Cpu resources (#642)

* fn: cpu quota implementation

api/models/config.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"strconv"
 )
 
 type Config map[string]string
@@ -125,3 +126,67 @@ func (h *Headers) Scan(value interface{}) error {
 	// otherwise, return an error
 	return fmt.Errorf("headers invalid db format: %T %T value, err: %v", value, bv, err)
 }
+
+// MilliCPU units
+type MilliCPUs uint64
+
+const (
+	MinMilliCPUs = 0       // 0 is unlimited
+	MaxMilliCPUs = 1024000 // 1024 CPUs
+)
+
+// implements fmt.Stringer
+func (c MilliCPUs) String() string {
+	if c == 0 {
+		return ""
+	}
+	return fmt.Sprintf("%dm", c)
+}
+
+// implements json.Unmarshaler
+func (c *MilliCPUs) UnmarshalJSON(data []byte) error {
+
+	outer := bytes.TrimSpace(data)
+	if !bytes.HasSuffix(outer, []byte("\"")) || !bytes.HasPrefix(outer, []byte("\"")) {
+		return ErrInvalidJSON
+	}
+
+	outer = bytes.TrimPrefix(outer, []byte("\""))
+	outer = bytes.TrimSuffix(outer, []byte("\""))
+	outer = bytes.TrimSpace(outer)
+	if len(outer) == 0 {
+		*c = 0
+		return nil
+	}
+
+	if bytes.HasSuffix(outer, []byte("m")) {
+
+		// Support milli cores as "100m"
+		outer = bytes.TrimSuffix(outer, []byte("m"))
+		mCPU, err := strconv.ParseUint(string(outer), 10, 64)
+		if err != nil || mCPU > MaxMilliCPUs || mCPU < MinMilliCPUs {
+			return ErrInvalidCPUs
+		}
+		*c = MilliCPUs(mCPU)
+	} else {
+		// Support for floating point "0.1" style CPU units
+		fCPU, err := strconv.ParseFloat(string(outer), 64)
+		if err != nil || fCPU < MinMilliCPUs/1000 || fCPU > MaxMilliCPUs/1000 {
+			return ErrInvalidCPUs
+		}
+		*c = MilliCPUs(fCPU * 1000)
+	}
+
+	return nil
+}
+
+// implements json.Marshaler
+func (c *MilliCPUs) MarshalJSON() ([]byte, error) {
+
+	if *c < MinMilliCPUs || *c > MaxMilliCPUs {
+		return nil, ErrInvalidCPUs
+	}
+
+	// always use milli cpus "1000m" format
+	return []byte(fmt.Sprintf("\"%s\"", c.String())), nil
+}