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// trace2 provides utilities to leverage Gits trace2 functionalities within
// Gitaly.
package trace2
import (
"context"
"fmt"
"io"
"os"
"os/exec"
"gitlab.com/gitlab-org/labkit/correlation"
)
const (
// By setting this environment variable for Git process, it will enable
// the trace 2. Furhter, the value it will be set to tells Git where
// to write the output to. Gitaly uses an open file descriptor.
trace2EventFDKey = "GIT_TRACE2_EVENT"
// Git continiously shells out to child processes and will set the SID
// as environment variable. The child than appends their own unique ID.
// For Gitaly we set the SID to the correlation ID to allow for
// correlation throughout GitLabs components.
sessionIDKey = "GIT_TRACE2_PARENT_SID"
)
// CopyHandler takes the trace2 stream, and copies it over to a passed io.Writer
// Note it still receives the stream on a fresh file descriptor, not 2.
// Returns environment variables which MUST be injected by the
// caller into the spawned Git process; else the sink will never be
// closed and a resource leak occurs.
func CopyHandler(ctx context.Context, cmd *exec.Cmd, sink io.Writer) ([]string, error) {
r, w, err := os.Pipe()
if err != nil {
return nil, err
}
cancelCtx, _ := context.WithCancel(ctx)
go func() {
for {
select {
case <-cancelCtx.Done():
w.Close()
r.Close()
break
default:
io.Copy(sink, r)
}
}
}()
cmd.ExtraFiles = append(cmd.ExtraFiles, w)
return []string{
// Plus 2 accounts for stdin (0), stdout (1), and stderr (2).
fmt.Sprintf("%s=%d", trace2EventFDKey, 2+len(cmd.ExtraFiles)),
fmt.Sprintf("%s=%s", sessionIDKey, correlation.ExtractFromContextOrGenerate(ctx)),
}, nil
}
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