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Expose PRG as fulfillment option supporting many random values per Request #30

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Expose PRG as fulfillment option supporting many random values per Request #30

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30 changes: 19 additions & 11 deletions contracts/RandomConsumer.cdc
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ access(all) contract RandomConsumer {
access(all) event RandomnessRequested(requestUUID: UInt64, block: UInt64)
access(all) event RandomnessSourced(requestUUID: UInt64, block: UInt64, randomSource: [UInt8])
access(all) event RandomnessFulfilled(requestUUID: UInt64, randomResult: UInt64)
access(all) event RandomnessFulfilledWithPRG(requestUUID: UInt64)

///////////////////
// PUBLIC FUNCTIONS
Expand All @@ -38,7 +39,7 @@ access(all) contract RandomConsumer {
return min + revertibleRandom<UInt64>(modulo: max - min + 1)
}

/// Retrieves a random number in the range [min, max] using the provided PRG
/// Retrieves a random number in the range [min, max] using the provided PRG
/// to source additional randomness if needed
///
/// @param prg: The PRG to use for random number generation
Expand Down Expand Up @@ -80,11 +81,11 @@ access(all) contract RandomConsumer {
shifts = 0
}
}

// Scale candidate to the range [min, max]
return min + candidate
}

/// Returns a new Consumer resource
///
/// @return A Consumer resource
Expand Down Expand Up @@ -225,7 +226,7 @@ access(all) contract RandomConsumer {
let reqUUID = request.uuid

// Create PRG from the provided request & generate a random number
let prg = self._getPRGFromRequest(request: <-request)
let prg = self.fulfillWithPRG(request: <-request)
let res = prg.nextUInt64()

emit RandomnessFulfilled(requestUUID: reqUUID, randomResult: res)
Expand All @@ -251,25 +252,32 @@ access(all) contract RandomConsumer {
.concat(min.toString()).concat(" and max of ".concat(max.toString()))
}
let reqUUID = request.uuid

// Create PRG from the provided request & generate a random number & generate a random number in the range
let prg = self._getPRGFromRequest(request: <-request)
let prg = self.fulfillWithPRG(request: <-request)
let res = RandomConsumer.getNumberInRange(prg: prg, min: min, max: max)

emit RandomnessFulfilled(requestUUID: reqUUID, randomResult: res)

return res
}

/* --- INTERNAL --- */
//
/// Creates a PRG from a Request, using the request's block height source of randomness and UUID as a salt
/// Creates a PRG from a Request, using the request's block height source of randomness and UUID as a salt.
/// This method fulfills the request, returning a PRG so that consumers can generate any number of random values
/// using the request's source of randomness, seeded with the request's UUID as a salt.
///
/// NOTE: The intention in exposing this method is for consumers to be able to generate several random values
/// per request, and the returned PRG should be used in association to a single request. IOW, while the PRG is
/// a storable object, it should be treated as ephemeral, discarding once all values have been generated
/// corresponding to the fulfilled request.
///
/// @param request: The Request to use for PRG creation
///
/// @return A PRG object
/// @return A PRG object from which to generate random values in assocation with the fulfilled request
///
access(self) fun _getPRGFromRequest(request: @Request): Xorshift128plus.PRG {
access(Reveal) fun fulfillWithPRG(request: @Request): Xorshift128plus.PRG {
emit RandomnessFulfilledWithPRG(requestUUID: request.uuid)

let source = request._fulfill()
let salt = request.uuid.toBigEndianBytes()
Burner.burn(<-request)
Expand Down
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