Implement BIP0023 getblocktemplate block proposals.

This commit implements block proposals as defined by BIP0023.

This is work towards btcsuite#124.

rpcserver.go

@@ -81,6 +81,12 @@ var (
 		Flags: hex.EncodeToString(btcscript.NewScriptBuilder().
 			AddData([]byte(coinbaseFlags)).Script()),
 	}
+
+	// gbtCapabilities describes additional capabilities returned with a
+	// block template generated by the getblocktemplate RPC.    It is
+	// declared here to avoid the overhead of creating the slice on every
+	// invocation for constant data.
+	gbtCapabilities = []string{"proposal"}
 )
 
 // Errors
@@ -1619,8 +1625,8 @@ func (state *gbtWorkState) blockTemplateResult(useCoinbaseValue bool, submitOld
 		Version:      header.Version,
 		LongPollID:   templateID,
 		SubmitOld:    submitOld,
-		MinTime:      state.minTimestamp.Unix(),
 		Target:       targetDifficulty,
+		Capabilities: gbtCapabilities,
 	}
 	if useCoinbaseValue {
 		reply.CoinbaseAux = gbtCoinbaseAux
@@ -1837,9 +1843,166 @@ func handleGetBlockTemplateRequest(s *rpcServer, request *btcjson.TemplateReques
 	return state.blockTemplateResult(useCoinbaseValue, nil)
 }
 
+// chainErrToGBTErrString converts an error returned from btcchain to a string
+// which matches the reasons and format described in BIP0022 for rejection
+// reasons.
+func chainErrToGBTErrString(err error) string {
+	// When the passed error is not a RuleError, just return a generic
+	// rejected string with the error text.
+	ruleErr, ok := err.(btcchain.RuleError)
+	if !ok {
+		return "rejected: " + err.Error()
+	}
+
+	switch ruleErr.ErrorCode {
+	case btcchain.ErrDuplicateBlock:
+		return "duplicate"
+	case btcchain.ErrBlockTooBig:
+		return "bad-block-size"
+	case btcchain.ErrBlockVersionTooOld:
+		return "bad-version"
+	case btcchain.ErrInvalidTime:
+		return "bad-time"
+	case btcchain.ErrTimeTooOld:
+		return "time-too-old"
+	case btcchain.ErrTimeTooNew:
+		return "time-too-new"
+	case btcchain.ErrDifficultyTooLow:
+		return "bad-diffbits"
+	case btcchain.ErrUnexpectedDifficulty:
+		return "bad-diffbits"
+	case btcchain.ErrHighHash:
+		return "high-hash"
+	case btcchain.ErrBadMerkleRoot:
+		return "bad-txnmrklroot"
+	case btcchain.ErrBadCheckpoint:
+		return "bad-checkpoint"
+	case btcchain.ErrForkTooOld:
+		return "fork-too-old"
+	case btcchain.ErrNoTransactions:
+		return "bad-txns-none"
+	case btcchain.ErrTooManyTransactions:
+		return "bad-txns-toomany"
+	case btcchain.ErrNoTxInputs:
+		return "bad-txns-noinputs"
+	case btcchain.ErrNoTxOutputs:
+		return "bad-txns-nooutputs"
+	case btcchain.ErrTxTooBig:
+		return "bad-txns-size"
+	case btcchain.ErrBadTxOutValue:
+		return "bad-txns-outputvalue"
+	case btcchain.ErrDuplicateTxInputs:
+		return "bad-txns-dupinputs"
+	case btcchain.ErrBadTxInput:
+		return "bad-txns-badinput"
+	case btcchain.ErrMissingTx:
+		return "bad-txns-missinginput"
+	case btcchain.ErrUnfinalizedTx:
+		return "bad-txns-unfinalizedtx"
+	case btcchain.ErrDuplicateTx:
+		return "bad-txns-duplicate"
+	case btcchain.ErrOverwriteTx:
+		return "bad-txns-overwrite"
+	case btcchain.ErrImmatureSpend:
+		return "bad-txns-maturity"
+	case btcchain.ErrDoubleSpend:
+		return "bad-txns-dblspend"
+	case btcchain.ErrSpendTooHigh:
+		return "bad-txns-highspend"
+	case btcchain.ErrBadFees:
+		return "bad-txns-fees"
+	case btcchain.ErrTooManySigOps:
+		return "high-sigops"
+	case btcchain.ErrFirstTxNotCoinbase:
+		return "bad-txns-nocoinbase"
+	case btcchain.ErrMultipleCoinbases:
+		return "bad-txns-multicoinbase"
+	case btcchain.ErrBadCoinbaseScriptLen:
+		return "bad-cb-length"
+	case btcchain.ErrBadCoinbaseValue:
+		return "bad-cb-value"
+	case btcchain.ErrMissingCoinbaseHeight:
+		return "bad-cb-height"
+	case btcchain.ErrBadCoinbaseHeight:
+		return "bad-cb-height"
+	case btcchain.ErrScriptMalformed:
+		return "bad-script-malformed"
+	case btcchain.ErrScriptValidation:
+		return "bad-script-validate"
+	}
+
+	return "rejected: " + err.Error()
+}
+
+// handleGetBlockTemplateProposal is a helper for handleGetBlockTemplate which
+// deals with block proposals.
+//
+// See https://en.bitcoin.it/wiki/BIP_0023 for more details.
+func handleGetBlockTemplateProposal(s *rpcServer, request *btcjson.TemplateRequest) (interface{}, error) {
+	hexData := request.Data
+	if hexData == "" {
+		return false, btcjson.Error{
+			Code: btcjson.ErrType.Code,
+			Message: fmt.Sprintf("data must contain the " +
+				"hex-encoded serialized block that is being " +
+				"proposed"),
+		}
+	}
+
+	// Ensure the provided data is sane and deserialize the proposed block.
+	if len(hexData)%2 != 0 {
+		hexData = "0" + hexData
+	}
+	dataBytes, err := hex.DecodeString(hexData)
+	if err != nil {
+		return false, btcjson.Error{
+			Code: btcjson.ErrDeserialization.Code,
+			Message: fmt.Sprintf("data must be "+
+				"hexadecimal string (not %q)", hexData),
+		}
+	}
+	var msgBlock btcwire.MsgBlock
+	if err := msgBlock.Deserialize(bytes.NewReader(dataBytes)); err != nil {
+		return nil, btcjson.Error{
+			Code:    btcjson.ErrDeserialization.Code,
+			Message: "Block decode failed: " + err.Error(),
+		}
+	}
+	block := btcutil.NewBlock(&msgBlock)
+
+	// Ensure the block is building from the expected previous block.
+	expectedPrevHash, _ := s.server.blockManager.chainState.Best()
+	prevHash := &block.MsgBlock().Header.PrevBlock
+	if expectedPrevHash == nil || !expectedPrevHash.IsEqual(prevHash) {
+		return "bad-prevblk", nil
+	}
+
+	flags := btcchain.BFDryRun | btcchain.BFNoPoWCheck
+	isOrphan, err := s.server.blockManager.ProcessBlock(block, flags)
+	if err != nil {
+		if _, ok := err.(btcchain.RuleError); !ok {
+			rpcsLog.Errorf("Failed to process block proposal: %v",
+				err)
+			return nil, btcjson.Error{
+				Code:    -25, // ErrRpcVerify
+				Message: err.Error(),
+			}
+		}
+
+		rpcsLog.Infof("Rejected block proposal: %v", err)
+		return chainErrToGBTErrString(err), nil
+	}
+	if isOrphan {
+		return "orphan", nil
+	}
+
+	return nil, nil
+}
+
 // handleGetBlockTemplate implements the getblocktemplate command.
 //
-// See https://en.bitcoin.it/wiki/BIP_0022 for more details.
+// See https://en.bitcoin.it/wiki/BIP_0022 and
+// https://en.bitcoin.it/wiki/BIP_0023 for more details.
 func handleGetBlockTemplate(s *rpcServer, cmd btcjson.Cmd, closeChan <-chan struct{}) (interface{}, error) {
 	c := cmd.(*btcjson.GetBlockTemplateCmd)
 	request := c.Request
@@ -1850,11 +2013,11 @@ func handleGetBlockTemplate(s *rpcServer, cmd btcjson.Cmd, closeChan <-chan stru
 		mode = request.Mode
 	}
 
-	// The only supported mode is currently "template".  Use a switch to
-	// make other modes easier to implement.
 	switch mode {
 	case "template":
 		return handleGetBlockTemplateRequest(s, request, closeChan)
+	case "proposal":
+		return handleGetBlockTemplateProposal(s, request)
 	}
 
 	return nil, btcjson.Error{