refactor!: remove go-git backend (#39487)

Removes the go-git backend so every build uses the git CLI backend. Its
Windows performance advantage is gone, it lacks SHA-256 support, and it
breaks repositories on Windows.

The performance changes moved to
https://github.com/go-gitea/gitea/pull/39526.

Fixes https://github.com/go-gitea/gitea/issues/38359
Fixes https://github.com/go-gitea/gitea/issues/34694

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/blob.go

@@ -12,11 +12,10 @@ import (
 	"io"
 	"strings"
 
+	"gitea.dev/modules/log"
 	"gitea.dev/modules/util"
 )
 
-// This file contains common functions between the gogit and !gogit variants for git Blobs
-
 // Name returns name of the tree entry this blob object was created from (or empty string)
 func (b *Blob) Name() string {
 	return b.name
@@ -114,3 +113,98 @@ loop:
 	_ = encoder.Close()
 	return base64buf.String(), nil
 }
+
+// Blob represents a Git object.
+type Blob struct {
+	ID ObjectID
+
+	gotSize bool
+	size    int64
+	name    string
+	repo    *Repository
+}
+
+// DataAsync gets a ReadCloser for the contents of a blob without reading it all.
+// Calling the Close function on the result will discard all unread output.
+func (b *Blob) DataAsync(ctx context.Context) (_ io.ReadCloser, retErr error) {
+	batch, cancel, err := b.repo.CatFileBatch()
+	if err != nil {
+		return nil, err
+	}
+	defer func() {
+		// if there was an error, cancel the batch right away,
+		// otherwise let the caller close it
+		if retErr != nil {
+			cancel()
+		}
+	}()
+
+	info, contentReader, err := batch.QueryContent(b.ID.String())
+	if err != nil {
+		return nil, err
+	}
+	b.gotSize = true
+	b.size = info.Size
+	return &blobReader{
+		rd:     contentReader,
+		n:      info.Size,
+		cancel: cancel,
+	}, nil
+}
+
+// Size returns the uncompressed size of the blob
+func (b *Blob) Size(ctx context.Context) int64 {
+	if b.gotSize {
+		return b.size
+	}
+
+	batch, cancel, err := b.repo.CatFileBatch()
+	if err != nil {
+		log.Debug("error whilst reading size for %s in %s. Error: %v", b.ID.String(), b.repo.LogString(), err)
+		return 0
+	}
+	defer cancel()
+	info, err := batch.QueryInfo(b.ID.String())
+	if err != nil {
+		log.Debug("error whilst reading size for %s in %s. Error: %v", b.ID.String(), b.repo.LogString(), err)
+		return 0
+	}
+	b.gotSize = true
+	b.size = info.Size
+	return b.size
+}
+
+type blobReader struct {
+	rd     BufferedReader
+	n      int64
+	cancel func()
+}
+
+func (b *blobReader) Read(p []byte) (n int, err error) {
+	if b.n <= 0 {
+		return 0, io.EOF
+	}
+	if int64(len(p)) > b.n {
+		p = p[0:b.n]
+	}
+	n, err = b.rd.Read(p)
+	b.n -= int64(n)
+	return n, err
+}
+
+// Close implements io.Closer
+func (b *blobReader) Close() error {
+	if b.rd == nil {
+		return nil
+	}
+
+	defer b.cancel()
+
+	if err := DiscardFull(b.rd, b.n+1); err != nil {
+		return err
+	}
+
+	b.rd = nil
+
+	return nil
+}