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PlantUML News and information PlantUML Text Encoding

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Codificación de texto PlantUML

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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 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 server#metadata).

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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:

  1. Encoded in UTF-8
  2. Compressed using Deflate algorithm
  3. Reencoded in ASCII using a transformation close to base64

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:

🎉 Copied! 

@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
@enduml

is compressed to 428-char string length using Deflate

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Running

You can use -encodeurl or -decodeurl in the command line flags to encode or decode the text.

Implementations of the encoder in various languages:

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Formato HEX sencillo

Si Deflate y Brotli le parecen demasiado complejos, puede probar con el formato HEX. En ese caso, sólo tiene que codificar cada carácter en formato hexadecimal.

Por ejemplo : 

@startuml
Alice->Bob : I am using hex
@enduml

se convertirá en: 

407374617274756d6c0a416c6963652d3e426f62203a204920616d207573696e67206865780a40656e64756d6c

Para indicar el uso del formato HEX, debe añadir ~h al principio de los datos enviados al servidor PlantUML.

http://www.plantuml.com/plantuml/uml/~h4073...

Como aquí no hay compresión, la URL se hará muy larga a medida que crezca el diagrama.