i think pub works

cmd/pg-pubsub-demo/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"database/sql"
+	"encoding/json"
 	"flag"
 	"fmt"
 	"io"
@@ -74,7 +75,37 @@ func run(ctx context.Context) error {
 		}
 
 		pub := func(topic string, a any) error {
-			return io.EOF
+			payload, _ := json.Marshal(a)
+			if _, err := pg.ExecContext(ctx, `
+				INSERT INTO "pubsub".topic (name)
+					VALUES ($1)
+					ON CONFLICT DO NOTHING;
+			`, topic); err != nil {
+				return err
+			}
+			_, err := pg.ExecContext(ctx, `
+				WITH topic AS (
+					SELECT
+						name,
+						FLOOR(100 * RANDOM())::INTEGER % partitions AS partition
+					FROM "pubsub".topic
+					WHERE name=$1
+				)
+				, partition_offset AS (
+					SELECT
+						topic.partition AS partition,
+						COALESCE(MAX(data.partition_offset), -1)+1 AS next_offset
+					FROM topic
+					LEFT JOIN "pubsub".data data ON data.topic_name=topic.name AND data.partition=topic.partition
+					GROUP BY topic.partition
+				)
+				INSERT INTO "pubsub".data
+					(topic_name, partition, partition_offset, payload)
+				SELECT
+					$1, partition_offset.partition, partition_offset.next_offset, $2
+				FROM partition_offset
+			`, topic, payload)
+			return err
 		}
 		sub := func(topic, group string) (int, any, error) {
 			return 0, nil, io.EOF