From 18f000174b291b76f28fef064f7c24b532fd2805 Mon Sep 17 00:00:00 2001
From: David Shiflet <david.shiflet@microsoft.com>
Date: Fri, 1 Dec 2023 21:42:47 -0600
Subject: [PATCH] implement -L for local instances (#483)

---
 cmd/sqlcmd/sqlcmd.go | 79 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 78 insertions(+), 1 deletion(-)

diff --git a/cmd/sqlcmd/sqlcmd.go b/cmd/sqlcmd/sqlcmd.go
index 77891cb1..1b9d7b20 100644
--- a/cmd/sqlcmd/sqlcmd.go
+++ b/cmd/sqlcmd/sqlcmd.go
@@ -5,15 +5,19 @@
 package sqlcmd
 
 import (
+	"context"
 	"errors"
 	"fmt"
+	"net"
 	"os"
 	"regexp"
 	"strconv"
 	"strings"
+	"time"
 
 	mssql "github.com/microsoft/go-mssqldb"
 	"github.com/microsoft/go-mssqldb/azuread"
+	"github.com/microsoft/go-mssqldb/msdsn"
 	"github.com/microsoft/go-sqlcmd/internal/localizer"
 	"github.com/microsoft/go-sqlcmd/pkg/console"
 	"github.com/microsoft/go-sqlcmd/pkg/sqlcmd"
@@ -216,7 +220,7 @@ func Execute(version string) {
 					fmt.Println()
 					fmt.Println(localizer.Sprintf("Servers:"))
 				}
-				fmt.Println("    ;UID:Login ID=?;PWD:Password=?;Trusted_Connection:Use Integrated Security=?;*APP:AppName=?;*WSID:WorkStation ID=?;")
+				listLocalServers()
 				os.Exit(0)
 			}
 			if len(argss) > 0 {
@@ -820,3 +824,76 @@ func run(vars *sqlcmd.Variables, args *SQLCmdArguments) (int, error) {
 	s.SetError(nil)
 	return s.Exitcode, err
 }
+
+func listLocalServers() {
+	bmsg := []byte{byte(msdsn.BrowserAllInstances)}
+	resp := make([]byte, 16*1024-1)
+	dialer := &net.Dialer{}
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
+	defer cancel()
+	conn, err := dialer.DialContext(ctx, "udp", ":1434")
+	// silently ignore failures to connect, same as ODBC
+	if err != nil {
+		return
+	}
+	defer conn.Close()
+	dl, _ := ctx.Deadline()
+	_ = conn.SetDeadline(dl)
+	_, err = conn.Write(bmsg)
+	if err != nil {
+		if !errors.Is(err, os.ErrDeadlineExceeded) {
+			fmt.Println(err)
+		}
+		return
+	}
+	read, err := conn.Read(resp)
+	if err != nil {
+		if !errors.Is(err, os.ErrDeadlineExceeded) {
+			fmt.Println(err)
+		}
+		return
+	}
+
+	data := parseInstances(resp[:read])
+	instances := make([]string, 0, len(data))
+	for s := range data {
+		if s == "MSSQLSERVER" {
+
+			instances = append(instances, "(local)", data[s]["ServerName"])
+		} else {
+			instances = append(instances, fmt.Sprintf(`%s\%s`, data[s]["ServerName"], s))
+		}
+	}
+	for _, s := range instances {
+		fmt.Println("  ", s)
+	}
+}
+
+func parseInstances(msg []byte) msdsn.BrowserData {
+	results := msdsn.BrowserData{}
+	if len(msg) > 3 && msg[0] == 5 {
+		out_s := string(msg[3:])
+		tokens := strings.Split(out_s, ";")
+		instdict := map[string]string{}
+		got_name := false
+		var name string
+		for _, token := range tokens {
+			if got_name {
+				instdict[name] = token
+				got_name = false
+			} else {
+				name = token
+				if len(name) == 0 {
+					if len(instdict) == 0 {
+						break
+					}
+					results[strings.ToUpper(instdict["InstanceName"])] = instdict
+					instdict = map[string]string{}
+					continue
+				}
+				got_name = true
+			}
+		}
+	}
+	return results
+}