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main.go
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main.go
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package main
import (
"bufio"
"bytes"
"crypto/md5"
"crypto/sha1"
"crypto/sha256"
"crypto/sha512"
"encoding/hex"
"flag"
"fmt"
"hash"
"io"
"io/ioutil"
"log"
"os"
"sort"
)
const usage = `Usage:
$ ... | ensure md5 1a79a4d60de6718e8e5b326e338ae533 | ...
Check the hash, then pass standard input to standard output.
Options:
-list List all supported algorithms.
-help Print this help message.
-quiet Suppress error messages.
`
func main() {
log.SetFlags(0)
var (
helpFlag = flag.Bool("help", false, "")
listFlag = flag.Bool("list", false, "")
quietFlag = flag.Bool("quiet", false, "")
)
flag.Usage = func() {
fmt.Fprint(flag.CommandLine.Output(), usage)
}
flag.Parse()
if *quietFlag {
log.SetOutput(ioutil.Discard)
}
if *helpFlag || (!*listFlag && flag.NArg() == 0) {
fmt.Fprint(flag.CommandLine.Output(), usage)
return
}
if !*listFlag && flag.NArg() != 2 {
log.Fatalln("ERROR: must provide algorithm and digest")
}
(&ensure{listMode: *listFlag}).Run(flag.Args())
}
var algorithms = map[string]hash.Hash{
"md5": md5.New(),
"sha1": sha1.New(),
"sha256": sha256.New(),
"sha512": sha512.New(),
}
type ensure struct {
listMode bool
algorithm, digest string
}
func (e *ensure) Run(args []string) {
if e.listMode {
e.list()
return
}
e.algorithm = args[0]
e.digest = args[1]
h, ok := algorithms[e.algorithm]
if !ok {
log.Fatalf("ERROR: %s is not a supported algorithm", e.algorithm)
}
r := bufio.NewReader(os.Stdin)
var saved bytes.Buffer
tee := io.TeeReader(r, &saved)
if _, err := io.Copy(h, tee); err != nil {
log.Fatal(err)
}
res := hex.EncodeToString(h.Sum(nil))
if res != e.digest {
log.Fatalf("ERROR: expected %s, got %s", res, e.digest)
}
fmt.Printf("%s", saved.String())
}
func (e *ensure) list() {
keys := make([]string, 0, len(algorithms))
for k := range algorithms {
keys = append(keys, k)
}
sort.Strings(keys)
for _, k := range keys {
fmt.Println(k)
}
}