From 9913b848c69abdc8c6887391b2c9d5665c60c206 Mon Sep 17 00:00:00 2001
From: Caleb Gardner <calebq23@gmail.com>
Date: Fri, 26 Feb 2021 01:53:16 -0600
Subject: [PATCH] Added some data writing logic.

---
 fragment.go        |   2 +-
 writer_compress.go | 109 ++++++++++++++++++++++++++++++++++++++++++++-
 writer_write.go    |   2 +-
 3 files changed, 110 insertions(+), 3 deletions(-)

diff --git a/fragment.go b/fragment.go
index 647853c..698e49b 100644
--- a/fragment.go
+++ b/fragment.go
@@ -12,7 +12,7 @@ import (
 type fragmentEntry struct {
 	Start uint64
 	Size  uint32
-	// Unused uint32
+	_     uint32 //unused
 }
 
 //GetFragmentDataFromInode returns the fragment data for a given inode.
diff --git a/writer_compress.go b/writer_compress.go
index f2f135f..af88746 100644
--- a/writer_compress.go
+++ b/writer_compress.go
@@ -1,11 +1,18 @@
 package squashfs
 
-import "reflect"
+import (
+	"io"
+	"reflect"
+	"sync"
+)
 
 func (w *Writer) compressData(data []byte) ([]byte, error) {
 	if reflect.DeepEqual(data, make([]byte, len(data))) {
 		return nil, nil
 	}
+	if w.Flags.UncompressedData || w.compressor == nil {
+		return data, nil
+	}
 	compressedData, err := w.compressor.Compress(data)
 	if err != nil {
 		return nil, err
@@ -15,3 +22,103 @@ func (w *Writer) compressData(data []byte) ([]byte, error) {
 	}
 	return compressedData, nil
 }
+
+//Writes the given fileHolder to the WriterAt at the given offset.
+//If fil.Reader implements io.ReaderAt, the process is threaded.
+func (w *Writer) writeFile(fil *fileHolder, write io.WriterAt, startOffset int64) (endOffset int64, err error) {
+	endOffset = startOffset
+	var sizes []uint32
+	if fil.fragIndex != -1 {
+		sizes = fil.blockSizes[:len(fil.blockSizes)-1]
+	} else {
+		sizes = fil.blockSizes
+	}
+	if rdrAt, ok := fil.reader.(io.ReaderAt); ok {
+		type writeReturn struct {
+			err  error
+			byts []byte
+			i    int
+		}
+		out := make(chan *writeReturn)
+		var filOffset int64
+		var sync sync.WaitGroup
+		sync.Add(len(sizes))
+		for i, size := range sizes {
+			go func(offset int64, size uint32, i int) {
+				var ret writeReturn
+				ret.i = i
+				defer func() {
+					out <- &ret
+				}()
+				ret.byts = make([]byte, size)
+				_, ret.err = rdrAt.ReadAt(ret.byts, offset)
+				if ret.err != nil {
+					return
+				}
+				ret.byts, ret.err = w.compressData(ret.byts)
+				sync.Done()
+			}(filOffset, size, i)
+			filOffset += int64(size)
+		}
+		var curInd int
+		var holdingArea []*writeReturn
+		for curInd < len(sizes) {
+			var tmp *writeReturn
+			for _, ret := range holdingArea {
+				if ret.i == curInd {
+					tmp = ret
+					break
+				}
+			}
+			if tmp == nil {
+				tmp = <-out
+				if tmp.err != nil {
+					sync.Wait()
+					return endOffset, tmp.err
+				}
+				if tmp.i != curInd {
+					holdingArea = append(holdingArea, tmp)
+					continue
+				}
+			}
+			fil.blockSizes[curInd] = uint32(len(tmp.byts))
+			if len(tmp.byts) == int(w.BlockSize) {
+				//set uncompressed bit if not compressed
+				fil.blockSizes[curInd] |= (1 << 24)
+			}
+			var n int
+			n, err = write.WriteAt(tmp.byts, endOffset)
+			endOffset += int64(n)
+			if err != nil {
+				sync.Wait()
+				return
+			}
+			curInd++
+		}
+		return
+	}
+	var byts []byte
+	for i, size := range sizes {
+		byts = make([]byte, size)
+		_, err = fil.reader.Read(byts)
+		if err != nil {
+			return
+		}
+		byts, err = w.compressData(byts)
+		if err != nil {
+			return
+		}
+		fil.blockSizes[i] = uint32(len(byts))
+		if len(byts) == int(w.BlockSize) {
+			//set uncompressed bit if not compressed
+			fil.blockSizes[i] |= (1 << 24)
+		}
+		var n int
+		n, err = write.WriteAt(byts, endOffset)
+		endOffset += int64(n)
+		if err != nil {
+			return
+		}
+	}
+	return
+}
diff --git a/writer_write.go b/writer_write.go
index 03e8609..0f19ab9 100644
--- a/writer_write.go
+++ b/writer_write.go
@@ -26,7 +26,7 @@ func (w *Writer) fixFolders() error {
 //are added with full permission (777).
 //
 //Not working. Yet.
-func (w *Writer) WriteTo(write io.Writer) (int64, error) {
+func (w *Writer) WriteTo(write io.WriterAt) (int64, error) {
 	err := w.fixFolders()
 	if err != nil {
 		return 0, err