- Clients should only need to communicate with a central server to find peers
and facilitate hole-punching (or assume that all clients have a listening port forwarded1).For the sake of the project deadline, we are assuming clients are port-forwarded or reachable. - Messages between clients should never go through any sort of central or relay server.
- All messages should be encrypted to facilitate secure transfer of data.
- Clients should be able to pair with each other to start messaging via a user ID
- For simplicity, users should be per-device, i.e. each client installation has a different user ID and messages do not sync between one person's devices if they use multiple.
-
Clients should attempt to contact the central server frequently to ensure the client's IP in the server's database is up-to-date.Clients keep a constant socket with the server, so the IP is updated any time the client is opened. - Clients should have a local database with multiple tables for user and message caching.
- One table for known user hashes, as well as a nickname for each user.
- One for messages which foreign key reference the known users table's ID column.
- The first time the client process is opened, it should connect to the server to receive a unique user hash.
- Clients should be able to pair using a QR code or nearby device scanning.
- Clients should be able to send small files or images to each other.
- Clients get rid of cached messages after a user-defined amount of time.
- By definition requires adding a posted date column to the message tables.
- The server should have a database with at least a table that holds a user ID and the corresponding IP.
- The server should support multiple user connections at once to be scale-able (for testing purposes, 2-4 is sufficient).
- The first time a new client connects, a new user hash should be generated and added to the user table, and then the hash should be sent back to the user.
- The server should accept requests from clients to contact other clients and facilitate their attempt at connecting to each other
via hole-punching.Doesn't use hole-punching now, just tells the requesting client the requested's IP so it can open a socket to it.
- Clients' local databases should use something lightweight such as SQLite
- Server's database should use something more reliable like MySQL
| ID | User Hash | Nickname |
|---|---|---|
| 1 | e2d38e18759ea68bace101ab39d62e41 | Andrea |
| 2 | 1c1eb4329e9b82168baaaa84b065209f | Travis |
| 3 | 3889ede791c6872162ed0ab8ce513cd7 | Spam Risk |
Clients should store their own user hash cached somewhere.
| Message ID | User ID (FK) | IsAuthor | Message Contents | File (Optional) |
|---|---|---|---|---|
| 1 | 1 | false | "Hello" | null |
| 2 | 1 | true | "Hi" | null |
| 3 | 1 | false | "Check out my cat" | catPic.jpg |
| 4 | 1 | true | "Cool cat" | null |
| 5 | 3 | false | "You or a loved one may be entitled to financial compensation." | null |
| ID | User Hash | Last-known IP |
|---|---|---|
| 1 | e2d38e18759ea68bace101ab39d62e41 | 64.82.8.109 |
| 2 | 1c1eb4329e9b82168baaaa84b065209f | 161.6.1.200 |
| 3 | 3889ede791c6872162ed0ab8ce513cd7 | 102.184.21.14 |
It should be sufficient to generate user IDs by passing some sort of randomly generated string2 into an MD5 hashing function. This will allow 16^32 total users (definitely overkill, but not really a problem).
Footnotes
-
If we go down this route, the user tables on the client side should also have the last-known IP for each client, so that peers can attempt to connect to each other without needing to check with a central server; then, if that fails, it can check with the central server to see if the IP of the user they are trying to connect to has changed. ↩
-
For example, the following code:
↩protected String getSaltString() { String SALTCHARS = "abcdefghijklmnopqrstuvwxyz1234567890"; StringBuilder salt = new StringBuilder(); SecureRandom rnd = new SecureRandom(); while (salt.length() < 32) { // length of the random string. int index = (int) (rnd.nextFloat() * SALTCHARS.length()); salt.append(SALTCHARS.charAt(index)); } String saltStr = salt.toString(); return saltStr; }
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