From bfb4f4b5ae3fc8cfdea76b40cdcb0e592e7442f1 Mon Sep 17 00:00:00 2001
From: Dave Ross <dave@davidmichaelross.com>
Date: Sat, 23 May 2020 22:12:33 -0400
Subject: [PATCH] Etags (#23)

* Calculate font file md5 on load

* etag header

* Support for a single If-None_Match header

* Support multiple If-None-Match headers
---
 fonts/main.go | 22 +++++++++++++++++++++-
 main.go       | 12 ++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/fonts/main.go b/fonts/main.go
index d1f7022..384048c 100644
--- a/fonts/main.go
+++ b/fonts/main.go
@@ -2,10 +2,12 @@ package fonts
 
 import (
 	"crypto/sha256"
+	"crypto/md5"
 	"encoding/hex"
 	"errors"
 	"log"
 	"os"
+	"io"
 	"path"
 	"regexp"
 	"strings"
@@ -21,6 +23,7 @@ type FontFileData struct {
 	FileName  string
 	Extension string
 	CSSFormat string
+	MD5       string
 }
 
 // FontVariant describes a variant (ex: "Black", "Italic") of a font
@@ -101,12 +104,13 @@ func LoadFont(filePath string, config adrianConfig.Config) {
 			Variants: make(map[string]FontVariant),
 		}
 	}
-
+	
 	fontFileData := FontFileData{
 		Name:      fontName,
 		CSSFormat: fontCSSFormat(fontFormat),
 		Extension: fontFormat,
 		Path:      filePath,
+		MD5:       calcFileMD5(filePath),
 	}
 
 	fontVariant, ok := fontData.Variants[fontName]
@@ -162,6 +166,22 @@ func calcUniqueID(fontVariant FontVariant, config adrianConfig.Config) string {
 	return fontVariant.Name
 }
 
+// calcFileMD5 calculates the MD5 hash of a file
+func calcFileMD5(filepath string) string {
+	file, err := os.Open(filepath)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+
+	hash := md5.New()
+	if _, err := io.Copy(hash, file); err != nil {
+		log.Fatal(err)
+	}
+
+	return hex.EncodeToString(hash.Sum(nil))
+}
+
 // fontCSSFormat determines the appropriate CSS font format given a FontData struct with Type set
 func fontCSSFormat(fileType string) string {
 	switch fileType {
diff --git a/main.go b/main.go
index 3414445..b0fdca9 100644
--- a/main.go
+++ b/main.go
@@ -123,6 +123,17 @@ func outputFont(c echo.Context, mimeType string) error {
 		log.Fatal("Invalid font format" + adrianFonts.GetCanonicalExtension(filename))
 	}
 
+	for i := range c.Request().Header["If-None-Match"] {
+		individualHashes := strings.Split(c.Request().Header["If-None-Match"][i], (", "))
+		for j := range individualHashes {
+			if individualHashes[j] == fontFileData.MD5 {
+				status := make(map[string]string)
+				status["message"] = "Not Modified"
+				return c.JSON(http.StatusNotModified, status)	
+			}
+		}
+	}
+
 	fontBinary, err := ioutil.ReadFile(fontFileData.Path) // just pass the file name
 	if err != nil {
 		log.Fatal("Can't read font file " + fontFileData.FileName)
@@ -130,6 +141,7 @@ func outputFont(c echo.Context, mimeType string) error {
 
 	c.Response().Header().Set("Content-Transfer-Encoding", "binary")
 	c.Response().Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))
+	c.Response().Header().Set("ETag", fontFileData.MD5)
 	return c.Blob(http.StatusOK, mimeType, fontBinary)
 
 }