Service Host

The service host is the runtime environment for hosting a service within a process.

A service can configure one or more endpoints inside a service host.

Creating a service host

Before creating a service host, a service needs to define its endpoints. An endpoint in service host is specified in the WS_SERVICE_ENDPOINT structure and it is defined by the following information:

• An address, which is the physical URI on which the service will be hosted.
• A WS_CHANNEL_TYPE structure that specifies the type of the underlying channel for the endpoint.
• A WS_CHANNEL_BINDING structure that specifies the binding of the channel.
• A WS_SECURITY_DESCRIPTION structure that contains the security description for the endpoint.
• A WS_SERVICE_CONTRACT structure that represents the service contract for the endpoint.
• A WS_SERVICE_SECURITY_CALLBACK structure that specifies an authorization callback function for the endpoint.
• A WS_SERVICE_ENDPOINT_PROPERTY structure that contains an array of service endpoint properties.

WS_SERVICE_ENDPOINT serviceEndpoint = {0};
const WS_SERVICE_ENDPOINT* serviceEndpoints[1];
serviceEndpoints[0] = &serviceEndpoint;
WS_STRING url = WS_STRING_VALUE(L"net.tcp://+/Example");

// Method based service contract for the service
static WS_SERVICE_CONTRACT calculatorContract = 
{
    &calculatorContractDescription, // comes from a generated header.
    NULL,
    &calculatorFunctions, // specified by the application
};

serviceEndpoint.address.url = &url;
serviceEndpoint.binding.channelBinding =  WS_TCP_CHANNEL_BINDING; 
serviceEndpoint.contract = &calculatorContract;  
serviceEndpoint.channelType = WS_CHANNEL_TYPE_DUPLEX_SESSION; 
serviceEndpoint.authorizationCallback = AuthorizationCallback; // Authorization callback.

Only one-way contracts are supported for SOAP over UDP, represented by WS_UDP_CHANNEL_BINDING in the WS_CHANNEL_BINDING enumeration.

After an endpoint is defined, it can be passed to the WsCreateServiceHost function, which takes an array of pointers to WS_SERVICE_ENDPOINT structures.

HRESULT hr = WsCreateServiceHost (serviceEndpoints, 1, NULL, 0, &host, error);

An application can optionally provide an array of service properties to WsCreateServiceHost to configure custom settings on the service host.

An application opens the service host to start accepting client requests.

WsOpenServiceHost(serviceHost, NULL, NULL);

After opening the service host, the application can close it if there are no more operations that require it. Note that this does not release its resources, and that it can be reopened with a subsequent call to WsResetServiceHost.

WsCloseServiceHost(serviceHost, NULL, NULL);

After closing the service host, an application may reset the service host for reuse.

WsResetServiceHost(serviceHost, NULL);

When the application is done with the service host it can free the resources associated with the service host by calling the WsFreeServiceHost function. Note that WsCloseServiceHost must be called before calling this function.

WsFreeServiceHost(serviceHost, NULL);

For information on attaching a custom state to the service host, see User Host State

For information on authorization in a service host for a given endpoint, see Service Authorization.

For iinformation on implementing service operations and service contracts for a service, see the service operations and service contracttopics.

Security

An application can use the followin properties to control the amount of resources the service host allocates on behalf of the application:

• WS_SERVICE_ENDPOINT_PROPERTY_MAX_ACCEPTING_CHANNELS,
• WS_SERVICE_ENDPOINT_PROPERTY_MAX_CONCURRENCY,
• WS_SERVICE_ENDPOINT_PROPERTY_MAX_CHANNELS,
• WS_SERVICE_ENDPOINT_PROPERTY_BODY_HEAP_MAX_SIZE,
• WS_SERVICE_ENDPOINT_PROPERTY_MAX_CALL_POOL_SIZE,
• WS_SERVICE_ENDPOINT_PROPERTY_MAX_CHANNEL_POOL_SIZE.

Secure defaults are chosen for each of these properties, an application must be careful if it wishes to modify these properties. Beyond the above-mentioned properties, channel, listener and message specific properties can also be modified by the application. Refer to the security considerations of these components before modifying any of these settings.

In addition, the following application design considerations should be carefully evaluated when using WWSAPI service host API:

• When using MEX, applications should be careful not to disclose any sensitive data. As a mitigation, if the nature of the data being exposed through MEX is sensitive, applications may choose to configure the MEX endpoint with a secure binding requiring authentication at the very least and implement authorization as part of the endpoint using the WS_SERVICE_SECURITY_CALLBACK.
• By default rich error information through faults is disabled on service host by WS_SERVICE_PROPERTY_FAULT_DISCLOSURE property. It is upon the discretion of the application to send rich error information as part of the fault. However, this can result in information disclosure and thus it is recommended that this setting is only changed for debugging scenarios.
• Beyond validation performed for Basic Profile 2.0 and XML serialization, service host performs no validation on the data content received as part of service operation parameters. It is the responsibility of the application to perform all parameter validations on its own.
• Authorization is not implemented as part of service host. However, applications can implement their own authorization scheme using WS_SECURITY_DESCRIPTION and the WS_SERVICE_SECURITY_CALLBACK.
• It is the responsibility of the application to use secure bindings on its endpoint. Service host does not provide any security beyond what is configured on the endpoint.

The following API elements are used with the service host.

Callback	Description
WS_SERVICE_ACCEPT_CHANNEL_CALLBACK	Invoked when a channel is accepted on an endpoint listener by the service host.
WS_SERVICE_CLOSE_CHANNEL_CALLBACK	Invoked when a channel is closed or aborted on an endpoint.

 

Enumeration	Description
WS_SERVICE_ENDPOINT_PROPERTY_ID	Optional parameters for configuring a WS_SERVICE_ENDPOINT.
WS_SERVICE_HOST_STATE	The states that a service host can be in.
WS_SERVICE_PROPERTY_ID	Optional parameters for configuring the service host.

 

Function	Description
WsAbortServiceHost	Interrupts and discontinues current operations on the service host.
WsCloseServiceHost	Closes all listeners so that no new channels are accepted from the client.
WsCreateServiceHost	Creates a service host.
WsFreeServiceHost	Releases the memory associated with a service host object.
WsGetServiceHostProperty	Retrieves a specified Service Host property.
WsOpenServiceHost	Opens a service host for communication and starts the listeners on all the endpoints.
WsResetServiceHost	Resets the service host for reuse and resets the underlying channel and listeners for reuse.

 

Handle	Description
WS_SERVICE_HOST	An opaque type used to reference a service host.

 

Structure	Description
WS_SERVICE_ENDPOINT	Represents an individual endpoint on a service host.
WS_SERVICE_ENDPOINT_PROPERTY	Specifies a service-specific setting.
WS_SERVICE_PROPERTY	Specifies a service-specific setting.
WS_SERVICE_PROPERTY_ACCEPT_CALLBACK	Specifies the callback which is called when a channel is successfully accepted.
WS_SERVICE_PROPERTY_CLOSE_CALLBACK	Specifies the callback which is called when a channel is about to be closed.