feat: DTail fork — server/client feature development

Squashed development of the snonux/dtail fork's product code (internal/, cmd/)
since diverging from mimecast/dtail. Major areas:

- Read/output path: the former "turbo" channel-less path is now the single,
  default server-side read/output path for cat/grep/tail and MapReduce; the old
  channel-based path and its config/env toggles were removed.
- MapReduce: single aggregate implementation (server + serverless) fed directly
  by a processor pipeline, with input-exhausted finalization via the shutdown
  coordinator; high-concurrency and data-race fixes.
- Journal source reads (journal:unit.service) via journalctl, Linux-gated behind
  a journal-v1 capability.
- Auth-key fast reconnect: in-memory per-user public-key cache with TTL/max-keys,
  registered over an authenticated session (AUTHKEY), checked before
  authorized_keys.
- Interactive query reload (--interactive-query) with SESSION START/UPDATE
  generation boundaries and capability negotiation.
- Client-side deadlines: --timeout / --shutdownAfter as context deadlines;
  follow shutdown handling.
- Client logging: diagnostics-only daily log by default, opt-in payload tee via
  --log-payload.
- Numerous correctness fixes (buffer-pool double-recycle races, EOF-sentinel
  leaks, glob-expansion cap, TOCTOU in CSV parsing) with accompanying unit tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/internal/io/signal/signal.go b/internal/io/signal/signal.go
index c01e82a..e94de42 100644
--- a/internal/io/signal/signal.go
+++ b/internal/io/signal/signal.go
@@ -10,7 +10,52 @@ import (
 	"github.com/mimecast/dtail/internal/config"
 )
 
+// InterruptChWithCancel returns a channel for "please print stats" signalling.
+// It accepts a cancel function to properly shutdown when termination signals are received.
+func InterruptChWithCancel(ctx context.Context, cancel context.CancelFunc) <-chan string {
+	sigIntCh := make(chan os.Signal, 10)
+	gosignal.Notify(sigIntCh, os.Interrupt)
+	sigOtherCh := make(chan os.Signal, 10)
+	gosignal.Notify(sigOtherCh, syscall.SIGHUP, syscall.SIGTERM, syscall.SIGQUIT)
+	statsCh := make(chan string)
+
+	go func() {
+		for {
+			select {
+			case <-sigIntCh:
+				select {
+				case statsCh <- "Hint: Hit Ctrl+C again to exit":
+					select {
+					case <-sigIntCh:
+						cancel()
+						// Wait longer to allow MapReduce cleanup, then force exit if still running
+						go func() {
+							time.Sleep(5 * time.Second)
+							os.Exit(0)
+						}()
+					case <-time.After(time.Second * time.Duration(config.InterruptTimeoutS)):
+					}
+				default:
+					// Stats already printed.
+				}
+			case <-sigOtherCh:
+				// Cancel context to allow graceful shutdown (MapReduce outfile cleanup, etc.)
+				cancel()
+				// Wait longer to allow MapReduce cleanup, then force exit if still running
+				go func() {
+					time.Sleep(5 * time.Second)
+					os.Exit(0)
+				}()
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+	return statsCh
+}
+
 // InterruptCh returns a channel for "please print stats" signalling.
+// Deprecated: Use InterruptChWithCancel for proper cleanup on termination signals.
 func InterruptCh(ctx context.Context) <-chan string {
 	sigIntCh := make(chan os.Signal, 10)
 	gosignal.Notify(sigIntCh, os.Interrupt)