Add proxy support

whatsMyIpServer.go

@@ -3,10 +3,24 @@ package main
 import (
 	"fmt"
 	"net/http"
+	"os"
 )
 
+var PROXY_HEADER string = os.Getenv("PROXY_HEADER")
+
 func respondWithIp(writer http.ResponseWriter, request *http.Request) {
-	fmt.Fprintf(writer, "%s\n", request.RemoteAddr)
+	remote := request.RemoteAddr
+	if PROXY_HEADER != "" {
+		ipHeader := request.Header[PROXY_HEADER]
+		if len(ipHeader) != 1 {
+			fmt.Println("Error: Reading proxy header", PROXY_HEADER, "in request from", request.RemoteAddr, "got", ipHeader)
+			writer.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprintf(writer, "Internal Server Error")
+			return
+		}
+		remote = ipHeader[0]
+	}
+	fmt.Fprintf(writer, "%s\n", remote)
 }
 
 func main() {