feat(main): add request logging and configurable server address

Add logging to `sendHandler` and `sendParamsHandler` to track incoming
requests. Update the server startup logic to use `HOST` and `PORT`
environment variables, defaulting to `localhost:660` if not provided.

main.go

@@ -6,6 +6,7 @@ import (
 	"html"
 	"log"
 	"net/http"
+	"os"
 	"strconv"
 	"strings"
 
@@ -208,6 +209,7 @@ var domainMap = map[string]EmailConfig{
 }
 
 func sendHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[send] INCOMING %s %s from %s", r.Method, r.URL.Path, r.RemoteAddr)
 	if r.Method != http.MethodPost {
 		http.Error(w, "POST only", http.StatusMethodNotAllowed)
 		return
@@ -301,6 +303,7 @@ func enableCors(handler http.HandlerFunc) http.HandlerFunc {
 //
 //	GET /[email protected]&pass=secret&server=smtp.example.com&port=465&[email protected]&[email protected]&subject=Hello&message=Hi
 func sendParamsHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[send-params] INCOMING %s %s from %s", r.Method, r.URL.Path, r.RemoteAddr)
 	if r.Method != http.MethodGet {
 		http.Error(w, "GET only", http.StatusMethodNotAllowed)
 		return
@@ -363,6 +366,16 @@ func main() {
 	http.HandleFunc("/", enableCors(rootHandler))
 	http.HandleFunc("/send", enableCors(sendHandler))
 	http.HandleFunc("/send-params", enableCors(sendParamsHandler))
-	log.Println("Server running on localhost:660")
+
-	log.Fatal(http.ListenAndServe("localhost:660", nil))
+	host := os.Getenv("HOST")
+	if host == "" {
+		host = "localhost"
+	}
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "660"
+	}
+	addr := host + ":" + port
+	log.Println("Server running on " + addr)
+	log.Fatal(http.ListenAndServe(addr, nil))
 }