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all: introduce lazy loading of ImageHDU
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First stab.

Updates #30.
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@sbinet
sbinet committed Nov 21, 2017
1 parent d0f5a01 commit c77c9c7
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Showing 3 changed files with 196 additions and 110 deletions.
273 changes: 172 additions & 101 deletions decode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -12,16 +12,16 @@ import (
"strings"
)

// Decoder is the interface that decodes FITS header/data-units.
type Decoder interface {
DecodeHDU() (HDU, error)
}

// NewDecoder creates a new Decoder according to the capabilities of the underlying io.Reader
func NewDecoder(r io.Reader) Decoder {
// FIXME(sbinet)
// if rr, ok := r.(io.ReadSeeker); ok {
// return &seekDecoder{r: rr}
// }
if r, ok := r.(io.ReadSeeker); ok {
return &seekDecoder{r: r}
}
return &streamDecoder{r: r}
}

Expand All @@ -35,6 +35,162 @@ func (dec *streamDecoder) DecodeHDU() (HDU, error) {
var err error
var hdu HDU

hdr, primary, err := decodeHeader(dec.r)
if err != nil {
return nil, err
}

switch htype := hdr.Type(); htype {
case IMAGE_HDU:
var data []byte
data, err = loadImageFromReader(dec.r, hdr)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading image: %v", err)
}

switch primary {
case true:
hdu = &primaryHDU{
imageHDU: imageHDU{
hdr: *hdr,
buf: data,
},
}
case false:
hdu = &imageHDU{
hdr: *hdr,
buf: data,
}
}

case BINARY_TBL:
hdu, err = loadTableFromReader(dec.r, hdr, htype)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading binary table: %v", err)
}

case ASCII_TBL:
hdu, err = loadTableFromReader(dec.r, hdr, htype)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading ascii table: %v", err)
}

case ANY_HDU:
fallthrough
default:
return nil, fmt.Errorf("fitsio: invalid HDU Type (%v)", htype)
}

return hdu, err
}

// seekDecoder is a decoder which can perform random access into
// the underlying Reader
type seekDecoder struct {
r io.ReadSeeker
}

func (dec *seekDecoder) DecodeHDU() (HDU, error) {
var err error
var hdu HDU

hdr, primary, err := decodeHeader(dec.r)
if err != nil {
return nil, err
}

switch htype := hdr.Type(); htype {
case IMAGE_HDU:
var pos int64
pos, err = dec.r.Seek(0, io.SeekCurrent)
if err != nil {
return nil, fmt.Errorf("fitsio: error getting current file position: %v", err)
}
r := dec.r
load := func() ([]byte, error) {
_, err := r.Seek(pos, io.SeekStart)
if err != nil {
return nil, err
}
data, err := loadImageFromReader(r, hdr)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading image: %v", err)
}
return data, nil
}

switch primary {
case true:
hdu = &primaryHDU{
imageHDU: imageHDU{
hdr: *hdr,
load: load,
},
}
case false:
hdu = &imageHDU{
hdr: *hdr,
load: load,
}
}

case BINARY_TBL:
hdu, err = loadTableFromReader(dec.r, hdr, htype)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading binary table: %v", err)
}

case ASCII_TBL:
hdu, err = loadTableFromReader(dec.r, hdr, htype)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading ascii table: %v", err)
}

case ANY_HDU:
fallthrough
default:
return nil, fmt.Errorf("fitsio: invalid HDU Type (%v)", htype)
}

return hdu, err
}

func hduTypeFrom(cards []Card) (HDUType, bool, error) {
var err error
var htype HDUType = -1
var primary bool

keys := make([]string, 0, len(cards))
for _, card := range cards {
keys = append(keys, card.Name)
switch card.Name {
case "SIMPLE":
primary = true
return IMAGE_HDU, primary, nil
case "XTENSION":
str := card.Value.(string)
switch str {
case "IMAGE":
htype = IMAGE_HDU
case "TABLE":
htype = ASCII_TBL
case "BINTABLE":
htype = BINARY_TBL
case "ANY", "ANY_HDU":
htype = ANY_HDU
default:
return htype, primary, fmt.Errorf("fitsio: invalid 'XTENSION' value: %q", str)
}

return htype, primary, err
}
}

return htype, primary, fmt.Errorf("fitsio: invalid header (missing 'SIMPLE' or 'XTENSION' card): keys=%v", keys)
}

func decodeHeader(r io.Reader) (*Header, bool, error) {
var err error
cards := make(map[string]int, 30)
slice := make([]Card, 0, 1)

Expand Down Expand Up @@ -67,17 +223,17 @@ func (dec *streamDecoder) DecodeHDU() (HDU, error) {
blocks_loop:
for {
iblock += 1
_, err = io.ReadFull(dec.r, buf)
_, err = io.ReadFull(r, buf)
if err != nil {
return nil, err
return nil, false, err
}

// each FITS header block is comprised of up to 36 80-byte lines
const maxlines = 36
for i := 0; i < maxlines; i++ {
card, err := parseHeaderLine(buf[i*80 : (i+1)*80])
if err != nil {
return nil, err
return nil, false, err
}
if card.Name == "CONTINUE" {
idx := len(slice) - 1
Expand Down Expand Up @@ -105,7 +261,7 @@ blocks_loop:
k := fmt.Sprintf("NAXIS%d", i+1)
c, ok := get_card(k)
if !ok {
return nil, fmt.Errorf("fitsio: missing '%s' key", k)
return nil, false, fmt.Errorf("fitsio: missing '%s' key", k)
}
axes[i] = c.Value.(int)
}
Expand All @@ -116,62 +272,21 @@ blocks_loop:

htype, primary, err := hduTypeFrom(slice)
if err != nil {
return nil, err
return nil, false, err
}

bitpix := 0
if card, ok := get_card("BITPIX"); ok {
bitpix = int(reflect.ValueOf(card.Value).Int())
} else {
return nil, fmt.Errorf("fitsio: missing 'BITPIX' card")
return nil, false, fmt.Errorf("fitsio: missing 'BITPIX' card")
}

hdr := NewHeader(slice, htype, bitpix, axes)
switch htype {
case IMAGE_HDU:
var data []byte
data, err = dec.loadImage(hdr)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading image: %v", err)
}

switch primary {
case true:
hdu = &primaryHDU{
imageHDU: imageHDU{
hdr: *hdr,
raw: data,
},
}
case false:
hdu = &imageHDU{
hdr: *hdr,
raw: data,
}
}

case BINARY_TBL:
hdu, err = dec.loadTable(hdr, htype)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading binary table: %v", err)
}

case ASCII_TBL:
hdu, err = dec.loadTable(hdr, htype)
if err != nil {
return nil, fmt.Errorf("fitsio: error loading ascii table: %v", err)
}

case ANY_HDU:
fallthrough
default:
return nil, fmt.Errorf("fitsio: invalid HDU Type (%v)", htype)
}

return hdu, err
return hdr, primary, nil
}

func (dec *streamDecoder) loadImage(hdr *Header) ([]byte, error) {
func loadImageFromReader(r io.Reader, hdr *Header) ([]byte, error) {
var err error
var buf []byte

Expand All @@ -194,7 +309,7 @@ func (dec *streamDecoder) loadImage(hdr *Header) ([]byte, error) {
return buf, nil
}

n, err := io.ReadFull(dec.r, buf)
n, err := io.ReadFull(r, buf)
if err != nil {
return nil, fmt.Errorf("fitsio: error reading buffer: %v", err)
}
Expand All @@ -205,7 +320,7 @@ func (dec *streamDecoder) loadImage(hdr *Header) ([]byte, error) {
// data array is also aligned at 2880-bytes blocks
pad := padBlock(n)
if pad > 0 {
n, err = dec.r.Read(make([]byte, pad))
n, err = r.Read(make([]byte, pad))
if err != nil {
return nil, fmt.Errorf("fitsio: error reading buffer: %v", err)
}
Expand All @@ -217,7 +332,7 @@ func (dec *streamDecoder) loadImage(hdr *Header) ([]byte, error) {
return buf, err
}

func (dec *streamDecoder) loadTable(hdr *Header, htype HDUType) (*Table, error) {
func loadTableFromReader(r io.Reader, hdr *Header, htype HDUType) (*Table, error) {
var err error
var table *Table

Expand Down Expand Up @@ -247,7 +362,7 @@ func (dec *streamDecoder) loadTable(hdr *Header, htype HDUType) (*Table, error)
blocksz := alignBlock(datasz + heapsz)

block := make([]byte, blocksz)
n, err := io.ReadFull(dec.r, block)
n, err := io.ReadFull(r, block)
if err != nil {
return nil, err
}
Expand Down Expand Up @@ -396,47 +511,3 @@ func (dec *streamDecoder) loadTable(hdr *Header, htype HDUType) (*Table, error)

return table, err
}

// seekDecoder is a decoder which can perform random access into
// the underlying Reader
type seekDecoder struct {
r io.ReadSeeker
}

func (dec *seekDecoder) DecodeHDU() (HDU, error) {
panic("not implemented")
}

func hduTypeFrom(cards []Card) (HDUType, bool, error) {
var err error
var htype HDUType = -1
var primary bool

keys := make([]string, 0, len(cards))
for _, card := range cards {
keys = append(keys, card.Name)
switch card.Name {
case "SIMPLE":
primary = true
return IMAGE_HDU, primary, nil
case "XTENSION":
str := card.Value.(string)
switch str {
case "IMAGE":
htype = IMAGE_HDU
case "TABLE":
htype = ASCII_TBL
case "BINTABLE":
htype = BINARY_TBL
case "ANY", "ANY_HDU":
htype = ANY_HDU
default:
return htype, primary, fmt.Errorf("fitsio: invalid 'XTENSION' value: %q", str)
}

return htype, primary, err
}
}

return htype, primary, fmt.Errorf("fitsio: invalid header (missing 'SIMPLE' or 'XTENSION' card): keys=%v", keys)
}
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