defining ‘UJMW’ (a message wrapper format for JSON based webservice calls)

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Do you implement WebAPIs which are NOT located on the persistence layer and therefore NOT focused on doing CRUD operations?

Then you should avoid to implement them as a ‘RESTful’ api, cause this makes no sense. Some HTTP-based APIs having a ‘call-based’ approach to known BL operations.

IN-, OUT- and return-arguments should not be transmitted over the URL. Instead you need to use request-/response- wrappers, which are very lightweight and are a compromise for broad support and adaptability in REST-inspired technologies as well as soap-inspired technologies – so lets see the definition document:

Motivation:

The world divides between two approaches. One is the idea of invoking a service-method on server side - we know this under the name Remote-Procedure-Call (RPC). The other idea is completely focused on the use cases, that are relevant to Create, Read, Update or Delete objects (formally known as CRUD-Operations), as they are seen in the role as a Data-Record over an repository.

In our meaning, REST is based on ideas, that are dead. What we mean specifically is the use of HTTP verbs (Get, Put, Post, Delete) to represent the CRUD operations! Also often mentioned is the alleged reliability that you always receive the same response via GET. Personally, i don't know of a single REST interface that does this cleanly. The mere fact that it is so incredibly widespread is no proof of the wisdom of continuing to rely on this horse in today's world. It actually uses the http protocol in exactly the way it was last 'planned', but the world has moved on. The demands regarding ever new security mechanisms on the web, firewalls, proxies and load balancing aspects have permanently affected the http transport layer. The layer is now definitely too deep to mix the use cases of the repository access level with it.

A second problem with REST is, that it is not really scalable. The hard patterns for the urls (containing the record ids) makes problems when using composite-keys. Pagination-Support or advanced Filtering scenarios were completely ignored during the design phase. At the end, GraphQL is the proof of the truth of all this.

But at least we still see any CRUD operations implicitly as a procedure call. This means that there can be standards for access to uniform repository services, but the problem domain of CRUD must have NOTHING to do with transport technology!

So the question is now: What RPC-Protocol is the best?

Ok - forget SOAP (we gonna skip this instead of writing a book of complexity here -> use Google, if you are still a fan of SOAP)

Using JSON-Serialization is state-of-the-art. Now we just wanted to have a very-very lightweight and smart standard :-), to declare the so-called "Message-Wrapper" It is just the root-object, which is invisible for the BL programmer and just existing to bundle the method-parameters for the procedure call.

Yes, we know that there are other standards (like JsonRpc, gRpc, ...), but for all of them we've found some issues when using them vanilla.

So we've designed this specification:

Transporting Arguments

Each request and response must have the wrapper object as json-root containing named Arguments as properties.

The wrapper capsule is ALWAYS required, also if there is none or just one argument

{
    "myNamedParam1": ...,
    "myNamedParam2": ...,
}

Naming:

DataTypes

Type Convention Sample
Date / Time must be in ISO8601 Format + should be UTC 2020-06-15T13:45:30.0000000Z
Byte[] / Binary must be in Base64 TWFuIGlzIGRpc3Rpbmd==
Numeric values must not have 1000-separator-chars + must have the char "." for separating the decimal places 123433454.23

Encoding

The "return"-Property

"return" is a constant name which is magic-value between the other argument Names. It represents the return-value of this Function, which is invoked. 

{
    "return": ...
}

VOID-Methods

If a VOID (a Method without a return-value) is invoked, the result-wrapper must not contain a "return" property. A "return"-property with a null-value is NOT allowed in this case, because this is reserved for Functions returning a null-value.

Why "return" instead of "result"

We never use "result" here because assuming that an return-value would have the semantic to be the "result" of an operation is highly BL-related and needs to be specified within the service-contract (using argument or method-names or comments) instead of the transport layer. "return" has the maximum level abstraction and is exactly right for this layer!

"Out"-Arguments

Same way as in arguments - a VOID which has only IN/OUT arguments will have exactly the same response-wrapper as the request-wrapper.

The "fault"-Property

Is also a constant name which is magic-value representing an Exception. This means, that only response-wrappers can contain a "fault" Property AND if it is exists, no other properties have to exist!

{
    "fault": "message"
}

Please note that the "fault"-Property should only used for critical, non-business Errors - like Exceptions. All regular possible failures of the executed operation should be transferred over other channels. For that were recommending the "returnCode"-Pattern as described below (maybe in combination with the "lastError" - SideChannel. Nevertheless also Exceptions from our BL should not affect the transport-layer technology. However, even exceptions from the BL should not affect the transport layer technology, and because of this, the usage of the fault-Property MUST NOT be accompanied by an http-response code other than 200!

The "returnCode"-Pattern

This is just a propose for using an OUT-Arg which usually should have a name like "returnCode" to do something like a Try...Methods (in some Languages). In this case were not blocking the primary "return" value just for delivering an information about the success of a invoked method.

  • The code does not have a dedicated semantic to always be an error - so it must not be called "errorCode"!

  • If an returnCode was delivered, which indicated an error, then some additional details can be placed within the "lastError"-SideChannel (as described below)

File/Binary transfers

There is an exception (coming with version 1.1) in which the use of a JSON wrapper should not be used. Whenever files need to be transferred! Here we want to stick as closely as possible to the traditional transmission methods, as this has some advantages if the client component is a single page application in the browser. On the server side, it also makes sense that files do not end up in RAM as byte[], but rather the streaming support of the respective transport technology (if available) can in principle be used.

So we now define method conventions, if they apply, the UJMW layers should automatically choose a different form of transmission:

downloads a simple byte-stream response (=classic browser download) and uploads in the form of a ['multipart/form-data'](https://stackoverflow.com/questions/8659808/how-does-http-file-upload -work) posts take place.

Convention for downloads (in C#)

Is fulfilled/activated by using the type 'Stream' as the return type, thereby enacting the following behavior:

  • There may (optionally) be an OUT parameter named 'fileName' of type string

  • There may (optionally) be an OUT parameter named 'fileContentType' of type string

  • Additional OUT or REF parameters are prohibited

  • The handling of IN parameters remains unaffected and can take place through a request with the JSON wrapper

Convention for uploads (in C#)

Is fulfilled/activated by using the Stream type as the type for at least one IN parameter, thereby enacting the following behavior:

  • Additional IN parameters that are not of the 'Stream' type are exceptionally transferred as query parameters within the URL

  • Any IN parameters that are of type 'Stream' each represent a file to be uploaded

  • IN parameters of the string type can bind additional information for one file at a time using a further convention (well-known names): the Parameter name corresponds to the pattern <name-of-the-corresponding-Steam-Paramter>ContentType (=ContentType of that file) OR <name-of-the-corresponding-Steam-Parameter>Name (=Name of that file) these are automatically transmitted by the transport layer via the relevant transport protocols (body/headers).

Side-Channels

This part is optional within the wrapper!

To avoid conflicts with the regular arguments, we need a sub-structure which is placed within a property named "_" (also a magic-value).

{
    "_": {
      "myAdditionalData": ...,
    },
}

'Ambience' is a very complex concern, so that we cant give a full introduction here. It relates to 'aspect orientation' (AOP) and 'contextual' programming principles. Our SmartAmbience Library will provide convenience for that and can easy be coupled with the UJMW side channel.

About the Tooling

Clients

for .NET Framework & .NET core

IS STABLE (see '/dotnet/UJMW.sln') The NuGet-Package ID is 'UJMW.DynamicClient'

for JavaScript / TypeScript

IS COMMING SOON The NPM-Package ID is 'UJMW.DynamicClient'

Server Facades

A Dynamic ServiceHost Factory for WCF (.NET fx 461)

IS STABLE (see '/dotnet/UJMW.sln' ) - a Demo-Service is also included... The NuGet-Package ID is 'UJMW.DynamicWcfHost' 

<system.serviceModel>
  <serviceHostingEnvironment aspNetCompatibilityEnabled="false" multipleSiteBindingsEnabled="true" >
    <serviceActivations>
      <add relativeAddress="YourService.svc" service="TheNamespace.YourService, AssName"
           factory="System.Web.UJMW.UjmwServiceHostFactory, UJMW.DynamicWcfHost" />

this could also be necessary:

<runtime>
  <assemblyBinding xmlns = "urn:schemas-microsoft-com:asm.v1" >
    <dependentAssembly>
      <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
      <bindingRedirect oldVersion = "0.0.0.0-14.0.0.0" newVersion="8.0.0.0" />
    </dependentAssembly>

you can configure behavior in this way:

<system.webServer>
 <modules runAllManagedModulesForAllRequests="true">
   <add name="ConfigurativeEntryPointModule" type="UJMW.DemoWcfService.EntryModule"/>
public class EntryModule : IHttpModule {

  public void Init(HttpApplication context) {
    UjmwServiceBehaviour.AuthHeaderEvaluator = ...
    UjmwServiceBehaviour.RequestSidechannelProcessor = ...
    UjmwServiceBehaviour.ResponseSidechannelCapturer = ...
    UjmwServiceBehaviour.ContractSelector = ...
    UjmwServiceBehaviour.ForceHttps = true;
  }

  public void Dispose() { }
}

A Dynamic Controller Factory for ASP.NET core WebAPI

The NuGet-Package ID is 'UJMW.DynamicController'

Controller Code Generator for ASP.NET core WebAPI

IS STABLE but discontinued (see '/Resources/for ASP.NET 5 MVC/...') The NuGet-Package ID is 'UJMW.Tools.CodeGen'

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