Convert floats to int64.

Following the example of bitcoind and the bitcoin wiki, provide a
function to convert floats (which are returned by the json-rpc server)
to int64 (which is the normal representation for most values involving
bitcoins).

jsonapi.go

@@ -742,3 +742,36 @@ func IsValidIdType(id interface{}) bool {
 		return false
 	}
 }
+
+// JSONToAmount Safely converts a floating point value to an int.
+// Clearly not all floating point numbers can be converted to ints (there
+// is no one-to-one mapping, but bitcoin's json api returns most numbers as
+// floats which are not safe to use when handling money.  Since bitcoins can
+// only be divided in a limited way, this methods works for the amounts returned
+// by the json api.  It is not for general use.
+// This follows the method described at:
+// https://en.bitcoin.it/wiki/Proper_Money_Handling_%28JSON-RPC%29
+func JSONToAmount(jsonAmount float64) (int64, error) {
+	var amount int64
+	var err error
+	if jsonAmount > 1.797693134862315708145274237317043567981e+300 {
+		err := fmt.Errorf("Error %d is too large to convert", jsonAmount)
+		return amount, err
+	}
+	if jsonAmount < -1.797693134862315708145274237317043567981e+300 {
+		err := fmt.Errorf("Error %d is too small to convert", jsonAmount)
+		return amount, err
+	}
+	tempVal := 1e8 * jsonAmount
+	// So we round properly.  float won't == 0 and if it did, that
+	// would be converted fine anyway.
+	if tempVal < 0 {
+		tempVal = tempVal - 0.5
+	}
+	if tempVal > 0 {
+		tempVal = tempVal + 0.5
+	}
+	// Then just rely on the integer truncating
+	amount = int64(tempVal)
+	return amount, err
+}

jsonapi_test.go

@@ -256,7 +256,7 @@ var idtests = []struct {
 }
 
 // TestIsValidIdType tests that IsValidIdType allows (and disallows the correct
-// types.
+// types).
 func TestIsValidIdType(t *testing.T) {
 	for _, tt := range idtests {
 		res := btcjson.IsValidIdType(tt.testId[0])
@@ -266,3 +266,34 @@ func TestIsValidIdType(t *testing.T) {
 	}
 	return
 }
+
+var floattests = []struct {
+	in   float64
+	out  int64
+	pass bool
+}{
+	{1.0, 100000000, true},
+	{-1.0, -100000000, true},
+	{0.0, 0, true},
+	{0.00000001, 1, true},
+	{-0.00000001, -1, true},
+	{-1.0e307, 0, false},
+	{1.0e307, 0, false},
+}
+
+// TestJSONtoAmount tests that JSONtoAmount returns the proper values.
+func TestJSONtoAmount(t *testing.T) {
+	for _, tt := range floattests {
+		res, err := btcjson.JSONToAmount(tt.in)
+		if tt.pass {
+			if res != tt.out || err != nil {
+				t.Errorf("Should not fail: ", tt.in)
+			}
+		} else {
+			if err == nil {
+				t.Errorf("Should not pass: ", tt.in)
+			}
+		}
+	}
+	return
+}

test_coverage.txt

@@ -1,5 +1,6 @@
 
 github.com/conformal/btcjson/jsonapi.go	 CreateMessage	 100.00% (310/310)
+github.com/conformal/btcjson/jsonapi.go	 JSONToAmount	 100.00% (15/15)
 github.com/conformal/btcjson/jsonfxns.go jsonRpcSend	 100.00% (7/7)
 github.com/conformal/btcjson/jsonfxns.go MarshallAndSend 100.00% (7/7)
 github.com/conformal/btcjson/jsonfxns.go GetRaw		 100.00% (6/6)
@@ -7,5 +8,5 @@ github.com/conformal/btcjson/jsonapi.go	 jsonWithArgs	 100.00% (5/5)
 github.com/conformal/btcjson/jsonapi.go	 IsValidIdType	 100.00% (3/3)
 github.com/conformal/btcjson/jsonapi.go	 RpcCommand	 66.67% (18/27)
 github.com/conformal/btcjson/jsonapi.go	 readResultCmd	 40.00% (20/50)
-github.com/conformal/btcjson		 --------------- 90.60% (376/415)
+github.com/conformal/btcjson		 --------------- 90.93% (391/430)