Structured data (YAML and JSON files) is very typical for UI development to keep settings, texts and other structured information.
EVA ICS provides a feature, called “serve as”, which allows to convert any structured data file on-the-flow and load it into UI applications in the most convenient way.
This feature is supported by both public UI (“/ui” URLs) and SFA PVT and enabled automatically for all files with suffixes “.yml”, “.yaml” and “.json”.
To convert a structured file into another format, request it as:
- yml (or yaml) - convert the file into YAML
- json - convert the file into JSON
e.g. let’s convert YAML, which is usually more human-editable and preferred to keep configs, into JSON:
An additional argument “lang” can be used to apply the chosen locale on all string fields of structured data file. Multi-line strings are processed correctly, string formatting (left and right white spaces) is preserved:
(as seen from the above example, “lang” can be combined with “as”).
Firstly, a locale file should be created. Create a directory EVA_DIR/pvt/locales (used for both UI and SFA PVT). After, create inside that directory language directories with LC_MESSAGES subdirectory inside each one. So the tree should look like e.g. (“cs” is for Czech language):
pvt └── locales └── cs └── LC_MESSAGES ├── messages.po ├── tests └────── test.po
“.po” files are standard Gettext files, which look like:
msgid "this is a test" msgstr "je to test"
or e.g. for Japanese (UTF-8):
#, fuzzy msgid "" msgstr "" "Content-Type: text/plain; charset=utf-8\n" msgid "this is a test" msgstr "これはテストです"
(note that if diacritic is used e.g. in Czech lang messages, the file should specify UTF-8 encoding as well)
The files can be compiled with “msgfmt” Linux command from “gettext” package (installed by default by majority Linux distributions):
msgfmt file.po -o file.mo
EVA ICS uses the following strategy to find locale files. E.g. if the document
is served, the message files are looked up in the following order:
(the last file is the standard common message file). If no message file is found, the strings are served as-is, without any conversion.
Altrenatively, locale files can be kept in EVA_DIR/ui/locales. SCADA Final Aggregator automatically searches for the locale files in “ui” if no locale files found in “pvt”.
The option “-o EVA_DIR/ui/locales” for gen-intl can be used to automatically generate / compile locale files in EVA_DIR/ui/locales.
To auto-generate / update “.po” files from JSON or YAML strings, a supplied tool “gen-intl” can be used (multiple languages can be specified at once):
/opt/eva/bin/gen-intl test.yml -l cs generate
The above command will auto-generate or update “test.po” file and put it to the corresponding locale path. E.g. if the file absolute path is /opt/eva/ui/tests/test.yml, the result “.po” file will be written to /opt/eva/pvt/locales/cs/LC_MESSAGES/tests/test.po.
After editing, compile “.po” file manually with “msgfmt”, or run
/opt/eva/bin/gen-intl test.yml -l cs compile
Message files are cached by EVA ICS gettext library, until the SCADA Final Aggregator server is restarted.
The cache can be turned off by setting development mode (server/development:true) field of config/sfa/main registry key
To serve structured data from EVA ICS registry, use the following request:
where REGISTRY-KEY - key name, relative to eva3/HOST/userdata/pub, e.g. to request a key “eva3/HOST/userdata/pub/settings” use the following request:
To serve private data, see Serving private data from EVA ICS Registry.
Why serving structure data from registry is more convenient:
- unified data storage
- data schemas