Merge pull request #252 from diskfs/useful-byte-comparison-utility

useful byte comparison utility for tests

util/printer.go

@@ -0,0 +1,137 @@
+package util
+
+import (
+	"fmt"
+)
+
+// DumpByteSlice dump a byte slice in hex and optionally ASCII format.
+// Optionally but position at the beginning of each row, like xxd.
+// Optionally convert to ASCII at end of each row, like xxd.
+// Can show positions at beginning of each row in hex, decimal or both.
+// Can filter out all rows except those containing given positions in showOnlyBytes. If showOnlyBytes is nil, all rows are shown.
+// If showOnlyBytes is not nil, even an empty slice, will only show those rows that contain the given positions.
+func DumpByteSlice(b []byte, bytesPerRow int, showASCII, showPosHex, showPosDec bool, showOnlyBytes []int) (out string) {
+	var ascii []byte
+	// go through each byte.
+	// At each position:
+	// - if we are at the end of a row, print the ASCII representation of the row.
+	// - if we are at the middle of a row, add an extra space
+	// - if we are still in the byte slice, print the byte in hex with a space before it.
+	// - if we are past the end of the row, print spaces.
+	showOnlyMap := make(map[int]bool)
+	for _, v := range showOnlyBytes {
+		showOnlyMap[v] = true
+	}
+	// run by rows
+	numRows := len(b) / bytesPerRow
+	if len(b)%bytesPerRow != 0 {
+		numRows++
+	}
+	for i := 0; i < numRows; i++ {
+		firstByte := i * bytesPerRow
+		lastByte := firstByte + bytesPerRow
+		var row string
+		// row header includes optional position numbers
+		if showPosHex {
+			row += fmt.Sprintf("%08x ", firstByte)
+		}
+		if showPosDec {
+			row += fmt.Sprintf("%4d ", firstByte)
+		}
+		row += ": "
+		for j := firstByte; j < lastByte; j++ {
+			// every 8 bytes add extra spacing to make it easier to read
+			if j%8 == 0 {
+				row += " "
+			}
+			// regular byte, print in hex
+			if j < len(b) {
+				hex := fmt.Sprintf(" %02x", b[j])
+				if showOnlyBytes != nil && showOnlyMap[j] {
+					hex = "\033[1m\033[31m" + hex + "\033[0m"
+				}
+				row += hex
+			} else {
+				row += "   "
+			}
+			switch {
+			case j >= len(b):
+				// past end of byte slice, print spaces
+				ascii = append(ascii, ' ')
+			case b[j] < 32 || b[j] > 126:
+				// unprintable characters, print a dot
+				ascii = append(ascii, '.')
+			default:
+				// printable characters, print the character
+				ascii = append(ascii, b[j])
+			}
+		}
+		// end of row, print the ASCII representation and a newline
+		if showASCII {
+			row += fmt.Sprintf("  %s", string(ascii))
+			ascii = ascii[:0]
+		}
+		row += "\n"
+
+		// calculate if we should include this row
+		var includeRow = true
+		if showOnlyBytes != nil {
+			includeRow = false
+			for j := firstByte; j < lastByte; j++ {
+				if showOnlyMap[j] {
+					includeRow = true
+					break
+				}
+			}
+		}
+		if includeRow {
+			out += row
+		}
+	}
+	return out
+}
+
+// diff
+type diff struct {
+	Offset int
+	ByteA  byte
+	ByteB  byte
+}
+
+// compareByteSlices compares two byte slices position by position. If the byte slices are identical, diffs is length 0,
+// otherwise it contains the positions of the differences.
+func compareByteSlices(a, b []byte) (diffs []diff) {
+	maxSize := len(a)
+	if len(b) > maxSize {
+		maxSize = len(b)
+	}
+	for i := 0; i < maxSize; i++ {
+		switch {
+		case i >= len(a):
+			diffs = append(diffs, diff{Offset: i, ByteA: 0, ByteB: b[i]})
+		case i >= len(b):
+			diffs = append(diffs, diff{Offset: i, ByteA: a[i], ByteB: 0})
+		case a[i] != b[i]:
+			diffs = append(diffs, diff{Offset: i, ByteA: a[i], ByteB: b[i]})
+		}
+	}
+	return diffs
+}
+
+// DumpByteSlicesWithDiffs show two byte slices in hex and ASCII format, with differences highlighted.
+func DumpByteSlicesWithDiffs(a, b []byte, bytesPerRow int, showASCII, showPosHex, showPosDec bool) (different bool, out string) {
+	diffs := compareByteSlices(a, b)
+	// if there are no differences, just return an empty string
+	if len(diffs) == 0 {
+		return false, ""
+	}
+
+	showOnlyBytes := make([]int, len(diffs))
+	for i, d := range diffs {
+		showOnlyBytes[i] = d.Offset
+	}
+	out = DumpByteSlice(a, bytesPerRow, showASCII, showPosHex, showPosDec, showOnlyBytes)
+	out += "\n"
+	out += DumpByteSlice(b, bytesPerRow, showASCII, showPosHex, showPosDec, showOnlyBytes)
+	return true, out
+}