Arrest

---

• Documentation: https://s-bose.github.io/arrest/

Enable data validation for REST APIs.

Arrest is an HTTP client library with an easy and declarative way of defining, managing, and calling RESTful HTTP APIs with type validation, retries, exception handling, and other batteries included.

Arrest lets you define your RESTful APIs in a simple encapsulation that takes care of the following:

1. Type validation for HTTP request and response data
2. HTTP request retries
3. Manage your services definitions in one place
4. Exception handling
5. Hooks for custom exceptions
6. Callbacks
7. Automatic code generation from OpenAPI Schema

Contents

1. Installation
2. Getting Started
3. Examples
4. Contributing
5. Roadmap

Installation

Using pip

pip install arrest

Using poetry

poetry add arrest

Using uv

uv add arrest

Getting Started

Assuming you already have arrest installed in your system, let us create a simple connection. We have a REST endpoint htthttps://www.xyz-service.default.local.cluster/api/v1 which has a resource /users with method GET.

import logging
from arrest import Resource, Service
from arrest.exceptions import ArrestHTTPException


xyz_service = Service(
    name="xyz",
    url="https://www.xyz-service.default.local.cluster/api/v1",
    resources=[
        Resource(
            route="/users",
            handlers=[
                ("GET", "/"),
                ("GET", "/{user_id:int}"),
                ("POST", "/")
            ]
        )
    ]
)

try:
    response = await xyz_service.users.get("/123")
except ArrestHTTPException as exc:
    logging.warning(f"{exc.status_code} {exc.data}")

This will make an HTTP GET request to https://www.xyz-service.default.local.cluster/api/v1/users/123.

You can also provide a request type for your handlers. This can be done by passing a third entry to your handler tuple containing the pydantic class, or pass it directly to the handler dict or ResourceHandler initialization.

from pydantic import BaseModel

class UserRequest(BaseModel):
    name: str
    email: str
    password: str
    role: str

Resource(
    route="/users,
    handlers=[
        ("POST", "/", UserRequest) # or ResourceHandler(method="POST", route="/", request=UserRequest)
                                   # or {"method": "POST", "route": "/", "request": UserRequest}
    ]
)

await service.users.post("/", request={
    "name": "John Doe",
    "email": "[email protected]",
    "password": "secret",
    "role": "admin"
    }
)

This gets automatically validated and parsed as UserRequest before sending the request payload to the server. If any validation error is raised the request won't go.

Similar to request, you can pass an additional fourth argument in the handler tuple for specifying a pydantic model for the handler. If provided it will automatically deserialize the returned success json response into either a model instance or a list of model instances.

class UserResponse(BaseModel):
    name: str
    email: str
    role: str
    created_at: datetime
    updated_at: datetime
    is_deleted: bool

Resource(
    route="/user",
    handlers=[
        ("GET", "/{user_id}", None, UserResponse), # if no request type to be supplied, leave it as `None`
    ]
)

user_id = "123"
response = await svc.user.get(f"/{user_id}") # type: UserResponse

Here, the JSON response from https://www.xyz-service.default.local.cluster/api/v1/users/123 will be deserialized into UserResponse model instance.

For more info, please check the docs

Examples

You can check out the example folder under the project repository to get a feel of how to use Arrest.

The example_service contains a minimal FastAPI application for task management with CRUD endpoints for users and tasks.

To generate the Arrest boilerplate from the OpenAPI specs, simply run the FastAPI application using uvicorn at http://127.0.0.1:8080/docs, and run the arrest CLI as followed:

$ arrest -u http://localhost:8080/openapi.json -d example_service

This will generate models.py, containing the Pydantic schemas corresponding to the OpenAPI components, a resources.py containing the RESTful resource definitions and a services.py containing the service definition that includes the resources.

To use the service, simply call example_service.users.get("").

Contributing

Please see the CONTRIBUTING.md for more information.

Roadmap

Arrest is under active development. Listed below are a few ideas for the next release. Any sort of contribution towards them is very much welcome.

1. Support for non-JSON request and response types.

Arrest is currently limited by its strict requirement of the APIs being JSON compliant. The following types would be supported in the next release:

• FormData requests

from arrest.types import FormData

class UserForm(FormData):
    username: str
    password: str

• UrlEncoded requests

  from arrest.types import UrlEncoded
  
  class UserRegister(UrlEncoded):
      email: str
      password: str

• XML responses

from pydantic import Field
from arrest.types import XMLResponse

class UserResponse(XMLResponse):
    id: str
    username: str
    email: str
    role: str = Field(alias="@role")

For requests, I think its beneficial to have types for application/form-data and application/x-www-form-urlencoded with the added parsing and validation of Pydantic. FormData and UrlEncoded classes themselves will be inherited from pydantic.BaseModel.

For responses, it would be nice to have a way to parse the XML response into some sort of data model, because you most probably would always do that (unless you like working with raw strings). XMLResponse is similarly inherited from pydantic.BaseModel. If you use just XMLResponse in declaring your handler response type, the response will automatically be converted into a python dictionary.

• As of now, I have no plans for making a request type for XML. But what would be a better alternative is the ability to do something like this:

from arrest import Resource
from arrest.types import XMLResponse

user = Resource(
    route="/users",
    handlers=[
        ("POST", "/user_data", str, XMLResponse)
    ]
)


user_data = """<User>
    <Id>123</Id>
    <Name>John</Name>
    <Email>john@email</Email>
    <Role>admin</Role>
</User>"""

response = await service.user.post("/user_data", data=user_data, headers={"Content-Type": "application/xml"})

assert response == {"Id": "123", "Name": "John", "Email": "john@email", "Role": "admin"}

The problem with using a data model for XML requests is the fact that the deserialization of the model might not always produce an XML string that conforms to the expected schema.

However, I would encourage anyone who has any idea about any of this, or a better way to support these types, to open an issue and start a discussion.