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scanner.go
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scanner.go
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package wkb
import (
"bytes"
"database/sql"
"database/sql/driver"
"encoding/hex"
"errors"
"fmt"
"io"
"github.com/dadadamarine/orb"
)
var (
_ sql.Scanner = &GeometryScanner{}
_ driver.Value = value{}
)
var (
// ErrUnsupportedDataType is returned by Scan methods when asked to scan
// non []byte data from the database. This should never happen
// if the driver is acting appropriately.
ErrUnsupportedDataType = errors.New("wkb: scan value must be []byte")
// ErrNotWKB is returned when unmarshalling WKB and the data is not valid.
ErrNotWKB = errors.New("wkb: invalid data")
// ErrIncorrectGeometry is returned when unmarshalling WKB data into the wrong type.
// For example, unmarshaling linestring data into a point.
ErrIncorrectGeometry = errors.New("wkb: incorrect geometry")
// ErrUnsupportedGeometry is returned when geometry type is not supported by this lib.
ErrUnsupportedGeometry = errors.New("wkb: unsupported geometry")
)
// GeometryScanner is a thing that can scan in sql query results.
// It can be used as a scan destination:
//
// var s wkb.GeometryScanner
// err := db.QueryRow("SELECT latlon FROM foo WHERE id=?", id).Scan(&s)
// ...
// if s.Valid {
// // use s.Geometry
// } else {
// // NULL value
// }
type GeometryScanner struct {
g interface{}
Geometry orb.Geometry
Valid bool // Valid is true if the geometry is not NULL
}
// Scanner will return a GeometryScanner that can scan sql query results.
// The geometryScanner.Geometry attribute will be set to the value.
// If g is non-nil, it MUST be a pointer to an orb.Geometry
// type like a Point or LineString. In that case the value will be written to
// g and the Geometry attribute.
//
// var p orb.Point
// err := db.QueryRow("SELECT latlon FROM foo WHERE id=?", id).Scan(wkb.Scanner(&p))
// ...
// // use p
//
// If the value may be null check Valid first:
//
// var point orb.Point
// s := wkb.Scanner(&point)
// err := db.QueryRow("SELECT latlon FROM foo WHERE id=?", id).Scan(&s)
// ...
// if s.Valid {
// // use p
// } else {
// // NULL value
// }
//
// Scanning directly from MySQL columns is supported. By default MySQL returns geometry
// data as WKB but prefixed with a 4 byte SRID. To support this, if the data is not
// valid WKB, the code will strip the first 4 bytes and try again.
// This works for most use cases.
func Scanner(g interface{}) *GeometryScanner {
return &GeometryScanner{g: g}
}
// Scan will scan the input []byte data into a geometry.
// This could be into the orb geometry type pointer or, if nil,
// the scanner.Geometry attribute.
func (s *GeometryScanner) Scan(d interface{}) error {
s.Geometry = nil
s.Valid = false
if d == nil {
return nil
}
data, ok := d.([]byte)
if !ok {
return ErrUnsupportedDataType
}
if data == nil {
return nil
}
// go-pg will return ST_AsBinary(*) data as `\xhexencoded` which
// needs to be converted to true binary for further decoding.
// Code detects the \x prefix and then converts the rest from Hex to binary.
if len(data) > 2 && data[0] == byte('\\') && data[1] == byte('x') {
n, err := hex.Decode(data, data[2:])
if err != nil {
return fmt.Errorf("thought the data was hex, but it is not: %v", err)
}
data = data[:n]
}
switch g := s.g.(type) {
case nil:
m, err := Unmarshal(data)
if err != nil {
return err
}
s.Geometry = m
s.Valid = true
return nil
case *orb.Point:
p, err := scanPoint(data)
if err != nil {
return err
}
*g = p
s.Geometry = p
s.Valid = true
return nil
case *orb.MultiPoint:
p, err := scanMultiPoint(data)
if err != nil {
return err
}
*g = p
s.Geometry = p
s.Valid = true
return nil
case *orb.LineString:
p, err := scanLineString(data)
if err != nil {
return err
}
*g = p
s.Geometry = p
s.Valid = true
return nil
case *orb.MultiLineString:
p, err := scanMultiLineString(data)
if err != nil {
return err
}
*g = p
s.Geometry = p
s.Valid = true
return nil
case *orb.Ring:
m, err := Unmarshal(data)
if err != nil {
return err
}
if p, ok := m.(orb.Polygon); ok && len(p) == 1 {
*g = p[0]
s.Geometry = p[0]
s.Valid = true
return nil
}
return ErrIncorrectGeometry
case *orb.Polygon:
m, err := scanPolygon(data)
if err != nil {
return err
}
*g = m
s.Geometry = m
s.Valid = true
return nil
case *orb.MultiPolygon:
m, err := scanMultiPolygon(data)
if err != nil {
return err
}
*g = m
s.Geometry = m
s.Valid = true
return nil
case *orb.Collection:
m, err := scanCollection(data)
if err != nil {
return err
}
*g = m
s.Geometry = m
s.Valid = true
return nil
case *orb.Bound:
m, err := Unmarshal(data)
if err != nil {
return err
}
b := m.Bound()
*g = b
s.Geometry = b
s.Valid = true
return nil
}
return ErrIncorrectGeometry
}
func scanPoint(data []byte) (orb.Point, error) {
order, typ, data, err := unmarshalByteOrderType(data)
if err != nil {
return orb.Point{}, err
}
// Checking for MySQL's SRID+WKB format where the SRID is 0.
// Common SRIDs would be handled in the unmarshalByteOrderType above.
if len(data) == 25 &&
data[0] == 0 && data[1] == 0 && data[2] == 0 && data[3] == 0 {
data = data[4:]
order, typ, data, err = unmarshalByteOrderType(data)
if err != nil {
return orb.Point{}, err
}
}
switch typ {
case pointType:
return unmarshalPoint(order, data[5:])
case multiPointType:
mp, err := unmarshalMultiPoint(order, data[5:])
if err != nil {
return orb.Point{}, err
}
if len(mp) == 1 {
return mp[0], nil
}
}
return orb.Point{}, ErrIncorrectGeometry
}
func scanMultiPoint(data []byte) (orb.MultiPoint, error) {
m, err := Unmarshal(data)
if err != nil {
return nil, err
}
switch p := m.(type) {
case orb.Point:
return orb.MultiPoint{p}, nil
case orb.MultiPoint:
return p, nil
}
return nil, ErrIncorrectGeometry
}
func scanLineString(data []byte) (orb.LineString, error) {
order, typ, data, err := unmarshalByteOrderType(data)
if err != nil {
return nil, err
}
switch typ {
case lineStringType:
return unmarshalLineString(order, data[5:])
case multiLineStringType:
mls, err := unmarshalMultiLineString(order, data[5:])
if err != nil {
return nil, err
}
if len(mls) == 1 {
return mls[0], nil
}
}
return nil, ErrIncorrectGeometry
}
func scanMultiLineString(data []byte) (orb.MultiLineString, error) {
order, typ, data, err := unmarshalByteOrderType(data)
if err != nil {
return nil, err
}
switch typ {
case lineStringType:
ls, err := unmarshalLineString(order, data[5:])
if err != nil {
return nil, err
}
return orb.MultiLineString{ls}, nil
case multiLineStringType:
return unmarshalMultiLineString(order, data[5:])
}
return nil, ErrIncorrectGeometry
}
func scanPolygon(data []byte) (orb.Polygon, error) {
order, typ, data, err := unmarshalByteOrderType(data)
if err != nil {
return nil, err
}
switch typ {
case polygonType:
return unmarshalPolygon(order, data[5:])
case multiPolygonType:
mp, err := unmarshalMultiPolygon(order, data[5:])
if err != nil {
return nil, err
}
if len(mp) == 1 {
return mp[0], nil
}
}
return nil, ErrIncorrectGeometry
}
func scanMultiPolygon(data []byte) (orb.MultiPolygon, error) {
order, typ, data, err := unmarshalByteOrderType(data)
if err != nil {
return nil, err
}
switch typ {
case polygonType:
p, err := unmarshalPolygon(order, data[5:])
if err != nil {
return nil, err
}
return orb.MultiPolygon{p}, nil
case multiPolygonType:
return unmarshalMultiPolygon(order, data[5:])
}
return nil, ErrIncorrectGeometry
}
func scanCollection(data []byte) (orb.Collection, error) {
m, err := NewDecoder(bytes.NewReader(data)).Decode()
if err == io.EOF || err == io.ErrUnexpectedEOF {
return nil, ErrNotWKB
}
if err != nil {
return nil, err
}
switch p := m.(type) {
case orb.Collection:
return p, nil
}
return nil, ErrIncorrectGeometry
}
type value struct {
v orb.Geometry
}
// Value will create a driver.Valuer that will WKB the geometry
// into the database query.
func Value(g orb.Geometry) driver.Valuer {
return value{v: g}
}
func (v value) Value() (driver.Value, error) {
val, err := Marshal(v.v)
if val == nil {
return nil, err
}
return val, err
}