mining: Remove testnet min diff reduction support.

This modifies the internal mining template generator and CPU miner to no
longer support the version 3 testnet minimum difficulty reduction logic
that no longer applies given all new blocks on testnet now enforce
difficulty throttling instead of the minimum difficulty reduction rule.

Note that this does not modify the consensus enforcement logic since it
is still required for all existing version 3 testnet blocks prior to the
difficulty throttling change.

internal/mining/bgblktmplgenerator.go

@@ -358,12 +358,8 @@ func NewBgBlkTmplGenerator(cfg *BgBlkTmplConfig) *BgBlkTmplGenerator {
 // UpdateBlockTime updates the timestamp in the passed header to the current
 // time while taking into account the median time of the last several blocks to
 // ensure the new time is after that time per the chain consensus rules.
-//
-// Finally, it will update the target difficulty if needed based on the new time
-// for the test networks since their target difficulty can change based upon
-// time.
-func (g *BgBlkTmplGenerator) UpdateBlockTime(header *wire.BlockHeader) error {
-	return g.tg.UpdateBlockTime(header)
+func (g *BgBlkTmplGenerator) UpdateBlockTime(header *wire.BlockHeader) {
+	g.tg.UpdateBlockTime(header)
 }
 
 // sendQueueRegenEvent sends the provided regen event on the internal queue

internal/mining/cpuminer/cpuminer.go

@@ -216,19 +216,6 @@ func (m *CPUMiner) submitBlock(block *dcrutil.Block) bool {
 			return false
 		}
 
-		// When the reduce min difficulty option is set it is possible that the
-		// required difficulty changed while a block was being solved and will
-		// therefore result in an error due to having the incorrect required
-		// difficulty set in the header.  In that case, only log the error as
-		// debug since it is expected to happen from time to time and not really
-		// an error.
-		if m.cfg.ChainParams.ReduceMinDifficulty &&
-			errors.Is(rErr, blockchain.ErrHighHash) {
-			log.Debugf("Block submitted via CPU miner rejected because of "+
-				"ReduceMinDifficulty time sync failure: %v", err)
-			return false
-		}
-
 		// Other rule errors should be reported.
 		log.Errorf("Block submitted via CPU miner rejected: %v", err)
 		return false
@@ -327,17 +314,11 @@ func (m *CPUMiner) solveBlock(ctx context.Context, header *wire.BlockHeader, sta
 					// Non-blocking select to fall through
 				}
 
-				err := m.g.UpdateBlockTime(header)
-				if err != nil {
-					log.Warnf("CPU miner unable to update block template "+
-						"time: %v", err)
-				}
+				m.g.UpdateBlockTime(header)
 
-				// Update the bits and time in the serialized header bytes
-				// directly too since they might have changed.
-				const bitsOffset = 116
+				// Update time in the serialized header bytes directly too since
+				// it might have changed.
 				const timestampOffset = 136
-				littleEndian.PutUint32(hdrBytes[bitsOffset:], header.Bits)
 				timestamp := uint32(header.Timestamp.Unix())
 				littleEndian.PutUint32(hdrBytes[timestampOffset:], timestamp)
 			}

internal/mining/mining.go

@@ -871,19 +871,6 @@ func (g *BlkTmplGenerator) handleTooFewVoters(nextHeight int64,
 		ts := g.medianAdjustedTime()
 		block.Header.Timestamp = ts
 
-		// If we're on testnet, the time since this last block listed as the
-		// parent must be taken into consideration.
-		if g.cfg.ChainParams.ReduceMinDifficulty {
-			parentHash := topBlock.MsgBlock().Header.PrevBlock
-
-			requiredDifficulty, err := g.cfg.CalcNextRequiredDifficulty(&parentHash, ts)
-			if err != nil {
-				return nil, makeError(ErrGettingDifficulty, err.Error())
-			}
-
-			block.Header.Bits = requiredDifficulty
-		}
-
 		// Recalculate the size.
 		block.Header.Size = uint32(block.SerializeSize())
 
@@ -2343,27 +2330,10 @@ nextPriorityQueueItem:
 // UpdateBlockTime updates the timestamp in the passed header to the current
 // time while taking into account the median time of the last several blocks to
 // ensure the new time is after that time per the chain consensus rules.
-//
-// Finally, it will update the target difficulty if needed based on the new time
-// for the test networks since their target difficulty can change based upon
-// time.
-func (g *BlkTmplGenerator) UpdateBlockTime(header *wire.BlockHeader) error {
+func (g *BlkTmplGenerator) UpdateBlockTime(header *wire.BlockHeader) {
 	// The new timestamp is potentially adjusted to ensure it comes after
 	// the median time of the last several blocks per the chain consensus
 	// rules.
 	newTimestamp := g.medianAdjustedTime()
 	header.Timestamp = newTimestamp
-
-	// If running on a network that requires recalculating the difficulty,
-	// do so now.
-	if g.cfg.ChainParams.ReduceMinDifficulty {
-		difficulty, err := g.cfg.CalcNextRequiredDifficulty(&header.PrevBlock,
-			newTimestamp)
-		if err != nil {
-			return makeError(ErrGettingDifficulty, err.Error())
-		}
-		header.Bits = difficulty
-	}
-
-	return nil
 }

internal/rpcserver/interface.go

@@ -528,7 +528,7 @@ type BlockTemplater interface {
 
 	// UpdateBlockTime updates the timestamp in the passed header to the current
 	// time while taking into account the consensus rules.
-	UpdateBlockTime(header *wire.BlockHeader) error
+	UpdateBlockTime(header *wire.BlockHeader)
 }
 
 // FiltererV2 provides an interface for retrieving a block's version 2 GCS

internal/rpcserver/rpcserver.go

@@ -3771,11 +3771,7 @@ func handleGetWorkRequest(ctx context.Context, s *Server) (interface{}, error) {
 	// consensus rules.  Note that the header is copied to avoid mutating the
 	// shared block template.
 	headerCopy := template.Block.Header
-	err := bt.UpdateBlockTime(&headerCopy)
-	if err != nil {
-		context := "Failed to update block time"
-		return nil, rpcInternalError(err.Error(), context)
-	}
+	bt.UpdateBlockTime(&headerCopy)
 
 	// Serialize the block header into a buffer large enough to hold the
 	// the block header and the internal blake256 padding that is added and
@@ -3788,7 +3784,7 @@ func handleGetWorkRequest(ctx context.Context, s *Server) (interface{}, error) {
 	// data[144:152] --> ExtraNonce
 	data := make([]byte, 0, getworkDataLen)
 	buf := bytes.NewBuffer(data)
-	err = headerCopy.Serialize(buf)
+	err := headerCopy.Serialize(buf)
 	if err != nil {
 		context := "Failed to serialize data"
 		return nil, rpcInternalError(err.Error(), context)

internal/rpcserver/rpcserverhandlers_test.go

@@ -1023,12 +1023,11 @@ func (s *testTemplateSubber) PublishTemplateNtfn(templateNtfn *mining.TemplateNt
 // testBlockTemplater provides a mock block templater by implementing the
 // mining.BlockTemplater interface.
 type testBlockTemplater struct {
-	subscriptions      map[*testTemplateSubber]struct{}
-	regenReason        mining.TemplateUpdateReason
-	currTemplate       *mining.BlockTemplate
-	currTemplateErr    error
-	updateBlockTimeErr error
-	simulateNewNtfn    bool
+	subscriptions   map[*testTemplateSubber]struct{}
+	regenReason     mining.TemplateUpdateReason
+	currTemplate    *mining.BlockTemplate
+	currTemplateErr error
+	simulateNewNtfn bool
 }
 
 // ForceRegen asks the block templater to generate a new template immediately.
@@ -1066,9 +1065,7 @@ func (b *testBlockTemplater) CurrentTemplate() (*mining.BlockTemplate, error) {
 
 // UpdateBlockTime updates the timestamp in the passed header to the current
 // time while taking into account the consensus rules.
-func (b *testBlockTemplater) UpdateBlockTime(header *wire.BlockHeader) error {
-	return b.updateBlockTimeErr
-}
+func (b *testBlockTemplater) UpdateBlockTime(header *wire.BlockHeader) {}
 
 // testTxMempooler provides a mock mempool transaction data source by
 // implementing the TxMempooler interface.
@@ -5765,18 +5762,6 @@ func TestHandleGetWork(t *testing.T) {
 		}(),
 		wantErr: true,
 		errCode: dcrjson.ErrRPCMisc,
-	}, {
-		name:            "handleGetWork: unable to update block time",
-		handler:         handleGetWork,
-		cmd:             &types.GetWorkCmd{},
-		mockMiningState: defaultMockMiningState(),
-		mockBlockTemplater: func() *testBlockTemplater {
-			templater := defaultMockBlockTemplater()
-			templater.updateBlockTimeErr = errors.New("unable to update block time")
-			return templater
-		}(),
-		wantErr: true,
-		errCode: dcrjson.ErrRPCInternal.Code,
 	}, {
 		name:    "handleGetWork: data is not equal to getworkDataLen (192 bytes)",
 		handler: handleGetWork,