Mu Python template

Template for running Python microservices

Using the template

1. Extend the samldd/mu-python-template and set a maintainer.

2. Configure your entrypoint through the environment variable APP_ENTRYPOINT (default: web.py).

3. Write the python requirements in a requirements.txt file. (Flask, SPARQLWrapper and rdflib are standard installed)

Create the entry point file and add methods with URL's. The flask app is added to the python builtin and can be accessed by using the app variable, as shown in following example:

@app.route(/exampleMethod)
def exampleMethod():
    return example

Example Dockerfile

FROM samldd/mu-python-template:latest
MAINTAINER Sam Landuydt <sam.landuydt@gmail.com>
# ONBUILD of mu-python-template takes care of everything

Configuration

The template supports the following environment variables:

• MU_SPARQL_ENDPOINT is used to configure the SPARQL endpoint.

  • By default this is set to http://database:8890/sparql. In that case the triple store used in the backend should be linked to the microservice container as database.

• MU_APPLICATION_GRAPH specifies the graph in the triple store the microservice will work in.

  • By default this is set to http://mu.semte.ch/application. The graph name can be used in the service via settings.graph.

• MU_SPARQL_TIMEOUT is used to configure the timeout (in seconds) for SPARQL queries.

Develop a microservice using the template

To use the template while developing your app, start a container in development mode with your code folder on the host machine mounted in /app:

docker run --volume /path/to/your/code:/app
           -e MODE=development
           -d python-template

Code changes will be automatically picked up by Flask.

Helper methods

The template provides the user with several helper methods. Most helpers can be used by calling: "helpers.", except the sparql_escape helper: "sparql_escape(var)".

log(msg)

The template provides a log object to the user for logging. Just do log("Hello world"). The log level can be set through the LOG_LEVEL environment variable (default: info, values: debug, info, warning, error, critical).

Logs are written to the /logs directory in the docker container.

generate_uuid()

Generate a random UUID (String).

session_id_header(request)

Get the session id from the HTTP request headers.

rewrite_url_header(request)

Get the rewrite URL from the HTTP request headers.

validate_json_api_content_type(request)

Validate whether the Content-Type header contains the JSONAPI Content-Type. Returns a 400 otherwise.

validate_resource_type(expected_type, data)

Validate whether the type specified in the JSON data is equal to the expected type. Returns a 409 otherwise.

error(title, status = 400)

Returns a JSONAPI compliant error response with the given status code (default: 400).

query(query)

Executes the given SPARQL select/ask/construct query.

update(query)

Executes the given SPARQL update query.

update_modified(subject, modified = datetime.now())

Executes a SPARQL query to update the modification date of the given subject URI (string). The date defaults to now.

sparql_escape(var)

This method can be used to avoid SPARQL injection by escaping user input while constructing a SPARQL query. The method checks the type of the given variable and returns the correct object string format, depending on the type of the object. Current supported variables are: datetime.time, datetime.date, str, int, float and boolean. For example:

query =  " INSERT DATA {"
query += "   GRAPH <http://mu.semte.ch/application> {"
query += "     < %s > a <foaf:Person> ;" % user_uri
query += "                   <foaf:name> %s ;" % sparql_escape(name)
query += "                   <dc:created> %s ." % sparql_escape(date)
query += "   }"
query += " }"

Example

There is one example method in the template: "/templateExample/" this methods returns all trippels in the tripple store from the sparql endpoint (beware for big databases!).