brydavis · October 30, 2018 00:02 · Oct 30, 2018
diff --git a/multiwriter.go b/multiwriter.go
@@ -0,0 +1,42 @@
+package main
+
+import (
+	"bytes"
+	"crypto/md5"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+)
+
+func main() {
+	sourceFile, _ := os.Open("source/ebook.pdf")
+
+	process := func(sourceReader io.Reader) {
+		targetFile, _ := os.Create("target/ebook.pdf")
+		defer targetFile.Close()
+
+		var buf1, buf2 bytes.Buffer
+		w := io.MultiWriter(targetFile, &buf1, &buf2)
+
+		if _, err := io.Copy(w, sourceReader); err != nil {
+			fmt.Println(err)
+		}
+
+		fmt.Println(checksum(&buf1))
+		fmt.Println(checksum(&buf2))
+	}
+
+	process(sourceFile)
+
+}
+
+func checksum(buf *bytes.Buffer) string {
+	h := md5.New()
+	b, _ := ioutil.ReadAll(buf)
+	if _, err := h.Write(b); err != nil {
+		fmt.Println(err)
+	}
+	return hex.EncodeToString(h.Sum(nil)[:16])
+}
diff --git a/teereader.go b/teereader.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"bytes"
+	"crypto/md5"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+)
+
+func main() {
+	sourceFile, _ := os.Open("source/ebook.pdf")
+
+	var buf bytes.Buffer
+	tee := io.TeeReader(sourceFile, &buf)
+
+	process := func(sourceReader io.Reader) {
+		targetFile, _ := os.Create("target/ebook.pdf")
+		defer targetFile.Close()
+		if _, err := io.Copy(targetFile, sourceReader); err != nil {
+			fmt.Println(err)
+		}
+	}
+
+	process(tee)
+	fmt.Println(checksum(&buf))
+}
+
+func checksum(buf *bytes.Buffer) string {
+	h := md5.New()
+	b, _ := ioutil.ReadAll(buf)
+	if _, err := h.Write(b); err != nil {
+		fmt.Println(err)
+	}
+	return hex.EncodeToString(h.Sum(nil)[:16])
+}