RESTful web service body format

Assume that you have some contract with XML request/response and some simple data contract:

[ServiceContract]
public interface IService
{
    ...
    [OperationContract]
    [WebInvoke(Method = "POST",
        ResponseFormat = WebMessageFormat.Json,
        RequestFormat = WebMessageFormat.Json,
        BodyStyle = WebMessageBodyStyle.Wrapped)]
    Entity DoWork(Entity entity);
    ...
}

[DataContract]
public class Entity
{
    [DataMember]
    public string Name;

    [DataMember]
    public string Value;
}

Depending on the combination of BodyStyle, RequestFormat and ResponseFormat you will have different formats but in general:

JSON and WebMessageBodyStyle.Bare request and response will be:

Request:

{"Name":"name","Value":"value"}

Response:

{"Name":"ResultName:name","Value":"ResultValue:value"}

JSON and WebMessageBodyStyle.Wrapped request and response will be:

Request:

{"entity":{"Name":"name","Value":"value"}}

Response:

{"DoWorkResult":{"Name":"name","Value":"value"}}

Note: you can change default DoWorkResult name to you own:

[return: MessageParameter(Name = "MyResult")]
Entity DoWork(Entity entity);`

so from now this will be:

{"MyResult":{"Name":"name","Value":"value"}}

XML and WebMessageBodyStyle.Bare request and response will be:

Request:

<Entity xmlns="http://schemas.datacontract.org/2004/07/WcfService" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
   <Name>name</Name>
   <Value>value</Value>
</Entity>

Response:

<Entity xmlns="http://schemas.datacontract.org/2004/07/WcfService" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
   <Name>name</Name>
   <Value>value</Value>
</Entity> 

XML and WebMessageBodyStyle.Wrapped request and response will be:

Request:

 <DoWork xmlns="http://tempuri.org/">
   <entity>
      <Name>name</Name>
      <Value>value</Value>
   </entity>
 </DoWork>

Response:

 <DoWorkResponse xmlns="http://tempuri.org/">
   <DoWorkResult xmlns:a="http://schemas.datacontract.org/2004/07/WcfService" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
      <a:Name>name</a:Name>
      <a:Value>value</a:Value>
   </DoWorkResult>
 </DoWorkResponse> 

Note: you can also change default DoWorkResult name with the return: MessageParameter

To answer to your question, which WebMessageBodyStyle you should use depends on your needs and there is no golden rule here. For interoperability, one or another format can be sometimes required. But keep in mind about one limitation of bare body style: as there is only one root in XML format and one object in JSON format, only one parameter can be passed to a method. In fact, if you changed a service contract to something like:

[OperationContract]
[WebInvoke(Method = "POST",
    ResponseFormat = WebMessageFormat.Json,
    RequestFormat = WebMessageFormat.Json,
    BodyStyle = WebMessageBodyStyle.Bare)]
Entity DoWork(string id, Entity entity);

a service would throw a exception:

Operation ” of contract ” specifies multiple request body parameters
to be serialized without any wrapper elements. At most one body
parameter can be serialized without wrapper elements. Either remove
the extra body parameters or set the BodyStyle property on the
WebGetAttribute/WebInvokeAttribute to Wrapped.