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, 62 insertions, 0 deletions

diff --git a/internal/mapr/server/parsername_test.go b/internal/mapr/server/parsername_test.go
new file mode 100644
index 0000000..cce1a45
--- /dev/null
+++ b/internal/mapr/server/parsername_test.go
@@ -0,0 +1,62 @@
+package server
+
+import (
+	"testing"
+
+	"github.com/mimecast/dtail/internal/mapr"
+)
+
+// TestResolveParserName locks the log-format selection rules that decide which
+// parser (and therefore which fields) a mapr query gets. These rules are the
+// root cause of a common surprise: a query without a "from TABLE" clause is
+// downgraded to the "generic" parser, which exposes none of the dynamic
+// key=value fields or the default-format "$"-variables. See
+// doc/querylanguage.md ("Selecting the log format and dynamic fields").
+func TestResolveParserName(t *testing.T) {
+	tests := []struct {
+		name       string
+		query      string
+		configured string
+		want       string
+	}{
+		{
+			name:  "explicit logformat wins over everything",
+			query: "from STATS select $line logformat generickv",
+			want:  "generickv",
+		},
+		{
+			name:  "explicit logformat wins even without a from clause",
+			query: "select service logformat generickv",
+			want:  "generickv",
+		},
+		{
+			name:  "no from clause downgrades to generic",
+			query: "select service,sum(bytes) group by service",
+			want:  "generic",
+		},
+		{
+			name:  "from TABLE without configured format uses default",
+			query: "from STATS select lifetimeConnections",
+			want:  "default",
+		},
+		{
+			name:       "from TABLE honours the configured default format",
+			query:      "from STATS select lifetimeConnections",
+			configured: "mimecast",
+			want:       "mimecast",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			query, err := mapr.NewQuery(tc.query)
+			if err != nil {
+				t.Fatalf("NewQuery(%q) failed: %v", tc.query, err)
+			}
+			if got := resolveParserName(query, tc.configured); got != tc.want {
+				t.Errorf("resolveParserName(%q, %q) = %q, want %q",
+					tc.query, tc.configured, got, tc.want)
+			}
+		})
+	}
+}