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, 218 insertions, 0 deletions

diff --git a/internal/io/fs/validatedreadtarget_test.go b/internal/io/fs/validatedreadtarget_test.go
new file mode 100644
index 0000000..30b9c8f
--- /dev/null
+++ b/internal/io/fs/validatedreadtarget_test.go
@@ -0,0 +1,218 @@
+package fs
+
+import (
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/mimecast/dtail/internal/io/dlog"
+	"github.com/mimecast/dtail/internal/lcontext"
+	"github.com/mimecast/dtail/internal/regex"
+)
+
+func TestValidatedCatFileStartWithProcessorOptimizedReadsAllLines(t *testing.T) {
+	resetCommonLogger(t)
+
+	filePath := writeProcessorTestFile(t, "alpha\nbeta\n")
+	target := mustValidatedReadTarget(t, filePath)
+	re := regex.NewNoop()
+
+	cat := NewValidatedCatFile(filePath, target, "glob-id", make(chan string, 1), defaultMaxLineLength)
+	processor := &captureProcessor{}
+
+	if err := cat.readFile.StartWithProcessorOptimized(
+		context.Background(),
+		lcontext.LContext{},
+		processor,
+		re,
+	); err != nil {
+		t.Fatalf("validated optimized reader start failed: %v", err)
+	}
+
+	want := []string{"alpha\n", "beta\n"}
+	if !reflect.DeepEqual(processor.lines, want) {
+		t.Fatalf("unexpected processed lines: got=%v want=%v", processor.lines, want)
+	}
+}
+
+func TestValidatedReadTargetOpenRejectsEscapingSymlinkSwap(t *testing.T) {
+	resetCommonLogger(t)
+
+	baseDir := t.TempDir()
+	rootDir := filepath.Join(baseDir, "root")
+	outsideDir := filepath.Join(baseDir, "outside")
+	if err := os.MkdirAll(rootDir, 0755); err != nil {
+		t.Fatalf("mkdir root dir: %v", err)
+	}
+	if err := os.MkdirAll(outsideDir, 0755); err != nil {
+		t.Fatalf("mkdir outside dir: %v", err)
+	}
+
+	filePath := filepath.Join(rootDir, "app.log")
+	if err := os.WriteFile(filePath, []byte("alpha\n"), 0600); err != nil {
+		t.Fatalf("write app log: %v", err)
+	}
+	escapePath := filepath.Join(outsideDir, "secret.log")
+	if err := os.WriteFile(escapePath, []byte("secret\n"), 0600); err != nil {
+		t.Fatalf("write secret log: %v", err)
+	}
+
+	target := mustValidatedReadTarget(t, filePath)
+
+	if err := os.Remove(filePath); err != nil {
+		t.Fatalf("remove app log: %v", err)
+	}
+	relativeEscape, err := filepath.Rel(rootDir, escapePath)
+	if err != nil {
+		t.Fatalf("relative escape path: %v", err)
+	}
+	if err := os.Symlink(relativeEscape, filePath); err != nil {
+		t.Fatalf("symlink escape path: %v", err)
+	}
+
+	if _, err := target.Open(); err == nil {
+		t.Fatal("expected rooted open to reject escaping symlink swap")
+	}
+}
+
+func TestValidatedReadTargetOpenRejectsSameRootSymlinkSwap(t *testing.T) {
+	resetCommonLogger(t)
+
+	baseDir := t.TempDir()
+	filePath := filepath.Join(baseDir, "app.log")
+	if err := os.WriteFile(filePath, []byte("alpha\n"), 0600); err != nil {
+		t.Fatalf("write app log: %v", err)
+	}
+	otherPath := filepath.Join(baseDir, "other.log")
+	if err := os.WriteFile(otherPath, []byte("other\n"), 0600); err != nil {
+		t.Fatalf("write other log: %v", err)
+	}
+
+	target := mustValidatedReadTarget(t, filePath)
+
+	if err := os.Remove(filePath); err != nil {
+		t.Fatalf("remove app log: %v", err)
+	}
+	if err := os.Symlink(filepath.Base(otherPath), filePath); err != nil {
+		t.Fatalf("symlink other log: %v", err)
+	}
+
+	_, err := target.Open()
+	if err == nil {
+		t.Fatal("expected rooted open to reject same-root symlink swap")
+	}
+	if !strings.Contains(err.Error(), "symlink") {
+		t.Fatalf("expected symlink rejection, got %v", err)
+	}
+}
+
+func TestNewValidatedJournalTargetRejectsAmbiguousUnits(t *testing.T) {
+	tests := []struct {
+		name string
+		spec string
+	}{
+		{
+			name: "empty unit",
+			spec: "journal:",
+		},
+		{
+			name: "leading dash",
+			spec: "journal:--output=json",
+		},
+		{
+			name: "space",
+			spec: "journal:ssh.service --output=json",
+		},
+		{
+			name: "newline",
+			spec: "journal:ssh.service\n--output=json",
+		},
+		{
+			name: "tab",
+			spec: "journal:ssh.service\t--output=json",
+		},
+		{
+			name: "control character",
+			spec: "journal:ssh.service\x00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if _, err := NewValidatedJournalTarget(tt.spec); err == nil {
+				t.Fatalf("NewValidatedJournalTarget(%q) succeeded, want error", tt.spec)
+			}
+		})
+	}
+}
+
+func TestNewValidatedJournalTargetAcceptsLiteralShellMetacharacters(t *testing.T) {
+	spec := "journal:ssh.service;touch$HOME`whoami`|cat"
+
+	target, err := NewValidatedJournalTarget(spec)
+	if err != nil {
+		t.Fatalf("NewValidatedJournalTarget(%q) error = %v", spec, err)
+	}
+	if target.Kind != JournalKind {
+		t.Fatalf("target.Kind = %v, want %v", target.Kind, JournalKind)
+	}
+}
+
+func TestValidatedTailFileTruncatedReopenDetectsTruncation(t *testing.T) {
+	resetCommonLogger(t)
+
+	filePath := writeProcessorTestFile(t, "alpha\nbeta\n")
+	target := mustValidatedReadTarget(t, filePath)
+
+	tail := NewValidatedTailFile(filePath, target, "glob-id", make(chan string, 1), defaultMaxLineLength)
+	fd, err := target.Open()
+	if err != nil {
+		t.Fatalf("open validated target: %v", err)
+	}
+	defer fd.Close()
+
+	if _, err := fd.Seek(0, io.SeekEnd); err != nil {
+		t.Fatalf("seek end: %v", err)
+	}
+	if err := os.Truncate(filePath, 1); err != nil {
+		t.Fatalf("truncate file: %v", err)
+	}
+
+	isTruncated, err := tail.readFile.truncated(fd)
+	if !isTruncated {
+		t.Fatal("expected truncation to be detected")
+	}
+	if err == nil || !strings.Contains(err.Error(), "truncated") {
+		t.Fatalf("expected truncation error, got %v", err)
+	}
+}
+
+func mustValidatedReadTarget(t *testing.T, path string) ValidatedReadTarget {
+	t.Helper()
+
+	absolutePath, err := filepath.Abs(path)
+	if err != nil {
+		t.Fatalf("abs path: %v", err)
+	}
+
+	target, err := NewValidatedReadTarget(absolutePath)
+	if err != nil {
+		t.Fatalf("create validated target: %v", err)
+	}
+
+	return target
+}
+
+func resetCommonLogger(t *testing.T) {
+	t.Helper()
+
+	originalLogger := dlog.Common
+	dlog.Common = &dlog.DLog{}
+	t.Cleanup(func() {
+		dlog.Common = originalLogger
+	})
+}