[#137] sdk: Implement netmap filtering and selection

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/netmap/filter.go

@@ -0,0 +1,129 @@
+package netmap
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
+)
+
+// MainFilterName is a name of the filter
+// which points to the whole netmap.
+const MainFilterName = "*"
+
+// applyFilter applies named filter to b.
+func (c *Context) applyFilter(name string, b *Node) bool {
+	return name == MainFilterName || c.match(c.Filters[name], b)
+}
+
+// processFilters processes filters and returns error is any of them is invalid.
+func (c *Context) processFilters(p *netmap.PlacementPolicy) error {
+	for _, f := range p.GetFilters() {
+		if err := c.processFilter(f, true); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (c *Context) processFilter(f *netmap.Filter, top bool) error {
+	if f == nil {
+		return fmt.Errorf("%w: FILTER", ErrMissingField)
+	}
+	if f.GetName() == MainFilterName {
+		return fmt.Errorf("%w: '*' is reserved", ErrInvalidFilterName)
+	}
+	if top && f.GetName() == "" {
+		return ErrUnnamedTopFilter
+	}
+	if !top && f.GetName() != "" && c.Filters[f.GetName()] == nil {
+		return fmt.Errorf("%w: '%s'", ErrFilterNotFound, f.GetName())
+	}
+	switch f.GetOp() {
+	case netmap.AND, netmap.OR:
+		for _, flt := range f.GetFilters() {
+			if err := c.processFilter(flt, false); err != nil {
+				return err
+			}
+		}
+	default:
+		if len(f.GetFilters()) != 0 {
+			return ErrNonEmptyFilters
+		} else if !top && f.GetName() != "" { // named reference
+			return nil
+		}
+		switch f.GetOp() {
+		case netmap.EQ, netmap.NE:
+		case netmap.GT, netmap.GE, netmap.LT, netmap.LE:
+			n, err := strconv.ParseUint(f.GetValue(), 10, 64)
+			if err != nil {
+				return fmt.Errorf("%w: '%s'", ErrInvalidNumber, f.GetValue())
+			}
+			c.numCache[f] = n
+		default:
+			return fmt.Errorf("%w: %d", ErrInvalidFilterOp, f.GetOp())
+		}
+	}
+	if top {
+		c.Filters[f.GetName()] = f
+	}
+	return nil
+}
+
+// match matches f against b. It returns no errors because
+// filter should have been parsed during context creation
+// and missing node properties are considered as a regular fail.
+func (c *Context) match(f *netmap.Filter, b *Node) bool {
+	switch f.GetOp() {
+	case netmap.AND, netmap.OR:
+		for _, lf := range f.GetFilters() {
+			if lf.GetName() != "" {
+				lf = c.Filters[lf.GetName()]
+			}
+			ok := c.match(lf, b)
+			if ok == (f.GetOp() == netmap.OR) {
+				return ok
+			}
+		}
+		return f.GetOp() == netmap.AND
+	default:
+		return c.matchKeyValue(f, b)
+	}
+}
+
+func (c *Context) matchKeyValue(f *netmap.Filter, b *Node) bool {
+	switch f.GetOp() {
+	case netmap.EQ:
+		return b.Attribute(f.GetKey()) == f.GetValue()
+	case netmap.NE:
+		return b.Attribute(f.GetKey()) != f.GetValue()
+	default:
+		var attr uint64
+		switch f.GetKey() {
+		case PriceAttr:
+			attr = b.Price
+		case CapacityAttr:
+			attr = b.Capacity
+		default:
+			var err error
+			attr, err = strconv.ParseUint(b.Attribute(f.GetKey()), 10, 64)
+			if err != nil {
+				// Note: because filters are somewhat independent from nodes attributes,
+				// We don't report an error here, and fail filter instead.
+				return false
+			}
+		}
+		switch f.GetOp() {
+		case netmap.GT:
+			return attr > c.numCache[f]
+		case netmap.GE:
+			return attr >= c.numCache[f]
+		case netmap.LT:
+			return attr < c.numCache[f]
+		case netmap.LE:
+			return attr <= c.numCache[f]
+		}
+	}
+	// will not happen if context was created from f (maybe panic?)
+	return false
+}