Add example of listen/notify support

refs #43

examples/README.md

@@ -1,5 +1,6 @@
 # Examples
 
+* chat is a command line chat program using listen/notify.
 * todo is a command line todo list that demonstrates basic CRUD actions.
 * url_shortener contains a simple example of using pgx in a web context.
 * [Tern](https://github.com/jackc/tern) is a migration tool that uses pgx (uses v1 of pgx).

examples/chat/README.md

@@ -0,0 +1,25 @@
+# Description
+
+This is a sample chat program implemented using PostgreSQL's listen/notify
+functionality with pgx.
+
+Start multiple instances of this program connected to the same database to chat
+between them.
+
+## Connection configuration
+
+The database connection is configured via enviroment variables.
+
+* CHAT_DB_HOST - defaults to localhost
+* CHAT_DB_USER - defaults to current OS user
+* CHAT_DB_PASSWORD - defaults to empty string
+* CHAT_DB_DATABASE - defaults to postgres
+
+You can either export them then run chat:
+
+    export CHAT_DB_HOST=/private/tmp
+    ./chat
+
+Or you can prefix the chat execution with the environment variables:
+
+    CHAT_DB_HOST=/private/tmp ./chat

examples/chat/main.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"github.com/jackc/pgx"
+	"os"
+	"time"
+)
+
+var pool *pgx.ConnPool
+
+func main() {
+	var err error
+	pool, err = pgx.NewConnPool(extractConfig())
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "Unable to connect to database:", err)
+		os.Exit(1)
+	}
+
+	go listen()
+
+	fmt.Println(`Type a message and press enter.
+
+This message should appear in any other chat instances connected to the same
+database.
+
+Type "exit" to quit.
+`)
+
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		msg := scanner.Text()
+		if msg == "exit" {
+			os.Exit(0)
+		}
+
+		_, err = pool.Exec("select pg_notify('chat', $1)", msg)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "Error sending notification:", err)
+			os.Exit(1)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		fmt.Fprintln(os.Stderr, "Error scanning from stdin:", err)
+		os.Exit(1)
+	}
+}
+
+func listen() {
+	conn, err := pool.Acquire()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "Error acquiring connection:", err)
+		os.Exit(1)
+	}
+	defer pool.Release(conn)
+
+	conn.Listen("chat")
+
+	for {
+		notification, err := conn.WaitForNotification(time.Second)
+		if err == pgx.ErrNotificationTimeout {
+			continue
+		}
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "Error waiting for notification:", err)
+			os.Exit(1)
+		}
+
+		fmt.Println("PID:", notification.Pid, "Channel:", notification.Channel, "Payload:", notification.Payload)
+	}
+}
+
+func extractConfig() pgx.ConnPoolConfig {
+	var config pgx.ConnPoolConfig
+
+	config.Host = os.Getenv("CHAT_DB_HOST")
+	if config.Host == "" {
+		config.Host = "localhost"
+	}
+
+	config.User = os.Getenv("CHAT_DB_USER")
+	if config.User == "" {
+		config.User = os.Getenv("USER")
+	}
+
+	config.Password = os.Getenv("CHAT_DB_PASSWORD")
+
+	config.Database = os.Getenv("CHAT_DB_DATABASE")
+	if config.Database == "" {
+		config.Database = "postgres"
+	}
+
+	return config
+}