added example package

vendor/github.com/IncSW/geoip2/reader.go

@@ -0,0 +1,124 @@
+package geoip2
+
+import (
+	"bytes"
+	"errors"
+	"net"
+	"strconv"
+)
+
+var ErrNotFound = errors.New("not found")
+
+type reader struct {
+	metadata          *Metadata
+	buffer            []byte
+	decoderBuffer     []byte
+	nodeBuffer        []byte
+	ipV4Start         uint
+	ipV4StartBitDepth uint
+	nodeOffsetMult    uint
+}
+
+func (r *reader) getOffset(ip net.IP) (uint, error) {
+	pointer, err := r.lookupPointer(ip)
+	if err != nil {
+		return 0, err
+	}
+	offset := pointer - uint(r.metadata.NodeCount) - uint(dataSectionSeparatorSize)
+	if offset >= uint(len(r.buffer)) {
+		return 0, errors.New("the MaxMind DB search tree is corrupt: " + strconv.Itoa(int(pointer)))
+	}
+	return offset, nil
+}
+
+func (r *reader) lookupPointer(ip net.IP) (uint, error) {
+	if ip == nil {
+		return 0, errors.New("IP cannot be nil")
+	}
+	ipV4 := ip.To4()
+	if ipV4 != nil {
+		ip = ipV4
+	}
+	if len(ip) == 16 && r.metadata.IPVersion == 4 {
+		return 0, errors.New("cannot look up an IPv6 address in an IPv4-only database")
+	}
+	bitCount := uint(len(ip)) * 8
+	node := uint(0)
+	if bitCount == 32 {
+		node = r.ipV4Start
+	}
+	nodeCount := uint(r.metadata.NodeCount)
+	i := uint(0)
+	for ; i < bitCount && node < nodeCount; i++ {
+		bit := 1 & (ip[i>>3] >> (7 - (i % 8)))
+		offset := node * r.nodeOffsetMult
+		if bit == 0 {
+			node = r.readLeft(offset)
+		} else {
+			node = r.readRight(offset)
+		}
+	}
+	if node == nodeCount {
+		return 0, ErrNotFound
+	} else if node > nodeCount {
+		return node, nil
+	}
+	return 0, errors.New("invalid node in search tree")
+}
+
+func (r *reader) readLeft(nodeNumber uint) uint {
+	switch r.metadata.RecordSize {
+	case 28:
+		return ((uint(r.nodeBuffer[nodeNumber+3]) & 0xF0) << 20) | (uint(r.nodeBuffer[nodeNumber]) << 16) | (uint(r.nodeBuffer[nodeNumber+1]) << 8) | uint(r.nodeBuffer[nodeNumber+2])
+	case 24:
+		return (uint(r.nodeBuffer[nodeNumber]) << 16) | (uint(r.nodeBuffer[nodeNumber+1]) << 8) | uint(r.nodeBuffer[nodeNumber+2])
+	default: // case 32:
+		return (uint(r.nodeBuffer[nodeNumber]) << 24) | (uint(r.nodeBuffer[nodeNumber+1]) << 16) | (uint(r.nodeBuffer[nodeNumber+2]) << 8) | uint(r.nodeBuffer[nodeNumber+3])
+	}
+}
+
+func (r *reader) readRight(nodeNumber uint) uint {
+	switch r.metadata.RecordSize {
+	case 28:
+		return ((uint(r.nodeBuffer[nodeNumber+3]) & 0x0F) << 24) | (uint(r.nodeBuffer[nodeNumber+4]) << 16) | (uint(r.nodeBuffer[nodeNumber+5]) << 8) | uint(r.nodeBuffer[nodeNumber+6])
+	case 24:
+		return (uint(r.nodeBuffer[nodeNumber+3]) << 16) | (uint(r.nodeBuffer[nodeNumber+4]) << 8) | uint(r.nodeBuffer[nodeNumber+5])
+	default: // case 32:
+		return (uint(r.nodeBuffer[nodeNumber+4]) << 24) | (uint(r.nodeBuffer[nodeNumber+5]) << 16) | (uint(r.nodeBuffer[nodeNumber+6]) << 8) | uint(r.nodeBuffer[nodeNumber+7])
+	}
+}
+
+func newReader(buffer []byte) (*reader, error) {
+	if len(buffer) == 0 {
+		return nil, errors.New("buffer is empty")
+	}
+
+	metadataStart := bytes.LastIndex(buffer, metadataStartMarker)
+	metadata, err := readMetadata(buffer[metadataStart+len(metadataStartMarker):])
+	if err != nil {
+		return nil, err
+	}
+	nodeOffsetMult := uint(metadata.RecordSize) / 4
+	searchTreeSize := uint(metadata.NodeCount) * nodeOffsetMult
+	dataSectionStart := searchTreeSize + dataSectionSeparatorSize
+	if dataSectionStart > uint(metadataStart) {
+		return nil, errors.New("the MaxMind DB contains invalid metadata")
+	}
+	reader := &reader{
+		metadata:       metadata,
+		buffer:         buffer,
+		decoderBuffer:  buffer[searchTreeSize+dataSectionSeparatorSize : metadataStart],
+		nodeBuffer:     buffer[:searchTreeSize],
+		nodeOffsetMult: nodeOffsetMult,
+	}
+	if metadata.IPVersion == 6 {
+		node := uint(0)
+		i := uint(0)
+		for ; i < 96 && node < uint(metadata.NodeCount); i++ {
+			node = reader.readLeft(node * nodeOffsetMult)
+		}
+		reader.ipV4Start = node
+		reader.ipV4StartBitDepth = i
+	}
+	return reader, nil
+}