[#266] Support per namespace placement policies configuration

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

cmd/s3-gw/namespaces.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
+)
+
+type NamespacesConfig struct {
+	Namespaces Namespaces `json:"namespaces"`
+}
+
+type Namespaces map[string]Namespace
+
+type Namespace struct {
+	Name                string              `json:"-"`
+	LocationConstraints LocationConstraints `json:"location_constraints"`
+	CopiesNumbers       map[string][]uint32 `json:"copies_numbers"`
+}
+
+type LocationConstraints map[string]netmap.PlacementPolicy
+
+func (c *Namespaces) UnmarshalJSON(data []byte) error {
+	namespaces := make(map[string]Namespace)
+	if err := json.Unmarshal(data, &namespaces); err != nil {
+		return err
+	}
+
+	for name, namespace := range namespaces {
+		namespace.Name = name
+		namespaces[name] = namespace
+	}
+
+	*c = namespaces
+
+	return nil
+}
+
+func (c *LocationConstraints) UnmarshalJSON(data []byte) error {
+	m := make(map[string]string)
+	if err := json.Unmarshal(data, &m); err != nil {
+		return err
+	}
+
+	*c = make(LocationConstraints, len(m))
+	for region, policy := range m {
+		var pp netmap.PlacementPolicy
+		if err := pp.DecodeString(policy); err == nil {
+			(*c)[region] = pp
+			continue
+		}
+
+		if err := pp.UnmarshalJSON([]byte(policy)); err == nil {
+			(*c)[region] = pp
+			continue
+		}
+
+		return fmt.Errorf("failed to parse location contraint '%s': '%s'", region, policy)
+	}
+
+	return nil
+}
+
+func (c LocationConstraints) MarshalJSON() ([]byte, error) {
+	m := make(map[string]string, len(c))
+
+	for region, policy := range c {
+		var sb strings.Builder
+		if err := policy.WriteStringTo(&sb); err != nil {
+			return nil, err
+		}
+
+		m[region] = sb.String()
+	}
+
+	return json.Marshal(m)
+}