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126 lines
3.0 KiB
Go
126 lines
3.0 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 decoder example.
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//
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// The decoder reverses the process of "simple-encoder.go"
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//
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// To build an executable use:
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//
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// go build simple-decoder.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 diviable 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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"io/ioutil"
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"os"
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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")
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var parShards = flag.Int("par", 2, "Number of parity shards")
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var outFile = flag.String("out", "", "Alternative output path/file")
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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, " simple-decoder [-flags] basefile.ext\nDo not add the number to the filename.\n")
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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 flags
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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 filenames given\n")
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flag.Usage()
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os.Exit(1)
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}
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fname := args[0]
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// Create matrix
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enc, err := reedsolomon.New(*dataShards, *parShards)
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checkErr(err)
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// Create shards and load the data.
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shards := make([][]byte, *dataShards+*parShards)
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for i := range shards {
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infn := fmt.Sprintf("%s.%d", fname, i)
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fmt.Println("Opening", infn)
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shards[i], err = ioutil.ReadFile(infn)
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if err != nil {
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fmt.Println("Error reading file", err)
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shards[i] = nil
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}
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}
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// Verify the shards
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ok, err := enc.Verify(shards)
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if ok {
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fmt.Println("No reconstruction needed")
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} else {
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fmt.Println("Verification failed. Reconstructing data")
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err = enc.Reconstruct(shards)
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if err != nil {
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fmt.Println("Reconstruct failed -", err)
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os.Exit(1)
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}
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ok, err = enc.Verify(shards)
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if !ok {
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fmt.Println("Verification failed after reconstruction, data likely corrupted.")
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os.Exit(1)
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}
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checkErr(err)
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}
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// Join the shards and write them
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outfn := *outFile
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if outfn == "" {
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outfn = fname
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}
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fmt.Println("Writing data to", outfn)
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f, err := os.Create(outfn)
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checkErr(err)
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// We don't know the exact filesize.
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err = enc.Join(f, shards, len(shards[0])**dataShards)
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checkErr(err)
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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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