From c5cd77676ec91b3867fc653d3257de95aed346d1 Mon Sep 17 00:00:00 2001
From: "Stephen McQuay (smcquay)" <stephen@mcquay.me>
Date: Wed, 16 Nov 2016 01:18:35 -0800
Subject: [PATCH] rearrange, rename, refactor

---
 check.go | 174 ++++++++++++++++++++++++++++---------------------------
 hash.go  | 120 ++++++++++++++++++++++++++++++++++++++
 main.go  | 108 ----------------------------------
 3 files changed, 209 insertions(+), 193 deletions(-)
 create mode 100644 hash.go

diff --git a/check.go b/check.go
index 1475b47..3318f2b 100644
--- a/check.go
+++ b/check.go
@@ -15,78 +15,38 @@ import (
 	"sync"
 )
 
-type checksum struct {
-	filename string
-	hash     hash.Hash
-	checksum string
-}
-
-func parseCS(line string) (checksum, error) {
-	elems := strings.Fields(line)
-	if len(elems) != 2 {
-		return checksum{}, fmt.Errorf("unexpected content: %d != 2", len(elems))
-	}
-	cs, f := elems[0], elems[1]
-	var hsh hash.Hash
-	switch len(cs) {
-	case 32:
-		hsh = md5.New()
-	case 40:
-		hsh = sha1.New()
-	case 64:
-		hsh = sha256.New()
-	case 128:
-		hsh = sha512.New()
-	default:
-		return checksum{}, fmt.Errorf("unknown format: %q", line)
-	}
-	return checksum{filename: f, hash: hsh, checksum: cs}, nil
-}
-
+// input contains a file-ish piece of work to perform
 type input struct {
 	f   io.ReadCloser
 	err error
 }
 
-type work struct {
-	cs  checksum
-	err error
+// checksum contains the path to a file, a way to hash it, and the results of
+// the hash
+type checksum struct {
+	filename string
+	hash     hash.Hash
+	checksum string
+	err      error
 }
 
-func streams(files []string) chan input {
-	r := make(chan input)
+// check is the entry point for -c operation.
+func check(args []string) chan error {
+	jobs := make(chan checksum)
 
 	go func() {
-		for _, name := range files {
-			f, err := os.Open(name)
-			r <- input{f, err}
-		}
-		if len(files) == 0 {
-			r <- input{f: os.Stdin}
-		}
-		close(r)
-	}()
-
-	return r
-}
-
-func check(files []string) chan error {
-	jobs := make(chan work)
-
-	go func() {
-		for stream := range streams(files) {
-			if stream.err != nil {
-				jobs <- work{err: stream.err}
+		for i := range toInput(args) {
+			if i.err != nil {
+				jobs <- checksum{err: i.err}
 				break
 			}
-			s := bufio.NewScanner(stream.f)
+			s := bufio.NewScanner(i.f)
 			for s.Scan() {
-				cs, err := parseCS(s.Text())
-				jobs <- work{cs, err}
+				jobs <- parseCS(s.Text())
 			}
-			stream.f.Close()
+			i.f.Close()
 			if s.Err() != nil {
-				jobs <- work{err: s.Err()}
+				jobs <- checksum{err: s.Err()}
 			}
 		}
 		close(jobs)
@@ -101,6 +61,77 @@ func check(files []string) chan error {
 	return merge(results)
 }
 
+// toInput converts args to a stream of input
+func toInput(args []string) chan input {
+	r := make(chan input)
+
+	go func() {
+		for _, name := range args {
+			f, err := os.Open(name)
+			r <- input{f, err}
+		}
+		if len(args) == 0 {
+			r <- input{f: os.Stdin}
+		}
+		close(r)
+	}()
+
+	return r
+}
+
+// parseCS picks apart a line from a checksum file and returns everything
+// needed to perform a checksum.
+func parseCS(line string) checksum {
+	elems := strings.Fields(line)
+	if len(elems) != 2 {
+		return checksum{err: fmt.Errorf("unexpected content: %d != 2", len(elems))}
+	}
+	cs, f := elems[0], elems[1]
+	var hsh hash.Hash
+	switch len(cs) {
+	case 32:
+		hsh = md5.New()
+	case 40:
+		hsh = sha1.New()
+	case 64:
+		hsh = sha256.New()
+	case 128:
+		hsh = sha512.New()
+	default:
+		return checksum{err: fmt.Errorf("unknown format: %q", line)}
+	}
+	return checksum{filename: f, hash: hsh, checksum: cs}
+}
+
+// verify does grunt work of verifying a stream of jobs (filenames).
+func verify(jobs chan checksum) chan error {
+	r := make(chan error)
+	go func() {
+		for job := range jobs {
+			if job.err != nil {
+				log.Printf("%+v", job.err)
+				continue
+			}
+			f, err := os.Open(job.filename)
+			if err != nil {
+				r <- err
+				continue
+			}
+			if _, err := io.Copy(job.hash, f); err != nil {
+				r <- err
+				continue
+			}
+			f.Close()
+			if fmt.Sprintf("%x", job.hash.Sum(nil)) != job.checksum {
+				r <- fmt.Errorf("%s: bad", job.filename)
+			}
+		}
+		close(r)
+	}()
+	return r
+}
+
+// merge is simple error fan-in
 func merge(cs []<-chan error) chan error {
 	out := make(chan error)
 
@@ -124,30 +155,3 @@ func merge(cs []<-chan error) chan error {
 	}()
 	return out
 }
-
-func verify(jobs chan work) chan error {
-	r := make(chan error)
-	go func() {
-		for job := range jobs {
-			if job.err != nil {
-				log.Printf("%+v", job.err)
-				continue
-			}
-			f, err := os.Open(job.cs.filename)
-			if err != nil {
-				r <- fmt.Errorf("open: %v", err)
-				continue
-			}
-			if _, err := io.Copy(job.cs.hash, f); err != nil {
-				r <- err
-				continue
-			}
-			f.Close()
-			if fmt.Sprintf("%x", job.cs.hash.Sum(nil)) != job.cs.checksum {
-				r <- fmt.Errorf("%s: bad", job.cs.filename)
-			}
-		}
-		close(r)
-	}()
-	return r
-}
diff --git a/hash.go b/hash.go
new file mode 100644
index 0000000..4a80a0e
--- /dev/null
+++ b/hash.go
@@ -0,0 +1,120 @@
+package main
+
+import (
+	"crypto/md5"
+	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/sha512"
+	"fmt"
+	"hash"
+	"io"
+	"os"
+	"sync"
+)
+
+// result is a message or error payload
+type result struct {
+	msg string
+	err error
+}
+
+// hashr exists so that we can make a thing that can return valid hash.Hash
+// interfaces.
+type hashr func() hash.Hash
+
+// hsh figures out which hash algo to use, and distributes the work of hashing
+func hsh(files []string) chan result {
+	var h hashr
+	switch *algo {
+	case "sha1", "1":
+		h = sha1.New
+	case "sha256", "256":
+		h = sha256.New
+	case "sha512", "512":
+		h = sha512.New
+	case "md5":
+		h = md5.New
+	default:
+		r := make(chan result)
+		go func() {
+			r <- result{err: fmt.Errorf("unsupported algorithm: %v", *algo)}
+		}()
+		return r
+	}
+
+	if len(files) == 0 {
+		hsh := h()
+		_, err := io.Copy(hsh, os.Stdin)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+			os.Exit(1)
+		}
+		fmt.Printf("%x  -\n", hsh.Sum(nil))
+		return nil
+	}
+
+	jobs := make(chan checksum)
+	go func() {
+		for _, name := range files {
+			jobs <- checksum{filename: name}
+		}
+		close(jobs)
+	}()
+
+	res := []<-chan result{}
+	for w := 0; w < *ngo; w++ {
+		res = append(res, compute(h, jobs))
+	}
+
+	return rmerge(res)
+}
+
+// compute is the checksumming workhorse
+func compute(h hashr, jobs chan checksum) chan result {
+	hsh := h()
+	r := make(chan result)
+	go func() {
+		for job := range jobs {
+			f, err := os.Open(job.filename)
+			if err != nil {
+				r <- result{err: err}
+				continue
+			}
+			hsh.Reset()
+			_, err = io.Copy(hsh, f)
+			f.Close()
+			if err != nil {
+				r <- result{err: err}
+				continue
+			}
+			r <- result{msg: fmt.Sprintf("%x  %s", hsh.Sum(nil), job.filename)}
+		}
+		close(r)
+	}()
+	return r
+}
+
+// rmerge implements fan-in
+func rmerge(cs []<-chan result) chan result {
+	out := make(chan result)
+
+	var wg sync.WaitGroup
+
+	output := func(c <-chan result) {
+		for n := range c {
+			out <- n
+		}
+		wg.Done()
+	}
+
+	wg.Add(len(cs))
+	for _, c := range cs {
+		go output(c)
+	}
+
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+	return out
+}
diff --git a/main.go b/main.go
index 1796293..661d02f 100644
--- a/main.go
+++ b/main.go
@@ -1,17 +1,10 @@
 package main
 
 import (
-	"crypto/md5"
-	"crypto/sha1"
-	"crypto/sha256"
-	"crypto/sha512"
 	"flag"
 	"fmt"
-	"hash"
-	"io"
 	"os"
 	"runtime"
-	"sync"
 )
 
 var algo = flag.String("a", "sha1", "algorithm to use")
@@ -46,104 +39,3 @@ func main() {
 		}
 	}
 }
-
-type hashr func() hash.Hash
-
-func hsh(files []string) chan result {
-	var h hashr
-	switch *algo {
-	case "sha1", "1":
-		h = sha1.New
-	case "sha256", "256":
-		h = sha256.New
-	case "sha512", "512":
-		h = sha512.New
-	case "md5":
-		h = md5.New
-	default:
-		r := make(chan result)
-		go func() {
-			r <- result{err: fmt.Errorf("unsupported algorithm: %v", *algo)}
-		}()
-		return r
-	}
-
-	if len(files) == 0 {
-		hsh := h()
-		_, err := io.Copy(hsh, os.Stdin)
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "%v\n", err)
-			os.Exit(1)
-		}
-		fmt.Printf("%x  -\n", hsh.Sum(nil))
-		return nil
-	}
-
-	jobs := make(chan work)
-	go func() {
-		for _, name := range files {
-			jobs <- work{cs: checksum{filename: name}}
-		}
-		close(jobs)
-	}()
-
-	res := []<-chan result{}
-	for w := 0; w < *ngo; w++ {
-		res = append(res, compute(h, jobs))
-	}
-
-	return rmerge(res)
-}
-
-type result struct {
-	msg string
-	err error
-}
-
-func compute(h hashr, jobs chan work) chan result {
-	hsh := h()
-	r := make(chan result)
-	go func() {
-		for job := range jobs {
-			f, err := os.Open(job.cs.filename)
-			if err != nil {
-				r <- result{err: err}
-				continue
-			}
-			hsh.Reset()
-			_, err = io.Copy(hsh, f)
-			f.Close()
-			if err != nil {
-				r <- result{err: err}
-				continue
-			}
-			r <- result{msg: fmt.Sprintf("%x  %s", hsh.Sum(nil), job.cs.filename)}
-		}
-		close(r)
-	}()
-	return r
-}
-
-func rmerge(cs []<-chan result) chan result {
-	out := make(chan result)
-
-	var wg sync.WaitGroup
-
-	output := func(c <-chan result) {
-		for n := range c {
-			out <- n
-		}
-		wg.Done()
-	}
-
-	wg.Add(len(cs))
-	for _, c := range cs {
-		go output(c)
-	}
-
-	go func() {
-		wg.Wait()
-		close(out)
-	}()
-	return out
-}