GetBlockTemplate RPC client implementation (#1629)

* GetBlockTemplate RPC client implementation

* Txid added to the getblocktemplate result

* Omitempty for TxID and improved comment for GetBlockTemplate 'rules' field

btcjson/chainsvrcmds.go

@@ -350,6 +350,10 @@ type TemplateRequest struct {
 	// "proposal".
 	Data   string `json:"data,omitempty"`
 	WorkID string `json:"workid,omitempty"`
+
+	// list of supported softfork deployments, by name
+	// Ref: https://en.bitcoin.it/wiki/BIP_0009#getblocktemplate_changes.
+	Rules []string `json:"rules,omitempty"`
 }
 
 // convertTemplateRequestField potentially converts the provided value as

btcjson/chainsvrresults.go

@@ -236,8 +236,10 @@ type GetBlockFilterResult struct {
 // GetBlockTemplateResultTx models the transactions field of the
 // getblocktemplate command.
 type GetBlockTemplateResultTx struct {
-	Data    string  `json:"data"`
-	Hash    string  `json:"hash"`
+	Data string `json:"data"`
+	Hash string `json:"hash"`
+	// TODO: remove omitempty once implemented in rpcserver
+	TxID    string  `json:"txid,omitempty"`
 	Depends []int64 `json:"depends"`
 	Fee     int64   `json:"fee"`
 	SigOps  int64   `json:"sigops"`

rpcclient/mining.go

@@ -461,4 +461,39 @@ func (c *Client) SubmitBlock(block *btcutil.Block, options *btcjson.SubmitBlockO
 	return c.SubmitBlockAsync(block, options).Receive()
 }
 
-// TODO(davec): Implement GetBlockTemplate
+// FutureGetBlockTemplateResponse is a future promise to deliver the result of a
+// GetBlockTemplateAsync RPC invocation (or an applicable error).
+type FutureGetBlockTemplateResponse chan *response
+
+// Receive waits for the response promised by the future and returns an error if
+// any occurred when retrieving the block template.
+func (r FutureGetBlockTemplateResponse) Receive() (*btcjson.GetBlockTemplateResult, error) {
+	res, err := receiveFuture(r)
+	if err != nil {
+		return nil, err
+	}
+
+	// Unmarshal result as a getwork result object.
+	var result btcjson.GetBlockTemplateResult
+	err = json.Unmarshal(res, &result)
+	if err != nil {
+		return nil, err
+	}
+
+	return &result, nil
+}
+
+// GetBlockTemplateAsync returns an instance of a type that can be used to get the
+// result of the RPC at some future time by invoking the Receive function on the
+// returned instance.
+//
+// See GetBlockTemplate for the blocking version and more details.
+func (c *Client) GetBlockTemplateAsync(req *btcjson.TemplateRequest) FutureGetBlockTemplateResponse {
+	cmd := btcjson.NewGetBlockTemplateCmd(req)
+	return c.sendCmd(cmd)
+}
+
+// GetBlockTemplate returns a new block template for mining.
+func (c *Client) GetBlockTemplate(req *btcjson.TemplateRequest) (*btcjson.GetBlockTemplateResult, error) {
+	return c.GetBlockTemplateAsync(req).Receive()
+}

rpcserverhelp.go

@@ -295,6 +295,7 @@ var helpDescsEnUS = map[string]string{
 	"templaterequest-target":       "The desired target for the block template (this parameter is ignored)",
 	"templaterequest-data":         "Hex-encoded block data (only for mode=proposal)",
 	"templaterequest-workid":       "The server provided workid if provided in block template (not applicable)",
+	"templaterequest-rules":        "Specific block rules that are to be enforced e.g. '[\"segwit\"]",
 
 	// GetBlockTemplateResultTx help.
 	"getblocktemplateresulttx-data":    "Hex-encoded transaction data (byte-for-byte)",
@@ -302,6 +303,7 @@ var helpDescsEnUS = map[string]string{
 	"getblocktemplateresulttx-depends": "Other transactions before this one (by 1-based index in the 'transactions'  list) that must be present in the final block if this one is",
 	"getblocktemplateresulttx-fee":     "Difference in value between transaction inputs and outputs (in Satoshi)",
 	"getblocktemplateresulttx-sigops":  "Total number of signature operations as counted for purposes of block limits",
+	"getblocktemplateresulttx-txid":    "The transaction id, can be different from hash.",
 	"getblocktemplateresulttx-weight":  "The weight of the transaction",
 
 	// GetBlockTemplateResultAux help.