To process a multipart response message, cast the Entity field of the response message to a MultipartEntity object, as shown in this example:

USING OpenEdge.Net.HTTP.*.
USING OpenEdge.Net.URI.
USING OpenEdge.Net.MessagePart.
USING OpenEdge.Net.MultipartEntity.


DEFINE VARIABLE oClient AS IHttpClient NO-UNDO.
DEFINE VARIABLE oURI AS URI NO-UNDO.
DEFINE VARIABLE oRequest AS IHttpRequest NO-UNDO. 
DEFINE VARIABLE oResponse AS IHttpResponse NO-UNDO.
DEFINE VARIABLE oResponseEntity AS MultipartEntity NO-UNDO.
DEFINE VARIABLE msgPart AS MessagePart NO-UNDO.
DEFINE VARIABLE partBody AS Progress.Lang.Object NO-UNDO.
DEFINE VARIABLE loop AS INTEGER NO-UNDO.

//Build a request
oURI = URI:Parse("http://httpbin.org/get").
oRequest = RequestBuilder:POST(oURI):Request.


//Execute a request
oClient = ClientBuilder:Build():Client.
oResponse = oClient:Execute(oRequest).

//Process the response
IF oResponse:StatusCode <> 200 THEN
    RETURN ERROR "Request Error: " + STRING(oResponse:StatusCode).
ELSE
    oResponseEntity = CAST(oResponse:Entity, MultipartEntity).
    DO loop = 1 to oResponseEntity:SIZE:
        ASSIGN msgPart  = oResponseEntity:GetPart(loop)
               partBody = msgPart:Body.
    END.