From e20a3a829e74e40e69e8ef948a1027ac46f4f3b3 Mon Sep 17 00:00:00 2001
From: Juliusz Chroboczek <jch@irif.fr>
Date: Thu, 11 Apr 2024 13:09:05 +0200
Subject: [PATCH] Implement precondition checking for objects with no ETag.

---
 webserver/precondition.go      | 50 ++++++++++++++++++++++++++++++++++
 webserver/precondition_test.go | 45 ++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/webserver/precondition.go b/webserver/precondition.go
index d13da32..a0f1012 100644
--- a/webserver/precondition.go
+++ b/webserver/precondition.go
@@ -70,6 +70,34 @@ func etagMatch(etag, header string) bool {
 	return false
 }
 
+// etagMatchNoEtag evaluates preconditions for an object with no ETag.
+func etagMatchNoEtag(exists bool, header string) bool {
+	if header == "" {
+		return false
+	}
+
+	for {
+		header = strings.TrimLeft(header, " \t\n\r")
+		if len(header) == 0 {
+			break
+		}
+		if header[0] == ',' {
+			header = header[1:]
+			continue
+		}
+		if header[0] == '*' {
+			return exists
+		}
+		e, remain := scanETag(header)
+		if e == "" {
+			break
+		}
+		header = remain
+	}
+
+	return false
+}
+
 func writeNotModified(w http.ResponseWriter) {
 	// RFC 7232 section 4.1:
 	// a sender SHOULD NOT generate representation metadata other than the
@@ -108,3 +136,25 @@ func checkPreconditions(w http.ResponseWriter, r *http.Request, etag string) (do
 
 	return false
 }
+
+// checkPreconditions evaluates request preconditions for an object with no ETag.
+// exists indicates whether the object exists.
+func checkPreconditionsNoEtag(w http.ResponseWriter, r *http.Request, exists bool) (done bool) {
+	im := r.Header.Get("If-Match")
+	if im != "" && !etagMatchNoEtag(exists, im) {
+		w.WriteHeader(http.StatusPreconditionFailed)
+		return true
+	}
+	inm := r.Header.Get("If-None-Match")
+	if inm != "" && etagMatchNoEtag(exists, inm) {
+		if r.Method == "GET" || r.Method == "HEAD" {
+			writeNotModified(w)
+			return true
+		} else {
+			w.WriteHeader(http.StatusPreconditionFailed)
+			return true
+		}
+	}
+
+	return false
+}
diff --git a/webserver/precondition_test.go b/webserver/precondition_test.go
index 5ed61b3..be80b7c 100644
--- a/webserver/precondition_test.go
+++ b/webserver/precondition_test.go
@@ -89,6 +89,8 @@ func TestCheckPreconditions(t *testing.T) {
 		{"POST", `"123"`, ``, `"123"`, 412},
 		{"GET", `"123"`, ``, `"124"`, 0},
 		{"GET", `"123"`, ``, `*`, 304},
+		{"POST", `"123"`, ``, `"124"`, 0},
+		{"POST", `"123"`, ``, `*`, 412},
 	}
 
 	for _, tst := range tests {
@@ -112,3 +114,46 @@ func TestCheckPreconditions(t *testing.T) {
 		}
 	}
 }
+
+func TestCheckPreconditionsNoEtag(t *testing.T) {
+	var tests = []struct {
+		method  string
+		exists  bool
+		im, inm string
+		result  int
+	}{
+		{"GET", false, ``, ``, 0},
+		{"GET", false, `*`, ``, 412},
+		{"GET", false, ``, `*`, 0},
+		{"POST", false, `*`, ``, 412},
+		{"POST", false, ``, `*`, 0},
+		{"GET", true, ``, ``, 0},
+		{"GET", true, `"124"`, ``, 412},
+		{"POST", true, `"124"`, ``, 412},
+		{"GET", true, `*`, ``, 0},
+		{"GET", true, ``, `*`, 304},
+		{"POST", true, `*`, ``, 0},
+		{"POST", true, ``, `*`, 412},
+	}
+
+	for _, tst := range tests {
+		var w testWriter
+		h := make(http.Header)
+		if tst.im != "" {
+			h.Set("If-Match", tst.im)
+		}
+		if tst.inm != "" {
+			h.Set("If-None-Match", tst.inm)
+		}
+		r := http.Request{
+			Method: tst.method,
+			Header: h,
+		}
+		done := checkPreconditionsNoEtag(&w, &r, tst.exists)
+		if done != (tst.result != 0) || w.statusCode != tst.result {
+			t.Errorf("%v %#v %#v: got %v, expected %v",
+				tst.exists, tst.im, tst.inm,
+				w.statusCode, tst.result)
+		}
+	}
+}