nats_stream_messages shows a body only on an event stream (issue 1966, review 1)

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

modules/nats/cmd/nats-tools/consumer.go

@@ -11,6 +11,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"regexp"
 	"strings"
 	"time"
 
@@ -109,6 +110,11 @@ const (
 	maxAsks = 3000
 )
 
+// eventStream is a stream that keeps events: the shared EVENTS and a seat's kept events SEAT_<SEAT>_EVENTS. Only these show
+// a body; every other stream holds calls and replies, asks, mail, dead letters, records or logs, whose bodies carry what
+// is not an event's to show. It fails closed: a stream not named here shows sequence, subject, time and size only.
+var eventStream = regexp.MustCompile(`^(EVENTS|SEAT_[A-Z0-9]+(_[A-Z0-9]+)*_EVENTS)$`)
+
 // MessageRow is one message of the answer.
 type MessageRow struct {
 	Seq         uint64    `json:"seq"`
@@ -266,7 +272,7 @@ func readTools(jsz func() ([]byte, error), open MsgOpen) []stdio.Tool {
 				return Consumer(doc, arg(a, "stream"), arg(a, "consumer"))
 			}},
 		{Name: "nats_stream_messages",
-			Description: "The messages a stream keeps for one subject (a filter with * or > is allowed), newest first: sequence, subject, time and size of each, and the body only when asked for and no larger than 4 KiB. Bounded by count (default 20, at most 200) and bytes (default 1 MiB); says when it stopped before the oldest the stream keeps. Read on the bus module's own credential. Refuses the streams of a module's kept state (KV_*, OBJ_*): their values are read through their owners' tools; this tool is for lost events.",
+			Description: "The messages a stream keeps for one subject (a filter with * or > is allowed), newest first: sequence, subject, time and size of each, and the body only when asked for, no larger than 4 KiB, and only on an event stream (EVENTS or a seat's kept events); on every other stream (asks, calls and replies, mail, dead letters, records, logs) only sequence, subject, time and size. Bounded by count (default 20, at most 200) and bytes (default 1 MiB); says when it stopped before the oldest the stream keeps. Read on the bus module's own credential. Refuses the streams of a module's kept state (KV_*, OBJ_*): their values are read through their owners' tools; this tool is for lost events.",
 			Input: map[string]any{"stream": str("the stream, e.g. EVENTS"), "subject": str("a subject or filter, e.g. mesh.mod.mesh-delivery-indexer.event.view-changed"),
 				"count": num("at most this many (default 20, at most 200)"), "bytes": num("at most this many bytes of messages (default 1048576)"),
 				"body": map[string]any{"type": "boolean", "description": "carry the body of each message of at most 4 KiB"}},
@@ -289,6 +295,10 @@ func readTools(jsz func() ([]byte, error), open MsgOpen) []stdio.Tool {
 				count, _ := a["count"].(float64)
 				bytes, _ := a["bytes"].(float64)
 				body, _ := a["body"].(bool)
+				bodyHidden := ""
+				if body && !eventStream.MatchString(stream) {
+					body, bodyHidden = false, stream+" is not an event stream (EVENTS or a seat's kept events): its bodies are not shown, only sequence, subject, time and size"
+				}
 				ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 				defer cancel()
 				get, closeBus, err := open(ctx)
@@ -296,7 +306,11 @@ func readTools(jsz func() ([]byte, error), open MsgOpen) []stdio.Tool {
 					return nil, err
 				}
 				defer closeBus()
-				return NewestMessages(ctx, get, stream, subject, first, last, int(count), int(bytes), body)
+				out, err := NewestMessages(ctx, get, stream, subject, first, last, int(count), int(bytes), body)
+				if err == nil && bodyHidden != "" {
+					out["body_not_shown"] = bodyHidden
+				}
+				return out, err
 			}},
 	}
 }

modules/nats/cmd/nats-tools/consumer_test.go

@@ -128,6 +128,35 @@ func TestTheReadToolsAreServedAndRefuseBadArguments(t *testing.T) {
 			t.Fatalf("%s was read: %v", st, err)
 		}
 	}
+	jszOf := strings.Replace(consumerJsz, `"name":"EVENTS"`, `"name":"ASKS"`, 1)
+	ask := readTools(func() ([]byte, error) { return []byte(jszOf), nil },
+		func(context.Context) (MsgGet, func(), error) {
+			return fake(map[uint64]string{50: "a.b"}, nil), func() {}, nil
+		})
+	for _, tl := range ask {
+		if tl.Name != "nats_stream_messages" {
+			continue
+		}
+		o, err := tl.Run(map[string]any{"stream": "ASKS", "subject": "a.b", "body": true})
+		m := o.(map[string]any)
+		if err != nil || m["body_not_shown"] == nil || m["messages"].([]MessageRow)[0].Body != "" {
+			t.Fatalf("an ask stream showed a body: %v %v", o, err)
+		}
+	}
+	ev, _ := by["nats_stream_messages"](map[string]any{"stream": "EVENTS", "subject": "a.b", "body": true})
+	if rows := ev.(map[string]any)["messages"].([]MessageRow); len(rows) != 1 || rows[0].Body != "body-50" {
+		t.Fatalf("an event stream showed no body: %v", ev)
+	}
+	for _, s := range []string{"EVENTS", "SEAT_NODE_BUILD_GO_EVENTS"} {
+		if !eventStream.MatchString(s) {
+			t.Fatalf("%s is an event stream", s)
+		}
+	}
+	for _, s := range []string{"SEAT_CHANNEL", "ASKS", "MAIL", "DEAD_LETTERS", "LOG_X", "SEAT_X_worker"} {
+		if eventStream.MatchString(s) {
+			t.Fatalf("%s is not an event stream", s)
+		}
+	}
 	if _, err := by["nats_stream_messages"](map[string]any{"stream": "EVENTS"}); err == nil {
 		t.Fatal("no subject answered")
 	}