From 7a9bdba6bbd42d2a4e39d5ea3067105c030cedd2 Mon Sep 17 00:00:00 2001
From: Milan Unger <30626125+milung@users.noreply.github.com>
Date: Tue, 23 Aug 2022 21:04:02 +0200
Subject: [PATCH] BASE href, config.json, and cache-control (#5)

* added support for base-href, config.json, and cache-control

* added support for base-href, config.json and cache-control

* handling of woff mime types

Co-authored-by: Milan Unger <nilan.unger@siemens-healthineers.com>
---
 Dockerfile |  2 +-
 README.md  |  5 +++++
 go.mod     |  2 +-
 main.go    | 39 ++++++++++++++++++++++++++++++++++++---
 4 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/Dockerfile b/Dockerfile
index ab9c25f..7df3f98 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:1.18-alpine as builder
+FROM golang:1.18 as builder
 LABEL maintainer="donato@wolfisberg.dev"
 WORKDIR /app
 
diff --git a/README.md b/README.md
index 221a65d..3319fc5 100644
--- a/README.md
+++ b/README.md
@@ -53,8 +53,13 @@ The following options can be configured through environment variables.
 | READ_TIMEOUT_SECONDS  | 5        | 
 | WRITE_TIMEOUT_SECONDS | 10       |
 | IDLE_TIMEOUT_SECONDS  | 120      |
+| BASE_HREF             | /        |
+| CONFIG_JSON           | {}       |
 
+* `BASE_HREF` is used to replace the `href` content in the `index.html`'s string `<base href="/"`, where the original string must match exactly the one mentioned here
+* `CONFIG_JSON` must be json object that will be provided as the response for the request path `/config.json`
 
+The `Cache-Control` is a one minute validity for `/index.html` and `/config.json`, and immutable for the rest of the responses.
 ## Build local
 
 ```shell
diff --git a/go.mod b/go.mod
index b693666..13caafa 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module spa-server
 
-go 1.16
+go 1.18
diff --git a/main.go b/main.go
index 916e5be..38e6427 100644
--- a/main.go
+++ b/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"embed"
 	"fmt"
 	"io/fs"
@@ -18,7 +19,8 @@ import (
 var embeddedFs embed.FS
 
 const dirPrefix = "public"
-const indexFile = "/index.html"
+const indexFileName = "/index.html"
+const configFileName = "/config.json"
 
 type loadedFile struct {
 	file []byte
@@ -61,14 +63,36 @@ func loadFilesFromEmbeddedFs() (map[string]loadedFile, error) {
 			return err
 		}
 		path = strings.TrimLeft(path, dirPrefix)
+		// apply base href correction
+		if path == indexFileName {
+			file = bytes.Replace(
+				file,
+				[]byte("<base href=\"/\""),
+				[]byte(fmt.Sprint("<base href=\"", getenvString("BASE_HREF", "/"), "\"")),
+				-1)
+		}
+		mimeType := "application/unknown"
+		switch ext := filepath.Ext(path); ext {
+		case ".woff":
+			mimeType = "font/woff"
+		case ".woff2":
+			mimeType = "font/woff2"
+		default:
+			mimeType = mime.TypeByExtension(filepath.Ext(path))
+		}
 		files[path] = loadedFile{
 			file: file,
-			mime: mime.TypeByExtension(filepath.Ext(path)),
+			mime: mimeType,
 		}
 		log.Printf("Loading file from embeded filessystem. file %s\n", path)
 		return nil
 	})
 
+	files[configFileName] = loadedFile{
+		file: []byte(getenvString("CONFIG_JSON", "{}")),
+		mime: mime.TypeByExtension(filepath.Ext(configFileName)),
+	}
+
 	if err != nil {
 		return nil, err
 	}
@@ -90,7 +114,7 @@ func main() {
 		log.Fatalf("Could not load files from embedded filesystem. err: %v", err)
 	}
 
-	indexFile, indexFileFound := files[indexFile]
+	indexFile, indexFileFound := files[indexFileName]
 	if !indexFileFound {
 		log.Fatalln("Could not find index.html")
 	}
@@ -103,6 +127,15 @@ func main() {
 				loadedFile = indexFile
 			}
 			w.Header().Add("Content-Type", loadedFile.mime)
+			switch req.URL.Path {
+			case indexFileName:
+				fallthrough
+			case configFileName:
+				w.Header().Add("Cache-Control", "public, max-age: 60") // refresh every 1 minute to ensure fresh-ness
+			default:
+				w.Header().Add("Cache-Control", "public, max-age: 604800, immutable")
+			}
+
 			_, err = w.Write(loadedFile.file)
 			if err != nil {
 				log.Printf("Could not send loadedFile to client. file: %s", req.URL.Path)