Add lint and go generate steps to CI (#254)

* Add lint and go generate stages to CI

Add CI step to verify `go generate` was run on repo.
Add linter stage to CI along with linter config file,
`.golangci.yml`.
Will likely prefer revive over static-check.

Updated README Contributing section on linting requirements.

Added sequence ordering to make sure lint and go generate stages run
before tests and build.
This way, build and tests are not run on code that could potentially:

    1. not build due to `gofmt` issues;
    2. contain bugs;
    3. have to be re-submitted after issues are fixed; or
    4. contain outdated Win32 syscall or other auto-generated files.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

* Fixed linter issues

Code changes to satisfy linters:

 - Ran `gofmt -s -w` on repo.
 - Broke up long lines.
 - When possible, changed names with incorrect initialism formatting
   - Added exceptions for exported variables.
 - Added exceptions for ALL_CAPS_WITH_UNDERSCORES code.
   - Switched to using `windows` or `syscall` definitions if possible;
     especially if some constants were unused.
 - Added `_ =` to satisfy error linter, and acknowledge that errors are
   being ignored.
 - Switched to using `errors.Is` and `As` in places, elsewhere added
   exceptions if error value was known to be `syscall.Errno`.
 - Removed bare returns.
 - Prevented variables from being overshadowed in certain places
   (ignoring cases of overshadowing `err`).
 - Renamed variables and functions (eg, `len`, `eventMetadata.bytes`) to
   prevent shadowing pre-built functions and imported pacakges.
 - Removed unused method receivers.
 - Added exceptions to certain unused (unexported) constants and
   functions.
   - Deleted unused `once` from `pkg/etw.providerMap`.
 - Renamed `noop.go` files to `main_other.go` or `doc.go`, to better fit
   style recommendations.
 - Added exceptions for non-secure use of SHA1 and weak crypto
   libraries.
 - Replaced `ioutil` with `io` and `os` (and `t.TempDir` in tests).
 - Added fully exhaustive checks for `switch` statements in `pkg/etw`.
 - Defined constant strings for `tools/mkwinsyscall`.
 - Removed unnecessary conversions.
 - Made sure `context.Cancel` was called.

Additionally, added `//go:build windows" constraints on files with
unexported code, since linter will complain about unused code on
non-Windows platforms.

Added a stub `main() {}` for `mkwinsyscall` for non-Windows builds, just in
case `//go:generate` directives are added to OS-agnostic files.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

* PR: spelling, constants, fuzzing

Moved HVSocket fuzzing tests to separate file with go 1.18 build
constraint.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

backuptar/doc.go

@@ -1,4 +1,3 @@
-// +build !windows
 // This file only exists to allow go get on non-Windows platforms.
 
 package backuptar

backuptar/strconv.go

@@ -1,3 +1,5 @@
+//go:build windows
+
 package backuptar
 
 import (

backuptar/tar.go

@@ -1,3 +1,4 @@
+//go:build windows
 // +build windows
 
 package backuptar
@@ -7,7 +8,6 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -18,17 +18,18 @@ import (
 	"golang.org/x/sys/windows"
 )
 
+//nolint:deadcode,varcheck // keep unused constants for potential future use
 const (
-	c_ISUID  = 04000   // Set uid
-	c_ISGID  = 02000   // Set gid
-	c_ISVTX  = 01000   // Save text (sticky bit)
-	c_ISDIR  = 040000  // Directory
-	c_ISFIFO = 010000  // FIFO
-	c_ISREG  = 0100000 // Regular file
-	c_ISLNK  = 0120000 // Symbolic link
-	c_ISBLK  = 060000  // Block special file
-	c_ISCHR  = 020000  // Character special file
-	c_ISSOCK = 0140000 // Socket
+	cISUID  = 0004000 // Set uid
+	cISGID  = 0002000 // Set gid
+	cISVTX  = 0001000 // Save text (sticky bit)
+	cISDIR  = 0040000 // Directory
+	cISFIFO = 0010000 // FIFO
+	cISREG  = 0100000 // Regular file
+	cISLNK  = 0120000 // Symbolic link
+	cISBLK  = 0060000 // Block special file
+	cISCHR  = 0020000 // Character special file
+	cISSOCK = 0140000 // Socket
 )
 
 const (
@@ -44,7 +45,7 @@ const (
 // zeroReader is an io.Reader that always returns 0s.
 type zeroReader struct{}
 
-func (zr zeroReader) Read(b []byte) (int, error) {
+func (zeroReader) Read(b []byte) (int, error) {
 	for i := range b {
 		b[i] = 0
 	}
@@ -55,7 +56,7 @@ func copySparse(t *tar.Writer, br *winio.BackupStreamReader) error {
 	curOffset := int64(0)
 	for {
 		bhdr, err := br.Next()
-		if err == io.EOF {
+		if err == io.EOF { //nolint:errorlint
 			err = io.ErrUnexpectedEOF
 		}
 		if err != nil {
@@ -71,8 +72,8 @@ func copySparse(t *tar.Writer, br *winio.BackupStreamReader) error {
 		}
 		// archive/tar does not support writing sparse files
 		// so just write zeroes to catch up to the current offset.
-		if _, err := io.CopyN(t, zeroReader{}, bhdr.Offset-curOffset); err != nil {
-			return fmt.Errorf("seek to offset %d: %s", bhdr.Offset, err)
+		if _, err = io.CopyN(t, zeroReader{}, bhdr.Offset-curOffset); err != nil {
+			return fmt.Errorf("seek to offset %d: %w", bhdr.Offset, err)
 		}
 		if bhdr.Size == 0 {
 			// A sparse block with size = 0 is used to mark the end of the sparse blocks.
@@ -106,7 +107,7 @@ func BasicInfoHeader(name string, size int64, fileInfo *winio.FileBasicInfo) *ta
 	hdr.PAXRecords[hdrCreationTime] = formatPAXTime(time.Unix(0, fileInfo.CreationTime.Nanoseconds()))
 
 	if (fileInfo.FileAttributes & syscall.FILE_ATTRIBUTE_DIRECTORY) != 0 {
-		hdr.Mode |= c_ISDIR
+		hdr.Mode |= cISDIR
 		hdr.Size = 0
 		hdr.Typeflag = tar.TypeDir
 	}
@@ -138,9 +139,7 @@ func SecurityDescriptorFromTarHeader(hdr *tar.Header) ([]byte, error) {
 // ExtendedAttributesFromTarHeader reads the EAs associated with the header of the
 // current file from the tar header and returns it as a byte slice.
 func ExtendedAttributesFromTarHeader(hdr *tar.Header) ([]byte, error) {
-	var eas []winio.ExtendedAttribute
-	var eadata []byte
-	var err error
+	var eas []winio.ExtendedAttribute //nolint:prealloc // len(eas) <= len(hdr.PAXRecords); prealloc is wasteful
 	for k, v := range hdr.PAXRecords {
 		if !strings.HasPrefix(k, hdrEaPrefix) {
 			continue
@@ -154,13 +153,15 @@ func ExtendedAttributesFromTarHeader(hdr *tar.Header) ([]byte, error) {
 			Value: data,
 		})
 	}
+	var eaData []byte
+	var err error
 	if len(eas) != 0 {
-		eadata, err = winio.EncodeExtendedAttributes(eas)
+		eaData, err = winio.EncodeExtendedAttributes(eas)
 		if err != nil {
 			return nil, err
 		}
 	}
-	return eadata, nil
+	return eaData, nil
 }
 
 // EncodeReparsePointFromTarHeader reads the ReparsePoint structure from the tar header
@@ -181,11 +182,9 @@ func EncodeReparsePointFromTarHeader(hdr *tar.Header) []byte {
 //
 // The additional Win32 metadata is:
 //
-// MSWINDOWS.fileattr: The Win32 file attributes, as a decimal value
-//
-// MSWINDOWS.rawsd: The Win32 security descriptor, in raw binary format
-//
-// MSWINDOWS.mountpoint: If present, this is a mount point and not a symlink, even though the type is '2' (symlink)
+//   - MSWINDOWS.fileattr: The Win32 file attributes, as a decimal value
+//   - MSWINDOWS.rawsd: The Win32 security descriptor, in raw binary format
+//   - MSWINDOWS.mountpoint: If present, this is a mount point and not a symlink, even though the type is '2' (symlink)
 func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size int64, fileInfo *winio.FileBasicInfo) error {
 	name = filepath.ToSlash(name)
 	hdr := BasicInfoHeader(name, size, fileInfo)
@@ -208,7 +207,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 	var dataHdr *winio.BackupHeader
 	for dataHdr == nil {
 		bhdr, err := br.Next()
-		if err == io.EOF {
+		if err == io.EOF { //nolint:errorlint
 			break
 		}
 		if err != nil {
@@ -216,21 +215,21 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 		}
 		switch bhdr.Id {
 		case winio.BackupData:
-			hdr.Mode |= c_ISREG
+			hdr.Mode |= cISREG
 			if !readTwice {
 				dataHdr = bhdr
 			}
 		case winio.BackupSecurity:
-			sd, err := ioutil.ReadAll(br)
+			sd, err := io.ReadAll(br)
 			if err != nil {
 				return err
 			}
 			hdr.PAXRecords[hdrRawSecurityDescriptor] = base64.StdEncoding.EncodeToString(sd)
 
 		case winio.BackupReparseData:
-			hdr.Mode |= c_ISLNK
+			hdr.Mode |= cISLNK
 			hdr.Typeflag = tar.TypeSymlink
-			reparseBuffer, err := ioutil.ReadAll(br)
+			reparseBuffer, _ := io.ReadAll(br)
 			rp, err := winio.DecodeReparsePoint(reparseBuffer)
 			if err != nil {
 				return err
@@ -241,7 +240,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 			hdr.Linkname = rp.Target
 
 		case winio.BackupEaData:
-			eab, err := ioutil.ReadAll(br)
+			eab, err := io.ReadAll(br)
 			if err != nil {
 				return err
 			}
@@ -275,7 +274,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 		}
 		for dataHdr == nil {
 			bhdr, err := br.Next()
-			if err == io.EOF {
+			if err == io.EOF { //nolint:errorlint
 				break
 			}
 			if err != nil {
@@ -310,7 +309,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 	//     range of the file containing the range contents. Finally there is a sparse block stream with
 	//     size = 0 and offset = <file size>.
 
-	if dataHdr != nil {
+	if dataHdr != nil { //nolint:nestif // todo: reduce nesting complexity
 		// A data stream was found. Copy the data.
 		// We assume that we will either have a data stream size > 0 XOR have sparse block streams.
 		if dataHdr.Size > 0 || (dataHdr.Attributes&winio.StreamSparseAttributes) == 0 {
@@ -318,13 +317,13 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 				return fmt.Errorf("%s: mismatch between file size %d and header size %d", name, size, dataHdr.Size)
 			}
 			if _, err = io.Copy(t, br); err != nil {
-				return fmt.Errorf("%s: copying contents from data stream: %s", name, err)
+				return fmt.Errorf("%s: copying contents from data stream: %w", name, err)
 			}
 		} else if size > 0 {
 			// As of a recent OS change, BackupRead now returns a data stream for empty sparse files.
 			// These files have no sparse block streams, so skip the copySparse call if file size = 0.
 			if err = copySparse(t, br); err != nil {
-				return fmt.Errorf("%s: copying contents from sparse block stream: %s", name, err)
+				return fmt.Errorf("%s: copying contents from sparse block stream: %w", name, err)
 			}
 		}
 	}
@@ -334,7 +333,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 	// been written. In practice, this means that we don't get EA or TXF metadata.
 	for {
 		bhdr, err := br.Next()
-		if err == io.EOF {
+		if err == io.EOF { //nolint:errorlint
 			break
 		}
 		if err != nil {
@@ -342,35 +341,30 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 		}
 		switch bhdr.Id {
 		case winio.BackupAlternateData:
-			altName := bhdr.Name
-			if strings.HasSuffix(altName, ":$DATA") {
-				altName = altName[:len(altName)-len(":$DATA")]
-			}
-			if (bhdr.Attributes & winio.StreamSparseAttributes) == 0 {
-				hdr = &tar.Header{
-					Format:     hdr.Format,
-					Name:       name + altName,
-					Mode:       hdr.Mode,
-					Typeflag:   tar.TypeReg,
-					Size:       bhdr.Size,
-					ModTime:    hdr.ModTime,
-					AccessTime: hdr.AccessTime,
-					ChangeTime: hdr.ChangeTime,
-				}
-				err = t.WriteHeader(hdr)
-				if err != nil {
-					return err
-				}
-				_, err = io.Copy(t, br)
-				if err != nil {
-					return err
-				}
-
-			} else {
+			if (bhdr.Attributes & winio.StreamSparseAttributes) != 0 {
 				// Unsupported for now, since the size of the alternate stream is not present
 				// in the backup stream until after the data has been read.
 				return fmt.Errorf("%s: tar of sparse alternate data streams is unsupported", name)
 			}
+			altName := strings.TrimSuffix(bhdr.Name, ":$DATA")
+			hdr = &tar.Header{
+				Format:     hdr.Format,
+				Name:       name + altName,
+				Mode:       hdr.Mode,
+				Typeflag:   tar.TypeReg,
+				Size:       bhdr.Size,
+				ModTime:    hdr.ModTime,
+				AccessTime: hdr.AccessTime,
+				ChangeTime: hdr.ChangeTime,
+			}
+			err = t.WriteHeader(hdr)
+			if err != nil {
+				return err
+			}
+			_, err = io.Copy(t, br)
+			if err != nil {
+				return err
+			}
 		case winio.BackupEaData, winio.BackupLink, winio.BackupPropertyData, winio.BackupObjectId, winio.BackupTxfsData:
 			// ignore these streams
 		default:
@@ -412,7 +406,7 @@ func FileInfoFromHeader(hdr *tar.Header) (name string, size int64, fileInfo *win
 		}
 		fileInfo.CreationTime = windows.NsecToFiletime(creationTime.UnixNano())
 	}
-	return
+	return name, size, fileInfo, err
 }
 
 // WriteBackupStreamFromTarFile writes a Win32 backup stream from the current tar file. Since this function may process multiple
@@ -473,7 +467,6 @@ func WriteBackupStreamFromTarFile(w io.Writer, t *tar.Reader, hdr *tar.Header) (
 		if err != nil {
 			return nil, err
 		}
-
 	}
 
 	if hdr.Typeflag == tar.TypeReg || hdr.Typeflag == tar.TypeRegA {

backuptar/tar_test.go

@@ -1,3 +1,4 @@
+//go:build windows
 // +build windows
 
 package backuptar
@@ -6,7 +7,6 @@ import (
 	"archive/tar"
 	"bytes"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -25,8 +25,7 @@ func ensurePresent(t *testing.T, m map[string]string, keys ...string) {
 }
 
 func setSparse(t *testing.T, f *os.File) {
-	const FSCTL_SET_SPARSE uint32 = 0x900c4
-	if err := windows.DeviceIoControl(windows.Handle(f.Fd()), FSCTL_SET_SPARSE, nil, 0, nil, 0, nil, nil); err != nil {
+	if err := windows.DeviceIoControl(windows.Handle(f.Fd()), windows.FSCTL_SET_SPARSE, nil, 0, nil, 0, nil, nil); err != nil {
 		t.Fatal(err)
 	}
 }
@@ -68,10 +67,12 @@ func compareReaders(t *testing.T, rActual io.Reader, rExpected io.Reader) {
 func TestRoundTrip(t *testing.T) {
 	// Each test case is a name mapped to a function which must create a file and return its path.
 	// The test then round-trips that file through backuptar, and validates the output matches the input.
+	//
+	//nolint:gosec // G306: Expect WriteFile permissions to be 0600 or less
 	for name, setup := range map[string]func(*testing.T) string{
 		"normalFile": func(t *testing.T) string {
 			path := filepath.Join(t.TempDir(), "foo.txt")
-			if err := ioutil.WriteFile(path, []byte("testing 1 2 3\n"), 0644); err != nil {
+			if err := os.WriteFile(path, []byte("testing 1 2 3\n"), 0644); err != nil {
 				t.Fatal(err)
 			}
 			return path