syncthing/vendor/github.com/oschwald/maxminddb-golang/reader.go
2016-07-04 13:34:34 +02:00

247 lines
7.3 KiB
Go

package maxminddb
import (
"bytes"
"errors"
"fmt"
"net"
"reflect"
)
const (
// NotFound is returned by LookupOffset when a matched root record offset
// cannot be found.
NotFound = ^uintptr(0)
dataSectionSeparatorSize = 16
)
var metadataStartMarker = []byte("\xAB\xCD\xEFMaxMind.com")
// Reader holds the data corresponding to the MaxMind DB file. Its only public
// field is Metadata, which contains the metadata from the MaxMind DB file.
type Reader struct {
hasMappedFile bool
buffer []byte
decoder decoder
Metadata Metadata
ipv4Start uint
}
// Metadata holds the metadata decoded from the MaxMind DB file. In particular
// in has the format version, the build time as Unix epoch time, the database
// type and description, the IP version supported, and a slice of the natural
// languages included.
type Metadata struct {
BinaryFormatMajorVersion uint `maxminddb:"binary_format_major_version"`
BinaryFormatMinorVersion uint `maxminddb:"binary_format_minor_version"`
BuildEpoch uint `maxminddb:"build_epoch"`
DatabaseType string `maxminddb:"database_type"`
Description map[string]string `maxminddb:"description"`
IPVersion uint `maxminddb:"ip_version"`
Languages []string `maxminddb:"languages"`
NodeCount uint `maxminddb:"node_count"`
RecordSize uint `maxminddb:"record_size"`
}
// FromBytes takes a byte slice corresponding to a MaxMind DB file and returns
// a Reader structure or an error.
func FromBytes(buffer []byte) (*Reader, error) {
metadataStart := bytes.LastIndex(buffer, metadataStartMarker)
if metadataStart == -1 {
return nil, newInvalidDatabaseError("error opening database: invalid MaxMind DB file")
}
metadataStart += len(metadataStartMarker)
metadataDecoder := decoder{buffer[metadataStart:]}
var metadata Metadata
rvMetdata := reflect.ValueOf(&metadata)
_, err := metadataDecoder.decode(0, rvMetdata)
if err != nil {
return nil, err
}
searchTreeSize := metadata.NodeCount * metadata.RecordSize / 4
dataSectionStart := searchTreeSize + dataSectionSeparatorSize
dataSectionEnd := uint(metadataStart - len(metadataStartMarker))
if dataSectionStart > dataSectionEnd {
return nil, newInvalidDatabaseError("the MaxMind DB contains invalid metadata")
}
d := decoder{
buffer[searchTreeSize+dataSectionSeparatorSize : metadataStart-len(metadataStartMarker)],
}
reader := &Reader{
buffer: buffer,
decoder: d,
Metadata: metadata,
ipv4Start: 0,
}
reader.ipv4Start, err = reader.startNode()
return reader, err
}
func (r *Reader) startNode() (uint, error) {
if r.Metadata.IPVersion != 6 {
return 0, nil
}
nodeCount := r.Metadata.NodeCount
node := uint(0)
var err error
for i := 0; i < 96 && node < nodeCount; i++ {
node, err = r.readNode(node, 0)
if err != nil {
return 0, err
}
}
return node, err
}
// Lookup takes an IP address as a net.IP structure and a pointer to the
// result value to Decode into.
func (r *Reader) Lookup(ipAddress net.IP, result interface{}) error {
pointer, err := r.lookupPointer(ipAddress)
if pointer == 0 || err != nil {
return err
}
return r.retrieveData(pointer, result)
}
// LookupOffset maps an argument net.IP to a corresponding record offset in the
// database. NotFound is returned if no such record is found, and a record may
// otherwise be extracted by passing the returned offset to Decode. LookupOffset
// is an advanced API, which exists to provide clients with a means to cache
// previously-decoded records.
func (r *Reader) LookupOffset(ipAddress net.IP) (uintptr, error) {
pointer, err := r.lookupPointer(ipAddress)
if pointer == 0 || err != nil {
return NotFound, err
}
return r.resolveDataPointer(pointer)
}
// Decode the record at |offset| into |result|. The result value pointed to
// must be a data value that corresponds to a record in the database. This may
// include a struct representation of the data, a map capable of holding the
// data or an empty interface{} value.
//
// If result is a pointer to a struct, the struct need not include a field
// for every value that may be in the database. If a field is not present in
// the structure, the decoder will not decode that field, reducing the time
// required to decode the record.
//
// As a special case, a struct field of type uintptr will be used to capture
// the offset of the value. Decode may later be used to extract the stored
// value from the offset. MaxMind DBs are highly normalized: for example in
// the City database, all records of the same country will reference a
// single representative record for that country. This uintptr behavior allows
// clients to leverage this normalization in their own sub-record caching.
func (r *Reader) Decode(offset uintptr, result interface{}) error {
rv := reflect.ValueOf(result)
if rv.Kind() != reflect.Ptr || rv.IsNil() {
return errors.New("result param must be a pointer")
}
_, err := r.decoder.decode(uint(offset), reflect.ValueOf(result))
return err
}
func (r *Reader) lookupPointer(ipAddress net.IP) (uint, error) {
if ipAddress == nil {
return 0, errors.New("ipAddress passed to Lookup cannot be nil")
}
ipV4Address := ipAddress.To4()
if ipV4Address != nil {
ipAddress = ipV4Address
}
if len(ipAddress) == 16 && r.Metadata.IPVersion == 4 {
return 0, fmt.Errorf("error looking up '%s': you attempted to look up an IPv6 address in an IPv4-only database", ipAddress.String())
}
return r.findAddressInTree(ipAddress)
}
func (r *Reader) findAddressInTree(ipAddress net.IP) (uint, error) {
bitCount := uint(len(ipAddress) * 8)
var node uint
if bitCount == 32 {
node = r.ipv4Start
}
nodeCount := r.Metadata.NodeCount
for i := uint(0); i < bitCount && node < nodeCount; i++ {
bit := uint(1) & (uint(ipAddress[i>>3]) >> (7 - (i % 8)))
var err error
node, err = r.readNode(node, bit)
if err != nil {
return 0, err
}
}
if node == nodeCount {
// Record is empty
return 0, nil
} else if node > nodeCount {
return node, nil
}
return 0, newInvalidDatabaseError("invalid node in search tree")
}
func (r *Reader) readNode(nodeNumber uint, index uint) (uint, error) {
RecordSize := r.Metadata.RecordSize
baseOffset := nodeNumber * RecordSize / 4
var nodeBytes []byte
var prefix uint64
switch RecordSize {
case 24:
offset := baseOffset + index*3
nodeBytes = r.buffer[offset : offset+3]
case 28:
prefix = uint64(r.buffer[baseOffset+3])
if index != 0 {
prefix &= 0x0F
} else {
prefix = (0xF0 & prefix) >> 4
}
offset := baseOffset + index*4
nodeBytes = r.buffer[offset : offset+3]
case 32:
offset := baseOffset + index*4
nodeBytes = r.buffer[offset : offset+4]
default:
return 0, newInvalidDatabaseError("unknown record size: %d", RecordSize)
}
return uint(uintFromBytes(prefix, nodeBytes)), nil
}
func (r *Reader) retrieveData(pointer uint, result interface{}) error {
if offset, err := r.resolveDataPointer(pointer); err != nil {
return err
} else {
return r.Decode(offset, result)
}
}
func (r *Reader) resolveDataPointer(pointer uint) (uintptr, error) {
var resolved = uintptr(pointer - r.Metadata.NodeCount - dataSectionSeparatorSize)
if resolved > uintptr(len(r.buffer)) {
return 0, newInvalidDatabaseError("the MaxMind DB file's search tree is corrupt")
}
return resolved, nil
}