luci-go/common/dirwalk: Code for walking a directory tree efficiently

common/dirwalk/tests/tools/gendir/content.go

Index: common/dirwalk/tests/tools/gendir/content.go
diff --git a/common/dirwalk/tests/tools/gendir/content.go b/common/dirwalk/tests/tools/gendir/content.go
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index 0000000000000000000000000000000000000000..f4248c78d3f4dfac9ab6fb778d038879d3351798
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+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package main
+
+import (
+	"io"
+	"math/rand"
+)
+
+// io.Reader which produces truly random binary data (totally uncompressible).
+func RandomBinaryGenerator(r *rand.Rand) io.Reader {
+	// rand.Rand already produces random binary data via Read()
+	return r
+}
+
+// io.Reader which produces a random text.
+type textRandomGenerator struct {
+	r *rand.Rand
+}
+
+func (g *textRandomGenerator) Read(p []byte) (n int, err error) {
+	i := 0
+	for {
+		bytes := []byte(string(randChar(g.r, textChars)))
+		if i+len(bytes) > len(p) {
+			break
+		}
+
+		for j := range bytes {
+			p[i+j] = bytes[j]
+		}
+		i += len(bytes)
+	}
+	return i, nil
+}
+
+// io.Reader which produces truly random text data (mostly uncompressible).
+func RandomTextGenerator(r *rand.Rand) io.Reader {
+	reader := textRandomGenerator{r: r}
+	return &reader
+}
+
+// Repeated sequence size range
+const (
+	SEQUENCE_MINSIZE uint64 = 16
+	SEQUENCE_MAXSIZE uint64 = 4 * 1024
+)
+
+// io.Reader which produces the given byte array repetitively.
+type repeatedByteGenerator struct {
+	data  []byte
+	index int
+}
+
+func (g *repeatedByteGenerator) Read(p []byte) (n int, err error) {
+	for i := range p {
+		p[i] = g.data[g.index]
+		g.index = (g.index + 1) % len(g.data)
+	}
+	return len(p), nil
+}
+
+// io.Reader which produces repeated binary data (some what compressible).
+func RepeatedBinaryGenerator(r *rand.Rand) io.Reader {
+	// Figure out how big the repeated sequence will be
+	sequence_size := randBetween(r, SEQUENCE_MINSIZE, SEQUENCE_MAXSIZE)
+
+	repeater := repeatedByteGenerator{index: 0, data: make([]byte, sequence_size)}
+	r.Read(repeater.data)
+
+	return &repeater
+}
+
+// io.Reader which produces repeated text data (very compressible).
+func RepeatedTextGenerator(r *rand.Rand) io.Reader {
+	// Figure out how big the repeated sequence will be
+	sequence_size := randBetween(r, SEQUENCE_MINSIZE, SEQUENCE_MAXSIZE)
+
+	repeater := repeatedByteGenerator{index: 0, data: []byte(randStr(r, sequence_size, textChars))}
+
+	return &repeater
+}
+
+// io.Reader which produces repeated Lorem Ipsum text data (very compressible).
+func LoremTextGenerator() io.Reader {
+	repeater := repeatedByteGenerator{index: 0, data: []byte(lorem)}
+	return &repeater
+}