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113 lines
2.8 KiB
Go
113 lines
2.8 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 encoder example
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//
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// The encoder encodes a simgle file into a number of shards
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// To reverse the process see "simpledecoder.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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"path/filepath"
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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, " simple-encoder [-flags] filename.ext\n\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 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.New(*dataShards, *parShards)
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checkErr(err)
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fmt.Println("Opening", fname)
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b, err := ioutil.ReadFile(fname)
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checkErr(err)
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// Split the file into equally sized shards.
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shards, err := enc.Split(b)
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checkErr(err)
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fmt.Printf("File split into %d data+parity shards with %d bytes/shard.\n", len(shards), len(shards[0]))
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// Encode parity
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err = enc.Encode(shards)
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checkErr(err)
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// Write out 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, shard := range shards {
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outfn := fmt.Sprintf("%s.%d", file, i)
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fmt.Println("Writing to", outfn)
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err = ioutil.WriteFile(filepath.Join(dir, outfn), shard, os.ModePerm)
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checkErr(err)
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}
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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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