Support in-place upgrades of new minio binary and releases. (#4961)

This PR allows 'minio update' to not only shows update banner
but also allows for in-place upgrades.

Updates are done safely by validating the downloaded
sha256 of the binary.

Fixes #4781

vendor/github.com/inconshreveable/go-update/internal/binarydist/patch.go

@@ -0,0 +1,109 @@
+package binarydist
+
+import (
+	"bytes"
+	"compress/bzip2"
+	"encoding/binary"
+	"errors"
+	"io"
+	"io/ioutil"
+)
+
+var ErrCorrupt = errors.New("corrupt patch")
+
+// Patch applies patch to old, according to the bspatch algorithm,
+// and writes the result to new.
+func Patch(old io.Reader, new io.Writer, patch io.Reader) error {
+	var hdr header
+	err := binary.Read(patch, signMagLittleEndian{}, &hdr)
+	if err != nil {
+		return err
+	}
+	if hdr.Magic != magic {
+		return ErrCorrupt
+	}
+	if hdr.CtrlLen < 0 || hdr.DiffLen < 0 || hdr.NewSize < 0 {
+		return ErrCorrupt
+	}
+
+	ctrlbuf := make([]byte, hdr.CtrlLen)
+	_, err = io.ReadFull(patch, ctrlbuf)
+	if err != nil {
+		return err
+	}
+	cpfbz2 := bzip2.NewReader(bytes.NewReader(ctrlbuf))
+
+	diffbuf := make([]byte, hdr.DiffLen)
+	_, err = io.ReadFull(patch, diffbuf)
+	if err != nil {
+		return err
+	}
+	dpfbz2 := bzip2.NewReader(bytes.NewReader(diffbuf))
+
+	// The entire rest of the file is the extra block.
+	epfbz2 := bzip2.NewReader(patch)
+
+	obuf, err := ioutil.ReadAll(old)
+	if err != nil {
+		return err
+	}
+
+	nbuf := make([]byte, hdr.NewSize)
+
+	var oldpos, newpos int64
+	for newpos < hdr.NewSize {
+		var ctrl struct{ Add, Copy, Seek int64 }
+		err = binary.Read(cpfbz2, signMagLittleEndian{}, &ctrl)
+		if err != nil {
+			return err
+		}
+
+		// Sanity-check
+		if newpos+ctrl.Add > hdr.NewSize {
+			return ErrCorrupt
+		}
+
+		// Read diff string
+		_, err = io.ReadFull(dpfbz2, nbuf[newpos:newpos+ctrl.Add])
+		if err != nil {
+			return ErrCorrupt
+		}
+
+		// Add old data to diff string
+		for i := int64(0); i < ctrl.Add; i++ {
+			if oldpos+i >= 0 && oldpos+i < int64(len(obuf)) {
+				nbuf[newpos+i] += obuf[oldpos+i]
+			}
+		}
+
+		// Adjust pointers
+		newpos += ctrl.Add
+		oldpos += ctrl.Add
+
+		// Sanity-check
+		if newpos+ctrl.Copy > hdr.NewSize {
+			return ErrCorrupt
+		}
+
+		// Read extra string
+		_, err = io.ReadFull(epfbz2, nbuf[newpos:newpos+ctrl.Copy])
+		if err != nil {
+			return ErrCorrupt
+		}
+
+		// Adjust pointers
+		newpos += ctrl.Copy
+		oldpos += ctrl.Seek
+	}
+
+	// Write the new file
+	for len(nbuf) > 0 {
+		n, err := new.Write(nbuf)
+		if err != nil {
+			return err
+		}
+		nbuf = nbuf[n:]
+	}
+
+	return nil
+}