ShortID

Two services using shortid

Description

Service A uses a UUID to uniquely identify entries (example 70f525c1-1e93-483c-9c92-b9459020462e). But service B uses an identifier of 20 alphanumerical characters. So service A needs some functionality to convert/match the UUID to service B's schema.

Problem

The UUID is 128bit long, mapping that to the 20 characters of the service B identifier would need 6.4 bits per character. That means 2^6.4 = 85 different figures! Alphanumeric is normal defined as A-Z + a-z + 0-9, that's 62 figures only. So the UUID can't be mapped on 20 alphanumeric characters, without loosing information.

Solution 1

62 is about 2^5.96, that means we would only get 5.96 bit per character, that's 119 bit for 20 characters. So that solution will lead to a loss of 9 bits which increases the chance of a collision! This means a higher chance, that 2 random UUIDs have the same representation in the 20 alphanumeric character representation.

Solution 2

Extend the meaning of alphanumeric so there are more figures to map all bits.The ASCII code has usable figures from position 33 to 126, that means one can choose his "alphabet" out of those 94 different figures.

As this is the only safe way, this project chooses solution 2.

Implementation details

• The services are just rudimentary, only create and retrieve is implemented!
• Create uses a POST to return the result with the uuid/uniqueId.
• Logging is neglected
• The service B is used to store a hash of the aggregation data, as example metadata. When retrieved, this hash is checked, difference result in an error response.
• The create method of service A is not transactional!

Build, run and test

To build everything run:

mvn clean package

Then start service A by executing in one shell:

java -jar servicea/target/servicea.jar

Then start service B by executing in another shell:

java -jar serviceb/target/serviceb.jar

When both services are up, you can test them with executing the script:

./test.sh