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|
package gitpipe
import (
"context"
"errors"
"fmt"
"io"
"sync"
"gitlab.com/gitlab-org/gitaly/v14/internal/git"
"gitlab.com/gitlab-org/gitaly/v14/internal/git/catfile"
)
// CatfileObjectResult is a result for the CatfileObject pipeline step.
type CatfileObjectResult struct {
// err is an error which occurred during execution of the pipeline.
err error
// ObjectName is the object name as received from the revlistResultChan.
ObjectName []byte
// Object is the object returned by the CatfileObject pipeline step. The object must
// be fully consumed.
git.Object
}
type catfileObjectRequest struct {
objectName []byte
err error
}
// CatfileObject processes catfileInfoResults from the given channel and reads associated objects
// into memory via `git cat-file --batch`. The returned channel will contain all processed objects.
// Any error received via the channel or encountered in this step will cause the pipeline to fail.
// Context cancellation will gracefully halt the pipeline. The returned object readers must always
// be fully consumed by the caller.
func CatfileObject(
ctx context.Context,
objectReader catfile.ObjectReader,
it ObjectIterator,
) (CatfileObjectIterator, error) {
queue, cleanup, err := objectReader.ObjectQueue(ctx)
if err != nil {
return nil, err
}
defer cleanup()
requestChan := make(chan catfileObjectRequest, 32)
go func() {
defer close(requestChan)
sendRequest := func(request catfileObjectRequest) bool {
// Please refer to `sendResult()` for why we treat the context specially.
select {
case <-ctx.Done():
return true
default:
}
select {
case requestChan <- request:
return false
case <-ctx.Done():
return true
}
}
var i int64
for it.Next() {
if err := queue.RequestRevision(it.ObjectID().Revision()); err != nil {
sendRequest(catfileObjectRequest{err: err})
return
}
if isDone := sendRequest(catfileObjectRequest{
objectName: it.ObjectName(),
}); isDone {
return
}
i++
if i%int64(cap(requestChan)) == 0 {
if err := queue.Flush(); err != nil {
sendRequest(catfileObjectRequest{err: err})
return
}
}
}
if err := it.Err(); err != nil {
sendRequest(catfileObjectRequest{err: err})
return
}
if err := queue.Flush(); err != nil {
sendRequest(catfileObjectRequest{err: err})
return
}
}()
resultChan := make(chan CatfileObjectResult)
go func() {
defer close(resultChan)
sendResult := func(result CatfileObjectResult) bool {
// In case the context has been cancelled, we have a race between observing
// an error from the killed Git process and observing the context
// cancellation itself. But if we end up here because of cancellation of the
// Git process, we don't want to pass that one down the pipeline but instead
// just stop the pipeline gracefully. We thus have this check here up front
// to error messages from the Git process.
select {
case <-ctx.Done():
return true
default:
}
select {
case resultChan <- result:
return false
case <-ctx.Done():
return true
}
}
var previousObject *synchronizingObject
// It's fine to iterate over the request channel without paying attention to
// context cancellation because the request channel itself would be closed if the
// context was cancelled.
for request := range requestChan {
if request.err != nil {
sendResult(CatfileObjectResult{err: request.err})
break
}
// We mustn't try to read another object before reading the previous object
// has concluded. Given that this is not under our control but under the
// control of the caller, we thus have to wait until the blocking reader has
// reached EOF.
if previousObject != nil {
select {
case <-previousObject.doneCh:
case <-ctx.Done():
return
}
}
object, err := queue.ReadObject()
if err != nil {
sendResult(CatfileObjectResult{
err: fmt.Errorf("requesting object: %w", err),
})
return
}
previousObject = &synchronizingObject{
Object: object,
doneCh: make(chan interface{}),
}
if isDone := sendResult(CatfileObjectResult{
ObjectName: request.objectName,
Object: previousObject,
}); isDone {
return
}
}
}()
return &catfileObjectIterator{
ctx: ctx,
ch: resultChan,
}, nil
}
type synchronizingObject struct {
git.Object
doneCh chan interface{}
closeOnce sync.Once
}
func (r *synchronizingObject) Read(p []byte) (int, error) {
n, err := r.Object.Read(p)
if errors.Is(err, io.EOF) {
r.closeOnce.Do(func() {
close(r.doneCh)
})
}
return n, err
}
func (r *synchronizingObject) WriteTo(w io.Writer) (int64, error) {
n, err := r.Object.WriteTo(w)
r.closeOnce.Do(func() {
close(r.doneCh)
})
return n, err
}
|
