zswag 1.2.0rc0

OpenAPI service transport layer for zserio.

Zswag

zswag is a set of libraries for using/hosting zserio services through OpenAPI.

Table of Contents:

• Components

• Setup

  • For Python Users

  • For C++ Users

• OpenAPI Generator CLI

  • Generator Usage Example

  • Documentation extraction

• Server Component (Python)

• Using the Python Client

• C++ Client

• Client Environment Settings

• HTTP Proxies and Authentication

• Swagger User Interface

• OpenAPI Options Interoperability

  • HTTP method

  • Request Body

  • URL Blob Parameter

  • URL Scalar Parameter

  • URL Array Parameter

  • URL Compound Parameter

  • Server URL Base Path

  • Authentication Schemes

Components

The zswag repository contains two main libraries which provide

OpenAPI layers for zserio Python and C++ clients. For Python, there

is even a generic zserio OpenAPI server layer.

The following UML diagram provides a more in-depth overview:

Here are some brief descriptions of the main components:

• zswagcl is a C++ Library which exposes the zserio OpenAPI service client OAClient

  as well as the more generic OpenApiClient and OpenApiConfig classes.

  The latter two are reused for the Python client library.

• zswag is a Python Library which provides both a zserio Python service client

  (OAClient) as well as a zserio-OpenAPI server layer based on Flask/Connexion

  (OAServer). It also contains the command-line tool zswag.gen, which can be

  used to generate an OpenAPI specification from a zserio Python service class.

• pyzswagcl is a binding library which exposes the C++-based OpenApi

  parsing/request functionality to Python. Please consider it "internal".

• httpcl is a wrapper around cpp-httplib,

  HTTP request configuration and OS secret storage abilities based on

  the keychain library.

Setup

For Python Users

Simply run pip install zswag. Note: This only works with ...

• 64-bit Python 3.8.x, pip --version >= 19.3

• 64-bit Python 3.9.x, pip --version >= 19.3

Note: On Windows, make sure that you have the Microsoft Visual C++ Redistributable Binaries installed. You can find the x64 installer here: https://aka.ms/vs/16/release/vc_redist.x64.exe

For C++ Users

Using CMake, you can ...

• 🌟run tests.

• 🌟build the zswag wheels for a custom Python version.

• 🌟integrate the C++ client into a C++ project.

The basic setup follows the usual CMake configure/build steps:

mkdir build && cd build

cmake ..

cmake --build .

Note: The Python environment used for configuration will be used

to build the resulting wheels. After building, you will find the Python

wheels under build/bin/wheel.

To run tests, just execute CTest at the top of the build directory:

cd build && ctest --verbose

OpenAPI Generator CLI

After installing zswag via pip as described above,

you can run python -m zswag.gen, a CLI to generate OpenAPI YAML files.

The CLI offers the following options

usage: Zserio OpenApi YAML Generator [-h] -s service-identifier -i

                                     zserio-or-python-path

                                     [-p top-level-package] [-c tags [tags ...]]

                                     [-o output] [-b BASE_CONFIG_YAML]



optional arguments:

  -h, --help

        show this help message and exit

  -s service-identifier, --service service-identifier



        Fully qualified zserio service identifier.



        Example:

            -s my.package.ServiceClass



  -i zserio-or-python-path, --input zserio-or-python-path



        Can be either ...

        (A) Path to a zserio .zs file.

        (B) Path to parent dir of a zserio Python package.



        Examples:

            -i path/to/schema/main.zs         (A)

            -i path/to/python/package/parent  (B)



  -p top-level-package, --package top-level-package



        When -i specifies a zs file (Option A), indicate

        that a top-level zserio package name should be used.



        Examples:

            -p zserio_pkg_name



  -c tags [tags ...], --config tags [tags ...]



        Configuration tags for a specific or all methods.

        The argument syntax follows this pattern:



           [(service-method-name):](comma-separated-tags)



        Note: The -c argument may be applied multiple times.

        The `comma-separated-tags` must be a list of tags

        which indicate OpenApi method generator preferences.

        The following tags are supported:



        get|put|post|delete : HTTP method tags

                query|path| : Parameter location tags

                header|body

                  flat|blob : Flatten request object,

                              or pass it as whole blob.

          (param-specifier) : Specify parameter name, format

                              and location for a specific

                              request-part. See below.

            security=(name) : Set a particular security

                              scheme to be used. The scheme

                              details must be provided through

                              the --base-config-yaml.

         path=(method-path) : Set a particular method path.

                              May contain placeholders for

                              path params.



        A (param-specifier) tag has the following schema:



            (field?name=...

                  &in=[path|body|query|header]

                  &format=[binary|base64|hex]

                  [&style=...]

                  [&explode=...])



        Examples:



          Expose all methods as POST, but `getLayerByTileId`

          as GET with flat path-parameters:



            `-c post getLayerByTileId:get,flat,path`



          For myMethod, put the whole request blob into the a

          query "data" parameter as base64:



            `-c myMethod:*?name=data&in=query&format=base64`



          For myMethod, set the "AwesomeAuth" auth scheme:



            `-c myMethod:security=AwesomeAuth`



          For myMethod, provide the path and place myField

          explicitely in a path placeholder:



            `-c 'myMethod:path=/my-method/{param},...

                 myField?name=param&in=path&format=string'`



        Note:

            * The HTTP-method defaults to `post`.

            * The parameter 'in' defaults to `query` for

              `get`, `body` otherwise.

            * If a method uses a parameter specifier, the

              `flat`, `body`, `query`, `path`, `header` and

              `body`-tags are ignored.

            * The `flat` tag is only meaningful in conjunction

              with `query` or `path`.

            * An unspecific tag list (no service-method-name)

              affects the defaults only for following, not

              preceding specialized tag assignments.



  -o output, --output output



        Output file path. If not specified, the output will be

        written to stdout.



  -b BASE_CONFIG_YAML, --base-config-yaml BASE_CONFIG_YAML



        Base configuration file. Can be used to fully or partially

        substitute --config arguments, and to provide additional

        OpenAPI information. The YAML file must look like this:



          method: # Optional method tags dictionary

            <method-name|*>: <list of config tags>

          securitySchemes: ... # Optional OpenAPI securitySchemes

          info: ...            # Optional OpenAPI info section

          servers: ...         # Optional OpenAPI servers section

          security: ...        # Optional OpenAPI global security

Generator Usage example

Let's consider the following zserio service saved under myapp/services.zs:

package services;



struct Request {

  int32 value;

};



struct Response {

  int32 value;

};



service MyService {

  Response myApi(Request);

};

An OpenAPI file api.yaml for MyService can now be

created with the following zswag.gen invocation:

cd myapp

python -m zswag.gen -s services.MyService -i services.zs -o api.yaml

You can further customize the generation using -c configuration

arguments. For example, -c get,flat,path will recursively "flatten"

the zserio request object into it's compound scalar fields using

x-zserio-request-part for all methods.

If you want to change OpenAPI parameters only for one particular

method, you can prefix the tag config argument with the method

name (-c methodName:tags...).

Documentation Extraction

When invoking zswag.gen with -i zserio-file an attempt

will be made to populate the service/method/request/response

descriptions with doc-strings that are extracted from the zserio

sources.

For structs and services, the documentation is expected to be

enclosed by /*! .... !*/ markers preceding the declaration:

/*!

### My Markdown Struct Doc

I choose to __highlight__ this word.

!*/



struct MyStruct {

    ...

};

For service methods, a single-line doc-string is parsed which

immediately precedes the declaration:

/** This method is documented. */

ReturnType myMethod(ArgumentType);

Server Component

The OAServer component gives you the power to marry a zserio-generated app

server class with a user-written app controller and a fitting OpenAPI specification.

It is based on Flask and

Connexion.

Integration Example

We consider the same myapp directory with a services.zs zserio file

as already used in the OpenAPI Generator Example.

Note:

• myapp must be available as a module (it must be

possible to import myapp).

• We recommend to run the zserio Python generator invocation

  inside the myapp module's __init__.py, like this:

import zserio

from os.path import dirname, abspath



working_dir = dirname(abspath(__file__))

zserio.generate(

  zs_dir=working_dir,

  main_zs_file="services.zs",

  gen_dir=working_dir)

A server script like myapp/server.py might then look as follows:

import zswag

import myapp.controller as controller

from myapp import working_dir



# This import only works after zserio generation.

import services.api as services



app = zswag.OAServer(

  controller_module=controller,

  service_type=services.MyService.Service,

  yaml_path=working_dir+"/api.yaml",

  zs_pkg_path=working_dir)



if __name__ == "__main__":

    app.run()

The server script above references two important components:

• An OpenAPI file (myapp/api.yaml): Upon startup, OAServer

  will output an error message if this file does not exist. The

  error message already contains the correct command to

  invoke the OpenAPI Generator CLI

  to generate myapp/api.yaml.

• A controller module (myapp/controller.py): This file provides

  the actual implementations for your service endpoints.

For the current example, controller.py might look as follows:

import services.api as services



# Written by you

def my_api(request: services.Request):

    return services.Response(request.value * 42)

Using the Python Client

The generic Python client talks to any zserio service that is running

via HTTP/REST, and provides an OpenAPI specification of it's interface.

Integration Example

As an example, consider a Python module called myapp which has the

same myapp/__init__.py and myapp/services.zs zserio definition as

previously mentioned. We consider

that the server is providing its OpenAPI spec under localhost:5000/openapi.json.

In this setting, a client myapp/client.py might look as follows:

from zswag import OAClient

import services.api as services



openapi_url = "http://localhost:5000/openapi.json"



# The client reads per-method HTTP details from the OpenAPI URL.

# You can also pass a local file by setting the `is_local_file` argument

# of the OAClient constructor.

client = services.MyService.Client(OAClient(openapi_url))



# This will trigger an HTTP request under the hood.

client.my_api(services.Request(1))

As you can see, an instance of OAClient is passed into the constructor

for zserio to use as the service client's transport implementation.

Note: While connecting, the client will also use ...

1. Persistent HTTP configuration.

2. Additional HTTP query/header/cookie/proxy/basic-auth configs passed

   into the OAClient constructor using an instance of zswag.HTTPConfig.

   For example:

   from zswag import OAClient, HTTPConfig
   
   import services.api as services
   
   config = HTTPConfig() \
   
       .header(key="X-My-Header", val="value") \  # Can be specified 
   
       .cookie(key="MyCookie", val="value")    \  # multiple times.
   
       .query(key="MyCookie", val="value")     \  # 
   
       .proxy(host="localhost", port=5050, user="john", pw="doe") \
   
       .basic_auth(user="john", pw="doe") \
   
       .bearer("bearer-token") \
   
       .api_key("token")
   
   
   
   client = services.MyService.Client(
   
       OAClient("http://localhost:8080/openapi.", config=config))
   
   
   
   # Alternative when specifying api-key or bearer
   
   client = services.MyService.Client(
   
       OAClient("http://localhost:8080/openapi.", api_key="token", bearer="token"))
   

   Note: The additional config will only enrich, not overwrite the

   default persistent configuration. If you would like to prevent persistent

   config from being considered at all, set HTTP_SETTINGS_FILE to empty,

   e.g. via os.environ['HTTP_SETTINGS_FILE']=''

C++ Client

The generic C++ client talks to any zserio service that is running

via HTTP/REST, and provides an OpenAPI specification of its interface.

When using the C++ OAClient with your zserio schema, make sure

that the flag -withTypeInfoCode is passed to the zserio C++ emitter.

Integration Example

As an example, we consider the myapp directory which contains a services.zs

zserio definition as previously mentioned.

We assume that zswag is added to myapp as a Git submodule

under myapp/zswag.

Next to myapp/services.zs, we place a myapp/CMakeLists.txt which describes our project:

project(myapp)



# This is how C++ will know about the zswag lib

# and its dependencies, such as zserio.

add_subdirectory(zswag)



# This command is provided by zswag to easily create

# a CMake C++ reflection library from zserio code.

add_zserio_library(${PROJECT_NAME}-zserio-cpp

  WITH_REFLECTION

  ROOT "${CMAKE_CURRENT_SOURCE_DIR}"

  ENTRY services.zs

  TOP_LEVEL_PKG myapp_services)



# We create a myapp client executable which links to

# the generated zserio C++ library and the zswag client

# library.

add_executable(${PROJECT_NAME} client.cpp)

target_link_libraries(${PROJECT_NAME}

    ${PROJECT_NAME}-zserio-cpp zswagcl)

The add_executable command above references the file myapp/client.cpp,

which contains the code to actually use the zswag C++ client.

#include "zswagcl/oaclient.hpp"

#include <iostream>

#include "myapp_services/services/MyService.h"



using namespace zswagcl;

using namespace httpcl;

using MyService = myapp_services::services::MyService;



int main (int argc, char* argv[])

{

    // Assume that the server provides its OpenAPI definition here

    auto openApiUrl = "http://localhost:5000/openapi.json";

    

    // Create an HTTP client to be used by our OpenAPI client

    auto httpClient = std::make_unique<HttpLibHttpClient>();

    

    // Fetch the OpenAPI configuration using the HTTP client

    auto openApiConfig = fetchOpenAPIConfig(specUrl, *httpClient);

    

    // Create a Zserio reflection-based OpenAPI client that

    // uses the OpenAPI configuration we just retrieved.

    auto openApiClient = OAClient(openApiConfig, std::move(httpClient));

        

    // Create a MyService client based on the OpenApi-Client

    // implementation of the zserio::IServiceClient interface.

    auto myServiceClient = MyService::Client(openApiClient);

    

    // Create the request object

    auto request = myapp_services::services::Request(2);



    // Invoke the REST endpoint. Mind that your method-

    // name from the schema is appended with a "...Method" suffix.

    auto response = myServiceClient.myApiMethod(request);

    

    // Print the response

    std::cout << "Got " << response.getValue() << std::endl;

}

Note: While connecting, HttpLibHttpClient will also use ...

1. Persistent HTTP configuration.

2. Additional HTTP query/header/cookie/proxy/basic-auth configs passed

   into the OAClient constructor using an instance of httpcl::Config.

   You can include this class via #include "httpcl/http-settings.hpp".

   The additional Config will only enrich, not overwrite the

   default persistent configuration. If you would like to prevent persistent

   config from being considered at all, set HTTP_SETTINGS_FILE to empty,

   e.g. via setenv.

Client Environment Settings

Both the Python and C++ Clients can be configured using the following

environment variables:

| Variable Name | Details |

| ------------- | --------- |

| HTTP_SETTINGS_FILE | Path to settings file for HTTP proxies and authentication, see next section |

| HTTP_LOG_LEVEL | Verbosity level for console/log output. Set to debug for detailed output. |

| HTTP_LOG_FILE | Logfile-path (including filename) to redirect console output. The log will rotate with three files (HTTP_LOG_FILE, HTTP_LOG_FILE-1, HTTP_LOG_FILE-2). |

| HTTP_LOG_FILE_MAXSIZE | Maximum size of the logfile, in bytes. Defaults to 1GB. |

| HTTP_TIMEOUT | Timeout for HTTP requests (connection+transfer) in seconds. Defaults to 60s. |

| HTTP_SSL_STRICT | Set to any nonempty value for strict SSL certificate validation. |

Persistent HTTP Headers, Proxy, Cookie and Authentication

Both the Python OAClient and C++ HttpLibHttpClient read a YAML file

stored under a path which is given by the HTTP_SETTINGS_FILE environment

variable. The YAML file contains a list of HTTP-related configs that are

applied to HTTP requests based on a regular expression which is matched

against the requested URL.

For example, the following entry would match all requests due to the .*

url-match-pattern:

- url: .*

  basic-auth:

    user: johndoe

    keychain: keychain-service-string

  proxy:

    host: localhost

    port: 8888

    user: test

    keychain: ...

  cookies:

    key: value

  headers:

    key: value

  query:

    key: value

  api-key: value

Note: For proxy configs, the credentials are optional.

The api-key setting will be applied under the correct

cookie/header/query parameter, if the service

you are connecting to uses an OpenAPI apiKey auth scheme.

Passwords can be stored in clear text by setting a password field instead

of the keychain field. Keychain entries can be made with different tools

on each platform:

• Linux secret-tool

• macOS add-generic-password

• Windows cmdkey

Swagger User Interface

If you have installed pip install "connexion[swagger-ui]", you can view

API docs of your service under [/prefix]/ui.

OpenAPI Options Interoperability

The Server, Clients and Generator offer various degrees of freedom

regarding the OpenAPI YAML file. The following sections detail which

components support which aspects of OpenAPI. The difference in compliance

is mostly due to limited development scopes. If you are missing a particular

OpenAPI feature for a particular component, feel free to create an issue!

Note: For all options that are not supported by zswag.gen, you

will need to manually edit the OpenAPI YAML file to achieve the desired

configuration. You will also need to edit the file manually to fill in

meta-info (provider name, service version, etc.).

HTTP method

To change the HTTP method, the desired method name is placed

as the key under the method path, such as in the following example:

paths:

  /methodName:

    {get|post|put|delete}:

      ...

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| get post put delete | ✔️ | ✔️ | ✔️ | ✔️ |

| patch | ❌️ | ❌️ | ❌️ | ❌️ |

Note: Patch is unsupported, because the required semantics of

a partial object update cannot be realized in the zserio transport

layer interface.

Request Body

A server can instruct clients to transmit their zserio request object in the

request body when using HTTP post, put or delete.

This is done by setting the OpenAPI requestBody/content to

application/x-zserio-object:

requestBody:

  content:

    application/x-zserio-object:

      schema:

        type: string

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| application/x-zserio-object | ✔️ | ✔️ | ✔️ | ✔️ |

URL Blob Parameter

Zswag tools support an additional OpenAPI method parameter

field called x-zserio-request-part. Through this field,

a service provider can express that a certain request parameter

only contains a part of, or the whole zserio request object.

When parameter contains the whole request object, x-zserio-request-part

should be set to an asterisk (*):

parameters:

- description: ''

  in: query|path|header

  name: parameterName

  required: true

  x-zserio-request-part: "*"

  schema:

    format: string|byte|base64|base64url|hex|binary

About the format specifier value:

• Both string and binary result in a raw URL-encoded string buffer.

• Both byte and base64 result in a standard Base64-encoded value.

  The base64url option indicates URL-safe Base64 format.

• The hex encoding produces a hexadecimal encoding of the request blob.

Note: When a parameter is passed with in=path, its value

must not be empty. This holds true for strings and bytes,

but also for arrays (see below).

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| x-zserio-request-part: * | ✔️ | ✔️ | ✔️ | ✔️ |

| format: string | ✔️ | ✔️ | ✔️ | ✔️ |

| format: byte | ✔️ | ✔️ | ✔️ | ✔️ |

| format: hex | ✔️ | ✔️ | ✔️ | ✔️ |

URL Scalar Parameter

Using x-zserio-request-part, it is also possible to transfer

only a single scalar (nested) member of the request object:

parameters:

- description: ''

  in: query|path|header

  name: parameterName

  required: true

  x-zserio-request-part: "[parent.]*member"

  schema:

    format: string|byte|base64|base64url|hex|binary

In this case, x-zserio-request-part should point to a scalar type,

such as uint8, float32, string etc.

The format value effect remains as explained above. A small

difference exists for integer types: Their hexadecimal representation

will be the natural numeric one, not binary.

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| x-zserio-request-part: <[parent.]*member> | ✔️ | ✔️ | ✔️ | ✔️ |

URL Array Parameter

The x-zserio-request-part may also point to an array member of

the zserio request struct, like so:

parameters:

- description: ''

  in: query|path|header

  style: form|simple|label|matrix

  explode: true|false

  name: parameterName

  required: true

  x-zserio-request-part: "[parent.]*array_member"

  schema:

    format: string|byte|base64|base64url|hex|binary

In this case, x-zserio-request-part should point to an array of

scalar types. The array will be encoded according

to the format, style and explode

specifiers.

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| x-zserio-request-part: <[parent.]*array_member> | ✔️ | ✔️ | ✔️ | ✔️ |

| style: simple | ✔️ | ✔️ | ✔️ | ✔️ |

| style: form | ✔️ | ✔️ | ✔️ | ✔️ |

| style: label | ✔️ | ✔️ | ❌ | ✔️ |

| style: matrix | ✔️ | ✔️ | ❌ | ✔️ |

| explode: true | ✔️ | ✔️ | ✔️ | ✔️ |

| explode: false | ✔️ | ✔️ | ✔️ | ✔️ |

URL Compound Parameter

In this case, x-zserio-request-part points to a zserio compound struct

instead of a field with a scalar value. This is currently not supported.

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| x-zserio-request-part: <[parent.]*compound_member> | ❌️ | ❌️ | ❌️ | ❌️ |

Server URL Base Path

OpenAPI allows for a servers field in the spec that lists URL path prefixes

under which the specified API may be reached. The OpenAPI clients

looks into this list to determine a URL base path from

the first entry in this list. A sample entry might look as follows:

servers:

- http://unused-host-information/path/to/my/api

The OpenAPI client will then call methods with your specified host

and port, but prefix the /path/to/my/api string.

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| servers | ✔️ | ✔️ | ✔️ | ✔️ |

Authentication Schemes

To facilitate the communication of authentication needs for the whole or parts

of a service, OpenAPI allows for securitySchemes and security fields in the spec.

Please refer to the relevant parts of the OpenAPI 3 specification for some

examples on how to integrate these fields into your spec.

Zswag currently understands the following authentication schemes:

• HTTP Basic Authorization: If a called endpoint requires HTTP basic auth,

  zswag will verify that the HTTP config contains basic-auth credentials.

  If there are none, zswag will throw a descriptive runtime error.

• HTTP Bearer Authorization: If a called endpoint requires HTTP bearer auth,

  zswag will verify that the HTTP config contains a header with the

  key name Authorization and the value Bearer <token>, case-sensitive.

• API-Key Cookie: If a called endpoint requires a Cookie API-Key,

  zswag will either apply the api-key setting, or verify that the

  HTTP config contains a cookie with the required name, case-sensitive.

• API-Key Query Parameter: If a called endpoint requires a Query API-Key,

  zswag will either apply the api-key setting, or verify that the

  HTTP config contains a query key-value pair with the required name, case-sensitive.

• API-Key Header: If a called endpoint requires an API-Key Header,

  zswag will either apply the api-key setting, or verify that the

  HTTP config contains a header key-value pair with the required name, case-sensitive.

Note: If you don't want to pass your Basic-Auth/Bearer/Query/Cookie/Header

credential through your persistent config,

you can pass a httpcl::Config/HTTPConfig object to the OAClient/OAClient.

constructor in C++/Python with the relevant detail.

Component Support

| Feature | C++ Client | Python Client | OAServer | zswag.gen |

| ------------------ | ---------- | ------------- | -------- | --------- |

| HTTP Basic-Auth HTTP Bearer-Auth Cookie API-Key Header API-Key Query API-Key | ✔️ | ✔️ | ✔️(**) | ✔️ |

| OpenID Connect OAuth2 | ❌️ | ❌️ | ✔️(**) | ❌️ |

(**): The server support for all authentication schemes depends on your

configuration of the WSGI server (Apache/Nginx/...) which wraps the zswag Flask app.