flask-docjson

A micro module to validate flask request and response json schemas via view function docstrings.

@app.route('/item/<id>', methods=['GET'])
@flask_docjson.validate
def get(id):
    """Get an item by id.

    Schema::

        GET /item/<i32:id>

        200
        {
            "id": i32,
            "name": string(32),
            "tags": [string, ...]
        }
    """
    pass

It's strongly recommended that you checkout example at first.

Installation

pip install flask-docjson

Usage

• Validate routes selectively via decorator:

  @app.route('/user/<int:id>', methods=['GET'])
  @flask_docjson.validate
  def get_user(id):
      """Schema::
          ...
      """

• Validate all routes, no need to decorate view functions one by one:

  # Must be called after all route definitions
  flask_docjson.register_all(app)

Schema

The validator only works when:

1. Given docstring contains a marker Schema:: or Schema:.
2. The marker is followed by a code block.

Here is an example schema:

Schema::

    POST/PUT /user
    {
        "name": string,
        "email": string,
        "class_no": i8
    }

    200
    {
        "id": i32,
        ...
    }
    4XX/5XX
    {"error": string}

A flask-docjson schema should contain one request and multiple responses descriptions, its structure:

Schema::

    <Methods> <Route>
    <Request-JSON-Schema>

    <StatusCode>
    <Response-JSON-Schema>
    ...

The first json schema is for request, and the following json schemas are for responses.

Methods contains a single or multiple http methods, e.g. DELETE, POST/PUT , all method names should in upper case. Supported method names are:

• POST
• GET
• PUT
• DELETE
• PATCH
• HEAD
• OPTIONS

Route is a flask url rule, but supports stricter variable types. e.g. /user/<i32:id>, /name/<string(32):name>. Note that these types are validators but not converters. We still need to use flask built-in converters:

@app.route("/<int:id>", methods=['GET'])  # OK
# @app.route("/<id>", methods=['GET'])  # BAD
def get(id):
    """Schema::

        GET /<i32:id>
        200
     """

JSON-Schema has json like structure, it may be an array of type definitions, or an object of key-type pairs. And both array and object are also types. Some examples:

• [u8, u16, u32] (array of base types)
• {"text": string(255), "id": i32} (object of base types)
• [{"key": i16}, ...] (array of objects)
• {"key": [u32, ...]} (object with array values)
• [u32, ...] (also called ellipsis array)
• {"id": i32, ...} (also called ellipsis object)

StatusCode contains a single or multiple status codes, e.g. 204/200. What's more, status code matcher like 4XX, 5XX are also supported.

In standard JSON, schema with a trailing comma (e.g. {"key": "value",}) is illegal, but our JSON schema allows this. Because that makes modifications by line convenient.

Base Types

• Boolean: bool
• Number: u8, u16, u32, u64, i8, i16, i32, i64, float
• String: string, string(maxlength) (e.g. string(32))

Container Types

• Array: e.g. [u8, i32, string], [u8, ...].
• Object: e.g. {"name": string(32)}, {"id": i32, ...}.

Ellipsis Array

An array definition with ellipsis is called "ellipsis array", for an example:

{
    "item": [u8, ...]
}

1. Empty list (aka []) is able to pass ellipsis array validation.
2. For this example, all elements in given items should be an u8.

Ellipsis Object

An object definition with ellipsis is called "ellipsis object", for an example:

{
    "id": i32,
    ...
}

1. An ellipsis object indicates given object value may contain more fields, but docjson won't (also can't) validate them.
2. For a non-ellipsis object definition, given object value shouldn't contain any keys that dosen't exist in the type definition.

Nullable Value

By default, values shouldn't be nullable and None value causes validation error. An example to change this behavior is:

{
    "optional-string": string(32)*,
    "optional-integer": i32*
}

And, nullable values are optional in objects, key not exists error won't throw.

But note that * can't be used with the whole request/response json schema, that is to say schemas like the following definition are illegal:

GET /

200
{
    "name": string
}*

No Content

Some requests or responses have no content, we just leave the json schema blank:

• Request schema without content example:

  GET /data
  200
  {"key": float}
  

• Response schema without content example:

  DELETE /data/<i32:id>
  204
  

Comments

We may want to comment on some json fields:

PUT /order
{
    "price": float, // precision:10, scale:2
}

200
{
    "id": i32,
     ...
}

Exceptions

• flask_docjson.Error: Raised when a flask-docjson error occurred.
• flask_docjson.ParserError: Raised when a parser error occurred.
• flask_docjson.LexerError: Raised when a lexer error (e.g. bad token) occurred.
• flask_docjson.GrammarError: Raised when a grammar error occurred.
• flask_docjson.ValidationError: Raised when some request or response data is invalid.
• flask_docjson.RequestValidationError: Raised some when request data is invalid.
• flask_docjson.ResponseValidationError: Raised some when response data is invalid.

Error is the base exception. ParserError only occurrs on flask app bootstrap, it won't be raised during processing requests.

ValidationError should be catched manually, we recommend to use the flask built-in decorator app.errorhandler. And we can also get code, reason and related value from a ValidationError instance:

@app.errorhandler(flask_docjson.ValidationError)
def on_validatino_error(err):
    return jsonify(message='Validation error:{0} {1} on {2}'.format(err.code, err.reason, err.value)), 400

Language Description

• Document: Schema ::= Request Response*.
• Request: Request ::= Method* Route JsonSchema
• Response: Response ::= StatusCode* JsonSchema
• Method: Method ::= POST|PUT|GET|DELETE|PATCH|HEAD|OPTIONS. Method separator is /.
• Route: Route ::= StaticRoute* RouteVar* StaticRoute*. e.g. /user/<i32:id>
• StatusCode: StatusCode ::= Integer|Matcher. e.g. 200, 4XX
• JsonSchema: JsonSchema ::= Array | Object.
• Array: Array ::= '[' Value* | Value* '...' ']'
• Object: Object ::= '{' KeyValue* '}'
• KeyValue: KeyValue ::= Key ':' Value
• Value: Array ::= BaseType | Array | Object

License

BSD.