Accessing Custom Options from .desc file in Protobuf - protocol-buffers

Question

I have a proto with the following definitions.
import "google/protobuf/descriptor.proto";
extend google.protobuf.FieldOptions{
optional bool is_key = 50002;
}
message Foo{
int64 id = 1 [(is_key) = true];
}
I generated a .desc file for the above. I was able to access all the Fields and Message defined by the FieldDescriptorProto and DescriptorProto types but not sure how to access the options defined and the value provided to it in this case is_key.
Could anyone provide me with a java version that could access the options from the .desc file

Answer 1

Not sure If this is the right way but all I was trying to do was read custom options from a descriptor_set.desc file.
I parsed the desc file, the problem is that it returns fileDescriptorProto Types. So I parsed them and built a dependencies graph. This helped me to create FileDescriptor Types.
Through FileDescriptor Types I was able to get Extensions and add them to extensionRegistry.
Post Which I parsed the .desc file once again but this time with extensionRegistry.
val filePathToFileDescriptorMap = mutableMapOf <String, FileDescriptor>(DescriptorProtos.getDescriptor().file.name to
DescriptorProtos.getDescriptor())
val extensionRegistry = ExtensionRegistry.newInstance()
fun buildDependencies(fileDescriptorProto: DescriptorProtos.FileDescriptorProto,
filePathToFileDescriptorProtoMap: Map<String, DescriptorProtos.FileDescriptorProto>) : FileDescriptor {
val dependencies = fileDescriptorProto.dependencyList.map { dependency ->
if(filePathToFileDescriptorMap.containsKey(dependency)) {
filePathToFileDescriptorMap[dependency]
}
else if(!filePathToFileDescriptorProtoMap.containsKey(dependency)) {
throw Exception("dependency not found $dependency")
}
else {
buildDependencies(filePathToFileDescriptorProtoMap[dependency]!!, filePathToFileDescriptorProtoMap)
}
}
filePathToFileDescriptorMap[fileDescriptorProto.name] =
FileDescriptor.buildFrom(fileDescriptorProto, dependencies.toTypedArray())
filePathToFileDescriptorMap[fileDescriptorProto.name]!!.extensions.forEach {
if(it.type == Descriptors.FieldDescriptor.Type.MESSAGE){
extensionRegistry.add(it, DynamicMessage.newBuilder(it.messageType).build())
}else{
extensionRegistry.add(it)
}
}
return filePathToFileDescriptorMap[fileDescriptorProto.name]!!
}
fun registerExtensions(){
val fileDescriptorSet = DescriptorProtos.FileDescriptorSet.parseFrom(
FileInputStream("src/generated/resources/desc_set.desc"),
)
val filePathToFileDescriptorProtoMap = fileDescriptorSet.fileList.associateBy { it.name }
fileDescriptorSet.fileList.forEach { fileDescriptorProto ->
if(!filePathToFileDescriptorMap.containsKey(fileDescriptorProto.name)){
buildDependencies(fileDescriptorProto, filePathToFileDescriptorProtoMap)
}
}
val fileDescriptorSetWithOptions = DescriptorProtos.FileDescriptorSet.parseFrom(
FileInputStream("src/generated/resources/desc_set.desc"),
extensionRegistry
)
println(fileDescriptorSetWithOptions)
}