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package main
import (
"crypto/md5"
"errors"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"sort"
"sync"
)
// walkFiles starts a goroutine to walk the directory tree at root and send the
// path of each regular file on the string channel. It sends the result of the
// walk on the error channel. If done is closed, walkFiles abandons its work.
func walkFiles(done <-chan struct{}, root string) (<-chan string, <-chan error) {
paths := make(chan string)
errc := make(chan error, 1)
go func() { // HL
// Close the paths channel after Walk returns.
defer close(paths) // HL
// No select needed for this send, since errc is buffered.
errc <- filepath.Walk(root, func(path string, info os.FileInfo, err error) error { // HL
if err != nil {
return err
}
if info.IsDir() {
return nil
}
select {
case paths <- path: // HL
case <-done: // HL
return errors.New("walk canceled")
}
return nil
})
}()
return paths, errc
}
// A result is the product of reading and summing a file using MD5.
type result struct {
path string
sum [md5.Size]byte
err error
}
// digester reads path names from paths and sends digests of the corresponding
// files on c until either paths or done is closed.
func digester(done <-chan struct{}, paths <-chan string, c chan<- result) {
for path := range paths { // HLpaths
data, err := ioutil.ReadFile(path)
select {
case c <- result{path, md5.Sum(data), err}:
case <-done:
return
}
}
}
// MD5All reads all the files in the file tree rooted at root and returns a map
// from file path to the MD5 sum of the file's contents. If the directory walk
// fails or any read operation fails, MD5All returns an error. In that case,
// MD5All does not wait for inflight read operations to complete.
func MD5All(root string) (map[string][md5.Size]byte, error) {
// MD5All closes the done channel when it returns; it may do so before
// receiving all the values from c and errc.
done := make(chan struct{})
defer close(done)
paths, errc := walkFiles(done, root)
// Start a fixed number of goroutines to read and digest files.
c := make(chan result) // HLc
var wg sync.WaitGroup
const numDigesters = 20
wg.Add(numDigesters)
for i := 0; i < numDigesters; i++ {
go func() {
digester(done, paths, c) // HLc
wg.Done()
}()
}
go func() {
wg.Wait()
close(c) // HLc
}()
// End of pipeline. OMIT
m := make(map[string][md5.Size]byte)
for r := range c {
if r.err != nil {
return nil, r.err
}
m[r.path] = r.sum
}
// Check whether the Walk failed.
if err := <-errc; err != nil { // HLerrc
return nil, err
}
return m, nil
}
func main() {
// Calculate the MD5 sum of all files under the specified directory,
// then print the results sorted by path name.
m, err := MD5All(os.Args[1])
if err != nil {
fmt.Println(err)
return
}
var paths []string
for path := range m {
paths = append(paths, path)
}
sort.Strings(paths)
for _, path := range paths {
fmt.Printf("%x %s\n", m[path], path)
}
}
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