T-Engines provide a /transform/config end point for clients (e.g. Transform-Router or Alfresco-Repository) that indicate what is supported. T-Engines store this configuration as a JSON resource file named engine_config.json.
The config can be found under alfresco-transform-core\<t-engine-name>\src\main\resources \engine_config.json; current configuration files are:
- Pdf-Renderer T-Engine configuration.
- ImageMagick T-Engine configuration.
- Libreoffice T-Engine configuration.
- Tika T-Engine configuration.
- Misc T-Engine configuration.
Snippet from Tika T-engine configuration:
{
"transformOptions": {
"tikaOptions": [
{"value": {"name": "targetEncoding"}}
],
"pdfboxOptions": [
{"value": {"name": "notExtractBookmarksText"}},
{"value": {"name": "targetEncoding"}}
]
},
"transformers": [
{
"transformerName": "PdfBox",
"supportedSourceAndTargetList": [
{"sourceMediaType": "application/pdf", "targetMediaType": "text/html"},
{"sourceMediaType": "application/pdf", "maxSourceSizeBytes": 26214400, "targetMediaType": "text/plain"}
],
"transformOptions": [
"pdfboxOptions"
]
},
{
"transformerName": "TikaAuto",
"supportedSourceAndTargetList": [
{"sourceMediaType": "application/msword", "priority": 55, "targetMediaType": "text/xml"}
],
"transformOptions": [
"tikaOptions"
]
},
{
"transformerName": "TextMining",
"supportedSourceAndTargetList": [
{"sourceMediaType": "application/msword", "targetMediaType": "text/xml"}
],
"transformOptions": [
"tikaOptions"
]
}
]
}- transformOptions provides a list of transform options that may be referenced for use in different transformers. This way common options don't need to be repeated for each transformer, they can be shared between T-Engines. In this example there are two groups of options called tikaOptions and pdfboxOptions which has a group of options targetEncoding and notExtractBookmarksText. Unless an option has a "required": true field it is considered to be optional. You don't need to specify sourceMimetype, targetMimetype, sourceExtension or targetExtension as options as these are automatically added.
Snippet from ImageMagick T-engine configuration:
"transformOptions": {
"imageMagickOptions": [
{"value": {"name": "alphaRemove"}},
{"group": {"transformOptions": [
{"value": {"name": "cropGravity"}},
{"value": {"name": "cropWidth"}},
{"value": {"name": "cropHeight"}},
{"value": {"name": "cropPercentage"}},
{"value": {"name": "cropXOffset"}},
{"value": {"name": "cropYOffset"}}
]}},
]
},- There are two types of transformOptions, transformOptionsValue and transformOptionsGroup:
- TransformOptionsValue is used to represent a single transformation option, it is defined by a name and an optional required field.
- TransformOptionGroup represents a group of one or more options, it is used to group options that define a characteristic. In the above snippet all the options for crop are defined under a group, it is recommended to use this approach as it is easier to read. A transformOptionsGroup can contain one or more transformOptionsValue and transformOptionsGroup.
Limitations:
- For a transformOptions to be referenced in a different T-engine, another transformer with the complete definition of the transformOptions needs to return the config to the client.
- In a transformOptions definition it is not allowed to use a reference to another tranformOption.
- transformers - A list of transformer definitions. Each transformer definition should have a unique transformerName, specify a supportedSourceAndTargetList and indicate which options it supports. As it is shown in the Tika snippet, an engine_config can describe one or more transformers, as a T-engine can have multiple transformers (e.g. Tika, Misc). A transformer configuration may specify references to 0 or more transformOptions.
- supportedSourceAndTargetList is simply a list of source and target Media Types that may be transformed, optionally specifying a maxSourceSizeBytes and a priority value.
- maxSourceSizeBytes is used to set the upper size limit of a transformation.
- If not specified, the default value for maxSourceSizeBytes is unlimited.
- priority it is used by clients to determine which transfomer to call or by T-engines
with multiple transformers to determine which one to use. In the above Tika snippet,
both TikaAuto and TextMining have the capability to transform "application/msword"
into "text/xml", the transformer containing the source-target media type with higher priority will be chosen by the
T-engine as the one to execute the transformation, in this case it will be TextMining, because:
- If not specified, the default value for priority is 50.
- Note: priority values are like the order in a queue, the lower the number the higher the priority is.
The ACS repository will use the T-Engine configuration to choose which T-Engine will perform a transform. A transformer definition contains a supported list of source and target Media Types. This is used for the most basic selection. This is further refined by checking that the definition also supports transform options (parameters) that have been supplied in a transform request or a Rendition Definition used in a rendition request. Order for selection is:
- Source->Target Media Types
- transformOptions
- maxSourceSizeBytes
- priority
Transformer 1 defines options: Op1, Op2
Transformer 2 defines options: Op1, Op2, Op3, Op4
Rendition provides values for options: Op2, Op3
If we assume both transformers support the required source and target Media Types, Transformer 2 will be selected because it knows about all the supplied options. The definition may also specify that some options are required or grouped.
Transformer 1 defines options: Op1, Op2, maxSize
Transformer 2 defines options: Op1, Op2, Op3
Rendition provides values for options: Op1, Op2
If we assume both transformers support the required source and target Media Types, and file size is greater than maxSize ,Transformer 2 will be selected because if can handle maxSourceSizeBytes for this transformation.
Transformer 1 defines options: Op1, Op2, priorty1
Transformer 2 defines options: Op1, Op2, Op3, priority2
Rendition provides values for options: Op1, Op2
If we assume both transformers support the required source and target Media Types and priority1 < priority2, Transformer 1 will be selected because its priority is higher.