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Source file src/compress/lzw/reader_test.go

Documentation: compress/lzw

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package lzw
     6  
     7  import (
     8  	"bytes"
     9  	"fmt"
    10  	"io"
    11  	"io/ioutil"
    12  	"math"
    13  	"runtime"
    14  	"strconv"
    15  	"strings"
    16  	"testing"
    17  )
    18  
    19  type lzwTest struct {
    20  	desc       string
    21  	raw        string
    22  	compressed string
    23  	err        error
    24  }
    25  
    26  var lzwTests = []lzwTest{
    27  	{
    28  		"empty;LSB;8",
    29  		"",
    30  		"\x01\x01",
    31  		nil,
    32  	},
    33  	{
    34  		"empty;MSB;8",
    35  		"",
    36  		"\x80\x80",
    37  		nil,
    38  	},
    39  	{
    40  		"tobe;LSB;7",
    41  		"TOBEORNOTTOBEORTOBEORNOT",
    42  		"\x54\x4f\x42\x45\x4f\x52\x4e\x4f\x54\x82\x84\x86\x8b\x85\x87\x89\x81",
    43  		nil,
    44  	},
    45  	{
    46  		"tobe;LSB;8",
    47  		"TOBEORNOTTOBEORTOBEORNOT",
    48  		"\x54\x9e\x08\x29\xf2\x44\x8a\x93\x27\x54\x04\x12\x34\xb8\xb0\xe0\xc1\x84\x01\x01",
    49  		nil,
    50  	},
    51  	{
    52  		"tobe;MSB;7",
    53  		"TOBEORNOTTOBEORTOBEORNOT",
    54  		"\x54\x4f\x42\x45\x4f\x52\x4e\x4f\x54\x82\x84\x86\x8b\x85\x87\x89\x81",
    55  		nil,
    56  	},
    57  	{
    58  		"tobe;MSB;8",
    59  		"TOBEORNOTTOBEORTOBEORNOT",
    60  		"\x2a\x13\xc8\x44\x52\x79\x48\x9c\x4f\x2a\x40\xa0\x90\x68\x5c\x16\x0f\x09\x80\x80",
    61  		nil,
    62  	},
    63  	{
    64  		"tobe-truncated;LSB;8",
    65  		"TOBEORNOTTOBEORTOBEORNOT",
    66  		"\x54\x9e\x08\x29\xf2\x44\x8a\x93\x27\x54\x04",
    67  		io.ErrUnexpectedEOF,
    68  	},
    69  	// This example comes from https://en.wikipedia.org/wiki/Graphics_Interchange_Format.
    70  	{
    71  		"gif;LSB;8",
    72  		"\x28\xff\xff\xff\x28\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff",
    73  		"\x00\x51\xfc\x1b\x28\x70\xa0\xc1\x83\x01\x01",
    74  		nil,
    75  	},
    76  	// This example comes from http://compgroups.net/comp.lang.ruby/Decompressing-LZW-compression-from-PDF-file
    77  	{
    78  		"pdf;MSB;8",
    79  		"-----A---B",
    80  		"\x80\x0b\x60\x50\x22\x0c\x0c\x85\x01",
    81  		nil,
    82  	},
    83  }
    84  
    85  func TestReader(t *testing.T) {
    86  	var b bytes.Buffer
    87  	for _, tt := range lzwTests {
    88  		d := strings.Split(tt.desc, ";")
    89  		var order Order
    90  		switch d[1] {
    91  		case "LSB":
    92  			order = LSB
    93  		case "MSB":
    94  			order = MSB
    95  		default:
    96  			t.Errorf("%s: bad order %q", tt.desc, d[1])
    97  		}
    98  		litWidth, _ := strconv.Atoi(d[2])
    99  		rc := NewReader(strings.NewReader(tt.compressed), order, litWidth)
   100  		defer rc.Close()
   101  		b.Reset()
   102  		n, err := io.Copy(&b, rc)
   103  		s := b.String()
   104  		if err != nil {
   105  			if err != tt.err {
   106  				t.Errorf("%s: io.Copy: %v want %v", tt.desc, err, tt.err)
   107  			}
   108  			if err == io.ErrUnexpectedEOF {
   109  				// Even if the input is truncated, we should still return the
   110  				// partial decoded result.
   111  				if n == 0 || !strings.HasPrefix(tt.raw, s) {
   112  					t.Errorf("got %d bytes (%q), want a non-empty prefix of %q", n, s, tt.raw)
   113  				}
   114  			}
   115  			continue
   116  		}
   117  		if s != tt.raw {
   118  			t.Errorf("%s: got %d-byte %q want %d-byte %q", tt.desc, n, s, len(tt.raw), tt.raw)
   119  		}
   120  	}
   121  }
   122  
   123  type devZero struct{}
   124  
   125  func (devZero) Read(p []byte) (int, error) {
   126  	for i := range p {
   127  		p[i] = 0
   128  	}
   129  	return len(p), nil
   130  }
   131  
   132  func TestHiCodeDoesNotOverflow(t *testing.T) {
   133  	r := NewReader(devZero{}, LSB, 8)
   134  	d := r.(*decoder)
   135  	buf := make([]byte, 1024)
   136  	oldHi := uint16(0)
   137  	for i := 0; i < 100; i++ {
   138  		if _, err := io.ReadFull(r, buf); err != nil {
   139  			t.Fatalf("i=%d: %v", i, err)
   140  		}
   141  		// The hi code should never decrease.
   142  		if d.hi < oldHi {
   143  			t.Fatalf("i=%d: hi=%d decreased from previous value %d", i, d.hi, oldHi)
   144  		}
   145  		oldHi = d.hi
   146  	}
   147  }
   148  
   149  // TestNoLongerSavingPriorExpansions tests the decoder state when codes other
   150  // than clear codes continue to be seen after decoder.hi and decoder.width
   151  // reach their maximum values (4095 and 12), i.e. after we no longer save prior
   152  // expansions. In particular, it tests seeing the highest possible code, 4095.
   153  func TestNoLongerSavingPriorExpansions(t *testing.T) {
   154  	// Iterations is used to calculate how many input bits are needed to get
   155  	// the decoder.hi and decoder.width values up to their maximum.
   156  	iterations := []struct {
   157  		width, n int
   158  	}{
   159  		// The final term is 257, not 256, as NewReader initializes d.hi to
   160  		// d.clear+1 and the clear code is 256.
   161  		{9, 512 - 257},
   162  		{10, 1024 - 512},
   163  		{11, 2048 - 1024},
   164  		{12, 4096 - 2048},
   165  	}
   166  	nCodes, nBits := 0, 0
   167  	for _, e := range iterations {
   168  		nCodes += e.n
   169  		nBits += e.n * e.width
   170  	}
   171  	if nCodes != 3839 {
   172  		t.Fatalf("nCodes: got %v, want %v", nCodes, 3839)
   173  	}
   174  	if nBits != 43255 {
   175  		t.Fatalf("nBits: got %v, want %v", nBits, 43255)
   176  	}
   177  
   178  	// Construct our input of 43255 zero bits (which gets d.hi and d.width up
   179  	// to 4095 and 12), followed by 0xfff (4095) as 12 bits, followed by 0x101
   180  	// (EOF) as 12 bits.
   181  	//
   182  	// 43255 = 5406*8 + 7, and codes are read in LSB order. The final bytes are
   183  	// therefore:
   184  	//
   185  	// xwwwwwww xxxxxxxx yyyyyxxx zyyyyyyy
   186  	// 10000000 11111111 00001111 00001000
   187  	//
   188  	// or split out:
   189  	//
   190  	// .0000000 ........ ........ ........   w = 0x000
   191  	// 1....... 11111111 .....111 ........   x = 0xfff
   192  	// ........ ........ 00001... .0001000   y = 0x101
   193  	//
   194  	// The 12 'w' bits (not all are shown) form the 3839'th code, with value
   195  	// 0x000. Just after decoder.read returns that code, d.hi == 4095 and
   196  	// d.last == 0.
   197  	//
   198  	// The 12 'x' bits form the 3840'th code, with value 0xfff or 4095. Just
   199  	// after decoder.read returns that code, d.hi == 4095 and d.last ==
   200  	// decoderInvalidCode.
   201  	//
   202  	// The 12 'y' bits form the 3841'st code, with value 0x101, the EOF code.
   203  	//
   204  	// The 'z' bit is unused.
   205  	in := make([]byte, 5406)
   206  	in = append(in, 0x80, 0xff, 0x0f, 0x08)
   207  
   208  	r := NewReader(bytes.NewReader(in), LSB, 8)
   209  	nDecoded, err := io.Copy(ioutil.Discard, r)
   210  	if err != nil {
   211  		t.Fatalf("Copy: %v", err)
   212  	}
   213  	// nDecoded should be 3841: 3839 literal codes and then 2 decoded bytes
   214  	// from 1 non-literal code. The EOF code contributes 0 decoded bytes.
   215  	if nDecoded != int64(nCodes+2) {
   216  		t.Fatalf("nDecoded: got %v, want %v", nDecoded, nCodes+2)
   217  	}
   218  }
   219  
   220  func BenchmarkDecoder(b *testing.B) {
   221  	buf, err := ioutil.ReadFile("../testdata/e.txt")
   222  	if err != nil {
   223  		b.Fatal(err)
   224  	}
   225  	if len(buf) == 0 {
   226  		b.Fatalf("test file has no data")
   227  	}
   228  
   229  	for e := 4; e <= 6; e++ {
   230  		n := int(math.Pow10(e))
   231  		b.Run(fmt.Sprint("1e", e), func(b *testing.B) {
   232  			b.StopTimer()
   233  			b.SetBytes(int64(n))
   234  			buf0 := buf
   235  			compressed := new(bytes.Buffer)
   236  			w := NewWriter(compressed, LSB, 8)
   237  			for i := 0; i < n; i += len(buf0) {
   238  				if len(buf0) > n-i {
   239  					buf0 = buf0[:n-i]
   240  				}
   241  				w.Write(buf0)
   242  			}
   243  			w.Close()
   244  			buf1 := compressed.Bytes()
   245  			buf0, compressed, w = nil, nil, nil
   246  			runtime.GC()
   247  			b.StartTimer()
   248  			for i := 0; i < b.N; i++ {
   249  				io.Copy(ioutil.Discard, NewReader(bytes.NewReader(buf1), LSB, 8))
   250  			}
   251  		})
   252  	}
   253  }
   254  

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