Generally these answers are:

  • What is the input that needs to be sent? Any URL parameters, like {id} and query parameters like {access_token} as well as the body of the request if required
  • What is the format of the input? The body will be in JSON format
  • What is the name/location/identity of the code to be run? This will be the URL and the specific verb to use
  • What is the output that will be returned? The response body and the response code
  • What is the format of the output? The body will be in JSON and the response code will be a number

HTTP response codes

THe various HTTP response codes come in five sections.

Code RangeDescription
100-199Informational responses. These are rarely seen in most APIs.
200-299Success. The response is some form of success. Some of the successes are more specific. For instance 201 indicates that there was a success and some new resource is created
300-399Redirection. Indicates that the required resource is located at a different URL
400-499Client error. Indicates that the client has not complied with the API in some way.
500-599Server error. The server experienced some form of error when handling the request

Here are some common HTTP response codes you are likely to see

CodeDescription
200All is ok. Data is likely included in the response
201All is ok and we created something on your behalf. Data is likely included in the response. Also a Location header indicating the URL of the new resource may be included
204No content. The request was a success but no content is being returned
206Partial content. Only part of the content requested is being returned
301Moved permanently. The resource has been moved to a new URL, which is included in the Location header. The client can cache this result and use the new URL from now on
302Moved temporarily. The resource can be located at a new URL, included in the Location header. The client should continue to use the original URL for future requests because the relocation is only temporary
304Not modified. Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match. In such case, there is no need to retransmit the resource since the client still has a previously-downloaded copy
400Bad request. The request could not be processed by the server. Perhaps the body was not parsable, or required parameters are missing
401Unauthorized. The resource requires authorization in order to process and no valid authorization was provided
404Not found. The requested resource cannot be found.
405Method not allowed. The verb specified is not supported by the server
406Not acceptable. The requested resource is capable of generating only content not acceptable according to the Accept headers sent in the request
500Internal server error. The server experienced an internal error. Perhaps there is a syntax error in the code, or the database is not working.
501Not implemented. The service to process this request is not implemented

Sites to look up response codes

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