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docs/transformerDebug.md

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+## TransformerDebug
+
+In addition to any normal logging, the t-engines, t-router and t-client also
+use the `TransformerDebug` class to provide request based logging. The
+following is an example from Alfresco after the upload of a `docx` file.
+
+~~~
+163               docx json AGM 2016 - Masters report.docx 14.8 KB -- metadataExtract --  TransformService
+163               workspace://SpacesStore/0db3a665-328d-4437-85ed-56b753cf19c8 1563306426
+163               docx json  14.8 KB -- metadataExtract -- PoiMetadataExtractor
+163                 cm:title=
+163                 cm:author=James Dobinson
+163               Finished in 664 ms
+...
+164               docx png  AGM 2016 - Masters report.docx 14.8 KB -- doclib --  TransformService
+164               workspace://SpacesStore/0db3a665-328d-4437-85ed-56b753cf19c8 1563306426
+164               docx png   14.8 KB -- doclib -- officeToImageViaPdf
+164.1             docx pdf   libreoffice
+164.2             pdf  png   pdfToImageViaPng
+164.2.1           pdf  png   pdfrenderer
+164.2.2           png  png   imagemagick
+164.2.2             endPage="0"
+164.2.2             resizeHeight="100"
+164.2.2             thumbnail="true"
+164.2.2             startPage="0"
+164.2.2             resizeWidth="100"
+164.2.2             autoOrient="true"
+164.2.2             allowEnlargement="false"
+164.2.2             maintainAspectRatio="true"
+164               Finished in 725 ms
+~~~
+
+This log happens to be from the t-client, but similar log lines exist in the
+t-router and individual t-engines.
+
+All lines start with a reference, which starts with the client’s request
+number (`163`, `164` if known) and then a nested pipeline or failover
+structure. The first request extracts metadata and the second creates a
+thumbnail rendition (called `doclib`). The second request is handled by a
+pipeline called `officeToImageViaPdf` which uses `libreoffice` to transform 
+to `pdf` and then another pipeline to convert to `png`. The last step
+(`164.2.2`) in the process resizes the `png` using a number of transform
+options.
+
+If requested, log information is passed back in the TransformReply's
+clientData.