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 calls via Protocol Buffers, with the Delegate making a sync call via an HTTP POST and returning the response bytes. This allows App Engine applications to use low-level APIs via Protocol Buffers over HTTP rather than directly making RPC calls.

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@