2 files changed, 201 insertions, 0 deletions
diff --git a/modules/httpcache/httpcache.go b/modules/httpcache/httpcache.go
new file mode 100644
index 0000000..30ce0a4
--- /dev/null
+++ b/modules/httpcache/httpcache.go
@@ -0,0 +1,101 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package httpcache
+
+import (
+	"io"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// SetCacheControlInHeader sets suitable cache-control headers in the response
+func SetCacheControlInHeader(h http.Header, maxAge time.Duration, additionalDirectives ...string) {
+	directives := make([]string, 0, 2+len(additionalDirectives))
+
+	// "max-age=0 + must-revalidate" (aka "no-cache") is preferred instead of "no-store"
+	// because browsers may restore some input fields after navigate-back / reload a page.
+	if setting.IsProd {
+		if maxAge == 0 {
+			directives = append(directives, "max-age=0", "private", "must-revalidate")
+		} else {
+			directives = append(directives, "private", "max-age="+strconv.Itoa(int(maxAge.Seconds())))
+		}
+	} else {
+		directives = append(directives, "max-age=0", "private", "must-revalidate")
+
+		// to remind users they are using non-prod setting.
+		h.Set("X-Gitea-Debug", "RUN_MODE="+setting.RunMode)
+		h.Set("X-Forgejo-Debug", "RUN_MODE="+setting.RunMode)
+	}
+
+	h.Set("Cache-Control", strings.Join(append(directives, additionalDirectives...), ", "))
+}
+
+func ServeContentWithCacheControl(w http.ResponseWriter, req *http.Request, name string, modTime time.Time, content io.ReadSeeker) {
+	SetCacheControlInHeader(w.Header(), setting.StaticCacheTime)
+	http.ServeContent(w, req, name, modTime, content)
+}
+
+// HandleGenericETagCache handles ETag-based caching for a HTTP request.
+// It returns true if the request was handled.
+func HandleGenericETagCache(req *http.Request, w http.ResponseWriter, etag string) (handled bool) {
+	if len(etag) > 0 {
+		w.Header().Set("Etag", etag)
+		if checkIfNoneMatchIsValid(req, etag) {
+			w.WriteHeader(http.StatusNotModified)
+			return true
+		}
+	}
+	SetCacheControlInHeader(w.Header(), setting.StaticCacheTime)
+	return false
+}
+
+// checkIfNoneMatchIsValid tests if the header If-None-Match matches the ETag
+func checkIfNoneMatchIsValid(req *http.Request, etag string) bool {
+	ifNoneMatch := req.Header.Get("If-None-Match")
+	if len(ifNoneMatch) > 0 {
+		for _, item := range strings.Split(ifNoneMatch, ",") {
+			item = strings.TrimPrefix(strings.TrimSpace(item), "W/") // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag#directives
+			if item == etag {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// HandleGenericETagTimeCache handles ETag-based caching with Last-Modified caching for a HTTP request.
+// It returns true if the request was handled.
+func HandleGenericETagTimeCache(req *http.Request, w http.ResponseWriter, etag string, lastModified *time.Time) (handled bool) {
+	if len(etag) > 0 {
+		w.Header().Set("Etag", etag)
+	}
+	if lastModified != nil && !lastModified.IsZero() {
+		// http.TimeFormat required a UTC time, refer to https://pkg.go.dev/net/http#TimeFormat
+		w.Header().Set("Last-Modified", lastModified.UTC().Format(http.TimeFormat))
+	}
+
+	if len(etag) > 0 {
+		if checkIfNoneMatchIsValid(req, etag) {
+			w.WriteHeader(http.StatusNotModified)
+			return true
+		}
+	}
+	if lastModified != nil && !lastModified.IsZero() {
+		ifModifiedSince := req.Header.Get("If-Modified-Since")
+		if ifModifiedSince != "" {
+			t, err := time.Parse(http.TimeFormat, ifModifiedSince)
+			if err == nil && lastModified.Unix() <= t.Unix() {
+				w.WriteHeader(http.StatusNotModified)
+				return true
+			}
+		}
+	}
+	SetCacheControlInHeader(w.Header(), setting.StaticCacheTime)
+	return false
+}
diff --git a/modules/httpcache/httpcache_test.go b/modules/httpcache/httpcache_test.go
new file mode 100644
index 0000000..65a8a9b
--- /dev/null
+++ b/modules/httpcache/httpcache_test.go
@@ -0,0 +1,100 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package httpcache
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func countFormalHeaders(h http.Header) (c int) {
+	for k := range h {
+		// ignore our headers for internal usage
+		if strings.HasPrefix(k, "X-Gitea-") {
+			continue
+		}
+		if strings.HasPrefix(k, "X-Forgejo-") {
+			continue
+		}
+		c++
+	}
+	return c
+}
+
+func TestHandleGenericETagCache(t *testing.T) {
+	etag := `"test"`
+
+	t.Run("No_If-None-Match", func(t *testing.T) {
+		req := &http.Request{Header: make(http.Header)}
+		w := httptest.NewRecorder()
+
+		handled := HandleGenericETagCache(req, w, etag)
+
+		assert.False(t, handled)
+		assert.Equal(t, 2, countFormalHeaders(w.Header()))
+		assert.Contains(t, w.Header(), "Cache-Control")
+		assert.Contains(t, w.Header(), "Etag")
+		assert.Equal(t, etag, w.Header().Get("Etag"))
+	})
+	t.Run("Wrong_If-None-Match", func(t *testing.T) {
+		req := &http.Request{Header: make(http.Header)}
+		w := httptest.NewRecorder()
+
+		req.Header.Set("If-None-Match", `"wrong etag"`)
+
+		handled := HandleGenericETagCache(req, w, etag)
+
+		assert.False(t, handled)
+		assert.Equal(t, 2, countFormalHeaders(w.Header()))
+		assert.Contains(t, w.Header(), "Cache-Control")
+		assert.Contains(t, w.Header(), "Etag")
+		assert.Equal(t, etag, w.Header().Get("Etag"))
+	})
+	t.Run("Correct_If-None-Match", func(t *testing.T) {
+		req := &http.Request{Header: make(http.Header)}
+		w := httptest.NewRecorder()
+
+		req.Header.Set("If-None-Match", etag)
+
+		handled := HandleGenericETagCache(req, w, etag)
+
+		assert.True(t, handled)
+		assert.Equal(t, 1, countFormalHeaders(w.Header()))
+		assert.Contains(t, w.Header(), "Etag")
+		assert.Equal(t, etag, w.Header().Get("Etag"))
+		assert.Equal(t, http.StatusNotModified, w.Code)
+	})
+	t.Run("Multiple_Wrong_If-None-Match", func(t *testing.T) {
+		req := &http.Request{Header: make(http.Header)}
+		w := httptest.NewRecorder()
+
+		req.Header.Set("If-None-Match", `"wrong etag", "wrong etag "`)
+
+		handled := HandleGenericETagCache(req, w, etag)
+
+		assert.False(t, handled)
+		assert.Equal(t, 2, countFormalHeaders(w.Header()))
+		assert.Contains(t, w.Header(), "Cache-Control")
+		assert.Contains(t, w.Header(), "Etag")
+		assert.Equal(t, etag, w.Header().Get("Etag"))
+	})
+	t.Run("Multiple_Correct_If-None-Match", func(t *testing.T) {
+		req := &http.Request{Header: make(http.Header)}
+		w := httptest.NewRecorder()
+
+		req.Header.Set("If-None-Match", `"wrong etag", `+etag)
+
+		handled := HandleGenericETagCache(req, w, etag)
+
+		assert.True(t, handled)
+		assert.Equal(t, 1, countFormalHeaders(w.Header()))
+		assert.Contains(t, w.Header(), "Etag")
+		assert.Equal(t, etag, w.Header().Get("Etag"))
+		assert.Equal(t, http.StatusNotModified, w.Code)
+	})
+}