Add ETag and Last-Modified handling for If-Range requests

httplib.h

@@ -1257,7 +1257,7 @@ private:
   bool listen_internal();
 
   bool routing(Request &req, Response &res, Stream &strm);
-  bool handle_file_request(const Request &req, Response &res);
+  bool handle_file_request(Request &req, Response &res);
   bool dispatch_request(Request &req, Response &res,
                         const Handlers &handlers) const;
   bool dispatch_request_for_content_reader(
@@ -3020,6 +3020,12 @@ 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] == '/'));
+}
+
 inline size_t to_utf8(int code, char *buff) {
   if (code < 0x0080) {
     buff[0] = static_cast<char>(code & 0x7F);
@@ -8313,7 +8319,7 @@ inline bool Server::read_content_core(
   return true;
 }
 
-inline bool Server::handle_file_request(const Request &req, Response &res) {
+inline bool Server::handle_file_request(Request &req, Response &res) {
   for (const auto &entry : base_dirs_) {
     // Prefix match
     if (!req.path.compare(0, entry.mount_point.size(), entry.mount_point)) {
@@ -8373,6 +8379,30 @@ inline bool Server::handle_file_request(const Request &req, Response &res) {
             }
           }
 
+          // Handle If-Range for partial content requests (RFC 9110
+          // Section 13.1.5) If-Range is only evaluated when Range header is
+          // present. If the validator matches, serve partial content; otherwise
+          // serve full content.
+          if (!req.ranges.empty() && req.has_header("If-Range")) {
+            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)
+              valid = (!etag.empty() && if_range == etag);
+            } else {
+              // HTTP-date comparison
+              auto if_range_time = detail::parse_http_date(if_range);
+              valid = (if_range_time != static_cast<time_t>(-1) &&
+                       mtime <= if_range_time);
+            }
+
+            if (!valid) {
+              // Validator doesn't match: ignore Range and serve full content
+              req.ranges.clear();
+            }
+          }
+
           auto mm = std::make_shared<detail::mmap>(path.c_str());
           if (!mm->is_open()) {
             output_error_log(Error::OpenFile, &req);

test/test.cc

@@ -12848,3 +12848,103 @@ TEST(ETagTest, VaryAcceptEncodingWithCompression) {
   svr.stop();
   t.join();
 }
+
+TEST(ETagTest, IfRangeWithETag) {
+  using namespace httplib;
+
+  // Create a test file with known content
+  const char *fname = "if_range_testfile.txt";
+  const std::string content = "0123456789ABCDEFGHIJ"; // 20 bytes
+  {
+    std::ofstream ofs(fname);
+    ofs << content;
+  }
+
+  Server svr;
+  svr.set_mount_point("/static", ".");
+  auto t = std::thread([&]() { svr.listen("localhost", 8090); });
+  svr.wait_until_ready();
+
+  Client cli("localhost", 8090);
+
+  // First request: get ETag
+  auto res1 = cli.Get("/static/if_range_testfile.txt");
+  ASSERT_TRUE(res1);
+  ASSERT_EQ(200, res1->status);
+  ASSERT_TRUE(res1->has_header("ETag"));
+  std::string etag = res1->get_header_value("ETag");
+
+  // Range request with matching If-Range (ETag): should get 206
+  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"));
+
+  // Range request with non-matching If-Range (ETag): should get 200 (full
+  // content)
+  Headers h3 = {{"Range", "bytes=0-4"}, {"If-Range", "W/\"wrong-etag\""}};
+  auto res3 = cli.Get("/static/if_range_testfile.txt", h3);
+  ASSERT_TRUE(res3);
+  EXPECT_EQ(200, res3->status);
+  EXPECT_EQ(content, res3->body);
+  EXPECT_FALSE(res3->has_header("Content-Range"));
+
+  svr.stop();
+  t.join();
+  std::remove(fname);
+}
+
+TEST(ETagTest, IfRangeWithDate) {
+  using namespace httplib;
+
+  // Create a test file
+  const char *fname = "if_range_date_testfile.txt";
+  const std::string content = "ABCDEFGHIJ0123456789"; // 20 bytes
+  {
+    std::ofstream ofs(fname);
+    ofs << content;
+  }
+
+  Server svr;
+  svr.set_mount_point("/static", ".");
+  auto t = std::thread([&]() { svr.listen("localhost", 8091); });
+  svr.wait_until_ready();
+
+  Client cli("localhost", 8091);
+
+  // First request: get Last-Modified
+  auto res1 = cli.Get("/static/if_range_date_testfile.txt");
+  ASSERT_TRUE(res1);
+  ASSERT_EQ(200, res1->status);
+  ASSERT_TRUE(res1->has_header("Last-Modified"));
+  std::string last_modified = res1->get_header_value("Last-Modified");
+
+  // Range request with matching If-Range (date): should get 206
+  Headers h2 = {{"Range", "bytes=5-9"}, {"If-Range", last_modified}};
+  auto res2 = cli.Get("/static/if_range_date_testfile.txt", h2);
+  ASSERT_TRUE(res2);
+  EXPECT_EQ(206, res2->status);
+  EXPECT_EQ("FGHIJ", res2->body);
+
+  // Range request with old If-Range date: should get 200 (full content)
+  Headers h3 = {{"Range", "bytes=5-9"},
+                {"If-Range", "Sun, 01 Jan 2000 00:00:00 GMT"}};
+  auto res3 = cli.Get("/static/if_range_date_testfile.txt", h3);
+  ASSERT_TRUE(res3);
+  EXPECT_EQ(200, res3->status);
+  EXPECT_EQ(content, res3->body);
+
+  // Range request with future If-Range date: should get 206
+  Headers h4 = {{"Range", "bytes=0-4"},
+                {"If-Range", "Sun, 01 Jan 2099 00:00:00 GMT"}};
+  auto res4 = cli.Get("/static/if_range_date_testfile.txt", h4);
+  ASSERT_TRUE(res4);
+  EXPECT_EQ(206, res4->status);
+  EXPECT_EQ("ABCDE", res4->body);
+
+  svr.stop();
+  t.join();
+  std::remove(fname);
+}