The document discusses using Protocol Buffers over HTTP for making synchronous API calls from an App Engine application to a backend service. It describes how ApiProxy and Delegate classes are used to make the calls, with the request and response encoded as Protocol Buffers and sent as HTTP requests. The backend service receives the request, decodes the Protocol Buffer, makes the API call, encodes the response as a Protocol Buffer, and returns it to the application via an HTTP response. This allows App Engine applications to make synchronous calls to backend services using Protocol Buffers over HTTP.

1. appengine
java night #2
ProtocolBuffer on HTTP
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2. ApiProxy#getDelegate()
Application Stub
LowLevelAPI
PB
ApiProxy
PB #getDelegate()

3. Delegate#makeSyncCall()
Service ,Method ,Request(byte[])
ApiProxy
#getDelegate()
#makeSyncCall()
PB(byte[]) Stub/

4. Server …
• ApiProxy.setDelegate(
Delegate)
ProtocolBuffer
•
ProtocolBuffer

5. • OreOreDelegate
#makeSyncCall() Stub
•
ApiProxy.getDelegate().makeSyncCall()
• OreOreDelegate
Low-Level API
• Low-Level API Application

6. ProtocolBuffer on HTTP
Application
LowLevelAPI
PB
PB OreOreServlet
OreOreDelegate
PB

7. MakeSyncCallServlet
makeSyncCall()
String serviceName =
req.getHeader(SERVICE_NAME);
String methodName = req.getHeader(METHOD_NAME);
byte[] requestBytes =
IOUtils.toByteArray(req.getInputStream());
byte[] responseBytes =
ApiProxy.getDelegate().makeSyncCall(
ApiProxy.getCurrentEnvironment(),
serviceName, methodName, requestBytes);
resp.getOutputStream().write(responseBytes);

8. MakeSyncCallDelegate
MakeSyncCall
public byte[] makeSyncCall(
Environment environment, String serviceName,
String methodName, byte[] request)
throws ApiProxyException {
return protocolBufferOnHttp(
environment,
serviceName, methodName, request);
}
byte[] protocolBufferOnHttp(.....) {
// makeSyncCall Post byte[]
}

9. • Datastore
" Datastore
• Datastore
" Datastore
• Memcache
" Memcache

10. shin1ogawa@