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Message Flow in the API Manager Gateway
The Gateway of an API Manager deployment is responsible for the main business functionality of serving API traffic. The following diagram illustrates the message flow in the Gateway at a very high level.
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The handlers
The handlers are request and response interceptors. The list of API handlers in WSO2 API-M are as follows:
- APIMgtLatencyStatsHandler
- CORSRequestHandler
- APIAuthenticationHandler
- ThrottleHandler
- APIMgtUsageHandler
- APIMgtGoogleAnalyticsTrackingHandler
- APIManagerExtensionHandler
Each handler performs a specific task as mentioned in the table below. Note that some handlers are functional both at the inflow and outflow of messages.
| Handler | Inflow | Outflow |
|---|---|---|
| APIMgtLatencyStatsHandler | Publish request and response latencies, if analytics is enabled | Publish request and response latencies, if analytics is enabled |
| CORSRequestHandler | Set CORS Headers | Set CORS Headers |
| APIAuthenticationHandler | Request authentication | N/A |
| ThrottleHandler | Request throttling | N/A |
| APIMgtUsageHandler | Publish request data, if analytics is enabled | N/A |
| APIMgtGoogleAnalyticsTrackingHandler | Publish data to Google Analytics, if Google Analytics is configured | N/A |
| APIManagerExtensionHandler | Execute custom mediation sequences at inflow | Execute custom mediation sequences at outflow |
Mediation extensions
Mediation extensions are the custom mediation logic that can be executed in either the inflow or the outflow. For more details on how to configure mediation extensions, see Adding Mediation Extensions.
In sequence and out sequence
The in sequence and out sequence carry the main business logic of the request flow. The in sequence handles sending the request from the client to the backend, while the out sequence routes the response sent from the backed to the client.