mvp with terrible conn handling

src/config.go

@@ -1,9 +1,12 @@
 package src
 
 import (
+	"bufio"
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"log"
 	"net"
 	"os"
 	"slices"
@@ -14,6 +17,7 @@ import (
 type Config struct {
 	Listen   string `json:"LISTEN"`
 	Forwards string `json:"FORWARDS"`
+	Hello    string `json:"HELLO_B64"`
 	forwards []*sync.Pool
 }
 
@@ -21,6 +25,7 @@ func NewConfig(ctx context.Context) (Config, error) {
 	config := Config{
 		Listen:   ":10000",
 		Forwards: "",
+		Hello:    base64.StdEncoding.EncodeToString([]byte("*1\r\n$4\r\nping\r\n")),
 	}
 	b, _ := json.Marshal(config)
 	var m map[string]any
@@ -37,6 +42,11 @@ func NewConfig(ctx context.Context) (Config, error) {
 		return config, err
 	}
 
+	hello, err := base64.StdEncoding.DecodeString(config.Hello)
+	if err != nil {
+		return config, err
+	}
+
 	forwards := strings.Split(config.Forwards, ",")
 	forwards = slices.DeleteFunc(forwards, func(s string) bool { return s == "" })
 	if len(forwards) == 0 {
@@ -44,12 +54,30 @@ func NewConfig(ctx context.Context) (Config, error) {
 	}
 	config.forwards = make([]*sync.Pool, len(forwards))
 	for i := range forwards {
+		forward := forwards[i]
 		config.forwards[i] = &sync.Pool{
 			New: func() any {
-				v, err := (&net.Dialer{}).DialContext(ctx, "tcp", forwards[i])
-				if err != nil {
+				if ctx.Err() != nil {
 					return nil
 				}
+				log.Printf("dialing %q with %q", forward, hello)
+				v, err := (&net.Dialer{}).DialContext(ctx, "tcp", forward)
+				if err != nil {
+					log.Printf("! failed dial %q: %v", forward, err)
+					return nil
+				}
+				if _, err := v.Write([]byte(hello)); err != nil {
+					log.Printf("! failed write hello %q: %v", forward, err)
+					v.Close()
+					return nil
+				}
+				if raw, _, err := readMessage(bufio.NewReader(v)); err != nil {
+					log.Printf("! failed read hello %q: %v", forward, err)
+					v.Close()
+					return nil
+				} else {
+					log.Printf("dial reply: %q", raw)
+				}
 				return v
 			},
 		}
@@ -61,13 +89,16 @@ func NewConfig(ctx context.Context) (Config, error) {
 func (c Config) Close() {
 	for i := range c.forwards {
 		if c.forwards[i] != nil {
-			c.forwards[i].New = nil
-			for {
-				got := c.forwards[i].Get()
-				if got != nil {
-					got.(net.Conn).Close()
+			i := i
+			go func() {
+				c.forwards[i].New = nil
+				for {
+					got := c.forwards[i].Get()
+					if got != nil {
+						go got.(net.Conn).Close()
+					}
 				}
-			}
+			}()
 		}
 	}
 }