/
datatable.go
153 lines (138 loc) · 3.41 KB
/
datatable.go
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package bin
import (
"encoding/binary"
"errors"
"io"
)
const (
initFieldCap = 16
)
var (
ErrUnbalancedTable = errors.New("unbalanced data table")
)
// DataTable will construct a Mapper that orchestrates reading and writing a data table.
// This is very helpful for situations where the caller is using the array of structs to struct of arrays optimization, and wants to persist this table.
// Each FieldMapper will be used to read a single field element, making up a DataTable row, before returning to the first FieldMapper to start the next row.
// The length parameter will set during read, and read during write to ensure that all mapped fields are of the same length.
func DataTable(length *uint32, mappers ...FieldMapper) Mapper {
if length == nil {
return nilMapping
}
return Any(
func(r io.Reader, endian binary.ByteOrder) error {
if err := Size(length).Read(r, endian); err != nil {
return err
}
l := *length
i := uint32(0)
for i < l {
for _, m := range mappers {
if err := m.readNext(r, endian); err != nil {
return err
}
}
i++
}
for _, m := range mappers {
m.apply()
}
return nil
},
func(w io.Writer, endian binary.ByteOrder) error {
l := *length
for _, m := range mappers {
if err := m.assertLen(l); err != nil {
return err
}
}
if err := Size(&l).Write(w, endian); err != nil {
return err
}
i := uint32(0)
for i < l {
for _, m := range mappers {
if err := m.writeNext(w, endian); err != nil {
return err
}
}
i++
}
return nil
},
)
}
// FieldMapper provides the logic necessary to read and write DataTable fields.
// Created with MapField.
type FieldMapper interface {
readNext(r io.Reader, endian binary.ByteOrder) error
apply()
assertLen(uint32) error
writeNext(w io.Writer, endian binary.ByteOrder) error
}
// MapField will associate a Mapper to each element in a target slice within a FieldMapper.
func MapField[T any](target *[]T, mapFn func(*T) Mapper) FieldMapper {
return &fieldMapper[T]{
fieldReader: &fieldReader[T]{
target: target,
fn: mapFn,
buf: make([]T, 0, initFieldCap),
},
fieldWriter: &fieldWriter[T]{
target: target,
fn: mapFn,
},
}
}
type fieldMapper[T any] struct {
*fieldReader[T]
*fieldWriter[T]
}
type fieldReader[T any] struct {
target *[]T
buf []T
fn func(*T) Mapper
}
func (fr *fieldReader[T]) readNext(r io.Reader, endian binary.ByteOrder) error {
var t T
if err := fr.fn(&t).Read(r, endian); err != nil {
return err
}
fr.buf = append(fr.buf, t)
if len(fr.buf) == cap(fr.buf) {
newBuf := make([]T, len(fr.buf), len(fr.buf)*2)
copy(newBuf, fr.buf)
fr.buf = newBuf
}
return nil
}
func (fr *fieldReader[T]) apply() {
*fr.target = make([]T, len(fr.buf))
copy(*fr.target, fr.buf)
fr.buf = fr.buf[:0]
}
type fieldWriter[T any] struct {
target *[]T
fn func(*T) Mapper
wrPtr uint32
}
func (fw *fieldWriter[T]) assertLen(length uint32) error {
if uint32(len(*fw.target)) != length {
return ErrUnbalancedTable
}
return nil
}
func (fw *fieldWriter[T]) next() *T {
var t T
t = (*fw.target)[fw.wrPtr]
return &t
}
func (fw *fieldWriter[T]) writeNext(w io.Writer, endian binary.ByteOrder) error {
if fw.wrPtr < uint32(len(*fw.target)) {
if err := fw.fn(fw.next()).Write(w, endian); err != nil {
return err
}
fw.wrPtr++
return nil
}
return errors.New("at the end of the source buffer in writeNext")
}