package memconservative import ( "errors" "fmt" "io" "os" "strings" "google.golang.org/protobuf/encoding/protowire" ) var ( errFailedToReadBytes = errors.New("failed to read bytes") errFailedToReadExpectedLenBytes = errors.New("failed to read expected length of bytes") errInvalidGeodataFile = errors.New("invalid geodata file") errInvalidGeodataVarintLength = errors.New("invalid geodata varint length") errCodeNotFound = errors.New("code not found") ) func emitBytes(f io.ReadSeeker, code string) ([]byte, error) { count := 1 isInner := false tempContainer := make([]byte, 0, 5) var result []byte var advancedN uint64 = 1 var geoDataVarintLength, codeVarintLength, varintLenByteLen uint64 = 0, 0, 0 Loop: for { container := make([]byte, advancedN) bytesRead, err := f.Read(container) if err == io.EOF { return nil, errCodeNotFound } if err != nil { return nil, errFailedToReadBytes } if bytesRead != len(container) { return nil, errFailedToReadExpectedLenBytes } switch count { case 1, 3: // data type ((field_number << 3) | wire_type) if container[0] != 10 { // byte `0A` equals to `10` in decimal return nil, errInvalidGeodataFile } advancedN = 1 count++ case 2, 4: // data length tempContainer = append(tempContainer, container...) if container[0] > 127 { // max one-byte-length byte `7F`(0FFF FFFF) equals to `127` in decimal advancedN = 1 goto Loop } lenVarint, n := protowire.ConsumeVarint(tempContainer) if n < 0 { return nil, errInvalidGeodataVarintLength } tempContainer = nil if !isInner { isInner = true geoDataVarintLength = lenVarint advancedN = 1 } else { isInner = false codeVarintLength = lenVarint varintLenByteLen = uint64(n) advancedN = codeVarintLength } count++ case 5: // data value if strings.EqualFold(string(container), code) { count++ offset := -(1 + int64(varintLenByteLen) + int64(codeVarintLength)) _, _ = f.Seek(offset, 1) // back to the start of GeoIP or GeoSite varint advancedN = geoDataVarintLength // the number of bytes to be read in next round } else { count = 1 offset := int64(geoDataVarintLength) - int64(codeVarintLength) - int64(varintLenByteLen) - 1 _, _ = f.Seek(offset, 1) // skip the unmatched GeoIP or GeoSite varint advancedN = 1 // the next round will be the start of another GeoIPList or GeoSiteList } case 6: // matched GeoIP or GeoSite varint result = container break Loop } } return result, nil } func Decode(filename, code string) ([]byte, error) { f, err := os.Open(filename) if err != nil { return nil, fmt.Errorf("failed to open file: %s, base error: %s", filename, err.Error()) } defer func(f *os.File) { _ = f.Close() }(f) geoBytes, err := emitBytes(f, code) if err != nil { return nil, err } return geoBytes, nil }