1 files changed, 347 insertions, 0 deletions
diff --git a/modules/git/batch_reader.go b/modules/git/batch_reader.go
new file mode 100644
index 00000000..c988d6ab
--- /dev/null
+++ b/modules/git/batch_reader.go
@@ -0,0 +1,347 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"math"
+	"runtime"
+	"strconv"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"github.com/djherbis/buffer"
+	"github.com/djherbis/nio/v3"
+)
+
+// WriteCloserError wraps an io.WriteCloser with an additional CloseWithError function
+type WriteCloserError interface {
+	io.WriteCloser
+	CloseWithError(err error) error
+}
+
+// EnsureValidGitRepository runs git rev-parse in the repository path - thus ensuring that the repository is a valid repository.
+// Run before opening git cat-file.
+// This is needed otherwise the git cat-file will hang for invalid repositories.
+func EnsureValidGitRepository(ctx context.Context, repoPath string) error {
+	stderr := strings.Builder{}
+	err := NewCommand(ctx, "rev-parse").
+		SetDescription(fmt.Sprintf("%s rev-parse [repo_path: %s]", GitExecutable, repoPath)).
+		Run(&RunOpts{
+			Dir:    repoPath,
+			Stderr: &stderr,
+		})
+	if err != nil {
+		return ConcatenateError(err, (&stderr).String())
+	}
+	return nil
+}
+
+// CatFileBatchCheck opens git cat-file --batch-check in the provided repo and returns a stdin pipe, a stdout reader and cancel function
+func CatFileBatchCheck(ctx context.Context, repoPath string) (WriteCloserError, *bufio.Reader, func()) {
+	batchStdinReader, batchStdinWriter := io.Pipe()
+	batchStdoutReader, batchStdoutWriter := io.Pipe()
+	ctx, ctxCancel := context.WithCancel(ctx)
+	closed := make(chan struct{})
+	cancel := func() {
+		ctxCancel()
+		_ = batchStdoutReader.Close()
+		_ = batchStdinWriter.Close()
+		<-closed
+	}
+
+	// Ensure cancel is called as soon as the provided context is cancelled
+	go func() {
+		<-ctx.Done()
+		cancel()
+	}()
+
+	_, filename, line, _ := runtime.Caller(2)
+	filename = strings.TrimPrefix(filename, callerPrefix)
+
+	go func() {
+		stderr := strings.Builder{}
+		err := NewCommand(ctx, "cat-file", "--batch-check").
+			SetDescription(fmt.Sprintf("%s cat-file --batch-check [repo_path: %s] (%s:%d)", GitExecutable, repoPath, filename, line)).
+			Run(&RunOpts{
+				Dir:    repoPath,
+				Stdin:  batchStdinReader,
+				Stdout: batchStdoutWriter,
+				Stderr: &stderr,
+
+				UseContextTimeout: true,
+			})
+		if err != nil {
+			_ = batchStdoutWriter.CloseWithError(ConcatenateError(err, (&stderr).String()))
+			_ = batchStdinReader.CloseWithError(ConcatenateError(err, (&stderr).String()))
+		} else {
+			_ = batchStdoutWriter.Close()
+			_ = batchStdinReader.Close()
+		}
+		close(closed)
+	}()
+
+	// For simplicities sake we'll use a buffered reader to read from the cat-file --batch-check
+	batchReader := bufio.NewReader(batchStdoutReader)
+
+	return batchStdinWriter, batchReader, cancel
+}
+
+// CatFileBatch opens git cat-file --batch in the provided repo and returns a stdin pipe, a stdout reader and cancel function
+func CatFileBatch(ctx context.Context, repoPath string) (WriteCloserError, *bufio.Reader, func()) {
+	// We often want to feed the commits in order into cat-file --batch, followed by their trees and sub trees as necessary.
+	// so let's create a batch stdin and stdout
+	batchStdinReader, batchStdinWriter := io.Pipe()
+	batchStdoutReader, batchStdoutWriter := nio.Pipe(buffer.New(32 * 1024))
+	ctx, ctxCancel := context.WithCancel(ctx)
+	closed := make(chan struct{})
+	cancel := func() {
+		ctxCancel()
+		_ = batchStdinWriter.Close()
+		_ = batchStdoutReader.Close()
+		<-closed
+	}
+
+	// Ensure cancel is called as soon as the provided context is cancelled
+	go func() {
+		<-ctx.Done()
+		cancel()
+	}()
+
+	_, filename, line, _ := runtime.Caller(2)
+	filename = strings.TrimPrefix(filename, callerPrefix)
+
+	go func() {
+		stderr := strings.Builder{}
+		err := NewCommand(ctx, "cat-file", "--batch").
+			SetDescription(fmt.Sprintf("%s cat-file --batch [repo_path: %s] (%s:%d)", GitExecutable, repoPath, filename, line)).
+			Run(&RunOpts{
+				Dir:    repoPath,
+				Stdin:  batchStdinReader,
+				Stdout: batchStdoutWriter,
+				Stderr: &stderr,
+
+				UseContextTimeout: true,
+			})
+		if err != nil {
+			_ = batchStdoutWriter.CloseWithError(ConcatenateError(err, (&stderr).String()))
+			_ = batchStdinReader.CloseWithError(ConcatenateError(err, (&stderr).String()))
+		} else {
+			_ = batchStdoutWriter.Close()
+			_ = batchStdinReader.Close()
+		}
+		close(closed)
+	}()
+
+	// For simplicities sake we'll us a buffered reader to read from the cat-file --batch
+	batchReader := bufio.NewReaderSize(batchStdoutReader, 32*1024)
+
+	return batchStdinWriter, batchReader, cancel
+}
+
+// ReadBatchLine reads the header line from cat-file --batch
+// We expect:
+// <sha> SP <type> SP <size> LF
+// sha is a hex encoded here
+func ReadBatchLine(rd *bufio.Reader) (sha []byte, typ string, size int64, err error) {
+	typ, err = rd.ReadString('\n')
+	if err != nil {
+		return sha, typ, size, err
+	}
+	if len(typ) == 1 {
+		typ, err = rd.ReadString('\n')
+		if err != nil {
+			return sha, typ, size, err
+		}
+	}
+	idx := strings.IndexByte(typ, ' ')
+	if idx < 0 {
+		log.Debug("missing space typ: %s", typ)
+		return sha, typ, size, ErrNotExist{ID: string(sha)}
+	}
+	sha = []byte(typ[:idx])
+	typ = typ[idx+1:]
+
+	idx = strings.IndexByte(typ, ' ')
+	if idx < 0 {
+		return sha, typ, size, ErrNotExist{ID: string(sha)}
+	}
+
+	sizeStr := typ[idx+1 : len(typ)-1]
+	typ = typ[:idx]
+
+	size, err = strconv.ParseInt(sizeStr, 10, 64)
+	return sha, typ, size, err
+}
+
+// ReadTagObjectID reads a tag object ID hash from a cat-file --batch stream, throwing away the rest of the stream.
+func ReadTagObjectID(rd *bufio.Reader, size int64) (string, error) {
+	var id string
+	var n int64
+headerLoop:
+	for {
+		line, err := rd.ReadBytes('\n')
+		if err != nil {
+			return "", err
+		}
+		n += int64(len(line))
+		idx := bytes.Index(line, []byte{' '})
+		if idx < 0 {
+			continue
+		}
+
+		if string(line[:idx]) == "object" {
+			id = string(line[idx+1 : len(line)-1])
+			break headerLoop
+		}
+	}
+
+	// Discard the rest of the tag
+	return id, DiscardFull(rd, size-n+1)
+}
+
+// ReadTreeID reads a tree ID from a cat-file --batch stream, throwing away the rest of the stream.
+func ReadTreeID(rd *bufio.Reader, size int64) (string, error) {
+	var id string
+	var n int64
+headerLoop:
+	for {
+		line, err := rd.ReadBytes('\n')
+		if err != nil {
+			return "", err
+		}
+		n += int64(len(line))
+		idx := bytes.Index(line, []byte{' '})
+		if idx < 0 {
+			continue
+		}
+
+		if string(line[:idx]) == "tree" {
+			id = string(line[idx+1 : len(line)-1])
+			break headerLoop
+		}
+	}
+
+	// Discard the rest of the commit
+	return id, DiscardFull(rd, size-n+1)
+}
+
+// git tree files are a list:
+// <mode-in-ascii> SP <fname> NUL <binary Hash>
+//
+// Unfortunately this 20-byte notation is somewhat in conflict to all other git tools
+// Therefore we need some method to convert these binary hashes to hex hashes
+
+// constant hextable to help quickly convert between binary and hex representation
+const hextable = "0123456789abcdef"
+
+// BinToHexHeash converts a binary Hash into a hex encoded one. Input and output can be the
+// same byte slice to support in place conversion without allocations.
+// This is at least 100x quicker that hex.EncodeToString
+func BinToHex(objectFormat ObjectFormat, sha, out []byte) []byte {
+	for i := objectFormat.FullLength()/2 - 1; i >= 0; i-- {
+		v := sha[i]
+		vhi, vlo := v>>4, v&0x0f
+		shi, slo := hextable[vhi], hextable[vlo]
+		out[i*2], out[i*2+1] = shi, slo
+	}
+	return out
+}
+
+// ParseTreeLine reads an entry from a tree in a cat-file --batch stream
+// This carefully avoids allocations - except where fnameBuf is too small.
+// It is recommended therefore to pass in an fnameBuf large enough to avoid almost all allocations
+//
+// Each line is composed of:
+// <mode-in-ascii-dropping-initial-zeros> SP <fname> NUL <binary HASH>
+//
+// We don't attempt to convert the raw HASH to save a lot of time
+func ParseTreeLine(objectFormat ObjectFormat, rd *bufio.Reader, modeBuf, fnameBuf, shaBuf []byte) (mode, fname, sha []byte, n int, err error) {
+	var readBytes []byte
+
+	// Read the Mode & fname
+	readBytes, err = rd.ReadSlice('\x00')
+	if err != nil {
+		return mode, fname, sha, n, err
+	}
+	idx := bytes.IndexByte(readBytes, ' ')
+	if idx < 0 {
+		log.Debug("missing space in readBytes ParseTreeLine: %s", readBytes)
+		return mode, fname, sha, n, &ErrNotExist{}
+	}
+
+	n += idx + 1
+	copy(modeBuf, readBytes[:idx])
+	if len(modeBuf) >= idx {
+		modeBuf = modeBuf[:idx]
+	} else {
+		modeBuf = append(modeBuf, readBytes[len(modeBuf):idx]...)
+	}
+	mode = modeBuf
+
+	readBytes = readBytes[idx+1:]
+
+	// Deal with the fname
+	copy(fnameBuf, readBytes)
+	if len(fnameBuf) > len(readBytes) {
+		fnameBuf = fnameBuf[:len(readBytes)]
+	} else {
+		fnameBuf = append(fnameBuf, readBytes[len(fnameBuf):]...)
+	}
+	for err == bufio.ErrBufferFull {
+		readBytes, err = rd.ReadSlice('\x00')
+		fnameBuf = append(fnameBuf, readBytes...)
+	}
+	n += len(fnameBuf)
+	if err != nil {
+		return mode, fname, sha, n, err
+	}
+	fnameBuf = fnameBuf[:len(fnameBuf)-1]
+	fname = fnameBuf
+
+	// Deal with the binary hash
+	idx = 0
+	length := objectFormat.FullLength() / 2
+	for idx < length {
+		var read int
+		read, err = rd.Read(shaBuf[idx:length])
+		n += read
+		if err != nil {
+			return mode, fname, sha, n, err
+		}
+		idx += read
+	}
+	sha = shaBuf
+	return mode, fname, sha, n, err
+}
+
+var callerPrefix string
+
+func init() {
+	_, filename, _, _ := runtime.Caller(0)
+	callerPrefix = strings.TrimSuffix(filename, "modules/git/batch_reader.go")
+}
+
+func DiscardFull(rd *bufio.Reader, discard int64) error {
+	if discard > math.MaxInt32 {
+		n, err := rd.Discard(math.MaxInt32)
+		discard -= int64(n)
+		if err != nil {
+			return err
+		}
+	}
+	for discard > 0 {
+		n, err := rd.Discard(int(discard))
+		discard -= int64(n)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}