Obsidian_Informatik/Semester 2/EIST/EIST CHEATSHEET.md

```table-of-contents
title: List of Contents
style: nestedOrderedList # TOC style (nestedList|nestedOrderedList|inlineFirstLevel)
minLevel: 1 # Include headings from the specified level
maxLevel: 1 # Include headings up to the specified level
include: 
exclude: 
includeLinks: true # Make headings clickable
hideWhenEmpty: false # Hide TOC if no headings are found
debugInConsole: false # Print debug info in Obsidian console
```

<div class="page-break"></div>

 # REST API General Tips

## HTTP Status Messages
HTTP response status codes indicate whether a specific HTTP request has been successfully completed. Responses are grouped in five classes:

1. **Informational responses (100 – 199)**
2. **Successful responses (200 – 299)**
3. **Redirection messages (300 – 399)**
4. **Client error responses (400 – 499)**
5. **Server error responses (500 – 599)**

Often used codes in excercises are:

| Code    | Name             | Purpose                                                                                                               |
| ------- | ---------------- | --------------------------------------------------------------------------------------------------------------------- |
| **2xx** | **Successful**   |                                                                                                                       |
| 200     | OK               | The request is OK (this is the standard response for successful HTTP requests)                                        |
| 201     | Created          | The request has been fulfilled, and a new resource is created                                                         |
| 204     | No Content       | The request has been successfully processed, but is not returning any content (may be returned for successful delete) |
| **4xx** | **Client Error** |                                                                                                                       |
| 400     | Bad Request      | The request cannot be fulfilled due to bad syntax or content                                                          |
| 404     | Not Found        | The requested page/resource could not be found                                                                        |

If you don't know an HTTP Code you can use `HttpStatus.<Message Name>.value()` class in Java
For example: `HttpStatus.OK.value()` returns `200`

<div class="page-break"></div>

# REST API in Java with Spring
- **Java reference:** https://www.baeldung.com/get-started-with-java-series
- **Java reference:** https://docs.oracle.com/en/java/javase/22/

- **Spring Boot:** https://www.baeldung.com/spring-boot
- **Spring Boot:** https://spring.io/projects/spring-boot
## Making REST API Requests

### With ***WebClient*** object:
(e.g Spring WebFlux)
#### GET
```java
public void getAllPersons(CustomerSortingOptions sortingOptions, Consumer<List<Customer>> customerConsumer) {
        webClient.get()
                .uri(uriBuilder -> uriBuilder
                        .path("customers")
                        .queryParam("sortField", sortingOptions.getSortField())
                        .queryParam("sortingOrder", sortingOptions.getSortingOrder())
                        .build())
                .retrieve()
                .bodyToMono(new ParameterizedTypeReference<List<Customer>>() {
                })
                .onErrorStop()
                .subscribe(newPersons -> {
                    customers.clear();
                    customers.addAll(newPersons);
                    customerConsumer.accept(customers);
                });
    }

```

#### POST
```java
public void addPerson(Customer customer, Consumer<List<Customer>> customerConsumer) {
	// TODO Part 2: Complete the http post request to the server
	webClient.post()
			.uri("customers")
			.bodyValue(customer)
			.retrieve()
			.bodyToMono(Customer.class)
			.onErrorStop()
			.subscribe(newCustomer -> {
				customers.add(newCustomer);
				customerConsumer.accept(customers);
			});
}
```

#### PUT
```java
public void updatePerson(Customer customer, Consumer<List<Customer>> customerConsumer) {
    // TODO Part 2: Complete the http put request to the server
    webClient.put()
            .uri("customers/" + customer.getId())
            .bodyValue(customer)
            .retrieve()
            .bodyToMono(Customer.class)
            .onErrorStop()
            .subscribe(newCustomer -> {
                customers.replaceAll(x -> x.getId().equals(customer.getId()) ? newCustomer : x);
                customerConsumer.accept(customers);
            });
}
```

#### DELETE
```java
public void deletePerson(Customer customer, Consumer<List<Customer>> customerConsumer) {
	// TODO Part 2: Make an http delete request to the server
	webClient.delete()
			.uri("customers/" + customer.getId())
			.retrieve()
			.toBodilessEntity()
			.onErrorStop()
			.subscribe(deletedCustomer -> {
				customers.remove(customer);
				customerConsumer.accept(customers);
			});
}
```

#### Just in case: webClient Constructor
```java
public CustomerController() {
	this.webClient = WebClient.builder()
			.baseUrl("http://localhost:8080/")
			.defaultHeader(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_VALUE)
			.defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
			.build();
	this.customers = new ArrayList<>();
}
```

#### With Request Parameters:
Endpoint:
```java
@GetMapping("persons")
public ResponseEntity<List<Person>> getAllPersons(PersonSortingOptions sortingOptions)  { // Don't use @RequestParams unless object is simple(for example String), for more complex objects Spring parses the object by itself
	List<Person> persons = personService.getAllPersons(sortingOptions);
	return ResponseEntity.ok(persons);
}
```
Request:
```java
public void getAllPersons(PersonSortingOptions sortingOptions, Consumer<List<Person>> personsConsumer) {
		this.webClient.get()
			.uri(uriBuilder -> uriBuilder // Use uriBuilder to build the path
					.path("persons")
					.queryParam("sortingOrder",sortingOptions.getSortingOrder()) // The fields are passed separately
					.queryParam("sortField",sortingOptions.getSortField())       // In the format: ("Name",value)
					.build()
			)
			.retrieve()
			.bodyToMono(new ParameterizedTypeReference<List<Person>>() {
			})
			.onErrorStop()
			.subscribe(persons -> {
				this.persons = persons;
				personsConsumer.accept(this.persons);
			});

}
```

### With *RestTemplate*:
```java
GetMapping("/getTimeLine/{id}")
public List<Tweet> getTimeLine(@PathVariable("id") int userID) { 
	headers.setContentType(MediaType.APPLICATION_JSON);
	
	ResponseEntity<List<Tweet>> response = restTemplate.exchange(
	getActivityURL + userID, // Set the uri HttpMethod.GET,
	null, // requestEntity = null as there is no body,
	new ParameterizedTypeReference<List<Tweet>>(){} // response body type );
		return response.getBody();
}
```
## REST API Endpoints

Example Java class:
```java
@RestController
@RequestMapping("/activity")
public class ActivityController {
    private Map<Integer, List<Tweet>> userActivityMap = new HashMap<>();
    private Map<Integer, List<User>> userFollowedMap = new HashMap<>();

    @GetMapping("/getActivity/{id}")
    public List<Tweet> getActivity(@PathVariable("id") int userID) {
        List<Tweet> userTweets = userActivityMap.get(userID);

        if(userTweets == null) return new ArrayList<>();

        return userTweets;
    }

    @PostMapping("/addActivity")
    public void addActivity(@RequestBody Tweet tweet) {
        userActivityMap.computeIfAbsent(tweet.getUser().getUserID(), x -> new LinkedList<>());
        userActivityMap.get(tweet.getUser().getUserID()).add(tweet);
    }

    @PostMapping("/addFollower")
    public void addFollower(@RequestBody FollowRequest followRequest) {
        User follower = followRequest.getFollower();
        User followed = followRequest.getFollowed();

        userFollowedMap.computeIfAbsent(follower.getUserID(),x -> new LinkedList<>())
                .add(followed);
    }

    @DeleteMapping("/deleteActivity")
    public void deleteActivity(@RequestBody Tweet tweet) {
        List<Tweet> userTweets = userActivityMap.get(tweet.getUser().getUserID());
        if(userTweets == null) return;

        userTweets.remove(tweet);
    }

    @DeleteMapping("/deleteFollower")
    public void deleteFollower(@RequestBody FollowRequest followRequest) {
        User follower = followRequest.getFollower();
        User followed = followRequest.getFollowed();

        List<User> followedUsers = userFollowedMap.get(follower.getUserID());
        if(followedUsers == null) return;

        followedUsers.remove(followed);
    }

    @GetMapping("/getFollowedList/{id}")
    public List<User> getFollowedList(@PathVariable("id") int userID) {
        // TODO: this method is also not complete, so you have to implement it accordingly :)
        List<User> followed = userFollowedMap.get(userID);
        if(followed == null) return new ArrayList<>();
        return followed;
    }
}
```

## Excersises:
-  L02PE01 TUM Social App
-  L02PE02 REST Architectural Style Part 2
-  L09PE02 Wizardry Character Creation 

<div class="page-break"></div>

# gRPC
- **Java reference:** https://www.baeldung.com/get-started-with-java-series
- **Java reference:** https://docs.oracle.com/en/java/javase/22/

- **gRPC reference**: https://grpc.io/docs/
 - **gRPC Java basics**: https://grpc.io/docs/languages/java/basics/

## Protobuf files
#### Defining classes:

Important tips: 
* Array in protobuf means ```repeated``` field

```protobuf
message Date {
  int32 day = 1; // Number specifies order
  int32 month = 2;
  int32 year = 3;
}

message Location {
  string city = 1;
  string country = 2;
}

message LocationDate {
  Location location = 1;
  Date date = 2;
}
```

#### Defining services:
```protobuf
service WeatherReporter {

  //Returning one object
  rpc GetCityWeatherSingleDay(LocationDate) returns (CityWeatherData) {}

  // Returning a stream of objects
  rpc GetCityWeatherMultipleDays(LocationDatePeriod) returns (stream CityWeatherData) {}
}
```

#### Example of services and objects with **repeated** fields
This will be utilized by some of the client side examples underneath
```protobuf
service MetadataService {
  rpc getTrackMetadata(EntitiesRequest) returns (Tracks) {}

  rpc getAlbumMetadata(EntitiesRequest) returns (Albums) {}
}

message EntitiesRequest {
  repeated uint32 id = 1;
}

message Track {
  uint64 id = 1;
  string name = 2;
  string album = 3;
  string artist = 4;
  uint32 duration = 5;
}

message Tracks {
  repeated Track track = 1;
}

message Album {
  uint64 id = 1;
  string name = 2;
  string artist = 3;
  repeated uint32 tracks = 4;
}

message Albums {
  repeated Album album = 1;
}

```
#### Generating classes from *.proto* files
1. Gradle tab in IDE and press "Tasks > other > generateProto")
2. The generated classes from the proto file should be in build/generated/source/proto/main folder

## Server side

In practice can be done with streams or with simple iteration
```java 
public void getCityWeatherSingleDay(LocationDate request, StreamObserver<CityWeatherData> responseObserver) {
	var data = allWeatherData.stream().filter(cityWeatherData -> cityWeatherData.getLocationDate().equals(request)).findFirst().orElse(null);
	if(data != null)responseObserver.onNext(data);
	responseObserver.onCompleted();
}
```

#### For returning a *stream* of data just call onNext multiple times
With iteration:
```Java
public void getCityWeatherMultipleDays(LocationDatePeriod request, StreamObserver<CityWeatherData> responseObserver) {
	for(CityWeatherData data : allWeatherData) {
		if(data.getLocationDate().getLocation().equals(request.getLocation())) {
			if(compareDate(data.getLocationDate().getDate(), request.getStartDate()) >= 0 && compareDate(data.getLocationDate().getDate(), request.getEndDate()) <= 0)
			{
				responseObserver.onNext(data);
			}
		}
	}
	responseObserver.onCompleted();
}
```

With streams:
```java 
public void getCityWeatherMultipleDays(LocationDatePeriod request, StreamObserver<CityWeatherData> responseObserver) {
	var startDate = request.getStartDate();
	var endDate = request.getEndDate();
	allWeatherData.stream()
			.filter(cityWeatherData -> cityWeatherData.getLocationDate().getLocation().equals(request.getLocation()))
			.filter(cityWeatherData -> compareDate(cityWeatherData.getLocationDate().getDate(),startDate) >= 0)
			.filter(cityWeatherData -> compareDate(cityWeatherData.getLocationDate().getDate(),endDate) <= 0)
			.forEach(responseObserver::onNext);
	responseObserver.onCompleted();
}
```

#### For returning an object which contains array of other objects (stupid???)
```java
public void getAlbumMetadata(EntitiesRequest request, StreamObserver<Albums> responseObserver) {
	Albums.Builder albumsBuilder = Albums.newBuilder();

	for(int i = 0; i < request.getIdCount();i++) {
		// Find the album by its id
		Album album = database.findAlbumById(request.getId(i));

		if(album != null) {
			albumsBuilder.addAlbum(album);
		}
	}

	// In case that an album isn't found builder builds empty list
	Albums albums = albumsBuilder.build();
	responseObserver.onNext(albums);
	responseObserver.onCompleted();
}
```

#### If you want to return an error
```java
public void getTrafficData(RouteRequest request, StreamObserver<TrafficResponse> responseObserver) {
	var trafficModel = db.getTrafficModel(request);
	var response = trafficModel.query(request);
	if(response.isPresent()) {
		responseObserver.onNext(response.get());
		responseObserver.onCompleted();
	} else {
		// Just pass an exception with the onError method
		responseObserver.onError(new Exception("No data available."));
	}
}
```
## Client Side

#### Setup

The **blocking stub** is a placeholder on which functions are called. It needs to be received from the gRPC object in some way.

```java
public WeatherClient(Channel channel) {
	// Get blocking stub from the gRPC object
	blockingStub = WeatherReporterGrpc.newBlockingStub(channel);
}
```
or
```java
public SpotifyClient(Channel channel) {
	// spotifyConnection is a wrapper defined in the excercise
	// this is just an example that there can be other ways to get the stub
	this.spotifyConnection = new SpotifyConnection(channel);
	this.blockingStub = spotifyConnection.getStub();
}
```

#### Calling method with ***single object*** return value
```java
public void getCityWeatherSingleDay(int day, int month, int year, String city, String country) {
	// Need to use builders to create the objects for the request
	Date date = Date.newBuilder().setDay(day).setMonth(month).setYear(year).build();
	Location location = Location.newBuilder().setCity(city).setCountry(country).build();

	// Building the locationDate which will be passed as a parameter
	LocationDate locationDate = LocationDate.newBuilder().setDate(date).setLocation(location).build();

	// Getting the returned object from calling the method on the stub
	CityWeatherData cityWeatherData = blockingStub.getCityWeatherSingleDay(locationDate);

	System.out.println(cityWeatherData.toString());
}
```

#### Calling method which returns ***stream***

```java
public void getCityWeatherMultipleDays(int startDay, int startMonth, int startYear, int endDay, int endMonth, int endYear, String city, String country) {
	// Building objects for the request
	Date startDate = Date.newBuilder()
			.setDay(startDay)
			.setMonth(startMonth)
			.setYear(startYear)
			.build();
	Date endDate = Date.newBuilder()
			.setDay(endDay)
			.setMonth(endMonth)
			.setYear(endYear)
			.build();
	Location location = Location.newBuilder().setCity(city).setCountry(country).build();

	// Building LocationDatePeriod object to be passed as parameter
	LocationDatePeriod locationDatePeriod = LocationDatePeriod.newBuilder()
			.setStartDate(startDate)
			.setEndDate(endDate)
			.setLocation(location)
			.build();

	// Method call returns Iterator<CityWeatherData> for the stream of CityWeatherData
	Iterator<CityWeatherData> iterator = blockingStub.getCityWeatherMultipleDays(locationDatePeriod);
	
	// Iterating over the objects
	while (iterator.hasNext()) {
		CityWeatherData cityWeatherData = iterator.next();
		System.out.println(cityWeatherData.toString());
	}
}
```

#### Calling method which has *parameter with **repeated** field*

```java
public String displayPlaylist(int[] playlist) throws SpotifyClientException {
	StringBuilder stringBuilder = new StringBuilder();

	EntitiesRequest.Builder builder = EntitiesRequest.newBuilder();

	// IMPORTANT for REPEATED fields
	// Add all id's to request
	for(int id : playlist) {
		builder.addId(id);
	}

	EntitiesRequest request = builder.build();

	// Unlike in earlier examplese returns OBJECT which contains multiple Tracks
	Tracks tracks;

	tracks = blockingStub.getTrackMetadata(request);
	if(tracks.getTrackCount() != playlist.length) throw new SpotifyClientException("Failed to get track metadata");


	for(int i = 0; i < tracks.getTrackCount();i++) {
		Track track = tracks.getTrack(i);

		int durationInSeconds = track.getDuration();
		int durationInMinutes = durationInSeconds / 60;
		durationInSeconds = durationInSeconds % 60;

		stringBuilder.append(String.format("%d. %s - %s (%d:%02d)%n", i+1,track.getName(), track.getArtist(), durationInMinutes, durationInSeconds));
	}

	return stringBuilder.toString();
}
```

## Excersises:
- L02PB01 Weather Reporter 
- L02P01 Spotify gRPC 
-  L03PE03 Gobblemaps 

# Flask API in Python
- **Python reference:** https://docs.python.org/3/reference/index.html
## *Server side* endpoints

#### GET
```python
@api.route("/<key>", methods=["GET"])
def get(key: str) -> Response:    
    """
    Retrieve the file-content associated with the given key owned by the user.
    If there is no user-id `uid` given in the request body or the user-id does not match, return error message and status.
    Otherwise, return the file-content and success status.
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff # type: ignore
    
    user_id = request_body.get("uid")

    if user_id is None:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)

    file = ff.get(key)

    if file is None:
        return Response(response=KEY_DOES_NOT_EXIST % key, status=NOT_FOUND)
    
    if file.uid != user_id:
        return Response(response=NO_ACCESS_TO_ENTRY % key, status=BAD_REQUEST)

    return Response(response=file.content,status=OK)
    pass
```
#### PUT
```python
@api.route("/<key>", methods=["PUT"])
def put(key: str) -> Response:    
    """
    Upsert a file-content associated with the given key owned by the user.
    If there is no user-id `uid` or file-content `content` given in the request body, return error message and status.
    Otherwise, return the success message and success status
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff

    if "uid" not in request_body:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)
    if "content" not in request_body:
        return Response(NO_CONTENT_IN_REQUEST_BODY,BAD_REQUEST)

    uid = request_body["uid"]
    file_content = request_body["content"]

    old_entry = ff.get(key)

    if old_entry is None:
        entry = Entry(uid,file_content)
        success = ff.put(key,entry)
        if success:
            return Response(PUT_SUCCESS,OK)
        else:
            return Response(NO_SPACE_IN_FILE_FOLDER,BAD_REQUEST)
        
    
    if uid != old_entry.uid:
        return Response(NO_ACCESS_TO_ENTRY % key,status=BAD_REQUEST)

    entry = Entry(uid,file_content)
    ff.put(key,entry)

    return Response(PUT_SUCCESS,OK)
    pass
```
#### DELETE
```python
@api.route("/<key>", methods=["DELETE"])
def remove(key: str) -> Response:
    """
    Remove the file-content associated with the given key owned by the user.
    If there is no user-id `uid` given in the request body or the user-id does not match, return error message and status.
    Otherwise, return the removed file-content and success status
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff

    if "uid" not in request_body:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)
    
    uid = request_body["uid"]
    
    entry = ff.get(key)

    if entry is None:
        return Response(KEY_DOES_NOT_EXIST % key,NOT_FOUND)
    if entry.uid != uid:
        return Response(NO_ACCESS_TO_ENTRY % key,BAD_REQUEST)
    
    ff.remove(key)

    return Response(entry.content,OK)
    pass
```
#### GET - all
```python
@api.route("/", methods=["GET"])
def list() -> Response:
    """
    List all (key, file-content) tuples owned by the user.
    If there is no user-id `uid` given in the request body, return error message and status.
    Otherwise, return the list of file-content and success status.
    """
    request_body: dict = request.json
    ff: FileFolder = current_app.ff

    if "uid" not in request_body:
        return Response(NO_UID_IN_REQUEST_BODY,BAD_REQUEST)
    
    uid = request_body["uid"]

    items = ff.items()

    output = []

    for key, entry in items:
        output.append(f"{key}:{entry.content}")
    output_string = ".".join(output)

    return Response(output_string,OK)
    pass
```

## Making requests on the *client side*

#### Helper method
```python
# make json request to server
def json_request(self, method: str, path: str, body: dict):
	self.conn.request(method, path, json.dumps(body), headers={"Content-Type": "application/json"})
	flask_response = self.conn.getresponse()
	return flask_response.read().decode()
```

#### PUT
```python
def put(self, key, content):
	"""
	Upsert (key, content) tuple into the file folder.
	Return the server response
	"""
	request_body = {"uid": self.user_id, "content": content}
	return self.json_request("PUT", f"/{key}",request_body)
	pass
```
#### GET
```python
def read(self, key):
	"""
	Retrieve the file-content associated with the given key owned by the user.
	Return the server response
	"""
	request_body = {"uid": self.user_id}
	return self.json_request("GET",f"/{key}",request_body)
	pass
```
#### DELETE
```python
def remove(self, key):
	"""
	Remove the file-content associated with the given key owned by the user.
	Return the server response
	"""

	request_body = {"uid": self.user_id}
	return self.json_request("DELETE",f"/{key}",request_body)
	pass
```
#### GET - ALL
```python
def list(self):
	"""
	List all file-content owned by the user.
	Return the server response
	"""

	request_body = {"uid": self.user_id}
	return self.json_request("GET","/",request_body)
	pass
```
## Excersises:
- L03PE01 Online FileFolder 

# Python - general syntax and tips
- **Python reference:** https://docs.python.org/3/reference/index.html
## Dictonaries
Dictionaries are initialized with `{}`
```python
thisdict = {  
  "brand": "Ford",  
  "model": "Mustang",  
  "year": 1964  
}  
print(thisdict["brand"])
```

```python
thisdict = dict(name = "John", age = 36, country = "Norway")  
print(thisdict)
```
You can check if a key exists with the keyword *in*:
```python
if "model" in thisdict:  
  print("Yes, 'model' is one of the keys in the thisdict dictionary")
```

You can loop over keys and values in dictionary:
```python
for x in thisdict: # Loop over keys 
  print(x)
for x in thisdict.keys():  #Another way to loop over keys
  print(x)
  
for x in thisdict:  # Loop over values
  print(thisdict[x])
for x in thisdict.values(): # Another way to loop over values
  print(x)
 
for x, y in thisdict.items():  # Looping over key-value pairs as tuples
  print(x, y)
```

Dictonaries are of type `dict`
### Dictionary methods
| Method       | Description                                                                                                 |
| ------------ | ----------------------------------------------------------------------------------------------------------- |
| clear()      | Removes all the elements from the dictionary                                                                |
| copy()       | Returns a copy of the dictionary                                                                            |
| fromkeys()   | Returns a dictionary with the specified keys and value                                                      |
| get()        | Returns the value of the specified key                                                                      |
| items()      | Returns a list containing a tuple for each key value pair                                                   |
| keys()       | Returns a list containing the dictionary's keys                                                             |
| pop()        | Removes the element with the specified key                                                                  |
| popitem()    | Removes the last inserted key-value pair                                                                    |
| setdefault() | Returns the value of the specified key. If the key does not exist: insert the key, with the specified value |
| update()     | Updates the dictionary with the specified key-value pairs                                                   |
| values()     | Returns a list of all the values in the dictionary                                                          |

## Lists
Lists are initialized with `[]`
```python
mylist = ["apple", "banana", "cherry"]
```


List items are ordered, changeable, and allow duplicate values.
List items are indexed, the first item has index `[0]`, the second item has index `[1]` etc.
```python
print mylist[0]
```
You can also negatively index a list from the end:
```python
print mylist[-1] # This refers to the last item
```

To determine how many items a list has, use the `len()` function:
```python
thislist = ["apple", "banana", "cherry"]  
print(len(thislist))
```
You can loop through lists like so:
```python
thislist = ["apple", "banana", "cherry"]  
for x in thislist:  
  print(x)
```

### Joining lists
You can easily join list using the `+` operator:
```python 
list1 = ["a", "b", "c"]  
list2 = [1, 2, 3]  
  
list3 = list1 + list2  
print(list3)
```
Or you can iterate through one of the lists and append the elements **one by one**:
```python
list1 = ["a", "b" , "c"]  
list2 = [1, 2, 3]  
  
for x in list2:  
  list1.append(x)  
  
print(list1)
```
Another way is to use the `extend()` function:
```python
list1 = ["a", "b" , "c"]  
list2 = [1, 2, 3]  
  
list1.extend(list2)  
print(list1)
```

List comprehension is like **Streams in Java** and offers a functional way to iterate over lists
```python
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]  

# Creates a new list from fruits which contains only the elements which contain "a"
newlist = [x for x in fruits if "a" in x]
  
print(newlist)
```

Lists are of type `list`

Other methods that you can use on lists are:

| Method    | Description                                                                  |
| --------- | ---------------------------------------------------------------------------- |
| append()  | Adds an element at the end of the list                                       |
| clear()   | Removes all the elements from the list                                       |
| copy()    | Returns a copy of the list                                                   |
| count()   | Returns the number of elements with the specified value                      |
| extend()  | Add the elements of a list (or any iterable), to the end of the current list |
| index()   | Returns the index of the first element with the specified value              |
| insert()  | Adds an element at the specified position                                    |
| pop()     | Removes the element at the specified position                                |
| remove()  | Removes the item with the specified value                                    |
| reverse() | Reverses the order of the list                                               |
| sort()    | Sorts the list                                                               |
## Strings

Strings in python are surrounded by either single quotation marks, or double quotation marks.
'hello' is the same as "hello".

Strings are of class `string`

You can access a character of a string like accessing an array or list
```python
a = "Hello, World!"  
print(a[1]) # This will print "e"
```
You can loop through a string:
```python
for x in "banana":  
  print(x)
```
You can get the length of a string:
```python
a = "Hello, World!"  
print(len(a))
```
To check if a string contains another string:
```python
txt = "The best things in life are free!"  
if "free" in txt:  
  print("Yes, 'free' is present.")
```
You can *slice* or get substrings from a string like so:
```python
b = "Hello, World!"  
print(b[2:5]) # From 2(inclusive) to 5(not inclusive)
print(b[:5]) # From 0 to 5(not inclusive)
print(b[2:]) # Fromt 2(inclusive) to end
```
### Modifying strings
The `upper()` method converts to uppercase
```python
a = "Hello, World!"  
print(a.upper()) # "HELLO, WORLD!"
```
The `lower()` method converts to lowercase
```python
print(a.lower()) # "hello, world!"
```
The `strip()` method removes any whitespace from the beginning or the end:
```python
a = " Hello, World! "  
print(a.strip()) # returns "Hello, World!"
```
The `replace()` method replaces a string with another string:
```python
a = "Hello, World!"  
print(a.replace("H", "J"))
```
The `split()` method splits the string into substrings if it finds instances of the separator:
```python
a = "Hello, World!"  
print(a.split(",")) # returns ['Hello', ' World!']
```

You can concatenate strings simply with `+`
### Format strings
F-strings allows you to format selected parts of a string.
To specify a string as an f-string, simply put an `f` in front of the string literal, like this:
To format values in an f-string, add placeholders `{}`, a placeholder can contain variables, operations, functions, and modifiers to format the value.
```python
price = 59  
txt = f"The price is {price} dollars"  
print(txt)
```
You can add modifiers like .2f for two decimals
```python
price = 59  
txt = f"The price is {price:.2f} dollars"  
print(txt)
```

<div class="page-break"></div>

# JUnit 
- **Java reference:** https://www.baeldung.com/get-started-with-java-series
- **Java reference:** https://docs.oracle.com/en/java/javase/22/
- **JUnit:** https://junit.org/junit5/docs/current/user-guide/

## assertThrows()
```java
@Test
public void testSetOnlineCourseUrlWithInvalidUrl() {
	OnlineCourse course = new OnlineCourse("test");
	// You need to pass the CLASS of the exception and a runnable which calls the function
	// then the test will pass if EXACTLY this exception is throwed
	// If you want to test for any exception pass Exception.class however, that is usually discouraged and not needed
	assertThrows(MalformedURLException.class,() -> course.setUrl("hjdahjsd"));
}
```
## assertDoesNotThrow()
```java
@Test
public void testSetOnlineCourseUrlWithValidUrl(){
	OnlineCourse course = new OnlineCourse("test");
	// Simply assertDoesNotThrow with a runnable
	assertDoesNotThrow(() -> course.setUrl("https://test"));

	// We need to handle constructor of URL throwing an exception despite knowing that it won't as we are passing it a correct URL
	try {
		assertEquals(new URL("https://test"),course.getUrl());
	} catch (MalformedURLException e) {
	}
}
```

## Excercises:
- L06P01 University App Unit Testing Part 2
- L06PB02 Chris Neapolitan Restaurant
- L06PB01 University App Unit Testing
- L06PE01 The Iron Bank of Braavos 

# EasyMock
- **Java reference:** https://www.baeldung.com/get-started-with-java-series
- **Java reference:** https://docs.oracle.com/en/java/javase/22/
- **EasyMock:** https://easymock.org/user-guide.html

`@TestSubject` annotations automatically calls the constructor with the mockObjects. However it is not applicable for constructors with other parameters that are not mocked(for example primitive types). In such cases you can call the constructor of the **test subject** as usual inside the test or in a @Before method or wherever you want.

**Second example contains how to expect *void* method calls**
## Example with TestSubject

```java
// Needs to extend the tests with EasyMock
// If not extended you would need to manually initialize Mock objects
@ExtendWith(EasyMockExtension.class)
class DiscussionTest {

	// TestSubject annotations automatically calls the constructor with the mockObjects
	// However it is not applicable for constructors with other parameters
	
    @TestSubject
    private Discussion discussion;


	// Mock objects need to be annotated with @Mock	
    @Mock
    private Course courseMock;

    @Mock
    private Comment commentMock;

    // TODO implement the tests

    @Test
    public void testComment() {
		// First we need to record
	    // Expect a function call and set a predetermined return value
	    // This expects the method to be called exactly once
        expect(commentMock.save()).andReturn(true);
        
        // After setting all expectations we need to replay the mock - e.g set it so it behaves the way we recorded
        replay(commentMock);
		
		// Test your objects as usual
        discussion = new Discussion();
        assertEquals(0,discussion.getNumberOfComments());
        assertTrue(discussion.addComment(commentMock));
        assertEquals(1,discussion.getNumberOfComments());
		
		// At the end you need to verify the mock - this checks whether the expected methods were actually called
        verify(commentMock);
    }

	// The methods below show the same usage
    @Test
    public void testCommentIfSavingFails() {
        expect(commentMock.save()).andReturn(false);
        replay(commentMock);

        discussion = new Discussion();
        assertEquals(0,discussion.getNumberOfComments());
        assertFalse(discussion.addComment(commentMock));
        assertEquals(0,discussion.getNumberOfComments());

        verify(commentMock);
    }

    @Test
    public void testStartCourseDiscussion() {
        Person person = new Lecturer("","",LocalDate.now());
        String testTopic = "testTopic";

        expect(courseMock.isDiscussionAllowed(person)).andReturn(true);

        replay(courseMock);
        assertTrue(discussion.startCourseDiscussion(courseMock,person,testTopic));
        assertEquals(courseMock,discussion.getCourse());
        assertEquals(testTopic,discussion.getTopic());

        verify(courseMock);
    }
```


## Example with custom Constructor (also contains expecting *void* call)

```java
@Mock
Platform platformMock;

...

@Test
public void addNoteGetsURIFromPlatform() throws URISyntaxException {
	URI uri = URI.create("https://notes.tum.de/examplePath"); // An example uri your mock can return
	String expectedWriteDataPath = uri.getPath(); // The path that the NotesServer should write to

	// Set the mock to expect the call and return the set URI
	expect(platformMock.nextURI()).andReturn(uri);
	
	// To expect a void method call you can just call the method like usual before **replaying** the mock
	platformMock.writeData(expectedWriteDataPath,"Some text");

	// Replay the mock
	replay(platformMock);

	// Instead of annotating with @TestSubject we instantiate the testServer(System Under Test) inside the Test
	NotesServer testServer = new NotesServer(platformMock, false, false);
	
	// Test like usual
	URI testUri = testServer.addNote("alice", "Some text");
	assertEquals(expectedWriteDataPath,testUri.getPath());

	// At the end you need to verify the mock - this checks whether the expected methods were actually called
	verify(platformMock);
}
```

## If you want multiple method invocations


| Method           | Behaviour                                                                              |
| ---------------- | -------------------------------------------------------------------------------------- |
| `.times(3)`      | Expects the method to be called **exactly** 3 times.                                   |
| `.times(2,5)`    | Expects the method to be called between **2 and 5** times (inclusive).                 |
| `.atLeastOnce()` | Expects the method to be called **1 or more** times.                                   |
| `.anyTimes()`    | The method can be called **0 or more** times (it will never cause `verify()` to fail). |
For *void* methods:

```java
commentMock.update();            // Call the void method
expectLastCall().times(3);       // Set the invocation count
```

### If you want to check that a method is NOT called just replay without expect()

```java
@Test
void testSubmitAbsenceDoesNotAlertInstructor() {
	/**
	 * TODO: Mock mailService.sendMail(...) to ensure that the instructor is not alerted
	 * Tip: By not specifying the behaviour of the mock you can afterwards verify if a method was NOT called
	 * Don't forget to use replay!
	 */
	Person person = personBuilder
			.withFirstName("Max")
			.withLastName("Mustermann")
			.withIsInstructor(false)
			.build();
	personService.save(person);

	Person instructor = personBuilder
			.withFirstName("Ivailo")
			.withLastName("Traikov")
			.withIsInstructor(true)
			.build();
	personService.save(instructor);
	List<Person> instructors = personService.getInstructors();


	Absence absence = new Absence();
	absence.setPerson(person);
	absence.setComment("test");
	LocalDate now = LocalDate.now();
	absence.setDate(now);
	absence.setId(Long.valueOf(1));


	replay(mailServiceMock);

	absenceService.submitAbsence(absence,false);

	verify(mailServiceMock);
}
```

## Excercises:
- L06PB02 Chris Neapolitan Restaurant
- L06P02 Discussion Forum Mock Testing 

<div class="page-break"></div>

# Static and dynamic analysis
- **C reference:** https://en.cppreference.com/w/c/language
- **AddressSanitizer**: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html
## Static analysis
### Gcc

With `-Wall`, `-Wextra` compiler flags
### Cmake

With `clang --analyze`
## Dynamic Analysis
### Undefined Behavior Sanitizer
Deals with undefined behaviour in the program such as **Integer overflow**
To use Undefined Behaviour Sanitizer **compile** with `-fsanitize=undefined`
It is available both on `gcc` and `clang`
```bash
gcc -fsanitize=undefined <source> -o <output>
```
### Address Sanitizer
**C Address Safety errors that can be caught by address sanitizer:**
 - **Buffer Overflow**: This occurs when a program writes data beyond the bounds of allocated memory. It can lead to data corruption, crashes, and even allow attackers to exploit the program.
- **Use-Stack-After-Return**: This involves accessing memory after it has been freed. It can lead to undefined behavior as the freed memory might be allocated again for a different purpose.
- **Double Free**: Calling `free()` twice on the same value can lead to undefined behavior. When a program calls `free()` twice with the same argument, the program’s memory management data structures become corrupted and could allow a malicious user to write values in arbitrary memory spaces.

Address Sanitizer is available on `gcc` and `clang`
To use Address Sanitizer compile with `-fsanitize=address`
```bash
clang -fsanitize=address -w <source> -lpthread -o <output_file>
```

### Memory Sanitizer

**Memory sanitizer specifically targets uninitialized memory reads**
It is only available on `clang` with the flag `-fsanitize=memory`
```bash
clang -fsanitize=memory <source> -o <output>
```


### Thread Sanitizer

**Thread Sanitizer deals specifically with data races**
It is available on both `gcc` and `clang` with the flag `-fsanitize=thread`
```bash
gcc -fsanitize=thread <source> -o <output>
```

In general to use multi threading in C you need to use the `-pthread` flag. So if you don't see it you may need to add that as well.


## Tips while doing dynamic analysis:

To test for **buffer overflow** you can try entering **too long inputs**, **going out of boundaries of lists, maps and such**

In general try testing every function while you are playing around with the program.

**Buffer overflows** caused by **`scanf()`** can be fixed with **`fgets()`**
This however does not **zero-terminate** the string so you have to do that manually
```C
char firstName[NAME_LENGTH];

printf("Enter first name: ");

fgets(firstName,NAME_LENGTH,stdin);
lastName[NAME_LENGTH-1] = 0;
```
## Excercises: 
- L09P02 Garching Best Software
- L08PE04 Spaceship 
- L07P02 Dynamic Code analysis for Priority Scheduling
- L07PE02 Playlist Manager -- Memory Debugging with MemorySanitizer
- L07PE03 Gym Threading 

<div class="page-break"></div>

# C Thread Synchronization primitives
- **C reference:** https://en.cppreference.com/w/c/language

## Mutex

The mutex is a simple lock that after locking blocks other threads from accessing the object/code until it is unlocked.
If a thread tries to lock the mutex while it is already locked by another it must wait until it is unlocked again.

### Type
Mutexes in C are of type `pthread_mutex_t` and can be declared like so:
```C
struct Shower {
  pthread_mutex_t showerLock;
};
```
### Initialization
Before they can be used they also need to be initialized
```C
struct Shower s;;
pthread_mutex_init(&s.showerLock,NULL);
```
The second parameter is a mutex attribute which determines what kind of mutex it is. The kind of a mutex determines whether it can be locked again by a thread that already owns it.
**For our purposes not specifying is okay and you can pass NULL.**
### Locking and unlocking

To lock a mutex call `pthread_mutex_lock()` and to unclock it `pthread_mutex_unlock()`
```C
void useShower(struct Shower *s, struct Member m) {
    pthread_mutex_lock(&s->showerLock);
    /////////////////////////////////
    logShower(1, m);
    usleep(rand() % 500000); // Member uses shower
    logShower(0, m);
    /////////////////////////////////
    pthread_mutex_unlock(&s->showerLock);
}
```


## Semaphores

Semaphores are counters which only let a fixed number of threads to access the shared resource at the same time.  To enter the thread needs to acquire a token with `sem_wait()`, when one is not available it waits. A thread also needs to return the acquired token by calling `sem_post()`
### Type
Semaphores in C are of type `sem_t` and can be declared like so:
```C
struct ChangingRoom {
  sem_t changingRoomSemaphore;
};
```
### Initialization
Before you can use a semaphore you need to initialize it
`int sem_init(sem_t *sem, int pshared, unsigned int value);`
`pshared` indicates if this semaphore is shared between threads of a process or between processes - 0 means between threads of a process and is fine for our exercises
`value` - how many threads can use the resource at the same time
```C
struct ChangingRoom cr;
sem_init(&cr.changingRoomSemaphore,0,3);
```
## Waiting and posting
```C
void useChangingRoom(struct ChangingRoom *cr, struct Member m) {
      sem_wait(&cr->changingRoomSemaphore);
      ////////////////////////////////////////
      logChangingRoom(1, m);
      usleep(rand() % 500000); // Member uses changing room
      logChangingRoom(0, m);
      ////////////////////////////////////////
      sem_post(&cr->changingRoomSemaphore);
}
```

<div class="page-break"></div>

# Git
- **Git reference:** https://git-scm.com/docs

## git checkout

Git checkout has two functions:
1. To change the current branch
2. To restore a version of a specified file

### Switching and creating **branches**

If you want to switch to an existing branch you can use:
```bash
git checkout <branch-name>
```

If you want to create a new branch and switch to it you can do:
```bash
git checkout -b <branch-name>
```
This starts the branch at the current commit.

### Restoring or taking a specific version of a file

To restore the file version from a specific commit:
```bash
git checkout <commit-hash> <file-path>
```

To restore the file version from a specific branch:
```bash
git checkout <branch-name> <file-path>
```

You can also checkout a whole commit.
```bash
git checkout <commit-hash>
```
This however creates a detached head state in which you cannot make new commits. It isn't the same as replacing all files in the current directory with the states from the commit. Think of it more as changing to the selected commit like you would change to a branch.

If you however want to replace all files in the current directory with the states from the commit
```bash
git checkout <commit-hash> .
```

## git merge

This merges the selected branch into the current branch. You can change the current branch with `git checkout`
Merging is usually done automatically but sometimes that cannot be done because the two branches have changes to the same code which cannot be merged automatically. This is called a merge conflict. When this is the case `git` puts conflict markers in the files which look like this:
```c
void calculate_bonus(struct employeeInfo *entry)
{
    //calculation of bonus factor
    float bonus_factor = 1000 / ( entry->salary);

    //calculation of grade factor
    float grade_factor = entry->performanceGrade / 10.0;

    //calculate_bonus
<<<<<<< HEAD // This ist the change from the current branch
    entry->bonus = entry->salary * bonus_factor * grade_factor * 0.5;
=======
    entry->bonus = entry->salary * bonus_factor * grade_factor * 2;
>>>>>>> feature/new_feature_E // This is the incoming change
}
```

To resolve the merge conflict you need to delete the conflict markers and keep the code you desire. You can even chose to resolve the conflict through writing code that isn't included in both of the changes. After that you need to commit the resolved code.


If you want to **squash** all commits on another branch and apply them as a **single** commit on the current branch you can use:
```bash
git merge --squash <branch-name>
```

## git rebase

Git **rebase** is usually used to take a series of commits and **replay** them on top of another commit.

This will take all commits on the current branch and **replay** them on main. Unlike merge it goes in the direction *current commit => main*
```bash
git rebase <onto-branch>
```
or if you want to select the branch to **replay**
```bash
git rebase <branch-name> <onto-branch>
```

Git rebase however can also be used to **squash** or **reorder** commits by running it in interactive mode on the last N commits.
```bash
git rebase -i HEAD~N
```
This opens this editor:

```pug
pick f7f3f6d Change my name a bit
pick 310154e Update README formatting and add blame
pick a5f4a0d Add cat-file

# Rebase 710f0f8..a5f4a0d onto 710f0f8
#
# Commands:
# p, pick <commit> = use commit
# r, reword <commit> = use commit, but edit the commit message
# e, edit <commit> = use commit, but stop for amending
# s, squash <commit> = use commit, but meld into previous commit
# f, fixup <commit> = like "squash", but discard this commit's log message
# x, exec <command> = run command (the rest of the line) using shell
# b, break = stop here (continue rebase later with 'git rebase --continue')
# d, drop <commit> = remove commit
# l, label <label> = label current HEAD with a name
# t, reset <label> = reset HEAD to a label
# m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
# .       create a merge commit using the original merge commit's
# .       message (or the oneline, if no original merge commit was
# .       specified). Use -c <commit> to reword the commit message.
#
# These lines can be re-ordered; they are executed from top to bottom.
#
# If you remove a line here THAT COMMIT WILL BE LOST.
#
# However, if you remove everything, the rebase will be aborted.
#
# Note that empty commits are commented out
```
Commits are listed from first to last chronologically.

If you want to **squash** all commits you still have to **pick** the **first** one.
```bash
pick f7f3f6d Change my name a bit
squash 310154e Update README formatting and add blame
squash a5f4a0d Add cat-file
```
After this another editor opens for the message of the commit which remains.

If you want to then copy squashed commits from another branch onto main you can `git merge` which will automatically fast-forward and just paste the squashed commit on main.

However this whole operation can also be done with `git merge --squash <branch-name>`

## git cherry-pick

This applies changes **ONLY** from the selected commit(s) to the current branch. By default this creates a new commit for each of them.

```bash
git cherry-pick <commit-hash> <commit-hash1> ...
```

If you don't want to create any commits automatically and manage it yourself you can do:
```bash
git cherry-pick --no-commit <commit-hash> <commit-hash1> ...
```

## git apply
`git apply <patch-file>` applies the changes in a .patch file (a file which describes these changes)  to the repository. This however does not commit them so you will still need to `git commit`

```bash
git apply patch_file.patch
```

<div class="page-break"></div>

# Bazel

## Java BUILD.bazel

```python
# You need to first load the java_binary and java_library rules
# How this is done depends on your MODULE.bazel file
load("@rules_java//java:defs.bzl", "java_binary", "java_library") 

java_binary(
    name = "client", # Name of the target
    srcs = ["src/eist/Main.java"], # Sources are the .java file(s)
    main_class = "eist.Main", # The main class is specified as such
    deps = [":event-facade",":model"] # Depends on Event Facade and the model
)
# TODO: Add a java_library target with the name 'event-facade'
java_library(
    name = "event-facade", # Name of the library
    srcs = ["src/eist/EventFacade.java"], # Sources. IMPORTANT - library has no main
    deps = [":event-client",":token-generator-client",":model"] # Dependencies
)

# TODO: Add a java_library target with the name 'event-client'
java_library(
    name = "event-client",
    srcs = ["src/eist/EventClient.java"],
    deps = ["@maven//:org_springframework_boot_spring_boot_starter_web",
            "@maven//:org_springframework_boot_spring_boot_starter_webflux",
            "@maven//:org_springframework_spring_web",
            ":model"
            ]
)

# TODO: Add a java_library target with the name 'token-generator-client'
java_library(
    name = "token-generator-client",
    srcs = ["src/eist/TokenGeneratorClient.java"],
    deps = ["@maven//:org_springframework_boot_spring_boot_starter_web",
            "@maven//:org_springframework_boot_spring_boot_starter_webflux",
            "@maven//:org_springframework_spring_web",
            ":model"
            ]
)

java_library( # Library for the model as it is used in all other classes
    name = "model",
    srcs = ["src/eist/Employee.java","src/eist/Event.java"]
)
```

``
## Python BUILD.bazel

```python
load("@rules_python//python:defs.bzl", "py_binary")

# TODO: Add a py_binary target with the name 'event_microservice'
py_binary(
    name = "event_microservice", # name of the binary for inside bazel
    srcs = ["src/event_microservice.py"], # the source files paths relative to the BUILD.bazel
    main = "src/event_microservice.py", # The main for python is just the source file
    deps = ["@pip_deps_server//flask"], # Dependencies - in this case we load from dependencies hub defined in the MODULE.bazel
)
```

## MODULE.bazel

```python
###############################################################################
# Bazel now uses Bzlmod by default to manage external dependencies.
# Please consider migrating your external dependencies from WORKSPACE to MODULE.bazel.
#
# For more details, please check https://github.com/bazelbuild/bazel/issues/18958
###############################################################################

bazel_dep(name = "rules_jvm_external", version = "6.7")
bazel_dep(name = "rules_java", version = "8.3.2")
maven = use_extension("@rules_jvm_external//:extensions.bzl", "maven")


maven.install(
  artifacts = [
    'org.springframework.boot:spring-boot-starter-web:2.1.6.RELEASE',
    'org.springframework.boot:spring-boot-starter-webflux:2.1.6.RELEASE',
    'org.springframework:spring-web:5.1.5.RELEASE',
  ],
  repositories = [
    'https://repo1.maven.org/maven2',
  ],
  fetch_sources = True,
)

use_repo(maven, "maven")

# Helpful documentation for Python rules can be found here:
# https://rules-python.readthedocs.io/en/latest/index.html

bazel_dep(name = "rules_python", version = "1.4.1")
python = use_extension("@rules_python//python/extensions:python.bzl", "python")

# Setup Python 3.8 environment
python.defaults(
    # The environment variable takes precedence if set.
    python_version = "3.8",
)
python.toolchain(
    python_version = "3.8",
)

pip = use_extension("@rules_python//python/extensions:pip.bzl", "pip")
pip.parse( # Create a rule for the requirements
    python_version = "3.8",
    hub_name = "pip_deps_server",
    requirements_lock = "//server-side:requirements_lock.txt"
)

# Imports the pip toolchain generated by the given module extension into the scope of the current module.
use_repo(pip, "pip_deps_server")
```

<div class="page-break"></div>

# DOCKER

**Docker reference: https://docs.docker.com/**
### Dockerfiles
https://docs.docker.com/get-started/docker-concepts/building-images/writing-a-dockerfile/
https://docs.docker.com/reference/dockerfile/

```dockerfile
FROM python:3.13
WORKDIR /usr/local/app

# Install the application dependencies
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

# Copy in the source code
COPY src ./src
EXPOSE 8080

# Setup an app user so the container doesn't run as the root user
RUN useradd app
USER app

CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8080"]
```

Some of the most common instructions in a `Dockerfile` include:

- `FROM <image>` - this specifies the base image that the build will extend.
- `WORKDIR <path>` - this instruction specifies the "working directory" or the path in the image where files will be copied and commands will be executed.
- `COPY <host-path> <image-path>` - this instruction tells the builder to copy files from the host and put them into the container image.
- `RUN <command>` - this instruction tells the builder to run the specified command.
- `ENV <name> <value>` - this instruction sets an environment variable that a running container will use.
- `EXPOSE <port-number>` - this instruction sets configuration on the image that indicates a port the image would like to expose.
- `USER <user-or-uid>` - this instruction sets the default user for all subsequent instructions.
- `CMD ["<command>", "<arg1>"]` - this instruction sets the default command a container using this image will run.

### Building docker

```bash
docker build -t <tag> .
```

### Docker processes
To list docker processes:
```bash
docker ps
```
#### Exercises
- L09P01 - Registry Office Service Deployment
- L09P02 - Garching Best Software
- L08PE04 - Spaceship

<div class="page-break"></div>

# Docker Compose

```yaml
# Services are defined in the services block
services:
  employee-manager-postgres:
    container_name: employee-manager-postgres # Set the container name
    image: postgres:latest # Set the image to a prebuilt image
    volumes: # Define a list of volumes
      - employee-manager-data: /var/lib/postgresql/data # - volume: <path>
    environment:
      - POSTGRES_DB=employee-manager # VAR=<Name>
      - POSTGRES_USER=admin
      - POSTGRES_PASSWORD=pass
    ports: # Open ports
      - "5432:5432"

  employee-manager-app:
    build: . # This builds the image from the current(application) directory
    container_name: employee-manager-app
    environment:
      - DB_SERVER=employee-manager-postgres
    ports:
      - "8080:8080"
    depends_on: # Set dependencies
      - employee-manager-postgres
    # These lines enable interactive shell mode
    stdin_open: true
    tty: true

#Define a list of volumes
volumes:
  employee-manager-data:
```

## Enviroment variables
Enviroment variables can be defined so:
```yaml
environment:
      - POSTGRES_DB=employee-manager # VAR=<Name>
      - POSTGRES_USER=admin
      - POSTGRES_PASSWORD=pass
```
or so
```yaml
environment:
      - POSTGRES_DB:"employee-manager" # VAR=<Name>
      - POSTGRES_USER:"admin"
      - POSTGRES_PASSWORD="pass"
```

However the **first** is historically preferred in exercises

To run Docker compose you use:
```bash
docker compose up
```

To run it in **detached** mode:
```bash
docker compose up -d
```

**!!!MOST EXERCISES WANT DETACHED MODE!!!**

<div class="page-break"></div>

# Make

## The essence of Make

Let's start with a hello world example:

```makefile
hello:
	echo "Hello, World"
	echo "This line will print if the file hello does not exist."
```

There's already a lot to take in here. Let's break it down:

- We have one _target_ called `hello`
- This target has two _commands_
- This target has no _prerequisites_

We'll then run `make hello`. As long as the `hello` file does not exist, the commands will run. If `hello` does exist, no commands will run.

It's important to realize that I'm talking about `hello` as both a _target_ and a _file_. That's because the two are directly tied together. Typically, when a target is run (aka when the commands of a target are run), the commands will create a file with the same name as the target. In this case, the `hello` _target_ does not create the `hello` _file_.

Let's create a more typical Makefile - one that compiles a single C file. But before we do, make a file called `blah.c` that has the following contents:

```makefile
// blah.c
int main() { return 0; }
```

Then create the Makefile (called `Makefile`, as always):

```makefile
blah:
	cc blah.c -o blah
```

This time, try simply running `make`. Since there's no target supplied as an argument to the `make` command, the first target is run. In this case, there's only one target (`blah`). The first time you run this, `blah` will be created. The second time, you'll see `make: 'blah' is up to date`. That's because the `blah` file already exists. But there's a problem: if we modify `blah.c` and then run `make`, nothing gets recompiled.

We solve this by adding a prerequisite:

```makefile
blah: blah.c
	cc blah.c -o blah
```

When we run `make` again, the following set of steps happens:

- The first target is selected, because the first target is the default target
- This has a prerequisite of `blah.c`
- Make decides if it should run the `blah` target. It will only run if `blah` doesn't exist, or `blah.c` is _newer than_ `blah`

This last step is critical, and is the **essence of make**. What it's attempting to do is decide if the prerequisites of `blah` have changed since `blah` was last compiled. That is, if `blah.c` is modified, running `make` should recompile the file. And conversely, if `blah.c` has not changed, then it should not be recompiled.

To make this happen, it uses the filesystem timestamps as a proxy to determine if something has changed. This is a reasonable heuristic, because file timestamps typically will only change if the files are modified. But it's important to realize that this isn't always the case. You could, for example, modify a file, and then change the modified timestamp of that file to something old. If you did, Make would incorrectly guess that the file hadn't changed and thus could be ignored.

Whew, what a mouthful. **Make sure that you understand this. It's the crux of Makefiles, and might take you a few minutes to properly understand**. Play around with the above examples or watch the video above if things are still confusing.

## More quick examples

The following Makefile ultimately runs all three targets. When you run `make` in the terminal, it will build a program called `blah` in a series of steps:

- Make selects the target `blah`, because the first target is the default target
- `blah` requires `blah.o`, so make searches for the `blah.o` target
- `blah.o` requires `blah.c`, so make searches for the `blah.c` target
- `blah.c` has no dependencies, so the `echo` command is run
- The `cc -c` command is then run, because all of the `blah.o` dependencies are finished
- The top `cc` command is run, because all the `blah` dependencies are finished
- That's it: `blah` is a compiled c program

```makefile
blah: blah.o
	cc blah.o -o blah # Runs third

blah.o: blah.c
	cc -c blah.c -o blah.o # Runs second

# Typically blah.c would already exist, but I want to limit any additional required files
blah.c:
	echo "int main() { return 0; }" > blah.c # Runs first
```

If you delete `blah.c`, all three targets will be rerun. If you edit it (and thus change the timestamp to newer than `blah.o`), the first two targets will run. If you run `touch blah.o` (and thus change the timestamp to newer than `blah`), then only the first target will run. If you change nothing, none of the targets will run. Try it out!

This next example doesn't do anything new, but is nontheless a good additional example. It will always run both targets, because `some_file` depends on `other_file`, which is never created.

```makefile
some_file: other_file
	echo "This will always run, and runs second"
	touch some_file

other_file:
	echo "This will always run, and runs first"
```

## Make clean

`clean` is often used as a target that removes the output of other targets, but it is not a special word in Make. You can run `make` and `make clean` on this to create and delete `some_file`.

Note that `clean` is doing two new things here:

- It's a target that is not first (the default), and not a prerequisite. That means it'll never run unless you explicitly call `make clean`
- It's not intended to be a filename. If you happen to have a file named `clean`, this target won't run, which is not what we want. See `.PHONY` later in this tutorial on how to fix this

```makefile
some_file: 
	touch some_file

clean:
	rm -f some_file
```

## .phony

Adding `.PHONY` to a target will prevent Make from confusing the phony target with a file name. In this example, if the file `clean` is created, make clean will still be run. Technically, I should have used it in every example with `all` or `clean`, but I wanted to keep the examples clean. Additionally, "phony" targets typically have names that are rarely file names, and in practice many people skip this.

```makefile
some_file:
	touch some_file
	touch clean

.PHONY: clean
clean:
	rm -f some_file
	rm -f clean
```

## Variables

Variables can only be strings. You'll typically want to use `:=`, but `=` also works. See Variables Pt 2.

Here's an example of using variables:

```makefile
files := file1 file2
some_file: $(files)
	echo "Look at this variable: " $(files)
	touch some_file

file1:
	touch file1
file2:
	touch file2

clean:
	rm -f file1 file2 some_file
```

Single or double quotes have no meaning to Make. They are simply characters that are assigned to the variable. Quotes _are_ useful to shell/bash, though, and you need them in commands like `printf`. In this example, the two commands behave the same:

```makefile
a := one two# a is set to the string "one two"
b := 'one two' # Not recommended. b is set to the string "'one two'"
all:
	printf '$a'
	printf $b
```

Reference variables using either `${}` or `$()`

```makefile
x := dude

all:
	echo $(x)
	echo ${x}

	# Bad practice, but works
	echo $x 
```

## Targets

### The all target

Making multiple targets and you want all of them to run? Make an `all` target. Since this is the first rule listed, it will run by default if `make` is called without specifying a target.

```makefile
all: one two three

one:
	touch one
two:
	touch two
three:
	touch three

clean:
	rm -f one two three
```

### Multiple targets

When there are multiple targets for a rule, the commands will be run for each target. `$@` is an automatic variable that contains the target name.

```makefile
all: f1.o f2.o

f1.o f2.o:
	echo $@
# Equivalent to:
# f1.o:
#	 echo f1.o
# f2.o:
#	 echo f2.o
```

## Automatic Variables and Wildcards

### * Wildcard

Both `*` and `%` are called wildcards in Make, but they mean entirely different things. `*` searches your filesystem for matching filenames. I suggest that you always wrap it in the `wildcard` function, because otherwise you may fall into a common pitfall described below.

```makefile
# Print out file information about every .c file
print: $(wildcard *.c)
	ls -la  $?
```

`*` may be used in the target, prerequisites, or in the `wildcard` function.

Danger: `*` may not be directly used in a variable definitions

Danger: When `*` matches no files, it is left as it is (unless run in the `wildcard` function)

```makefile
thing_wrong := *.o # Don't do this! '*' will not get expanded
thing_right := $(wildcard *.o)

all: one two three four

# Fails, because $(thing_wrong) is the string "*.o"
one: $(thing_wrong)

# Stays as *.o if there are no files that match this pattern :(
two: *.o 

# Works as you would expect! In this case, it does nothing.
three: $(thing_right)

# Same as rule three
four: $(wildcard *.o)
```

### Automatic Variables

There are many automatic variables, but often only a few show up:

```makefile
hey: one two
	# Outputs "hey", since this is the target name
	echo $@

	# Outputs all prerequisites newer than the target
	echo $?

	# Outputs all prerequisites
	echo $^

	# Outputs the first prerequisite
	echo $<

	touch hey

one:
	touch one

two:
	touch two

clean:
	rm -f hey one two
```

<div class="page-break"></div>

## Gcc and make compiler flags
`-c` flag only compiles the source file inot `.o` files
And then youcan link all `.o` files into an output file

## Example makefile
```makefile
DEPENDENCIES=reservation.o room.o utils.o

.PHONY:clean

all: main test
main: main.o $(DEPENDENCIES)
	clang main.o $(DEPENDENCIES) -o main
test: test.o $(DEPENDENCIES)
	clang test.o $(DEPENDENCIES) -o test
test.o: 
	clang -c test.c -o test.o
main.o:
	clang -c main.c -o main.o
reservation.o: reservation.c
	clang -c reservation.c -o reservation.o
room.o: room.c
	clang -c room.c -o room.o
utils.o: utils.c
	clang -c utils.c -o utils.o
clean:
	rm -rf *.o $(DEPENDENCIES) main test
```
or simpler example
```
OBJS = room.c reservation.c utils.c

all: main test
main:
	clang main.c $(OBJS) -o main
test:
	clang test.c $(OBJS) -o test
clean:
	rm -rf *.o main test
```
or more compilcated but more efficient and shorter
```makefile
CC = clang
DEPENDENCIES = reservation.o room.o utils.o

all: main test

main: main.o $(DEPENDENCIES)
	$(CC) $^ -o $@

test: test.o $(DEPENDENCIES)
	$(CC) $^ -o $@

# Pattern rule for all object files
%.o: %.c
	$(CC) -c $< -o $@

clean:
	rm -rf *.o main test
```
# Useful Java structures

## ObjectMapper
Jackson Object mappper can be used to serialize/deserialize json


### Java object to Json
Let’s see a first example of serializing a Java object into JSON using the _writeValue_ method of the _ObjectMapper_ class:

```java
ObjectMapper objectMapper = new ObjectMapper();
Car car = new Car("yellow", "renault");
objectMapper.writeValue(new File("target/car.json"), car);
```

The output of the above in the file will be:

```javascript
{"color":"yellow","type":"renault"}
```

The methods _writeValueAsString_ and _writeValueAsBytes_ of _ObjectMapper_ class generate a JSON from a Java object and return the generated JSON as a string or as a byte array:

```java
String carAsString = objectMapper.writeValueAsString(car);
```

### Json to Java object
Alternatively, a JSON can be parsed into a _JsonNode_ object and used to retrieve data from a specific node:

```java
String json = "{ \"color\" : \"Black\", \"type\" : \"FIAT\" }";
JsonNode jsonNode = objectMapper.readTree(json);
String color = jsonNode.get("color").asText();
// Output: color -> Black
```


## LinkedHashMap for caching
A `LinkedHashMap` stores keys and values, and keeps them in the same order you put them in/used them in.
That's why it can be used as a **FIFO/LIFO or LRU/MRU cache**. 

The consructor `LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder)` takes 3 parameters:
`int initialCapacity` - self-explanatory, however does not hard limit the size. You have to do that yourself and evict old entries
`float loadFactor` - Should be left at 0.75
`boolean accessOrder` - the ordering mode - true for access-order, false for insertion-order


```java
public final int MAX_CACHED = 3;
private final StorageStrategy storage;
private LinkedHashMap<String,Note> cache;
String lastNotePath;

public CachedStorage(StorageStrategy storage) {
	this.cache = new LinkedHashMap<>(3,0.75f,true);
	this.storage = storage;
}
```

**Or you can simply store a second dictionary with timestamps and use .stream() to select an element to evict based on the cache strategy.**

# Random personal Linux fixes

## If SELinux has issues with docker containers

To turn it off:
```bash
sudo setenforce 0
```

## To change java version
```bash
sudo alternatives --config java
sudo alternatives --config javac
```

## To cancel an automatic shutdown
```bash
sudo shutdown -c
```

<div class="page-break"></div>

# ALL RESOURCE LINKS:
- **Lecture slides (PDF)**
- **Your own homework solutions (cloned)**
- **Cheat-sheets/self-written notes (printed/on paper/PDF)**
- **C reference:** https://en.cppreference.com/w/c/language
- **Python reference:** https://docs.python.org/3/reference/index.html
- **Java reference:** https://www.baeldung.com/get-started-with-java-series
- **Java reference:** https://docs.oracle.com/en/java/javase/22/
- **gRPC reference:** https://grpc.io/docs/
- **Spotbugs**: https://spotbugs.readthedocs.io
- **AddressSanitizer**: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html
- **Spring Boot:** https://www.baeldung.com/spring-boot
- **Spring Boot:** https://spring.io/projects/spring-boot
- **Docker:** https://docs.docker.com/
- **JavaFX:** https://openjfx.io/openjfx-docs
- **Gradle:** https://docs.gradle.org/current/userguide/userguide.html
- **Git:** https://git-scm.com/docs
- **JUnit:** https://junit.org/junit5/docs/current/user-guide/
- **Mockito:** https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html
- **EasyMock:** https://easymock.org/user-guide.html
- **man pages (command line, not online)**

# Excersises:
- **L09P02** Garching Best Software
- **L10PE01** Tutor Meeting Management
- **L09P01** Registry Office Service Deployment
- **L09PE01** TUMPixel
- **L09PE02** Wizardry Character Creation
- **L09PE03** Your First Kubernetes Deployment
- **L08P01** Oops Another Git Merge Conflict
- **L08P02** Multilingual Codebase using Bazel
- **L08PE01** Continuous Integration
- **L08PE02** Merge the Right Merge
- **L08PE03** Defend FoodPalace
- **L08PE04** Spaceship
- **L07P01** Spot the Bugs
- **L07P02** Dynamic Code analysis for Priority Scheduling
- **L07PE01** The Recovery of Aniruddhs Restaurant Part 2
- **L07PE02** Playlist Manager -- Memory Debugging with MemorySanitizer
- **L07PE03** Gym Threading
- **L06P01** University App Unit Testing Part 2
- **L06P02** Discussion Forum Mock Testing
- **L06PE01** The Iron Bank of Braavos
- **L06PE02** Student Absences System Testing
- **L06PE03** Tutorial Service
- **L05P01** Database Sharding and Recovery
- **L05P02** Searching in e-BOOKist
- **L05P03** Old Beer Factory Digitalization
- **L05PE01** Capability-based File Sharing
- **L05PE02** Thermometer Adapter
- **L05PE03** Observer Pattern
- **L04P01** Swimming Pool Facility Management
- **L04P02** Book Management System
- **L04PE01** Caching and its policies
- **L04PE02** Scalable Kitchen Simulation
- **L04PE03** Voices in the Void
- **L04PE04** The Shaft
- **L04PE05** German Meteorological Service
- **L03P01** Event Registration Application part 2
- **L03P02** Monkey Business
- **L03PE01** Online FileFolder
- **L03PE02** Shopingu
- **L03PE03** Gobblemaps
- **L03PE04** Harry Plotter and the Deathly Derivative
- **L02P01** Spotify gRPC
- **L02P02** TUM Social App
- **L02PE01** TUM Social App
- **L02PE02** REST Architectural Style Part 2