From dc774638960f575922f1371a84bc2d9babd15aa0 Mon Sep 17 00:00:00 2001
From: yhirose <yuji.hirose.bug@gmail.com>
Date: Fri, 5 Dec 2025 00:09:01 -0500
Subject: [PATCH] Refactor ETag handling: separate strong and weak ETag checks
 for If-Range requests

---
 httplib.h    | 20 ++++++++++++++------
 test/test.cc | 21 +++++++++++++++++----
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/httplib.h b/httplib.h
index 3c2dff2..5f0537d 100644
--- a/httplib.h
+++ b/httplib.h
@@ -3032,10 +3032,14 @@ inline time_t parse_http_date(const std::string &date_str) {
 #endif
 }
 
-// Check if the string is an ETag (starts with '"' or 'W/"')
-inline bool is_etag(const std::string &s) {
-  return !s.empty() &&
-         (s[0] == '"' || (s.size() > 2 && s[0] == 'W' && s[1] == '/'));
+// Check if the string is a weak ETag (starts with 'W/"')
+inline bool is_weak_etag(const std::string &s) {
+  return s.size() > 3 && s[0] == 'W' && s[1] == '/' && s[2] == '"';
+}
+
+// Check if the string is a strong ETag (starts with '"' but not 'W/"')
+inline bool is_strong_etag(const std::string &s) {
+  return !s.empty() && s[0] == '"';
 }
 
 inline size_t to_utf8(int code, char *buff) {
@@ -8399,9 +8403,13 @@ inline bool Server::handle_file_request(Request &req, Response &res) {
             auto if_range = req.get_header_value("If-Range");
             auto valid = false;
 
-            if (detail::is_etag(if_range)) {
-              // ETag comparison (weak comparison for If-Range per RFC 9110)
+            if (detail::is_strong_etag(if_range)) {
+              // RFC 9110 Section 13.1.5: If-Range requires strong ETag
+              // comparison.
               valid = (!etag.empty() && if_range == etag);
+            } else if (detail::is_weak_etag(if_range)) {
+              // Weak ETags are not valid for If-Range (RFC 9110 Section 13.1.5)
+              valid = false;
             } else {
               // HTTP-date comparison
               auto if_range_time = detail::parse_http_date(if_range);
diff --git a/test/test.cc b/test/test.cc
index a9dcf8b..d93a27b 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -12875,13 +12875,16 @@ TEST(ETagTest, IfRangeWithETag) {
   ASSERT_TRUE(res1->has_header("ETag"));
   std::string etag = res1->get_header_value("ETag");
 
-  // Range request with matching If-Range (ETag): should get 206
+  // RFC 9110 Section 13.1.5: If-Range requires strong ETag comparison.
+  // Since our server generates weak ETags (W/"..."), If-Range with our
+  // ETag should NOT result in partial content - it should return full content.
   Headers h2 = {{"Range", "bytes=0-4"}, {"If-Range", etag}};
   auto res2 = cli.Get("/static/if_range_testfile.txt", h2);
   ASSERT_TRUE(res2);
-  EXPECT_EQ(206, res2->status);
-  EXPECT_EQ("01234", res2->body);
-  EXPECT_TRUE(res2->has_header("Content-Range"));
+  // Weak ETag in If-Range -> full content (200), not partial (206)
+  EXPECT_EQ(200, res2->status);
+  EXPECT_EQ(content, res2->body);
+  EXPECT_FALSE(res2->has_header("Content-Range"));
 
   // Range request with non-matching If-Range (ETag): should get 200 (full
   // content)
@@ -12892,6 +12895,16 @@ TEST(ETagTest, IfRangeWithETag) {
   EXPECT_EQ(content, res3->body);
   EXPECT_FALSE(res3->has_header("Content-Range"));
 
+  // Range request with strong ETag (hypothetical - our server doesn't generate
+  // strong ETags, but if client sends a strong ETag that doesn't match, it
+  // should return full content)
+  Headers h4 = {{"Range", "bytes=0-4"}, {"If-Range", "\"strong-etag\""}};
+  auto res4 = cli.Get("/static/if_range_testfile.txt", h4);
+  ASSERT_TRUE(res4);
+  EXPECT_EQ(200, res4->status);
+  EXPECT_EQ(content, res4->body);
+  EXPECT_FALSE(res4->has_header("Content-Range"));
+
   svr.stop();
   t.join();
   std::remove(fname);