Type casting

The first argument of the function decorated by @broker.handle is the decrypted body of the incoming message.

Incoming message body can be of three types:

• str - if the message has the header content-type: text/plain
• dict - if the message has the header content-type: application/json
• bytes - if the message has any other header

Either these types can be used as an annotation, or any primitive types to which pydantic can cast incoming arguments (for example, str -> float).

A few examples:

text/plain

@broker.handle("test")
async def base_handler(body: str):
    '''
    We are expecting a text/plain message
    Messages of a different kind will raise an error
    '''

application/json

@broker.handle("test")
async def base_handler(body: dict):
    '''
    We are expecting an application/json message
    Messages of a different kind will raise an error
    '''

Any type

@broker.handle("test")
async def base_handler(body: bytes):
    '''
    We are expecting a 'raw' message
    Messages of a different kind will raise an error
    '''

Pydantic

Also, if you use a pydantic object as the type annotation, Propan will also result in an incoming message of this kind, if possible:

from pydantic import BaseModel

class Message(BaseModel):
    key: float

@broker.handle("test")
async def base_handler(body: Message):
    '''
    We are expecting an application/json message
    Type { key: 1.0 }
    Messages of a different kind will raise an error
    '''

Multiple arguments

When annotating multiple incoming arguments, the result will be equivalent to using a similar `pydantic' model.

from pydantic import BaseModel

class Message(BaseModel):
    a: int
    b: float

@broker.handle("test")
async def base_handler(a: int, b: float):
# async def base_handler(body: Message): - equivalent to using separate parameters
    '''
    We are expecting an application/json message
    Type { a: 1, b: 1.0 }
    Messages of a different kind will raise an error
    '''