Contains for io.Reader

ioreader_contain.go

// https://play.golang.org/p/0CnyWvQ8rY
package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"strings"
)

const bufSize = 2 << 15

func Contains(r io.Reader, substr string) bool {
	return ContainsBytes(r, []byte(substr))
}

func ContainsBytes(r io.Reader, subslice []byte) bool {
	size := bufSize
	subsliceLen := len(subslice)
	if bufSize < subsliceLen {
		size = subsliceLen * 2
	}
	br := bufio.NewReader(r)
	for {
		bs, _ := br.Peek(size)
		if len(bs) == 0 {
			return false
		}
		if bytes.Contains(bs, subslice) {
			return true
		}
		br.Discard(size - subsliceLen)
	}
	return false
}

var ContainsTests = []struct {
	str, substr string
	expected    bool
}{
	{"abc", "bc", true},
	{"abc", "bcd", false},
	{"abc", "", true},
	{"", "a", false},

	// cases to cover code in runtime/asm_amd64.s:indexShortStr
	// 2-byte needle
	{"xxxxxx", "01", false},
	{"01xxxx", "01", true},
	{"xx01xx", "01", true},
	{"xxxx01", "01", true},
	{"01xxxxx"[1:], "01", false},
	{"xxxxx01"[:6], "01", false},
	// 3-byte needle
	{"xxxxxxx", "012", false},
	{"012xxxx", "012", true},
	{"xx012xx", "012", true},
	{"xxxx012", "012", true},
	{"012xxxxx"[1:], "012", false},
	{"xxxxx012"[:7], "012", false},
	// 4-byte needle
	{"xxxxxxxx", "0123", false},
	{"0123xxxx", "0123", true},
	{"xx0123xx", "0123", true},
	{"xxxx0123", "0123", true},
	{"0123xxxxx"[1:], "0123", false},
	{"xxxxx0123"[:8], "0123", false},
	// 5-7-byte needle
	{"xxxxxxxxx", "01234", false},
	{"01234xxxx", "01234", true},
	{"xx01234xx", "01234", true},
	{"xxxx01234", "01234", true},
	{"01234xxxxx"[1:], "01234", false},
	{"xxxxx01234"[:9], "01234", false},
	// 8-byte needle
	{"xxxxxxxxxxxx", "01234567", false},
	{"01234567xxxx", "01234567", true},
	{"xx01234567xx", "01234567", true},
	{"xxxx01234567", "01234567", true},
	{"01234567xxxxx"[1:], "01234567", false},
	{"xxxxx01234567"[:12], "01234567", false},
	// 9-15-byte needle
	{"xxxxxxxxxxxxx", "012345678", false},
	{"012345678xxxx", "012345678", true},
	{"xx012345678xx", "012345678", true},
	{"xxxx012345678", "012345678", true},
	{"012345678xxxxx"[1:], "012345678", false},
	{"xxxxx012345678"[:13], "012345678", false},
	// 16-byte needle
	{"xxxxxxxxxxxxxxxxxxxx", "0123456789ABCDEF", false},
	{"0123456789ABCDEFxxxx", "0123456789ABCDEF", true},
	{"xx0123456789ABCDEFxx", "0123456789ABCDEF", true},
	{"xxxx0123456789ABCDEF", "0123456789ABCDEF", true},
	{"0123456789ABCDEFxxxxx"[1:], "0123456789ABCDEF", false},
	{"xxxxx0123456789ABCDEF"[:20], "0123456789ABCDEF", false},
	// 17-31-byte needle
	{"xxxxxxxxxxxxxxxxxxxxx", "0123456789ABCDEFG", false},
	{"0123456789ABCDEFGxxxx", "0123456789ABCDEFG", true},
	{"xx0123456789ABCDEFGxx", "0123456789ABCDEFG", true},
	{"xxxx0123456789ABCDEFG", "0123456789ABCDEFG", true},
	{"0123456789ABCDEFGxxxxx"[1:], "0123456789ABCDEFG", false},
	{"xxxxx0123456789ABCDEFG"[:21], "0123456789ABCDEFG", false},

	// partial match cases
	{"xx01x", "012", false},                             // 3
	{"xx0123x", "01234", false},                         // 5-7
	{"xx01234567x", "012345678", false},                 // 9-15
	{"xx0123456789ABCDEFx", "0123456789ABCDEFG", false}, // 17-31, issue 15679
}

func main() {
	for _, ct := range ContainsTests {
		if Contains(strings.NewReader(ct.str), ct.substr) != ct.expected {
			fmt.Printf("Contains(%s, %s) = %v, want %v\n",
				ct.str, ct.substr, !ct.expected, ct.expected)
		}
	}
}