poei-file-storage

File storage service

Backend service to store files

Contract

You will need to develop the following HTTP APIs:

• API to upload a file
• API to fetch all file metadata
• API to download a file

File upload

HTTP Request (input)

POST http://localhost:8080/file-storage/file

• Content of the file in the parameter file

Expected HTTP Responses (output)

• HTTP Status: 200
• Response body (JSON):

{
  "fileId": 1,
  "name": "poei.pdf"
}

Fetch file metadata

HTTP Request (input)

GET http://locahost:8080/file-storage/file

Expected HTTP Responses (output)

• HTTP Status: 200
• Response body (JSON):

[{
  "fileId": 1,
  "name": "poei.pdf"
}, {
  "fileId": 2,
  "name": "foobar.doc"
}]

File download

HTTP Request (input)

GET http://localhost:8080/file-storage/file/{fileId}

Path variable:

Name	Type	Description
fileId	integer	The file id to download

Expected HTTP Responses (output)

• HTTP Status: 200
• File download

Getting started

Running the service with the IDE

Main class: com.oodrive.poei.filestorage.PoeiFileStorageApplication

Running the service with Maven

./mvnw clean spring-boot:run

Exercises

1 - File upload

Goal

Expose a HTTP API to upload files

The path to call the HTTP API must be the following:

POST http://localhost:8080/file-storage/file

• Content of the file in the parameter file

The output of the HTTP request must be the following:

• HTTP Status: 200
• Response body (JSON):

{
  "fileId": 1,
  "name": "poei.pdf"
}

Instructions

• Create Java classes:
  • to represents a file metadata without its content (id, file name, absolute path to the stored file)
  • to store the file metadata in memory
  • to store a file in file system
    • 💡 you can use the java.nio.file.Files.createTempFile() API to create the files in a temporary directory
    • 💡 track the file absolute path so you can fetch them again when we will download them
• Create a controller that uses the previous Java classes

2 - Fetch file metadata

Goal

Expose a HTTP API to fetch all file metadata

The path to call the HTTP API must be the following:

GET http://locahost:8080/file-storage/file

The output of the HTTP request must be the following:

• HTTP Status: 200
• Response body (JSON):

[{
  "fileId": 1,
  "name": "poei.pdf"
}, {
  "fileId": 2,
  "name": "foobar.doc"
}]

Instructions

• Create Java classes to fetch all uploaded file metadata
• Update the controller to fetch the file metadata

3 - File download

Goal

Expose a HTTP API to download files

The path to call the HTTP API must be the following:

GET http://localhost:8080/file-storage/file/{fileId}

Path variable:

Name	Type	Description
fileId	integer	The file id to download

The output of the HTTP request must be the following:

• HTTP Status: 200
• File download

Instructions

• Create Java classes:
  • that fetch a file entity from a given file id
  • that fetch the file content from the path provided by the file entity
• Update the controller to download the file
  • return a HTTP Status 404 if the file does not exist
  • 💡 you can use the Spring annotation @org.springframework.web.bind.annotation.ResponseStatus on an exception to return the corresponding HTTP status

4 - Save file entities in database

Goal

Storing file entities in memory is easy to develop, however, the data created will be purged when the application stops.

We will then store file entities in database in order to persist the data after each restart.

Instructions

• Modify the pom.xml file to use the dependencies spring-boot-starter-jdbc and postgresql
  • ⚠️ the application is already configured to use the database file_storage, so you may have to create the database beforehand
• Create a SQL table that will contain the file entities
• Create the Java DAO class that read and write lines in the database
• Update the Java classes to store, update and fetch the file entities in database instead of in memory

5 - Encrypt/Decrypt file content

Goal

For security purpose, the file content must not be in plain text readable by a human.

One way is to encrypt the file content using a common cryptographic technique: symmetric encryption.

The principle is to use an encryption key to convert a sensitive data into a non-readable data by employing a two-way algorithm, i.e. the encryption and decryption are performed using the same encryption key.

Instructions

• Create Java classes to:
  • generate an encryption key supported by AES (Advanced Encryption Standard) implementation
    • you can use the Java class javax.crypto.SecretKey for the encryption key
    • the storage of the encryption key's password is up to you
      • directly in the code
      • in the database
      • using Spring @org.springframework.beans.factory.annotation.Value
    • ⚠️ AES only supports 16, 24 or 32 bytes blocks, so fill up the block if the length of the given password is not enough
    • 💡 SHA-256 hashes are also 32 bytes long, so you can hash your password to use it to create the javax.crypto.SecretKey
  • encrypt file content
    • you can use the Java class javax.crypto.CipherOutputStream
  • decrypt file content
    • you can use the Java class javax.crypto.CipherInputStream
• Update your code to include the encryption and decryption of file contents