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util-service.md

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Util Service

The Util Service is a service that handles utility operations. Currently, the only functionality provided by this service is the generation of pseudorandom numbers.

Table of Contents

Protobuf Definitions

Protobuf, or Protocol Buffers, is a method of serializing structured data. The Util Service uses it to define the structure of our transactions. Here are some of the Protobuf definitions used in the Util Service:

  • util_service.proto: This file defines the UtilService which includes the prng RPC for generating pseudorandom numbers.
  • util_prng.proto: This file defines the UtilPrngTransactionBody message which is used in the prng RPC. It includes a range field which, if provided and is positive, returns a 32-bit pseudorandom number from the given range in the transaction record. If not set or set to zero, will return a 384-bit pseudorandom number in the record.

UtilPrngTransactionBody

The UtilPrngTransactionBody message is a crucial part of the prng RPC in the Util Service. It is defined in the util_prng.proto file and is used to specify the range for the pseudorandom number generation.

message UtilPrngTransactionBody {
    int32 range = 1;
}

The UtilPrngTransactionBody message contains a single field, range. This field is used to determine the range of the pseudorandom number that will be generated.

  • If range is provided and is positive, the Util Service will return a 32-bit pseudorandom number from the given range in the transaction record.
  • If range is not set or set to zero, the Util Service will return a 384-bit pseudorandom number in the transaction record.

This message is used in the prng RPC of the UtilService defined in util_service.proto. The prng RPC is responsible for generating pseudorandom numbers, and the UtilPrngTransactionBody message provides the necessary input for this operation.

Handlers

Handlers are responsible for executing the transactions. Each type of transaction has its own handler. All the Handlers implement the TransactionHandler interface and provide implementations of pureChecks, preHandle, handle, and calculateFees methods.

  • UtilHandlers.java: This class includes a prngHandler which is an instance of UtilPrngHandler.

  • UtilPrngHandler.java: This class is a TransactionHandler for handling UTIL_PRNG transactions. It uses the n-3 running hash to generate a pseudo-random number. The n-3 running hash is updated and maintained by the application, based on the record files generated based on preceding transactions. In this way, the number is both essentially unpredictable and deterministic.

Configuration

UtilPrngConfig is a configuration class used in the Hedera Hashgraph network. This class is used to configure the behavior of the UtilPrngHandler. The UtilPrngConfig class is a record that contains a single boolean property, isEnabled. This property is annotated with @ConfigProperty and @NetworkProperty, indicating that it can be configured via the network's configuration file. The isEnabled property determines whether the UtilPrngHandler allows a transaction to proceed. If isEnabled is set to true, the UtilPrngHandler will allow the transaction. If isEnabled is set to false, the UtilPrngHandler will not allow the transaction.