Using goroutine to build Zip, slice is out of range, capacity is 4096-Golang-php.cn

使用 goroutine 构建 Zip，切片超出范围，容量为 4096

php editor Xiaoxin has brought a technical article about using goroutine to build Zip. In this article, we will learn how to use goroutine to perform Zip operations concurrently to improve the efficiency of the program. In addition, we will discuss the issue of slice out-of-range and show how to use a slice with a capacity of 4096 to solve this problem. Whether you are a beginner or an experienced developer, this article will help you better understand and apply the knowledge related to goroutines and slicing. Let’s explore together!

Question content

I'm trying to improve the function that builds the zip by adding a goroutine to handle each file that must be archived. But it ended in panicpanic: runtime error: slice out of range [4126:4096]

The target directory contains 190 files (500 mo). I really don't understand what's wrong Thanks in advance for your help

Function:

func buildarchive() error { var files []string err := filepath.walk("/tmp/dir-to-zip", func(filepath string, info os.fileinfo, err error) error { if info.isdir() { return nil } if err != nil { fmt.println(err) return err } files = append(files, filepath) return nil }) if err != nil { return err } bundle, err := os.create("/tmp/archive.zip") if err != nil { return err } bundlewriter := zip.newwriter(bundle) var wg sync.waitgroup wg.add(len(files)) for _, filepath := range files { go func(filepath string) { defer wg.done() relpath := strings.trimprefix(filepath, fmt.sprintf("%v/", filepath.dir("/tmp/dir-to-zip"))) bundlefile, err := bundlewriter.create(relpath) if err != nil { fmt.println(err) } fsfile, err := os.open(filepath) if err != nil { fmt.println(err) } _, err = io.copy(bundlefile, fsfile) if err != nil { fmt.println(err) } }(filepath) } wg.wait() err = bundlewriter.close() if err != nil { return err } return nil }

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The error occurred here:

_, err = io.copy(bundlefile, fsfile) if err != nil { fmt.println(err) }

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Stack trace:

goroutine 48 [running]: bufio.(*Writer).Write(0xc00002a100, {0xc00041a400?, 0x3d?, 0xc00041a400?}) /usr/local/go/src/bufio/bufio.go:670 +0x1c8 archive/zip.(*countWriter).Write(0xc00000c138, {0xc00041a400?, 0x3d?, 0x4afa20?}) /usr/local/go/src/archive/zip/writer.go:601 +0x2e io.WriteString({0x4e7538, 0xc00000c138}, {0xc0000212c9, 0x3d}) /usr/local/go/src/io/io.go:314 +0x91 archive/zip.writeHeader({0x4e7538, 0xc00000c138}, 0xc000220090) /usr/local/go/src/archive/zip/writer.go:422 +0x5ec archive/zip.(*Writer).CreateHeader(0xc0000760a0, 0xc00021e1b0) /usr/local/go/src/archive/zip/writer.go:378 +0x797 archive/zip.(*Writer).Create(0x4e7698?, {0xc0000212c9, 0x3d}) /usr/local/go/src/archive/zip/writer.go:223 +0x6c main.BuildArchive.func2({0xc0000212c0, 0x46}) /home/simba/go/src/foobar/main.go:79 +0x1c5 created by main.BuildArchive /home/simba/go/src/foobar/main.go:73 +0x5aa panic: runtime error: slice bounds out of range [:4126] with capacity 4096 goroutine 6 [running]: bufio.(*Writer).Flush(0xc00002a100) /usr/local/go/src/bufio/bufio.go:634 +0x171 bufio.(*Writer).Write(0xc00002a100, {0xc0001b4200?, 0xc000199b20?, 0xc000199b20?}) /usr/local/go/src/bufio/bufio.go:672 +0xd8 archive/zip.(*countWriter).Write(0xc00000c138, {0xc0001b4200?, 0x0?, 0xc000199b40?}) /usr/local/go/src/archive/zip/writer.go:601 +0x2e archive/zip.(*countWriter).Write(0xc000220018, {0xc0001b4200?, 0xc0001b02c0?, 0xc0001b02f0?}) /usr/local/go/src/archive/zip/writer.go:601 +0x2e compress/flate.(*huffmanBitWriter).write(...) /usr/local/go/src/compress/flate/huffman_bit_writer.go:136 compress/flate.(*huffmanBitWriter).writeCode(0xc0001b41e0?, {0x6000?, 0x22?}) /usr/local/go/src/compress/flate/huffman_bit_writer.go:347 +0xe5 compress/flate.(*huffmanBitWriter).writeTokens(0xc0001b41e0, {0xc002558000, 0x4001, 0x403f800000403f?}, {0xc0001aa900, 0x11e, 0x108129000000000f?}, {0xc0001ac100, 0x1e, 0x1e}) /usr/local/go/src/compress/flate/huffman_bit_writer.go:583 +0xb9 compress/flate.(*huffmanBitWriter).writeBlock(0xc0001b41e0, {0xc002558000?, 0x20?, 0xd79?}, 0x0, {0x0, 0x0, 0x0}) /usr/local/go/src/compress/flate/huffman_bit_writer.go:495 +0x490 compress/flate.(*compressor).writeBlock(0xc0005a2000, {0xc002558000?, 0xc000032f00?, 0xc000199d28?}, 0x47739b?) /usr/local/go/src/compress/flate/deflate.go:170 +0x9c compress/flate.(*compressor).deflate(0xc0005a2000) /usr/local/go/src/compress/flate/deflate.go:509 +0x59b compress/flate.(*compressor).write(0xc0005a2000, {0xc00256a000?, 0x8000, 0xf311b6fd?}) /usr/local/go/src/compress/flate/deflate.go:554 +0x82 compress/flate.(*Writer).Write(...) /usr/local/go/src/compress/flate/deflate.go:712 archive/zip.(*pooledFlateWriter).Write(0xc00020c040?, {0xc00256a000?, 0x8000?, 0x4af140?}) /usr/local/go/src/archive/zip/register.go:51 +0xc5 archive/zip.(*countWriter).Write(...) /usr/local/go/src/archive/zip/writer.go:601 archive/zip.(*fileWriter).Write(0xc000222000, {0xc00256a000, 0x8000, 0x8000}) /usr/local/go/src/archive/zip/writer.go:533 +0x97 io.copyBuffer({0x4e7558, 0xc000222000}, {0x4e7678, 0xc0001f8008}, {0x0, 0x0, 0x0}) /usr/local/go/src/io/io.go:428 +0x204 io.Copy(...) /usr/local/go/src/io/io.go:385 main.BuildArchive.func2({0xc00001c0c0, 0x35}) /home/simba/go/src/foobar/main.go:89 +0x385 created by main.BuildArchive /home/simba/go/src/foobar/main.go:73 +0x5aa exit status 2

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Solution

zip.WriterNot safe for concurrent use. You start multiple goroutines, each goroutine creates and writes zip entries (files).

Writer.Create()Record:

Create adds the file to the zip file using the provided name. It returns a Writer into which the file contents should be written.

[...]The file contents must be written to io.Writer before the next call to Create, CreateHeader, or Close.

You cannot create zips at the same time. Each zip entry'sio.Writers write to the same underlying file (or in general the sameio.Writer), even if your application doesn't panic or crash. The resulting zip archive may also be invalid.

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