Source: composite_type.go in package github.com/jackc/pgtype

package pgtype

import (
	"encoding/binary"
	"errors"
	"fmt"
	"reflect"
	"strings"

	"github.com/jackc/pgio"
)

type CompositeTypeField struct {
	Name string
	OID  uint32
}

type CompositeType struct {
	status Status

	typeName string

	fields           []CompositeTypeField
	valueTranscoders []ValueTranscoder
}

NewCompositeType creates a CompositeType from fields and ci. ci is used to find the ValueTranscoders used for fields. All field OIDs must be previously registered in ci.

func NewCompositeType(typeName string, fields []CompositeTypeField, ci *ConnInfo) (*CompositeType, error) {
	valueTranscoders := make([]ValueTranscoder, len(fields))

	for i := range fields {
		dt, ok := ci.DataTypeForOID(fields[i].OID)
		if !ok {
			return nil, fmt.Errorf("no data type registered for oid: %d", fields[i].OID)
		}

		value := NewValue(dt.Value)
		valueTranscoder, ok := value.(ValueTranscoder)
		if !ok {
			return nil, fmt.Errorf("data type for oid does not implement ValueTranscoder: %d", fields[i].OID)
		}

		valueTranscoders[i] = valueTranscoder
	}

	return &CompositeType{typeName: typeName, fields: fields, valueTranscoders: valueTranscoders}, nil
}

NewCompositeTypeValues creates a CompositeType from fields and values. fields and values must have the same length. Prefer NewCompositeType unless overriding the transcoding of fields is required.

func NewCompositeTypeValues(typeName string, fields []CompositeTypeField, values []ValueTranscoder) (*CompositeType, error) {
	if len(fields) != len(values) {
		return nil, errors.New("fields and valueTranscoders must have same length")
	}

	return &CompositeType{typeName: typeName, fields: fields, valueTranscoders: values}, nil
}

func (src CompositeType) Get() interface{} {
	switch src.status {
	case Present:
		results := make(map[string]interface{}, len(src.valueTranscoders))
		for i := range src.valueTranscoders {
			results[src.fields[i].Name] = src.valueTranscoders[i].Get()
		}
		return results
	case Null:
		return nil
	default:
		return src.status
	}
}

func (ct *CompositeType) NewTypeValue() Value {
	a := &CompositeType{
		typeName:         ct.typeName,
		fields:           ct.fields,
		valueTranscoders: make([]ValueTranscoder, len(ct.valueTranscoders)),
	}

	for i := range ct.valueTranscoders {
		a.valueTranscoders[i] = NewValue(ct.valueTranscoders[i]).(ValueTranscoder)
	}

	return a
}

func (ct *CompositeType) TypeName() string {
	return ct.typeName
}

func (ct *CompositeType) Fields() []CompositeTypeField {
	return ct.fields
}

func (dst *CompositeType) Set(src interface{}) error {
	if src == nil {
		dst.status = Null
		return nil
	}

	switch value := src.(type) {
	case []interface{}:
		if len(value) != len(dst.valueTranscoders) {
			return fmt.Errorf("Number of fields don't match. CompositeType has %d fields", len(dst.valueTranscoders))
		}
		for i, v := range value {
			if err := dst.valueTranscoders[i].Set(v); err != nil {
				return err
			}
		}
		dst.status = Present
	case *[]interface{}:
		if value == nil {
			dst.status = Null
			return nil
		}
		return dst.Set(*value)
	default:
		return fmt.Errorf("Can not convert %v to Composite", src)
	}

	return nil
}

AssignTo should never be called on composite value directly

func (src CompositeType) AssignTo(dst interface{}) error {
	switch src.status {
	case Present:
		switch v := dst.(type) {
		case []interface{}:
			if len(v) != len(src.valueTranscoders) {
				return fmt.Errorf("Number of fields don't match. CompositeType has %d fields", len(src.valueTranscoders))
			}
			for i := range src.valueTranscoders {
				if v[i] == nil {
					continue
				}

				err := assignToOrSet(src.valueTranscoders[i], v[i])
				if err != nil {
					return fmt.Errorf("unable to assign to dst[%d]: %v", i, err)
				}
			}
			return nil
		case *[]interface{}:
			return src.AssignTo(*v)
		default:
			if isPtrStruct, err := src.assignToPtrStruct(dst); isPtrStruct {
				return err
			}

			if nextDst, retry := GetAssignToDstType(dst); retry {
				return src.AssignTo(nextDst)
			}
			return fmt.Errorf("unable to assign to %T", dst)
		}
	case Null:
		return NullAssignTo(dst)
	}
	return fmt.Errorf("cannot decode %#v into %T", src, dst)
}

func assignToOrSet(src Value, dst interface{}) error {
	assignToErr := src.AssignTo(dst)

Try to use get / set instead -- this avoids every type having to be able to AssignTo type of self.

		setSucceeded := false
		if setter, ok := dst.(Value); ok {
			err := setter.Set(src.Get())
			setSucceeded = err == nil
		}
		if !setSucceeded {
			return assignToErr
		}
	}

	return nil
}

func (src CompositeType) assignToPtrStruct(dst interface{}) (bool, error) {
	dstValue := reflect.ValueOf(dst)
	if dstValue.Kind() != reflect.Ptr {
		return false, nil
	}

	if dstValue.IsNil() {
		return false, nil
	}

	dstElemValue := dstValue.Elem()
	dstElemType := dstElemValue.Type()

	if dstElemType.Kind() != reflect.Struct {
		return false, nil
	}

	exportedFields := make([]int, 0, dstElemType.NumField())
	for i := 0; i < dstElemType.NumField(); i++ {
		sf := dstElemType.Field(i)
		if sf.PkgPath == "" {
			exportedFields = append(exportedFields, i)
		}
	}

	if len(exportedFields) != len(src.valueTranscoders) {
		return false, nil
	}

	for i := range exportedFields {
		err := assignToOrSet(src.valueTranscoders[i], dstElemValue.Field(exportedFields[i]).Addr().Interface())
		if err != nil {
			return true, fmt.Errorf("unable to assign to field %s: %v", dstElemType.Field(exportedFields[i]).Name, err)
		}
	}

	return true, nil
}

func (src CompositeType) EncodeBinary(ci *ConnInfo, buf []byte) (newBuf []byte, err error) {
	switch src.status {
	case Null:
		return nil, nil
	case Undefined:
		return nil, errUndefined
	}

	b := NewCompositeBinaryBuilder(ci, buf)
	for i := range src.valueTranscoders {
		b.AppendEncoder(src.fields[i].OID, src.valueTranscoders[i])
	}

	return b.Finish()
}

DecodeBinary implements BinaryDecoder interface. Opposite to Record, fields in a composite act as a "schema" and decoding fails if SQL value can't be assigned due to type mismatch

func (dst *CompositeType) DecodeBinary(ci *ConnInfo, buf []byte) error {
	if buf == nil {
		dst.status = Null
		return nil
	}

	scanner := NewCompositeBinaryScanner(ci, buf)

	for _, f := range dst.valueTranscoders {
		scanner.ScanDecoder(f)
	}

	if scanner.Err() != nil {
		return scanner.Err()
	}

	dst.status = Present

	return nil
}

func (dst *CompositeType) DecodeText(ci *ConnInfo, buf []byte) error {
	if buf == nil {
		dst.status = Null
		return nil
	}

	scanner := NewCompositeTextScanner(ci, buf)

	for _, f := range dst.valueTranscoders {
		scanner.ScanDecoder(f)
	}

	if scanner.Err() != nil {
		return scanner.Err()
	}

	dst.status = Present

	return nil
}

func (src CompositeType) EncodeText(ci *ConnInfo, buf []byte) (newBuf []byte, err error) {
	switch src.status {
	case Null:
		return nil, nil
	case Undefined:
		return nil, errUndefined
	}

	b := NewCompositeTextBuilder(ci, buf)
	for _, f := range src.valueTranscoders {
		b.AppendEncoder(f)
	}

	return b.Finish()
}

type CompositeBinaryScanner struct {
	ci  *ConnInfo
	rp  int
	src []byte

	fieldCount int32
	fieldBytes []byte
	fieldOID   uint32
	err        error
}

NewCompositeBinaryScanner a scanner over a binary encoded composite balue.

func NewCompositeBinaryScanner(ci *ConnInfo, src []byte) *CompositeBinaryScanner {
	rp := 0
	if len(src[rp:]) < 4 {
		return &CompositeBinaryScanner{err: fmt.Errorf("Record incomplete %v", src)}
	}

	fieldCount := int32(binary.BigEndian.Uint32(src[rp:]))
	rp += 4

	return &CompositeBinaryScanner{
		ci:         ci,
		rp:         rp,
		src:        src,
		fieldCount: fieldCount,
	}
}

ScanDecoder calls Next and decodes the result with d.

func (cfs *CompositeBinaryScanner) ScanDecoder(d BinaryDecoder) {
	if cfs.err != nil {
		return
	}

	if cfs.Next() {
		cfs.err = d.DecodeBinary(cfs.ci, cfs.fieldBytes)
	} else {
		cfs.err = errors.New("read past end of composite")
	}
}

ScanDecoder calls Next and scans the result into d.

func (cfs *CompositeBinaryScanner) ScanValue(d interface{}) {
	if cfs.err != nil {
		return
	}

	if cfs.Next() {
		cfs.err = cfs.ci.Scan(cfs.OID(), BinaryFormatCode, cfs.Bytes(), d)
	} else {
		cfs.err = errors.New("read past end of composite")
	}
}

Next advances the scanner to the next field. It returns false after the last field is read or an error occurs. After Next returns false, the Err method can be called to check if any errors occurred.

func (cfs *CompositeBinaryScanner) Next() bool {
	if cfs.err != nil {
		return false
	}

	if cfs.rp == len(cfs.src) {
		return false
	}

	if len(cfs.src[cfs.rp:]) < 8 {
		cfs.err = fmt.Errorf("Record incomplete %v", cfs.src)
		return false
	}
	cfs.fieldOID = binary.BigEndian.Uint32(cfs.src[cfs.rp:])
	cfs.rp += 4

	fieldLen := int(int32(binary.BigEndian.Uint32(cfs.src[cfs.rp:])))
	cfs.rp += 4

	if fieldLen >= 0 {
		if len(cfs.src[cfs.rp:]) < fieldLen {
			cfs.err = fmt.Errorf("Record incomplete rp=%d src=%v", cfs.rp, cfs.src)
			return false
		}
		cfs.fieldBytes = cfs.src[cfs.rp : cfs.rp+fieldLen]
		cfs.rp += fieldLen
	} else {
		cfs.fieldBytes = nil
	}

	return true
}

func (cfs *CompositeBinaryScanner) FieldCount() int {
	return int(cfs.fieldCount)
}

Bytes returns the bytes of the field most recently read by Scan().

func (cfs *CompositeBinaryScanner) Bytes() []byte {
	return cfs.fieldBytes
}

OID returns the OID of the field most recently read by Scan().

func (cfs *CompositeBinaryScanner) OID() uint32 {
	return cfs.fieldOID
}

Err returns any error encountered by the scanner.

func (cfs *CompositeBinaryScanner) Err() error {
	return cfs.err
}

type CompositeTextScanner struct {
	ci  *ConnInfo
	rp  int
	src []byte

	fieldBytes []byte
	err        error
}

NewCompositeTextScanner a scanner over a text encoded composite value.

func NewCompositeTextScanner(ci *ConnInfo, src []byte) *CompositeTextScanner {
	if len(src) < 2 {
		return &CompositeTextScanner{err: fmt.Errorf("Record incomplete %v", src)}
	}

	if src[0] != '(' {
		return &CompositeTextScanner{err: fmt.Errorf("composite text format must start with '('")}
	}

	if src[len(src)-1] != ')' {
		return &CompositeTextScanner{err: fmt.Errorf("composite text format must end with ')'")}
	}

	return &CompositeTextScanner{
		ci:  ci,
		rp:  1,
		src: src,
	}
}

ScanDecoder calls Next and decodes the result with d.

func (cfs *CompositeTextScanner) ScanDecoder(d TextDecoder) {
	if cfs.err != nil {
		return
	}

	if cfs.Next() {
		cfs.err = d.DecodeText(cfs.ci, cfs.fieldBytes)
	} else {
		cfs.err = errors.New("read past end of composite")
	}
}

ScanDecoder calls Next and scans the result into d.

func (cfs *CompositeTextScanner) ScanValue(d interface{}) {
	if cfs.err != nil {
		return
	}

	if cfs.Next() {
		cfs.err = cfs.ci.Scan(0, TextFormatCode, cfs.Bytes(), d)
	} else {
		cfs.err = errors.New("read past end of composite")
	}
}

Next advances the scanner to the next field. It returns false after the last field is read or an error occurs. After Next returns false, the Err method can be called to check if any errors occurred.

func (cfs *CompositeTextScanner) Next() bool {
	if cfs.err != nil {
		return false
	}

	if cfs.rp == len(cfs.src) {
		return false
	}

	switch cfs.src[cfs.rp] {
	case ',', ')': // null
		cfs.rp++
		cfs.fieldBytes = nil
		return true
	case '"': // quoted value
		cfs.rp++
		cfs.fieldBytes = make([]byte, 0, 16)
		for {
			ch := cfs.src[cfs.rp]

			if ch == '"' {
				cfs.rp++
				if cfs.src[cfs.rp] == '"' {
					cfs.fieldBytes = append(cfs.fieldBytes, '"')
					cfs.rp++
				} else {
					break
				}
			} else {
				cfs.fieldBytes = append(cfs.fieldBytes, ch)
				cfs.rp++
			}
		}
		cfs.rp++
		return true
	default: // unquoted value
		start := cfs.rp
		for {
			ch := cfs.src[cfs.rp]
			if ch == ',' || ch == ')' {
				break
			}
			cfs.rp++
		}
		cfs.fieldBytes = cfs.src[start:cfs.rp]
		cfs.rp++
		return true
	}
}

Bytes returns the bytes of the field most recently read by Scan().

func (cfs *CompositeTextScanner) Bytes() []byte {
	return cfs.fieldBytes
}

Err returns any error encountered by the scanner.

func (cfs *CompositeTextScanner) Err() error {
	return cfs.err
}

type CompositeBinaryBuilder struct {
	ci         *ConnInfo
	buf        []byte
	startIdx   int
	fieldCount uint32
	err        error
}

func NewCompositeBinaryBuilder(ci *ConnInfo, buf []byte) *CompositeBinaryBuilder {
	startIdx := len(buf)
	buf = append(buf, 0, 0, 0, 0) // allocate room for number of fields
	return &CompositeBinaryBuilder{ci: ci, buf: buf, startIdx: startIdx}
}

func (b *CompositeBinaryBuilder) AppendValue(oid uint32, field interface{}) {
	if b.err != nil {
		return
	}

	dt, ok := b.ci.DataTypeForOID(oid)
	if !ok {
		b.err = fmt.Errorf("unknown data type for OID: %d", oid)
		return
	}

	err := dt.Value.Set(field)
	if err != nil {
		b.err = err
		return
	}

	binaryEncoder, ok := dt.Value.(BinaryEncoder)
	if !ok {
		b.err = fmt.Errorf("unable to encode binary for OID: %d", oid)
		return
	}

	b.AppendEncoder(oid, binaryEncoder)
}

func (b *CompositeBinaryBuilder) AppendEncoder(oid uint32, field BinaryEncoder) {
	if b.err != nil {
		return
	}

	b.buf = pgio.AppendUint32(b.buf, oid)
	lengthPos := len(b.buf)
	b.buf = pgio.AppendInt32(b.buf, -1)
	fieldBuf, err := field.EncodeBinary(b.ci, b.buf)
	if err != nil {
		b.err = err
		return
	}
	if fieldBuf != nil {
		binary.BigEndian.PutUint32(fieldBuf[lengthPos:], uint32(len(fieldBuf)-len(b.buf)))
		b.buf = fieldBuf
	}

	b.fieldCount++
}

func (b *CompositeBinaryBuilder) Finish() ([]byte, error) {
	if b.err != nil {
		return nil, b.err
	}

	binary.BigEndian.PutUint32(b.buf[b.startIdx:], b.fieldCount)
	return b.buf, nil
}

type CompositeTextBuilder struct {
	ci         *ConnInfo
	buf        []byte
	startIdx   int
	fieldCount uint32
	err        error
	fieldBuf   [32]byte
}

func NewCompositeTextBuilder(ci *ConnInfo, buf []byte) *CompositeTextBuilder {
	buf = append(buf, '(') // allocate room for number of fields
	return &CompositeTextBuilder{ci: ci, buf: buf}
}

func (b *CompositeTextBuilder) AppendValue(field interface{}) {
	if b.err != nil {
		return
	}

	if field == nil {
		b.buf = append(b.buf, ',')
		return
	}

	dt, ok := b.ci.DataTypeForValue(field)
	if !ok {
		b.err = fmt.Errorf("unknown data type for field: %v", field)
		return
	}

	err := dt.Value.Set(field)
	if err != nil {
		b.err = err
		return
	}

	textEncoder, ok := dt.Value.(TextEncoder)
	if !ok {
		b.err = fmt.Errorf("unable to encode text for value: %v", field)
		return
	}

	b.AppendEncoder(textEncoder)
}

func (b *CompositeTextBuilder) AppendEncoder(field TextEncoder) {
	if b.err != nil {
		return
	}

	fieldBuf, err := field.EncodeText(b.ci, b.fieldBuf[0:0])
	if err != nil {
		b.err = err
		return
	}
	if fieldBuf != nil {
		b.buf = append(b.buf, quoteCompositeFieldIfNeeded(string(fieldBuf))...)
	}

	b.buf = append(b.buf, ',')
}

func (b *CompositeTextBuilder) Finish() ([]byte, error) {
	if b.err != nil {
		return nil, b.err
	}

	b.buf[len(b.buf)-1] = ')'
	return b.buf, nil
}

var quoteCompositeReplacer = strings.NewReplacer(`\`, `\\`, `"`, `\"`)

func quoteCompositeField(src string) string {
	return `"` + quoteCompositeReplacer.Replace(src) + `"`
}

func quoteCompositeFieldIfNeeded(src string) string {
	if src == "" || src[0] == ' ' || src[len(src)-1] == ' ' || strings.ContainsAny(src, `(),"\`) {
		return quoteCompositeField(src)
	}
	return src