Dump: add output format tar and output to stdout (#10376)

* Dump: Use mholt/archive/v3 to support tar including many compressions

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: Allow dump output to stdout

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: Fixed bug present since #6677 where SessionConfig.Provider is never "file"

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: never pack RepoRootPath, LFS.ContentPath and LogRootPath when they are below AppDataPath

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: also dump LFS (fixes #10058)

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: never dump CustomPath if CustomPath is a subdir of or equal to AppDataPath (fixes #10365)

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Use log.Info instead of fmt.Fprintf

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* import ordering

* make fmt

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Matti R <matti@mdranta.net>

vendor/github.com/mholt/archiver/v3/lz4.go

@@ -0,0 +1,56 @@
+package archiver
+
+import (
+	"fmt"
+	"io"
+	"path/filepath"
+
+	"github.com/pierrec/lz4"
+)
+
+// Lz4 facilitates LZ4 compression.
+type Lz4 struct {
+	CompressionLevel int
+}
+
+// Compress reads in, compresses it, and writes it to out.
+func (lz *Lz4) Compress(in io.Reader, out io.Writer) error {
+	w := lz4.NewWriter(out)
+	w.Header.CompressionLevel = lz.CompressionLevel
+	defer w.Close()
+	_, err := io.Copy(w, in)
+	return err
+}
+
+// Decompress reads in, decompresses it, and writes it to out.
+func (lz *Lz4) Decompress(in io.Reader, out io.Writer) error {
+	r := lz4.NewReader(in)
+	_, err := io.Copy(out, r)
+	return err
+}
+
+// CheckExt ensures the file extension matches the format.
+func (lz *Lz4) CheckExt(filename string) error {
+	if filepath.Ext(filename) != ".lz4" {
+		return fmt.Errorf("filename must have a .lz4 extension")
+	}
+	return nil
+}
+
+func (lz *Lz4) String() string { return "lz4" }
+
+// NewLz4 returns a new, default instance ready to be customized and used.
+func NewLz4() *Lz4 {
+	return &Lz4{
+		CompressionLevel: 9, // https://github.com/lz4/lz4/blob/1b819bfd633ae285df2dfe1b0589e1ec064f2873/lib/lz4hc.h#L48
+	}
+}
+
+// Compile-time checks to ensure type implements desired interfaces.
+var (
+	_ = Compressor(new(Lz4))
+	_ = Decompressor(new(Lz4))
+)
+
+// DefaultLz4 is a default instance that is conveniently ready to use.
+var DefaultLz4 = NewLz4()