From 9956e64f2c9f8c055c60bc82fcbb1e979bfb0b47 Mon Sep 17 00:00:00 2001
From: Mike Crute <mike@crute.us>
Date: Thu, 17 Aug 2023 07:49:29 -0700
Subject: echo: support etags for static files

---
 echo/static_file.go | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/echo/static_file.go b/echo/static_file.go
index 9723db7..258c832 100644
--- a/echo/static_file.go
+++ b/echo/static_file.go
@@ -1,6 +1,8 @@
 package echo
 
 import (
+	"crypto/sha256"
+	"encoding/base64"
 	"io"
 	"io/fs"
 	"net/http"
@@ -12,7 +14,16 @@ import (
 
 type routeFunc func(string, echo.HandlerFunc, ...echo.MiddlewareFunc) *echo.Route
 
+func StaticFSSha256Etags(get routeFunc, f fs.FS, prefix, root string, m ...echo.MiddlewareFunc) *echo.Route {
+	return staticFS(get, f, prefix, root, true, m...)
+}
+
 func StaticFS(get routeFunc, f fs.FS, prefix, root string, m ...echo.MiddlewareFunc) *echo.Route {
+	return staticFS(get, f, prefix, root, false, m...)
+}
+
+// TODO: This should support HEAD requests
+func staticFS(get routeFunc, f fs.FS, prefix, root string, addEtags bool, m ...echo.MiddlewareFunc) *echo.Route {
 	if root == "" {
 		root = "." // For security we want to restrict to CWD.
 	}
@@ -52,6 +63,25 @@ func StaticFS(get routeFunc, f fs.FS, prefix, root string, m ...echo.MiddlewareF
 			return echo.ErrInternalServerError
 		}
 
+		// Only do this if the consumer requests it since it could be expensive
+		// for high traffic sites as it requires a full read and SHA256
+		// computation
+		// TODO: Cache this?
+		if addEtags {
+			h := sha256.New()
+			if _, err := io.Copy(h, fs); err != nil {
+				c.Logger().Errorf("Error checksumming file %s: %s", p, err)
+				return echo.ErrInternalServerError
+			}
+			etag := base64.RawStdEncoding.EncodeToString(h.Sum(nil))
+			c.Response().Header().Add("ETag", etag)
+
+			if _, err := fs.Seek(0, io.SeekStart); err != nil {
+				c.Logger().Errorf("Error seeking 0 in file %s: %s", p, err)
+				return echo.ErrInternalServerError
+			}
+		}
+
 		http.ServeContent(c.Response(), c.Request(), fi.Name(), fi.ModTime(), fs)
 		return nil
 	}
-- 
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