add bitcoin balance endpoint

bitcoin/examples.json

@@ -11,5 +11,17 @@
         "price": 34682.74
       }
     }
+  ],
+  "balance": [
+    {
+      "title": "Get a bitcoin address balance",
+      "description": "Returns the balance of a bitcoin address",
+      "request": {
+        "address": "1MDUoxL1bGvMxhuoDYx6i11ePytECAk9QK"
+      },
+      "response": {
+        "balance": 4134
+      }
+    }
   ]
 }

bitcoin/handler/bitcoin.go

@@ -48,6 +48,40 @@ func New() *Bitcoin {
 	}
 }
 
+func (b *Bitcoin) Balance(ctx context.Context, req *pb.BalanceRequest, rsp *pb.BalanceResponse) error {
+	if len(req.Address) == 0 {
+		return errors.BadRequest("bitcoin.balance", "missing address")
+	}
+
+	uri := fmt.Sprintf("https://blockchain.info/balance?active=%s", req.Address)
+
+	resp, err := http.Get(uri)
+	if err != nil {
+		logger.Errorf("Failed to get balance: %v\n", err)
+		return errors.InternalServerError("bitcoin.balance", "failed to get price")
+	}
+	defer resp.Body.Close()
+
+	buf, _ := ioutil.ReadAll(resp.Body)
+
+	if resp.StatusCode != 200 {
+		logger.Errorf("Failed to get price (non 200): %d %v\n", resp.StatusCode, string(buf))
+		return errors.InternalServerError("bitcoin.balance", "failed to get price")
+	}
+
+	var respBody map[string]interface{}
+
+	if err := json.Unmarshal(buf, &respBody); err != nil {
+		logger.Errorf("Failed to unmarshal balance: %v\n", err)
+		return errors.InternalServerError("bitcoin.balance", "failed to get price")
+	}
+
+	info := respBody[req.Address].(map[string]interface{})
+	rsp.Balance = int64(info["final_balance"].(float64))
+
+	return nil
+}
+
 func (b *Bitcoin) Price(ctx context.Context, req *pb.PriceRequest, rsp *pb.PriceResponse) error {
 	if len(req.Symbol) <= 0 {
 		req.Symbol = "BTCUSD"

bitcoin/proto/bitcoin.proto

@@ -6,6 +6,7 @@ option go_package = "./proto;bitcoin";
 
 service Bitcoin {
 	rpc Price(PriceRequest) returns (PriceResponse) {}
+	rpc Balance(BalanceRequest) returns (BalanceResponse) {}
 }
 
 // Get the price of bitcoin
@@ -20,3 +21,14 @@ message PriceResponse {
 	// The price of bitcoin
 	double price = 2;
 }
+
+// Get the BTC balance of an address
+message BalanceRequest {
+	// address to lookup
+	string address = 1;
+}
+
+message BalanceResponse {
+	// total BTC as satoshis
+	int64 balance = 1;
+}