forked from cridenour/go-postgis
/
decode.go
56 lines (46 loc) · 1.23 KB
/
decode.go
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package postgis
import (
"bytes"
"encoding/binary"
"encoding/hex"
"errors"
"io"
)
const (
wkbXDR byte = 0
wkbNDR byte = 1
)
// Helper functions to read the EWKB (well-known binary) from PostGIS
// Format document available at http://trac.osgeo.org/postgis/browser/trunk/doc/ZMSgeoms.txt
// Since Postgres by default returns hex encoded strings we need to first get bytes back, only used from Scan
func decode(value interface{}) (io.Reader, error) {
ewkb, err := hex.DecodeString(string(value.([]byte)))
if err != nil {
return nil, err
}
return bytes.NewReader(ewkb), nil
}
func readEWKB(reader io.Reader, g Geometry) error {
var byteOrder binary.ByteOrder
var wkbByteOrder byte
var wkbType uint32
// Read as Little Endian to attempt to determine byte order
if err := binary.Read(reader, binary.LittleEndian, &wkbByteOrder); err != nil {
return err
}
// Decide byte order
switch wkbByteOrder {
case wkbXDR:
byteOrder = binary.BigEndian
case wkbNDR:
byteOrder = binary.LittleEndian
default:
return errors.New("Unsupported byte order")
}
// Determine the geometery type
if err := binary.Read(reader, byteOrder, &wkbType); err != nil {
return err
}
// Decode into our struct
return binary.Read(reader, byteOrder, g)
}