# RESTful API
\
## What is RESTful API?
* **R**epresentational
* **S**tate
* **T**ransfer
1. One form of `Software Architecture` for `Hypermedia systems` such as the WWW (World Wide Web)
2. A `REST Server` allows clients to access and modify server information using the **HTTP Protocol**
3. Information is provided in `text`, `xml`, `json` formats
* Nowadays `json` is the mainstream!
\
## HTTP method
> 4 commonly used methods in REST-based architecture
1. **GET**
: Retrieve
2. **PUT**
: Create and `update`
3. **DELETE**
: Remove
4. **POST**
: Create
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## Creating a Database
* Create a JSON-based user database
> Test04\_RESTful > data > user.json
```json
{
"first_user": {
"password": "first_pass",
"name": "chloe"
},
"second_user":{
"password": "second_pass",
"name": "bella"
}
}
```
\
### 1. API: GET/list
* Create a `GET API` that outputs all user lists
> router > main.js
```javascript
module.exports = function(app,fs){
app.get('/', function(request, response) {
response.render('index', {
title: "MY HOMEPAGE",
length: 5
})
});
app.get('/list', function(request, response){
fs.readFile(__dirname + "../data/" + "user.json", "utf8", function(error, data){
console.log(data);
response.end(data);
})
})
}
```
* `__dirname`
* Represents the location of the current module
* Since the **router** module is inside the router folder, you need to use a relative path to access the data folder!
> After running the server, access
\
### 2. API: GET/getUser/:username
* Create a `GET API` that retrieves detailed information for a specific username!
> Add to router > main.js
```javascript
app.get('/getUser/:username', function(req, res){
fs.readFile( __dirname + "/../data/user.json", 'utf8', function (err, data) {
var users = JSON.parse(data);
res.json(users[req.params.username]);
});
});
```
* After reading the file, it finds and outputs the user id
* If the user is found, it outputs the user data
* If not found, it outputs {}
* Since reading a file with `fs.readFile()` returns the data in text format, you need to use `JSON.parse()`!
> After restarting the server, access
\
### 3. API: POST addUser/:username
#### body: { "password": "***", "name": "***" }
> Add to router > main.js
```javascript
app.post('/addUser/:username', function(req, res){
var result = { };
var username = req.params.username;
// CHECK REQ VALIDITY
if(!req.body["password"] || !req.body["name"]){
result["success"] = 0;
result["error"] = "invalid request";
res.json(result);
return;
}
// LOAD DATA & CHECK DUPLICATION
fs.readFile( __dirname + "/../data/user.json", 'utf8', function(err, data){
var users = JSON.parse(data);
if(users[username]){
// DUPLICATION FOUND
result["success"] = 0;
result["error"] = "duplicate";
res.json(result);
return;
}
// ADD TO DATA
users[username] = req.body;
// SAVE DATA
fs.writeFile(__dirname + "/../data/user.json",
JSON.stringify(users, null, '\t'), "utf8", function(err, data){
result = {"success": 1};
res.json(result);
})
})
});
```
* Returns an error if the `JSON` format is **Invalid**
* If **valid**, opens the file, checks for `username` duplication, then adds to the `JSON` data and saves again
* `stringify(users, null, 2)` is for JSON **pretty-print**
\
### 4. **API: PUT updateUser/:username**
#### **body: { "password": "*****", "name": "*****" }**
* An API that updates user information
* Uses the `PUT` method
* An **idempotent** `PUT API`
* Must guarantee the same result no matter how many times the request is made!
> Add to router > main.js
```javascript
app.put('/updateUser/:username', function(req, res){
var result = { };
var username = req.params.username;
// CHECK REQ VALIDITY
if(!req.body["password"] || !req.body["name"]){
result["success"] = 0;
result["error"] = "invalid request";
res.json(result);
return;
}
// LOAD DATA
fs.readFile( __dirname + "/../data/user.json", 'utf8', function(err, data){
var users = JSON.parse(data);
// ADD/MODIFY DATA
users[username] = req.body;
// SAVE DATA
fs.writeFile(__dirname + "/../data/user.json",
JSON.stringify(users, null, '\t'), "utf8", function(err, data){
result = {"success": 1};
res.json(result);
})
})
});
```
\
### 5. **API: DELETE deleteUser/:username**
* An API that deletes user data
* Uses the `DELETE` method
> Add to router > main.js
```javascript
app.delete('/deleteUser/:username', function(req, res){
var result = { };
//LOAD DATA
fs.readFile(__dirname + "/../data/user.json", "utf8", function(err, data){
var users = JSON.parse(data);
// IF NOT FOUND
if(!users[req.params.username]){
result["success"] = 0;
result["error"] = "not found";
res.json(result);
return;
}
// DELETE FROM DATA
delete users[req.params.username];
// SAVE FILE
fs.writeFile(__dirname + "/../data/user.json",
JSON.stringify(users, null, '\t'), "utf8", function(err, data){
result["success"] = 1;
res.json(result);
return;
})
})
});
```