asset integrity

src/main.go

@@ -32,12 +32,14 @@ func NewTemplates() *Templates {
 type Page struct {
 	Boxes       []boxes.Box
 	BuildNumber string
+	Integrity   *util.AssetIntegrity
 }
 
 func newPage(boxes []boxes.Box) Page {
 	return Page{
 		Boxes:       boxes,
 		BuildNumber: util.GetBuildNumber(),
+		Integrity:   util.CalculateAssetIntegrities(),
 	}
 }
 
@@ -58,6 +60,7 @@ func main() {
 	e.GET("/health", func(c echo.Context) error {
 		return c.Render(200, "health", Page{
 			BuildNumber: util.GetBuildNumber(),
+			Integrity:   util.CalculateAssetIntegrities(),
 		})
 	})
 

src/util/util.go

@@ -1,6 +1,10 @@
 package util
 
 import (
+	"crypto/sha256"
+	"encoding/base64"
+	"fmt"
+	"io"
 	"os"
 )
 
@@ -11,3 +15,52 @@ func GetBuildNumber() string {
 func IsProd() bool {
 	return len(GetBuildNumber()) > 0
 }
+
+// CalculateFileIntegrity calculates SHA256 hash for SRI
+func CalculateFileIntegrity(filePath string) (string, error) {
+	file, err := os.Open(filePath)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	hasher := sha256.New()
+	if _, err := io.Copy(hasher, file); err != nil {
+		return "", err
+	}
+
+	hash := hasher.Sum(nil)
+	return fmt.Sprintf("sha256-%s", base64.StdEncoding.EncodeToString(hash)), nil
+}
+
+// AssetIntegrity holds file integrity information
+type AssetIntegrity struct {
+	CSS map[string]string
+	JS  map[string]string
+}
+
+// CalculateAssetIntegrities calculates hashes for all assets
+func CalculateAssetIntegrities() *AssetIntegrity {
+	integrity := &AssetIntegrity{
+		CSS: make(map[string]string),
+		JS:  make(map[string]string),
+	}
+
+	// CSS files
+	cssFiles := []string{"main.css", "boxes.css"}
+	for _, file := range cssFiles {
+		if hash, err := CalculateFileIntegrity("css/" + file); err == nil {
+			integrity.CSS[file] = hash
+		}
+	}
+
+	// JS files
+	jsFiles := []string{"ws.js", "boxes.js", "draw.js"}
+	for _, file := range jsFiles {
+		if hash, err := CalculateFileIntegrity("js/" + file); err == nil {
+			integrity.JS[file] = hash
+		}
+	}
+
+	return integrity
+}