void descriptorTests(){
// Objective is to make this Server class independent of generated protobuf structures
// Move dependency from compile/link-time to run-time.
//
// Read the allProto.desc file descriptor set
// File generated by protoc --descriptor_set_out=allProto.desc path/to/proto-files.proto (performed by make)
//
// c++ fstream method for opening the file
// fstream in("allProto.desc", ios::in | ios::binary);
// io::IstreamInputStream raw_in(&in);
// cfile is a c file descriptor (not to be confused with a protobuf FileDescriptor object)
int cfile = open("allProto.desc", O_RDONLY);
FileDescriptorSet fds;
// Parse a FileDescriptorSet object directly from the file
// Has the format of a protobuf Message - subclass FileDescriptorSet, defined in <google/protobuf/descriptor.pb.h>
// https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.descriptor.pb#FieldOptions_CType.details
fds.ParseFromFileDescriptor(cfile);
// Use FileDescriptorSet method to print to screen
fds.SerializeToOstream(&cout);
// Re-open file. Example of an alternative means for reading
// FileInputStream
cfile = open("allProto.desc", O_RDONLY);
io::FileInputStream fis(cfile);
// Another means may be to use a CodedInputStream, but don't need the extra features at this time
// e.g. io::CodedInputStream cis(fis); See http://www.mail-archive.com/[email protected]/msg03417.html
const void* buffer;
int size;
while(fis.Next(&buffer, &size)){
cout.write((const char*)buffer, size);
cout << endl << size << endl;
}
// End of alternative read example
close(cfile);
// fds is a protobuf message containing a collection of FileDescriptorProto objects (Message instances)
// There are (several?) ways to convert such objects into live Descriptor objects
// How many files in the set?
cout << "Num protos " << fds.file_size() << endl;
FileDescriptorProto fdp;
// Example of indexing and examining properties
fdp = fds.file(1);
cout << fdp.name() << endl;
// A DescriptorPool is required: provides methods to identify and manage message types at run-time
// DescriptorPool can be populated from a SimpleDescriptorDatabase, which can be populated with FileDescriptorProto objects
SimpleDescriptorDatabase sddb;
for ( int i = 0; i < fds.file_size() ; i++ ){
//Iterate over the "file" collection in the FileDescriptorSet
//Populate the sddb
sddb.Add(fds.file(i));
}
// Now construct the DescriptorPool
DescriptorPool dp(&sddb);
// DynamicMessageFactory is constucted from a populated DescriptorPool
// DescriptorPool, Descriptor, FieldDescriptor etc.: see descriptor.h -
// https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.descriptor
DynamicMessageFactory dmf(&dp);
const Descriptor* desc;
desc = dp.FindMessageTypeByName("Person");
// Example of dynamically creating a message from a Descriptor, retrieved by name string
Message *msg = dmf.GetPrototype(desc)->New();
// Messages with required fields - Need populated.
// Requires FieldDescriptor objects to access
const FieldDescriptor* idField = desc->FindFieldByName("id");
const FieldDescriptor* nameField = desc->FindFieldByName("name");
// Reflection object provides R/W access to dynamic message fields, using FieldDescriptors
//
// https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.message#Message.GetReflection.details
// Good example of Reflection at top of that page
const Reflection *msgRefl = msg->GetReflection();
msgRefl->SetInt32( msg, idField, 8123);
msgRefl->SetString( msg, nameField, "Does it work?");
//Now that required fields are populated, the dynamic message can be serialized and printed out.
string data;
// msg->SerializeToString(&data);
cout << data << endl;
// Useful examples of dynamic protobuf logic here : http://www.programmershare.com/2803644/
// (English not very good)
// 3.4 also describes dynamic compilation Uses google::protobuf::compiler Importer class
// Another link : dynamic stuff :
// http://stackoverflow.com/questions/11996557/how-to-dynamically-build-a-new-protobuf-from-a-set-of-already-defined-descriptor
// https://bitbucket.org/g19fanatic/prototest/src/dfd73a577dcc9bb51cbb3e99319cad352bfc60a8/src/main.cpp?at=master&fileviewer=file-view-default
}
