Add ArchiveAsync(); context no longer optional (#320)

Following Go best-practices.

Zip and Tar now support ArchiveAsync, which reads files from a channel
instead of a slice.

fs.go

@@ -221,6 +221,14 @@ type ArchiveFS struct {
 	Context context.Context // optional
 }
 
+// context always return a context, preferring f.Context if not nil.
+func (f ArchiveFS) context() context.Context {
+	if f.Context != nil {
+		return f.Context
+	}
+	return context.Background()
+}
+
 // Open opens the named file from within the archive. If name is "." then
 // the archive file itself will be opened as a directory file.
 func (f ArchiveFS) Open(name string) (fs.File, error) {
@@ -312,7 +320,7 @@ func (f ArchiveFS) Open(name string) (fs.File, error) {
 		inputStream = io.NewSectionReader(f.Stream, 0, f.Stream.Size())
 	}
 
-	err = f.Format.Extract(f.Context, inputStream, []string{name}, handler)
+	err = f.Format.Extract(f.context(), inputStream, []string{name}, handler)
 	if err != nil && fsFile != nil {
 		if ef, ok := fsFile.(extractedFile); ok {
 			if ef.parentArchive != nil {
@@ -377,7 +385,7 @@ func (f ArchiveFS) Stat(name string) (fs.FileInfo, error) {
 	if f.Stream != nil {
 		inputStream = io.NewSectionReader(f.Stream, 0, f.Stream.Size())
 	}
-	err = f.Format.Extract(f.Context, inputStream, []string{name}, handler)
+	err = f.Format.Extract(f.context(), inputStream, []string{name}, handler)
 	if err != nil && result.FileInfo == nil {
 		return nil, err
 	}
@@ -446,7 +454,7 @@ func (f ArchiveFS) ReadDir(name string) ([]fs.DirEntry, error) {
 		inputStream = io.NewSectionReader(f.Stream, 0, f.Stream.Size())
 	}
 
-	err = f.Format.Extract(f.Context, inputStream, filter, handler)
+	err = f.Format.Extract(f.context(), inputStream, filter, handler)
 	return entries, err
 }
 

interfaces.go

@@ -56,10 +56,22 @@ type Decompressor interface {
 type Archiver interface {
 	// Archive writes an archive file to output with the given files.
 	//
-	// Context is optional, but if given, cancellation must be honored.
+	// Context cancellation must be honored.
 	Archive(ctx context.Context, output io.Writer, files []File) error
 }
 
+// ArchiverAsync is an Archiver that can also create archives
+// asynchronously by pumping files into a channel as they are
+// discovered.
+type ArchiverAsync interface {
+	Archiver
+
+	// Use ArchiveAsync if you can't pre-assemble a list of all
+	// the files for the archive. Close the files channel after
+	// all the files have been sent.
+	ArchiveAsync(ctx context.Context, output io.Writer, files <-chan File) error
+}
+
 // Extractor can extract files from an archive.
 type Extractor interface {
 	// Extract reads the files at pathsInArchive from sourceArchive.
@@ -68,14 +80,14 @@ type Extractor interface {
 	// If a path refers to a directory, all files within it are extracted.
 	// Extracted files are passed to the handleFile callback for handling.
 	//
-	// Context is optional, but if given, cancellation must be honored.
+	// Context cancellation must be honored.
 	Extract(ctx context.Context, sourceArchive io.Reader, pathsInArchive []string, handleFile FileHandler) error
 }
 
 // Inserter can insert files into an existing archive.
 type Inserter interface {
 	// Insert inserts the files into archive.
 	//
-	// Context is optional, but if given, cancellation must be honored.
+	// Context cancellation must be honored.
 	Insert(ctx context.Context, archive io.ReadWriteSeeker, files []File) error
 }

rar.go

@@ -56,10 +56,6 @@ func (r Rar) Archive(_ context.Context, _ io.Writer, _ []File) error {
 }
 
 func (r Rar) Extract(ctx context.Context, sourceArchive io.Reader, pathsInArchive []string, handleFile FileHandler) error {
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	var options []rardecode.Option
 	if r.Password != "" {
 		options = append(options, rardecode.Password(r.Password))

tar.go

@@ -42,19 +42,28 @@ func (t Tar) Match(filename string, stream io.Reader) (MatchResult, error) {
 }
 
 func (t Tar) Archive(ctx context.Context, output io.Writer, files []File) error {
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	tw := tar.NewWriter(output)
 	defer tw.Close()
 
 	for _, file := range files {
-		if err := ctx.Err(); err != nil {
-			return err // honor context cancellation
+		if err := t.writeFileToArchive(ctx, tw, file); err != nil {
+			if t.ContinueOnError && ctx.Err() == nil { // context errors should always abort
+				log.Printf("[ERROR] %v", err)
+				continue
+			}
+			return err
 		}
-		err := t.writeFileToArchive(ctx, tw, file)
-		if err != nil {
+	}
+
+	return nil
+}
+
+func (t Tar) ArchiveAsync(ctx context.Context, output io.Writer, files <-chan File) error {
+	tw := tar.NewWriter(output)
+	defer tw.Close()
+
+	for file := range files {
+		if err := t.writeFileToArchive(ctx, tw, file); err != nil {
 			if t.ContinueOnError && ctx.Err() == nil { // context errors should always abort
 				log.Printf("[ERROR] %v", err)
 				continue
@@ -67,6 +76,10 @@ func (t Tar) Archive(ctx context.Context, output io.Writer, files []File) error
 }
 
 func (Tar) writeFileToArchive(ctx context.Context, tw *tar.Writer, file File) error {
+	if err := ctx.Err(); err != nil {
+		return err // honor context cancellation
+	}
+
 	hdr, err := tar.FileInfoHeader(file, file.LinkTarget)
 	if err != nil {
 		return fmt.Errorf("file %s: creating header: %w", file.NameInArchive, err)
@@ -91,10 +104,6 @@ func (Tar) writeFileToArchive(ctx context.Context, tw *tar.Writer, file File) er
 }
 
 func (t Tar) Insert(ctx context.Context, into io.ReadWriteSeeker, files []File) error {
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	// Tar files may end with some, none, or a lot of zero-byte padding. The spec says
 	// it should end with two 512-byte trailer records consisting solely of null/0
 	// bytes: https://www.gnu.org/software/tar/manual/html_node/Standard.html. However,
@@ -165,10 +174,6 @@ func (t Tar) Insert(ctx context.Context, into io.ReadWriteSeeker, files []File)
 }
 
 func (t Tar) Extract(ctx context.Context, sourceArchive io.Reader, pathsInArchive []string, handleFile FileHandler) error {
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	tr := tar.NewReader(sourceArchive)
 
 	// important to initialize to non-nil, empty value due to how fileIsIncluded works

zip.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
+	"log"
 	"path"
 	"strings"
 
@@ -101,54 +102,77 @@ func (z Zip) Match(filename string, stream io.Reader) (MatchResult, error) {
 }
 
 func (z Zip) Archive(ctx context.Context, output io.Writer, files []File) error {
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	zw := zip.NewWriter(output)
 	defer zw.Close()
 
 	for i, file := range files {
-		if err := ctx.Err(); err != nil {
-			return err // honor context cancellation
+		if err := z.archiveOneFile(ctx, zw, i, file); err != nil {
+			return err
 		}
+	}
 
-		hdr, err := zip.FileInfoHeader(file)
-		if err != nil {
-			return fmt.Errorf("getting info for file %d: %s: %w", i, file.Name(), err)
-		}
-		hdr.Name = file.NameInArchive // complete path, since FileInfoHeader() only has base name
+	return nil
+}
 
-		// customize header based on file properties
-		if file.IsDir() {
-			if !strings.HasSuffix(hdr.Name, "/") {
-				hdr.Name += "/" // required
-			}
-			hdr.Method = zip.Store
-		} else if z.SelectiveCompression {
-			// only enable compression on compressable files
-			ext := strings.ToLower(path.Ext(hdr.Name))
-			if _, ok := compressedFormats[ext]; ok {
-				hdr.Method = zip.Store
-			} else {
-				hdr.Method = z.Compression
+func (z Zip) ArchiveAsync(ctx context.Context, output io.Writer, files <-chan File) error {
+	zw := zip.NewWriter(output)
+	defer zw.Close()
+
+	var i int
+	for file := range files {
+		if err := z.archiveOneFile(ctx, zw, i, file); err != nil {
+			if z.ContinueOnError && ctx.Err() == nil { // context errors should always abort
+				log.Printf("[ERROR] %v", err)
+				continue
 			}
+			return err
 		}
+		i++
+	}
 
-		w, err := zw.CreateHeader(hdr)
-		if err != nil {
-			return fmt.Errorf("creating header for file %d: %s: %w", i, file.Name(), err)
-		}
+	return nil
+}
 
-		// directories have no file body
-		if file.IsDir() {
-			continue
+func (z Zip) archiveOneFile(ctx context.Context, zw *zip.Writer, idx int, file File) error {
+	if err := ctx.Err(); err != nil {
+		return err // honor context cancellation
+	}
+
+	hdr, err := zip.FileInfoHeader(file)
+	if err != nil {
+		return fmt.Errorf("getting info for file %d: %s: %w", idx, file.Name(), err)
+	}
+	hdr.Name = file.NameInArchive // complete path, since FileInfoHeader() only has base name
+
+	// customize header based on file properties
+	if file.IsDir() {
+		if !strings.HasSuffix(hdr.Name, "/") {
+			hdr.Name += "/" // required
 		}
-		if err := openAndCopyFile(file, w); err != nil {
-			return fmt.Errorf("writing file %d: %s: %w", i, file.Name(), err)
+		hdr.Method = zip.Store
+	} else if z.SelectiveCompression {
+		// only enable compression on compressable files
+		ext := strings.ToLower(path.Ext(hdr.Name))
+		if _, ok := compressedFormats[ext]; ok {
+			hdr.Method = zip.Store
+		} else {
+			hdr.Method = z.Compression
 		}
 	}
 
+	w, err := zw.CreateHeader(hdr)
+	if err != nil {
+		return fmt.Errorf("creating header for file %d: %s: %w", idx, file.Name(), err)
+	}
+
+	// directories have no file body
+	if file.IsDir() {
+		return nil
+	}
+	if err := openAndCopyFile(file, w); err != nil {
+		return fmt.Errorf("writing file %d: %s: %w", idx, file.Name(), err)
+	}
+
 	return nil
 }
 
@@ -159,10 +183,6 @@ func (z Zip) Archive(ctx context.Context, output io.Writer, files []File) error
 // with. Due to the nature of the zip archive format, if sourceArchive is not an io.Seeker
 // and io.ReaderAt, an error is returned.
 func (z Zip) Extract(ctx context.Context, sourceArchive io.Reader, pathsInArchive []string, handleFile FileHandler) error {
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	sra, ok := sourceArchive.(seekReaderAt)
 	if !ok {
 		return fmt.Errorf("input type must be an io.ReaderAt and io.Seeker because of zip format constraints")