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143 lines
3.3 KiB
Go
143 lines
3.3 KiB
Go
//+build ignore
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// Copyright 2015, Klaus Post, see LICENSE for details.
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//
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// Simple stream encoder example
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//
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// The encoder encodes a single file into a number of shards
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// To reverse the process see "stream-decoder.go"
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//
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// To build an executable use:
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//
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// go build stream-encoder.go
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//
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// Simple Encoder/Decoder Shortcomings:
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// * If the file size of the input isn't dividable by the number of data shards
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// the output will contain extra zeroes
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//
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// * If the shard numbers isn't the same for the decoder as in the
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// encoder, invalid output will be generated.
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//
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// * If values have changed in a shard, it cannot be reconstructed.
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//
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// * If two shards have been swapped, reconstruction will always fail.
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// You need to supply the shards in the same order as they were given to you.
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//
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// The solution for this is to save a metadata file containing:
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//
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// * File size.
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// * The number of data/parity shards.
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// * HASH of each shard.
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// * Order of the shards.
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//
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// If you save these properties, you should abe able to detect file corruption
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// in a shard and be able to reconstruct your data if you have the needed number of shards left.
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package main
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import (
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"flag"
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"fmt"
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"os"
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"path/filepath"
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"io"
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"github.com/klauspost/reedsolomon"
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)
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var dataShards = flag.Int("data", 4, "Number of shards to split the data into, must be below 257.")
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var parShards = flag.Int("par", 2, "Number of parity shards")
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var outDir = flag.String("out", "", "Alternative output directory")
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func init() {
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flag.Usage = func() {
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fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
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fmt.Fprintf(os.Stderr, " %s [-flags] filename.ext\n\n", os.Args[0])
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fmt.Fprintf(os.Stderr, "Valid flags:\n")
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flag.PrintDefaults()
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}
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}
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func main() {
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// Parse command line parameters.
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flag.Parse()
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args := flag.Args()
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if len(args) != 1 {
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fmt.Fprintf(os.Stderr, "Error: No input filename given\n")
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flag.Usage()
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os.Exit(1)
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}
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if *dataShards > 257 {
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fmt.Fprintf(os.Stderr, "Error: Too many data shards\n")
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os.Exit(1)
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}
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fname := args[0]
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// Create encoding matrix.
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enc, err := reedsolomon.NewStream(*dataShards, *parShards)
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checkErr(err)
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fmt.Println("Opening", fname)
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f, err := os.Open(fname)
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checkErr(err)
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instat, err := f.Stat()
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checkErr(err)
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shards := *dataShards + *parShards
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out := make([]*os.File, shards)
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// Create the resulting files.
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dir, file := filepath.Split(fname)
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if *outDir != "" {
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dir = *outDir
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}
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for i := range out {
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outfn := fmt.Sprintf("%s.%d", file, i)
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fmt.Println("Creating", outfn)
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out[i], err = os.Create(filepath.Join(dir, outfn))
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checkErr(err)
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}
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// Split into files.
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data := make([]io.Writer, *dataShards)
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for i := range data {
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data[i] = out[i]
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}
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// Do the split
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err = enc.Split(f, data, instat.Size())
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checkErr(err)
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// Close and re-open the files.
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input := make([]io.Reader, *dataShards)
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for i := range data {
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out[i].Close()
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f, err := os.Open(out[i].Name())
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checkErr(err)
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input[i] = f
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defer f.Close()
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}
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// Create parity output writers
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parity := make([]io.Writer, *parShards)
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for i := range parity {
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parity[i] = out[*dataShards+i]
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defer out[*dataShards+i].Close()
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}
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// Encode parity
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err = enc.Encode(input, parity)
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checkErr(err)
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fmt.Printf("File split into %d data + %d parity shards.\n", *dataShards, *parShards)
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}
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func checkErr(err error) {
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if err != nil {
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fmt.Fprintf(os.Stderr, "Error: %s", err.Error())
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os.Exit(2)
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}
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}
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