Introduction
PlantUML defines a standardized way to encode diagram text description to a simple string of characters that contains only digits, letters, underscore and minus character. The goal of such an encoding is to facilitate communication of diagrams through URL (see link::server[server]). This encoding includes compression to keep encoded strings as short as possible.
The encoded metadata is stored in the generated PNG, so the diagram source can be extracted from the diagram itself! (see link::server#metadata[server#metadata]).
Compression
Deflate algorithm is used by default.
You can also use simple HEX encoding, see below. An initial ~h is added to indicate this encoding.
Principle
For example, the following uml text description:
@startuml Alice -> Bob: Authentication Request Bob --> Alice: Authentication Response @enduml
is encoded as:
Syp9J4vLqBLJSCfFib9mB2t9ICqhoKnEBCdCprC8IYqiJIqkuGBAAUW2rO0LOr5LN92VLvpA1G00
To achieve such encoding, the text diagram is:
Why not use Base64?
The main reason is historic: this format was not created to be public at first. Now, it’s too late to change it. However, the only difference is in character order.
Where in base64 the mapping array for values 0-63 is:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
For PlantUML, the mapping array for values 0-63 is:
0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_
Compression comparison
The following diagram:
@startuml
skinparam backgroundColor #EEEBDC
skinparam handwritten true
skinparam sequenceArrowColor DeepSkyBlue
skinparam sequenceActorBorderColor DeepSkyBlue
skinparam sequenceLifeLineBorderColor blue
skinparam sequenceLifeLineBackgroundColor #A9DCDF
skinparam sequenceParticipantBorderColor DeepSkyBlue
skinparam sequenceParticipantBackgroundColor DodgerBlue
skinparam sequenceParticipantFontName Impact
skinparam sequenceParticipantFontSize 17
skinparam sequenceParticipantFontColor #A9DCDF
skinparam sequenceActorBackgroundColor aqua
skinparam sequenceActorFontColor DeepSkyBlue
skinparam sequenceActorFontSize 17
skinparam sequenceActorFontName Aapex
actor User
participant "First Class" as ParticipantA
participant "Second Class" as ParticipantB
participant "Last Class" as ParticipantC
User -> ParticipantA: DoWork
activate ParticipantA
ParticipantA -> ParticipantB: Create Request
activate ParticipantB
ParticipantB -> ParticipantC: DoWork
activate ParticipantC
ParticipantC --> ParticipantB: WorkDone
destroy ParticipantC
ParticipantB --> ParticipantA: Request Created
deactivate ParticipantB
ParticipantA --> User: Done
deactivate ParticipantA
@endumlis compressed to a
Running
You can use -encodeurl or -decodeurl in the link::command-line[command line] flags to encode or decode the text.
You will find here some implementation of this encoder:
-
link::code-php[Code in PHP]
-
link::code-javascript-synchronous[Code in Javascript]
Simple HEX format
If you find Deflate and Brotli too complex, you can try the HEX format. In that case, you just have to encode each character in hexadecimal format.
For example :
@startuml Alice->Bob : I am using hex @enduml
will be turned into:
407374617274756d6c0a416c6963652d3e426f62203a204920616d207573696e67206865780a40656e64756d6c
To indicate the use of HEX format, you must add ~h at the start of the data sent to PlantUML server.
http://www.plantuml.com/plantuml/uml/h407374617274756d6c0a416c6963652d3e426f62203a204920616d207573696e67206865780a40656e64756d6c[http://www.plantuml.com/plantuml/uml/h4073…]
Since there is no compression here, the URL will become very long as the diagram grows.