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internal/util/float.go

@@ -0,0 +1,64 @@
+package util
+
+import (
+	"math"
+	"strconv"
+)
+
+// Go's JSON encoder for floats does not support NaN (https://github.com/golang/go/issues/3480).
+// This program uses NaN as a signal for missing data.
+// For the HTTP JSON API to be able to handle NaN values,
+// we have to use our own type which implements encoding/json.Marshaler itself.
+type Float float64
+
+var (
+	NaN         Float  = Float(math.NaN())
+	nullAsBytes []byte = []byte("null")
+)
+
+func (f Float) IsNaN() bool {
+	return math.IsNaN(float64(f))
+}
+
+func (f Float) MarshalJSON() ([]byte, error) {
+	if math.IsNaN(float64(f)) {
+		return nullAsBytes, nil
+	}
+
+	return strconv.AppendFloat(make([]byte, 0, 10), float64(f), 'f', 3, 64), nil
+}
+
+func (f *Float) UnmarshalJSON(input []byte) error {
+	if string(input) == "null" {
+		*f = NaN
+		return nil
+	}
+
+	val, err := strconv.ParseFloat(string(input), 64)
+	if err != nil {
+		return err
+	}
+	*f = Float(val)
+	return nil
+}
+
+// Same as `[]Float`, but can be marshaled to JSON with less allocations.
+type FloatArray []Float
+
+func (fa FloatArray) MarshalJSON() ([]byte, error) {
+	buf := make([]byte, 0, 2+len(fa)*8)
+	buf = append(buf, '[')
+	for i := 0; i < len(fa); i++ {
+		if i != 0 {
+			buf = append(buf, ',')
+		}
+
+		if fa[i].IsNaN() {
+			buf = append(buf, `null`...)
+		} else {
+			buf = strconv.AppendFloat(buf, float64(fa[i]), 'f', 3, 64)
+		}
+	}
+	buf = append(buf, ']')
+	return buf, nil
+}