From ece4a91ec3a285a5f41ddfae176b4c917d357900 Mon Sep 17 00:00:00 2001
From: Alex Tan <alex-tan@users.noreply.github.com>
Date: Fri, 9 Jul 2021 22:52:01 -0500
Subject: [PATCH] Add `Regex` option for HeaderConfig

---
 .gitignore            |  1 +
 customHeaders.go      | 43 +++++++++++++++++++++++++++++++++++--------
 docs/header-config.md | 39 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 74 insertions(+), 9 deletions(-)

diff --git a/.gitignore b/.gitignore
index bd4655a..d4930fa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 vendor/
 goStatic
+.DS_Store
diff --git a/customHeaders.go b/customHeaders.go
index 1e819bf..7e9a2e3 100644
--- a/customHeaders.go
+++ b/customHeaders.go
@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 )
 
@@ -17,9 +18,22 @@ type HeaderConfigArray struct {
 
 // HeaderConfig is a single header rule specification
 type HeaderConfig struct {
+	Regex         string            `json:"regex"`
 	Path          string            `json:"path"`
 	FileExtension string            `json:"fileExtension"`
 	Headers       []HeaderDefiniton `json:"headers"`
+
+	CompiledRegex *regexp.Regexp
+}
+
+func (config *HeaderConfig) Init() {
+	if config.UsesRegex() {
+		config.CompiledRegex = regexp.MustCompile(config.Regex)
+	}
+}
+
+func (config *HeaderConfig) UsesRegex() bool {
+	return len(config.Regex) > 0
 }
 
 // HeaderDefiniton is a key value pair of a specified header rule
@@ -28,7 +42,7 @@ type HeaderDefiniton struct {
 	Value string `json:"value"`
 }
 
-var headerConfigs HeaderConfigArray
+var headerConfigs *HeaderConfigArray
 
 func fileExists(filename string) bool {
 	info, err := os.Stat(filename)
@@ -38,9 +52,13 @@ func fileExists(filename string) bool {
 	return !info.IsDir()
 }
 
-func logHeaderConfig(config HeaderConfig) {
-	fmt.Println("Path: " + config.Path)
-	fmt.Println("FileExtension: " + config.FileExtension)
+func logHeaderConfig(config *HeaderConfig) {
+	if config.UsesRegex() {
+		fmt.Println("Regex: " + config.Regex)
+	} else {
+		fmt.Println("Path: " + config.Path)
+		fmt.Println("FileExtension: " + config.FileExtension)
+	}
 
 	for j := 0; j < len(config.Headers); j++ {
 		headerRule := config.Headers[j]
@@ -69,7 +87,8 @@ func initHeaderConfig(headerConfigPath string) bool {
 				fmt.Println("------------------------------")
 
 				for i := 0; i < len(headerConfigs.Configs); i++ {
-					configEntry := headerConfigs.Configs[i]
+					configEntry := &headerConfigs.Configs[i]
+					configEntry.Init()
 					logHeaderConfig(configEntry)
 				}
 			} else {
@@ -89,11 +108,19 @@ func customHeadersMiddleware(next http.Handler) http.Handler {
 
 		for i := 0; i < len(headerConfigs.Configs); i++ {
 			configEntry := headerConfigs.Configs[i]
+			var matches bool
 
-			fileMatch := configEntry.FileExtension == "*" || reqFileExtension == "."+configEntry.FileExtension
-			pathMatch := configEntry.Path == "*" || strings.HasPrefix(r.URL.Path, configEntry.Path)
+			if configEntry.UsesRegex() {
+				if configEntry.CompiledRegex.MatchString(r.URL.Path) {
+					matches = true
+				}
+			} else {
+				fileMatch := configEntry.FileExtension == "*" || reqFileExtension == "."+configEntry.FileExtension
+				pathMatch := configEntry.Path == "*" || strings.HasPrefix(r.URL.Path, configEntry.Path)
+				matches = fileMatch && pathMatch
+			}
 
-			if fileMatch && pathMatch {
+			if matches {
 				for j := 0; j < len(configEntry.Headers); j++ {
 					headerEntry := configEntry.Headers[j]
 					w.Header().Set(headerEntry.Key, headerEntry.Value)
diff --git a/docs/header-config.md b/docs/header-config.md
index b97255d..f498759 100644
--- a/docs/header-config.md
+++ b/docs/header-config.md
@@ -4,7 +4,44 @@ With the header config, you can specify custom [HTTP Header](https://developer.m
 
 ## Config
 
-You have to create a JSON file that serves as a config. The JSON must contain a `configs` array. For every entry, you can specify a certain path that must be matched as well as a file extension. You can use the `*` symbol to use the config entry for any path or filename. Note that the path option only matches the requested path from the start. Thatswhy you have to start with a `/` and can use paths like `/files/static/css`. The `headers` array includes a key-value pair of the actual header rule. The headers are not parsed so double check your spelling and test your site.
+You have to create a JSON file that serves as a config. The JSON must contain a `configs` array. For every entry, you can specify the rule in one of two ways:
+
+1. A regular expression that the path must meet, e.g.:
+
+```json
+{
+  "regex": "/$",
+  "headers": [
+    {
+      "key": "cache-control",
+      "value": "no-cache, no-store, must-revalidate"
+    }
+  ]
+}
+```
+
+This rule would match any path ending in `/` which is useful if you never want to cache the `index.html` that a directory leads to.
+
+2. You may specify a combination of `path` and `fileExtension`:
+
+```json
+{
+  "path": "*",
+  "fileExtension": "html",
+  "headers": [
+    {
+      "key": "cache-control",
+      "value": "public, max-age=0, must-revalidate"
+    },
+    {
+      "key": "Strict-Transport-Security",
+      "value": "max-age=31536000; includeSubDomains;"
+    }
+  ]
+}
+```
+
+You can use the `*` symbol to use the config entry for any path or filename. Note that the path option only matches the requested path from the start. That's why you have to start with a `/` and can use paths like `/files/static/css`. The `headers` array includes a key-value pair of the actual header rule. The headers are not parsed so double check your spelling and test your site.
 
 The created JSON config has to be mounted into the container via a volume into `/config/headerConfig.json` per default. When this file does not exist inside the container, the header middleware will not be active.