concept: move the PoC out of the root directory

concept/main.go

@@ -0,0 +1,91 @@
+// +build ignore
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+
+	"github.com/vbatts/tar-split/archive/tar"
+)
+
+func main() {
+	flag.Parse()
+	log.SetOutput(os.Stderr)
+	for _, arg := range flag.Args() {
+		func() {
+			// Open the tar archive
+			fh, err := os.Open(arg)
+			if err != nil {
+				log.Fatal(err, arg)
+			}
+			defer fh.Close()
+
+			output, err := os.Create(fmt.Sprintf("%s.out", arg))
+			if err != nil {
+				log.Fatal(err)
+			}
+			defer output.Close()
+			log.Printf("writing %q to %q", fh.Name(), output.Name())
+
+			fi, err := fh.Stat()
+			if err != nil {
+				log.Fatal(err, fh.Name())
+			}
+			size := fi.Size()
+			var sum int64
+			tr := tar.NewReader(fh)
+			tr.RawAccounting = true
+			for {
+				hdr, err := tr.Next()
+				if err != nil {
+					if err != io.EOF {
+						log.Println(err)
+					}
+					// even when an EOF is reached, there is often 1024 null bytes on
+					// the end of an archive. Collect them too.
+					post := tr.RawBytes()
+					output.Write(post)
+					sum += int64(len(post))
+
+					fmt.Printf("EOF padding: %d\n", len(post))
+					break
+				}
+
+				pre := tr.RawBytes()
+				output.Write(pre)
+				sum += int64(len(pre))
+
+				var i int64
+				if i, err = io.Copy(output, tr); err != nil {
+					log.Println(err)
+					break
+				}
+				sum += i
+
+				fmt.Println(hdr.Name, "pre:", len(pre), "read:", i)
+			}
+
+			// it is allowable, and not uncommon that there is further padding on the
+			// end of an archive, apart from the expected 1024 null bytes
+			remainder, err := ioutil.ReadAll(fh)
+			if err != nil && err != io.EOF {
+				log.Fatal(err, fh.Name())
+			}
+			output.Write(remainder)
+			sum += int64(len(remainder))
+			fmt.Printf("Remainder: %d\n", len(remainder))
+
+			if size != sum {
+				fmt.Printf("Size: %d; Sum: %d; Diff: %d\n", size, sum, size-sum)
+				fmt.Printf("Compare like `cmp -bl %s %s | less`\n", fh.Name(), output.Name())
+			} else {
+				fmt.Printf("Size: %d; Sum: %d\n", size, sum)
+			}
+		}()
+	}
+}