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, 202 insertions, 0 deletions

diff --git a/internal/server/continuous_test.go b/internal/server/continuous_test.go
new file mode 100644
index 0000000..12d9f18
--- /dev/null
+++ b/internal/server/continuous_test.go
@@ -0,0 +1,202 @@
+package server
+
+import (
+	"context"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/mimecast/dtail/internal/clients"
+	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/io/dlog"
+)
+
+func TestSameCalendarDay(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		a    time.Time
+		b    time.Time
+		want bool
+	}{
+		{
+			name: "same day",
+			a:    time.Date(2026, time.January, 15, 10, 0, 0, 0, time.UTC),
+			b:    time.Date(2026, time.January, 15, 23, 59, 59, 0, time.UTC),
+			want: true,
+		},
+		{
+			name: "same day-of-month in different months",
+			a:    time.Date(2026, time.January, 15, 10, 0, 0, 0, time.UTC),
+			b:    time.Date(2026, time.February, 15, 10, 0, 0, 0, time.UTC),
+			want: false,
+		},
+		{
+			name: "same day-of-month across years",
+			a:    time.Date(2025, time.December, 31, 10, 0, 0, 0, time.UTC),
+			b:    time.Date(2026, time.January, 31, 10, 0, 0, 0, time.UTC),
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := sameCalendarDay(tt.a, tt.b); got != tt.want {
+				t.Fatalf("sameCalendarDay(%v, %v) = %v, want %v", tt.a, tt.b, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestContinuousRunJobsReleasesDayChangeWatcherAcrossRetries(t *testing.T) {
+	dlog.Server = &dlog.DLog{}
+
+	c := newContinuous(config.RuntimeConfig{
+		Server: &config.ServerConfig{
+			SSHBindAddress: "127.0.0.1",
+		},
+	})
+	c.retryInterval = 25 * time.Millisecond
+
+	var watcherStarts int32
+	var watcherExits int32
+	started := make(chan struct{}, 1)
+	release := make(chan struct{}, 1)
+	c.newMaprClient = func(args config.Args, mode clients.MaprClientMode) (continuousClient, error) {
+		return blockingContinuousClient{
+			started: started,
+			release: release,
+		}, nil
+	}
+	c.dayChangeWatcher = func(ctx context.Context) bool {
+		atomic.AddInt32(&watcherStarts, 1)
+		defer atomic.AddInt32(&watcherExits, 1)
+		return c.waitForDayChange(ctx)
+	}
+
+	job := config.Continuous{}
+	job.Enable = true
+	job.RestartOnDayChange = true
+	c.cfg.Server.Continuous = []config.Continuous{job}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	done := make(chan struct{})
+	go func() {
+		c.runJobs(ctx)
+		close(done)
+	}()
+
+	for i := int32(1); i <= 5; i++ {
+		select {
+		case <-started:
+		case <-time.After(2 * time.Second):
+			t.Fatalf("timed out waiting for retry %d to start", i)
+		}
+
+		waitForCounterAtLeast(t, func() int32 {
+			return atomic.LoadInt32(&watcherStarts)
+		}, i)
+
+		release <- struct{}{}
+
+		waitForCounterAtLeast(t, func() int32 {
+			return atomic.LoadInt32(&watcherExits)
+		}, i)
+	}
+
+	cancel()
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("continuous job runner did not stop after cancellation")
+	}
+}
+
+func TestContinuousWaitForDayChangeDetectsMonthBoundary(t *testing.T) {
+	dlog.Server = &dlog.DLog{}
+
+	c := newContinuous(config.RuntimeConfig{})
+
+	start := time.Date(2026, time.January, 31, 23, 59, 59, 0, time.UTC)
+	sameDay := time.Date(2026, time.January, 31, 23, 59, 59, 500_000_000, time.UTC)
+	nextDay := time.Date(2026, time.February, 1, 0, 0, 0, 0, time.UTC)
+
+	var nowCalls int32
+	c.now = func() time.Time {
+		switch atomic.AddInt32(&nowCalls, 1) {
+		case 1:
+			return start
+		case 2:
+			return sameDay
+		default:
+			return nextDay
+		}
+	}
+
+	tickCh := make(chan time.Time, 2)
+	c.newTicker = func(time.Duration) (<-chan time.Time, func()) {
+		return tickCh, func() {}
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	result := make(chan bool, 1)
+	go func() {
+		result <- c.waitForDayChange(ctx)
+	}()
+
+	tickCh <- start
+	select {
+	case got := <-result:
+		t.Fatalf("waitForDayChange returned after same-day tick: %v", got)
+	case <-time.After(100 * time.Millisecond):
+	}
+
+	tickCh <- nextDay
+	select {
+	case got := <-result:
+		if !got {
+			t.Fatal("waitForDayChange returned false after the month boundary tick")
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for waitForDayChange to detect the month boundary")
+	}
+}
+
+type blockingContinuousClient struct {
+	started chan<- struct{}
+	release <-chan struct{}
+}
+
+func (f blockingContinuousClient) Start(context.Context, <-chan string) int {
+	f.started <- struct{}{}
+	<-f.release
+	return 0
+}
+
+func waitForCounterAtLeast(t *testing.T, current func() int32, min int32) {
+	t.Helper()
+
+	deadline := time.NewTimer(2 * time.Second)
+	defer deadline.Stop()
+
+	ticker := time.NewTicker(10 * time.Millisecond)
+	defer ticker.Stop()
+
+	for {
+		if current() >= min {
+			return
+		}
+
+		select {
+		case <-deadline.C:
+			t.Fatalf("timed out waiting for counter to reach %d, got %d", min, current())
+		case <-ticker.C:
+		}
+	}
+}