Golang io.NewSectionReader函数代码示例

func getPack(t *testing.T) *PackReader {
	// Take a random packfile in our own repository.
	packs, err := filepath.Glob("../.git/objects/pack/pack-*.pack")
	if err != nil || len(packs) == 0 {
		t.Fatalf("globbing failed: %v", err, packs)
	}
	pname := packs[0]
	pack, err := os.Open(pname)
	if err != nil {
		t.Fatalf("count not open %s: %s", pname, err)
	}
	idx, err := os.Open(pname[:len(pname)-5] + ".idx")
	if err != nil {
		t.Fatal(err)
	}
	packstat, err := pack.Stat()
	if err != nil {
		t.Fatal("stat pack", err)
	}
	idxstat, err := idx.Stat()
	if err != nil {
		t.Fatal("stat idx", err)
	}
	t.Logf("opening pack %s (%d bytes)", pname, packstat.Size())
	pk, err := NewPackReader(
		io.NewSectionReader(pack, 0, packstat.Size()),
		io.NewSectionReader(idx, 0, idxstat.Size()))
	if err != nil {
		t.Fatal(err)
	}
	return pk
}

// Open returns a ReadCloser that provides access to the File's contents.
func (f *File) Open() (rc io.ReadCloser, err os.Error) {
	off := int64(f.headerOffset)
	size := int64(f.CompressedSize)
	if f.bodyOffset == 0 {
		r := io.NewSectionReader(f.zipr, off, f.zipsize-off)
		if err = readFileHeader(f, r); err != nil {
			return
		}
		if f.bodyOffset, err = r.Seek(0, os.SEEK_CUR); err != nil {
			return
		}
		if size == 0 {
			size = int64(f.CompressedSize)
		}
	}
	if f.hasDataDescriptor() && size == 0 {
		// permit SectionReader to see the rest of the file
		size = f.zipsize - (off + f.bodyOffset)
	}
	r := io.NewSectionReader(f.zipr, off+f.bodyOffset, size)
	switch f.Method {
	case Store: // (no compression)
		rc = ioutil.NopCloser(r)
	case Deflate:
		rc = flate.NewReader(r)
	default:
		err = UnsupportedMethod
	}
	if rc != nil {
		rc = &checksumReader{rc, crc32.NewIEEE(), f, r}
	}
	return
}

func TestNewRequestContentLength(t *testing.T) {
	readByte := func(r io.Reader) io.Reader {
		var b [1]byte
		r.Read(b[:])
		return r
	}
	tests := []struct {
		r    io.Reader
		want int64
	}{
		{bytes.NewReader([]byte("123")), 3},
		{bytes.NewBuffer([]byte("1234")), 4},
		{strings.NewReader("12345"), 5},
		{strings.NewReader(""), 0},
		{NoBody, 0},

		// Not detected. During Go 1.8 we tried to make these set to -1, but
		// due to Issue 18117, we keep these returning 0, even though they're
		// unknown.
		{struct{ io.Reader }{strings.NewReader("xyz")}, 0},
		{io.NewSectionReader(strings.NewReader("x"), 0, 6), 0},
		{readByte(io.NewSectionReader(strings.NewReader("xy"), 0, 6)), 0},
	}
	for i, tt := range tests {
		req, err := NewRequest("POST", "http://localhost/", tt.r)
		if err != nil {
			t.Fatal(err)
		}
		if req.ContentLength != tt.want {
			t.Errorf("test[%d]: ContentLength(%T) = %d; want %d", i, tt.r, req.ContentLength, tt.want)
		}
	}
}

func TestNewRequestContentLength(t *testing.T) {
	readByte := func(r io.Reader) io.Reader {
		var b [1]byte
		r.Read(b[:])
		return r
	}
	tests := []struct {
		r    io.Reader
		want int64
	}{
		{bytes.NewReader([]byte("123")), 3},
		{bytes.NewBuffer([]byte("1234")), 4},
		{strings.NewReader("12345"), 5},
		// Not detected:
		{struct{ io.Reader }{strings.NewReader("xyz")}, 0},
		{io.NewSectionReader(strings.NewReader("x"), 0, 6), 0},
		{readByte(io.NewSectionReader(strings.NewReader("xy"), 0, 6)), 0},
	}
	for _, tt := range tests {
		req, err := NewRequest("POST", "http://localhost/", tt.r)
		if err != nil {
			t.Fatal(err)
		}
		if req.ContentLength != tt.want {
			t.Errorf("ContentLength(%T) = %d; want %d", tt.r, req.ContentLength, tt.want)
		}
	}
}

func parseSFNT(r io.ReaderAt, headerOffset int64, table map[int64]Table) (SFNT, error) {
	header := new(SfntHeader)
	headerSize := int64(binary.Size(header))
	sr := io.NewSectionReader(r, headerOffset, headerSize)
	if err := binary.Read(sr, binary.BigEndian, header); err != nil {
		return nil, err
	}
	numTables := header.NumTables
	offsetTable := make([]OffsetEntry, numTables)
	sr = io.NewSectionReader(r, headerOffset+headerSize, int64(binary.Size(offsetTable)))
	if err := binary.Read(sr, binary.BigEndian, offsetTable); err != nil {
		return nil, err
	}
	tableMap := make(SFNT)
	for _, entry := range offsetTable {
		tag := entry.Tag.String()
		offset := int64(entry.Offset)
		size := int64(entry.Length)
		if v, ok := table[offset]; ok {
			tableMap[tag] = v
		} else {
			v = &DefaultTable{entry.Tag, io.NewSectionReader(r, offset, size)}
			table[offset] = v
			tableMap[tag] = v
		}
	}
	for _, p := range DefaultParser {
		for i, v := range tableMap {
			tableMap[i] = p.Parse(tableMap, v)
		}
	}
	return tableMap, nil
}

// Open returns a ReadCloser that provides access to the File's contents.
// Multiple files may be read concurrently.
func (f *File) Open() (rc io.ReadCloser, err error) {
	bodyOffset, err := f.findBodyOffset()
	if err != nil {
		return
	}
	size := int64(f.CompressedSize64)
	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
	dcomp := f.zip.decompressor(f.Method)
	if dcomp == nil {
		err = ErrAlgorithm
		return
	}
	rc = dcomp(r)
	var desr io.Reader
	if f.hasDataDescriptor() {
		desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
	}
	rc = &checksumReader{
		rc:   rc,
		hash: crc32.NewIEEE(),
		f:    f,
		desr: desr,
	}
	return
}

func ExampleBytes() {
	buf := newWriter(make([]byte, 0, 10))
	io.Copy(os.Stdout, buf)
	io.Copy(os.Stdout, io.NewSectionReader(*&buf, 0, 100))

	io.WriteString(buf, "Hello ")
	r := io.NewSectionReader(*&buf, 0, int64(buf.Len()))
	io.CopyN(os.Stdout, r, 5)
	io.CopyN(os.Stdout, buf, 5)
	io.WriteString(buf, "World")
	r = io.NewSectionReader(*&buf, 0, int64(buf.Len()))
	io.CopyN(os.Stdout, r, 6)

	io.WriteString(buf, "abcdefg")
	io.Copy(os.Stdout, buf)
	io.Copy(os.Stdout, buf)

	io.WriteString(buf, "Hello World")
	r = io.NewSectionReader(*&buf, 0, int64(buf.Len()))
	io.CopyN(os.Stdout, r, 5)
	io.CopyN(os.Stdout, buf, 4)

	io.WriteString(buf, "abcdefg")
	io.Copy(os.Stdout, buf)
	io.Copy(os.Stdout, buf)
	//Output:
	// HelloHello World WorldabcdefgHelloHello Worldabcdefg
}

// Open returns a ReadCloser that provides access to the File's contents.
// Multiple files may be read concurrently.
func (f *File) Open() (rc io.ReadCloser, err error) {
	bodyOffset, err := f.findBodyOffset()
	if err != nil {
		return
	}
	size := int64(f.CompressedSize64)
	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
	switch f.Method {
	case Store: // (no compression)
		rc = ioutil.NopCloser(r)
	case Deflate:
		rc, err = zlib.NewReader(r)
		if err != nil {
			return
		}
	default:
		err = ErrAlgorithm
		return
	}
	var desr io.Reader
	if f.hasDataDescriptor() {
		desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
	}
	rc = &checksumReader{rc, crc32.NewIEEE(), f, desr, nil}
	return
}

func ExamplePackReader_Extract() {
	base := ".git/objects/pack/pack-bb4afc76654154e3a9f198723ba89873ecb14293"
	fpack, err := os.Open(base + ".pack")
	if err != nil {
		log.Fatal(err)
	}
	fidx, err := os.Open(base + ".idx")
	if err != nil {
		log.Fatal(err)
	}
	defer fpack.Close()
	defer fidx.Close()

	packsize, err1 := fpack.Seek(0, os.SEEK_END)
	idxsize, err2 := fidx.Seek(0, os.SEEK_END)
	if err1 != nil || err2 != nil {
		log.Fatal(err1, err2)
	}
	pk, err := NewPackReader(
		io.NewSectionReader(fpack, 0, packsize),
		io.NewSectionReader(fidx, 0, idxsize))
	if err != nil {
		log.Fatal(err)
	}
	var hash Hash
	hex.Decode(hash[:], []byte("2e16bbf779131a90346eab585e9e5c4736d3aeac"))
	obj, err := pk.Extract(hash)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("%+v", obj)
}

// Decode reads a TIFF image from r and returns it as an image.Image.
// The type of Image returned depends on the contents of the TIFF.
func Decode(r io.Reader) (img image.Image, err os.Error) {
	d, err := newDecoder(r)
	if err != nil {
		return
	}

	// Check if we have the right number of strips, offsets and counts.
	rps := int(d.firstVal(tRowsPerStrip))
	numStrips := (d.config.Height + rps - 1) / rps
	if rps == 0 || len(d.features[tStripOffsets]) < numStrips || len(d.features[tStripByteCounts]) < numStrips {
		return nil, FormatError("inconsistent header")
	}

	switch d.mode {
	case mGray, mGrayInvert:
		img = image.NewGray(d.config.Width, d.config.Height)
	case mPaletted:
		img = image.NewPaletted(d.config.Width, d.config.Height, d.palette)
	case mNRGBA:
		img = image.NewNRGBA(d.config.Width, d.config.Height)
	case mRGB, mRGBA:
		img = image.NewRGBA(d.config.Width, d.config.Height)
	}

	var p []byte
	for i := 0; i < numStrips; i++ {
		ymin := i * rps
		// The last strip may be shorter.
		if i == numStrips-1 && d.config.Height%rps != 0 {
			rps = d.config.Height % rps
		}
		offset := int64(d.features[tStripOffsets][i])
		n := int64(d.features[tStripByteCounts][i])
		switch d.firstVal(tCompression) {
		case cNone:
			// TODO(bsiegert): Avoid copy if r is a tiff.buffer.
			p = make([]byte, 0, n)
			_, err = d.r.ReadAt(p, offset)
		case cLZW:
			r := lzw.NewReader(io.NewSectionReader(d.r, offset, n), lzw.MSB, 8)
			p, err = ioutil.ReadAll(r)
			r.Close()
		case cDeflate, cDeflateOld:
			r, err := zlib.NewReader(io.NewSectionReader(d.r, offset, n))
			if err != nil {
				return nil, err
			}
			p, err = ioutil.ReadAll(r)
			r.Close()
		default:
			err = UnsupportedError("compression")
		}
		if err != nil {
			return
		}
		err = d.decode(img, p, ymin, ymin+rps)
	}
	return
}

func TestFile(t *testing.T) {
	if *path == "" {
		t.Logf("skipping since no input file specified")
		return
	}
	r, err := OpenFile(*path)
	if err != nil {
		t.Fatal(err)
	}
	info, err := r.Info()
	if err != nil {
		t.Error(err)
	}
	sects := info.Sections
	info.Sections = nil
	t.Logf("%+v", info)
	for _, sec := range sects {
		t.Logf("%s: %+v", secNames[sec.Type], sec)
	}

	// Test messages.
	for _, sec := range sects {
		if sec.Type == SecMessages {
			for id, off := range sec.Folders {
				r := io.NewSectionReader(r.File, off, sec.Offset+16+sec.Length-off)
				title, msgs, err := parseMessageFolder(r)
				if err != nil {
					t.Error(err)
				}
				t.Logf("Folder %d %q", id, title)
				t.Logf("%d messages", len(msgs))
				if len(msgs) > 0 {
					t.Logf("First message: %s", msgs[0])
					t.Logf("Last message: %s", msgs[len(msgs)-1])
				}
			}
		}
		if sec.Type == SecMMS {
			for id, off := range sec.Folders {
				r := io.NewSectionReader(r.File, off, sec.Offset+16+sec.Length-off)
				title, msgs, err := parseMMSFolder(r)
				if err != nil {
					t.Error(err)
				}
				t.Logf("Folder %d %q", id, title)
				t.Logf("%d messages", len(msgs))
				if len(msgs) > 0 {
					first, last := msgs[0], msgs[len(msgs)-1]
					t.Logf("First message: %q...%q", first[:40], first[len(first)-40:])
					t.Logf("Last message: %q...%q", last[:40], last[len(last)-40:])
				}
			}
		}
	}
}

func (s *subset) Read() (err error) {
	a := io.NewSectionReader(s.fh[0], s.offsets[0], chunkSize)
	b := io.NewSectionReader(s.fh[1], s.offsets[1], chunkSize)
	s.read[0], err = a.Read(s.b[0])
	if err != nil && err != io.EOF {
		return err
	}
	s.read[1], err = b.Read(s.b[1])
	if err != nil && err != io.EOF {
		return err
	}
	return
}

func (i *Idx) Part(part string, idxFilePath string, idxLength int64) (pos int64, length int64, err error) {
	// this function is for returning a single pos and length for a given range
	// used for non-subset indices where the records are contiguous for the data file
	f, err := os.Open(idxFilePath)
	if err != nil {
		err = errors.New(e.IndexNoFile)
		return
	}
	defer f.Close()

	if strings.Contains(part, "-") {
		startend := strings.Split(part, "-")
		start, startEr := strconv.ParseInt(startend[0], 10, 64)
		end, endEr := strconv.ParseInt(startend[1], 10, 64)
		if startEr != nil || endEr != nil || start <= 0 || start > int64(idxLength) || end <= 0 || end > int64(idxLength) {
			err = errors.New(e.InvalidIndexRange)
			return
		}

		// read start offset and length from index file
		sr := io.NewSectionReader(f, (start-1)*16, 16)
		srec := make([]int64, 2)
		binary.Read(sr, binary.LittleEndian, &srec[0])
		binary.Read(sr, binary.LittleEndian, &srec[1])

		// read end offset and length from index file
		sr = io.NewSectionReader(f, (end-1)*16, 16)
		erec := make([]int64, 2)
		binary.Read(sr, binary.LittleEndian, &erec[0])
		binary.Read(sr, binary.LittleEndian, &erec[1])

		pos = srec[0]
		length = (erec[0] - srec[0]) + erec[1]
	} else {
		p, er := strconv.ParseInt(part, 10, 64)
		if er != nil || p <= 0 || p > int64(idxLength) {
			err = errors.New(e.IndexOutBounds)
			return
		}

		// read offset and length from index file
		sr := io.NewSectionReader(f, (p-1)*16, 16)
		rec := make([]int64, 2)
		binary.Read(sr, binary.LittleEndian, &rec[0])
		binary.Read(sr, binary.LittleEndian, &rec[1])

		pos = rec[0]
		length = rec[1]
	}
	return
}

func main() {
	reader, _ := os.Open("test.txt")
	defer reader.Close()
	sectionReader := io.NewSectionReader(reader, 5, 10)
	fmt.Println(reflect.TypeOf(sectionReader))
	var n, total int
	var err error
	p := make([]byte, 15)
	//Read
	for {
		n, err = sectionReader.Read(p)
		if err == io.EOF {
			fmt.Println("Find EOF so end total", total)
			break
		}
		total = total + n
		fmt.Println("Read value:", string(p[0:n]))
		fmt.Println("Read count:", n)
	}
	//ReadAt
	p = make([]byte, 15)
	n, _ = sectionReader.ReadAt(p, 4)
	fmt.Println("Read value:", string(p[0:n]))
	fmt.Println("Read count:", n)
	//Seek
	sectionReader1 := io.NewSectionReader(reader, 2, 20)
	sectionReader1.Seek(2, 0)
	p = make([]byte, 10)
	n, _ = sectionReader1.Read(p)
	fmt.Println("First read value:", string(p[0:n]))
	fmt.Println("First read count:", n)
	a, _ := sectionReader.Seek(2, 1)
	fmt.Println("off - base is", a)
	n, _ = sectionReader.Read(p)
	fmt.Println("Second Read value:", string(p[0:n]))
	fmt.Println("Second Read count:", n)
	sectionReader.Seek(8, 2)
	n, _ = sectionReader.Read(p)
	fmt.Println("Third read value:", string(p[0:n]))
	fmt.Println("Third read count:", n)

	//size
	sectionReader2 := io.NewSectionReader(reader, 5, 20)
	fmt.Println("Can read count:", sectionReader2.Size())
	p = make([]byte, 10)
	n, _ = sectionReader2.Read(p)
	fmt.Println("Read count:", n)
	fmt.Println("Can read count:", sectionReader2.Size())
}

// Open returns a new ReadSeeker reading the ELF section.
// Even if the section is stored compressed in the ELF file,
// the ReadSeeker reads uncompressed data.
func (s *Section) Open() io.ReadSeeker {
	if s.Flags&SHF_COMPRESSED == 0 {
		return io.NewSectionReader(s.sr, 0, 1<<63-1)
	}
	if s.compressionType == COMPRESS_ZLIB {
		return &readSeekerFromReader{
			reset: func() (io.Reader, error) {
				fr := io.NewSectionReader(s.sr, s.compressionOffset, int64(s.FileSize)-s.compressionOffset)
				return zlib.NewReader(fr)
			},
			size: int64(s.Size),
		}
	}
	err := &FormatError{int64(s.Offset), "unknown compression type", s.compressionType}
	return errorReader{err}
}