My error and fix was different from the answers above.
The specific issue I had was accessing a mediaReadLink endpoint in my ODataController in WebApi 2.2.
OData has a 'default stream' property in the spec which allows a returned entity to have an attachment. So the e.g. json object for filter etc describes the object, and then there is a media link embedded which can also be accessed. In my case it is a PDF version of the object being described.
There's a few curly issues here, the first comes from the config:
<system.web>
<customErrors mode="Off" />
<compilation debug="true" targetFramework="4.7.1" />
<httpRuntime targetFramework="4.5" />
<!-- etc -->
</system.web>
At first I was trying to return a FileStreamResult, but i believe this isn't the default net45 runtime. so the pipeline can't format it as a response, and a 406 not acceptable ensues.
The fix here was to return a HttpResponseMessage and build the content manually:
[System.Web.Http.HttpGet]
[System.Web.Http.Route("myobjdownload")]
public HttpResponseMessage DownloadMyObj(string id)
{
try
{
var myObj = GetMyObj(id); // however you do this
if (null != myObj )
{
HttpResponseMessage result = Request.CreateResponse(HttpStatusCode.OK);
byte[] bytes = GetMyObjBytes(id); // however you do this
result.Content = new StreamContent(bytes);
result.Content.Headers.ContentType = new MediaTypeWithQualityHeaderValue("application/pdf");
result.Content.Headers.LastModified = DateTimeOffset.Now;
result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue(DispositionTypeNames.Attachment)
{
FileName = string.Format("{0}.pdf", id),
Size = bytes.length,
CreationDate = DateTimeOffset.Now,
ModificationDate = DateTimeOffset.Now
};
return result;
}
}
catch (Exception e)
{
// log, throw
}
return null;
}
My last issue here was getting an unexpected 500 error after returning a valid result. After adding a general exception filter I found the error was Queries can not be applied to a response content of type 'System.Net.Http.StreamContent'. The response content must be an ObjectContent.. The fix here was to remove the [EnableQuery] attribute from the top of the controller declaration, and only apply it at the action level for the endpoints that were returning entity objects.
The [System.Web.Http.Route("myobjdownload")] attribute is how to embed and use media links in OData V4 using web api 2.2. I'll dump the full setup of this below for completeness.
Firstly, in my Startup.cs:
[assembly: OwinStartup(typeof(MyAPI.Startup))]
namespace MyAPI
{
public class Startup
{
public void Configuration(IAppBuilder app)
{
// DI etc
// ...
GlobalConfiguration.Configure(ODataConfig.Register); // 1st
GlobalConfiguration.Configure(WebApiConfig.Register); // 2nd
// ... filters, routes, bundles etc
GlobalConfiguration.Configuration.EnsureInitialized();
}
}
}
ODataConfig.cs:
// your ns above
public static class ODataConfig
{
public static void Register(HttpConfiguration config)
{
ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
var entity1 = builder.EntitySet<MyObj>("myobj");
entity1.EntityType.HasKey(x => x.Id);
// etc
var model = builder.GetEdmModel();
// tell odata that this entity object has a stream attached
var entityType1 = model.FindDeclaredType(typeof(MyObj).FullName);
model.SetHasDefaultStream(entityType1 as IEdmEntityType, hasStream: true);
// etc
config.Formatters.InsertRange(
0,
ODataMediaTypeFormatters.Create(
new MySerializerProvider(),
new DefaultODataDeserializerProvider()
)
);
config.Select().Expand().Filter().OrderBy().MaxTop(null).Count();
// note: this calls config.MapHttpAttributeRoutes internally
config.Routes.MapODataServiceRoute("ODataRoute", "data", model);
// in my case, i want a json-only api - ymmv
config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeWithQualityHeaderValue("text/html"));
config.Formatters.Remove(config.Formatters.XmlFormatter);
}
}
WebApiConfig.cs:
// your ns above
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
// https://stackoverflow.com/questions/41697934/catch-all-exception-in-asp-net-mvc-web-api
//config.Filters.Add(new ExceptionFilter());
// ymmv
var cors = new EnableCorsAttribute("*", "*", "*");
config.EnableCors(cors);
// so web api controllers still work
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
// this is the stream endpoint route for odata
config.Routes.MapHttpRoute("myobjdownload", "data/myobj/{id}/content", new { controller = "MyObj", action = "DownloadMyObj" }, null);
// etc MyObj2
}
}
MySerializerProvider.cs:
public class MySerializerProvider: DefaultODataSerializerProvider
{
private readonly Dictionary<string, ODataEdmTypeSerializer> _EntitySerializers;
public SerializerProvider()
{
_EntitySerializers = new Dictionary<string, ODataEdmTypeSerializer>();
_EntitySerializers[typeof(MyObj).FullName] = new MyObjEntitySerializer(this);
//etc
}
public override ODataEdmTypeSerializer GetEdmTypeSerializer(IEdmTypeReference edmType)
{
if (edmType.IsEntity())
{
string stripped_type = StripEdmTypeString(edmType.ToString());
if (_EntitySerializers.ContainsKey(stripped_type))
{
return _EntitySerializers[stripped_type];
}
}
return base.GetEdmTypeSerializer(edmType);
}
private static string StripEdmTypeString(string t)
{
string result = t;
try
{
result = t.Substring(t.IndexOf('[') + 1).Split(' ')[0];
}
catch (Exception e)
{
//
}
return result;
}
}
MyObjEntitySerializer.cs:
public class MyObjEntitySerializer : DefaultStreamAwareEntityTypeSerializer<MyObj>
{
public MyObjEntitySerializer(ODataSerializerProvider serializerProvider) : base(serializerProvider)
{
}
public override Uri BuildLinkForStreamProperty(MyObj entity, EntityInstanceContext context)
{
var url = new UrlHelper(context.Request);
string id = string.Format("?id={0}", entity.Id);
var routeParams = new { id }; // add other params here
return new Uri(url.Link("myobjdownload", routeParams), UriKind.Absolute);
}
public override string ContentType
{
get { return "application/pdf"; }
}
}
DefaultStreamAwareEntityTypeSerializer.cs:
public abstract class DefaultStreamAwareEntityTypeSerializer<T> : ODataEntityTypeSerializer where T : class
{
protected DefaultStreamAwareEntityTypeSerializer(ODataSerializerProvider serializerProvider)
: base(serializerProvider)
{
}
public override ODataEntry CreateEntry(SelectExpandNode selectExpandNode, EntityInstanceContext entityInstanceContext)
{
var entry = base.CreateEntry(selectExpandNode, entityInstanceContext);
var instance = entityInstanceContext.EntityInstance as T;
if (instance != null)
{
entry.MediaResource = new ODataStreamReferenceValue
{
ContentType = ContentType,
ReadLink = BuildLinkForStreamProperty(instance, entityInstanceContext)
};
}
return entry;
}
public virtual string ContentType
{
get { return "application/octet-stream"; }
}
public abstract Uri BuildLinkForStreamProperty(T entity, EntityInstanceContext entityInstanceContext);
}
The end result is my json objects get these odata properties embedded:
odata.mediaContentType=application/pdf
odata.mediaReadLink=http://myhost/data/myobj/%3fid%3dmyid/content
And the following the decoded media link http://myhost/data/myobj/?id=myid/content fires the endpoint on your MyObjController : ODataController.
