ipam/host-local: support sets of disjoint ranges

In real-world address allocations, disjoint address ranges are common.
Therefore, the host-local allocator should support them.

This change still allows for multiple IPs in a single configuration, but
also allows for a "set of subnets."

Fixes: #45

plugins/ipam/host-local/backend/allocator/range_set.go

@@ -0,0 +1,97 @@
+// Copyright 2017 CNI authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package allocator
+
+import (
+	"fmt"
+	"net"
+	"strings"
+)
+
+// Contains returns true if any range in this set contains an IP
+func (s *RangeSet) Contains(addr net.IP) bool {
+	r, _ := s.RangeFor(addr)
+	return r != nil
+}
+
+// RangeFor finds the range that contains an IP, or nil if not found
+func (s *RangeSet) RangeFor(addr net.IP) (*Range, error) {
+	if err := canonicalizeIP(&addr); err != nil {
+		return nil, err
+	}
+
+	for _, r := range *s {
+		if r.Contains(addr) {
+			return &r, nil
+		}
+	}
+
+	return nil, fmt.Errorf("%s not in range set %s", addr.String(), s.String())
+}
+
+// Overlaps returns true if any ranges in any set overlap with this one
+func (s *RangeSet) Overlaps(p1 *RangeSet) bool {
+	for _, r := range *s {
+		for _, r1 := range *p1 {
+			if r.Overlaps(&r1) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// Canonicalize ensures the RangeSet is in a standard form, and detects any
+// invalid input. Call Range.Canonicalize() on every Range in the set
+func (s *RangeSet) Canonicalize() error {
+	if len(*s) == 0 {
+		return fmt.Errorf("empty range set")
+	}
+
+	fam := 0
+	for i, _ := range *s {
+		if err := (*s)[i].Canonicalize(); err != nil {
+			return err
+		}
+		if i == 0 {
+			fam = len((*s)[i].RangeStart)
+		} else {
+			if fam != len((*s)[i].RangeStart) {
+				return fmt.Errorf("mixed address families")
+			}
+		}
+	}
+
+	// Make sure none of the ranges in the set overlap
+	l := len(*s)
+	for i, r1 := range (*s)[:l-1] {
+		for _, r2 := range (*s)[i+1:] {
+			if r1.Overlaps(&r2) {
+				return fmt.Errorf("subnets %s and %s overlap", r1.String(), r2.String())
+			}
+		}
+	}
+
+	return nil
+}
+
+func (s *RangeSet) String() string {
+	out := []string{}
+	for _, r := range *s {
+		out = append(out, r.String())
+	}
+
+	return strings.Join(out, ",")
+}