func readSectionHeader(load loader.L, expectId byte, idError string) (ok bool) {
id, err := load.ReadByte()
if err != nil {
if err == io.EOF {
return
}
panic(err)
}
if id != expectId {
panic(errors.New(idError))
}
load.Varuint32() // payload len
ok = true
return
}
func copySection(w io.Writer, r reader.Reader, expectId byte) (ok bool) {
store := storer{w}
load := loader.L{Reader: r}
loop:
for {
id, err := load.ReadByte()
if err != nil {
if err == io.EOF {
return
}
panic(err)
}
switch {
case id == sectionids.Unknown:
payloadLen := load.Varuint32()
if _, err := io.CopyN(ioutil.Discard, load, int64(payloadLen)); err != nil {
panic(err)
}
case id == expectId:
store.Byte(id)
break loop
default:
load.UnreadByte()
return
}
}
payloadLen := load.Varuint32()
store.Varuint32(payloadLen)
if _, err := io.CopyN(store, load, int64(payloadLen)); err != nil {
panic(err)
}
ok = true
return
}
func (m moduleLoader) loadUntil(load loader.L, untilSection byte) byte {
var header struct {
MagicNumber uint32
Version uint32
}
if err := binary.Read(load, binary.LittleEndian, &header); err != nil {
panic(err)
}
if header.MagicNumber != moduleMagicNumber {
panic(errors.New("not a WebAssembly module"))
}
if header.Version != moduleVersion {
panic(fmt.Errorf("unsupported module version: %d", header.Version))
}
var skipSection func(byte, uint32) error
if m.UnknownSectionLoader != nil {
skipSection = func(id byte, payloadLen uint32) (err error) {
if id == sectionids.Unknown {
err = m.UnknownSectionLoader(load, payloadLen)
} else {
_, err = io.CopyN(ioutil.Discard, load, int64(payloadLen))
}
return
}
} else {
skipSection = func(id byte, payloadLen uint32) (err error) {
_, err = io.CopyN(ioutil.Discard, load, int64(payloadLen))
return
}
}
var seenId byte
for {
id, err := load.ReadByte()
if err != nil {
if err == io.EOF {
return 0
}
panic(err)
}
if id != sectionids.Unknown {
if id <= seenId {
panic(fmt.Errorf("section 0x%x follows section 0x%x", id, seenId))
}
seenId = id
}
if id >= untilSection {
load.UnreadByte()
return id
}
payloadLen := load.Varuint32()
if f := sectionLoaders[id]; f != nil {
f(m, load)
} else if err := skipSection(id, payloadLen); err != nil {
panic(err)
}
}
}