Merge commit from fork

* Ensure payload_max_length_ is respected for compressed payloads

* Fix Denial of service (DOS) using zip bomb

---------

Co-authored-by: Hritik Vijay <hey@hritik.sh>

httplib.h

@@ -8982,14 +8982,11 @@ inline bool Server::read_content(Stream &strm, Request &req, Response &res) {
           strm, req, res,
           // Regular
           [&](const char *buf, size_t n) {
-            // Prevent arithmetic overflow when checking sizes.
-            // Avoid computing (req.body.size() + n) directly because
-            // adding two unsigned `size_t` values can wrap around and
-            // produce a small result instead of indicating overflow.
-            // Instead, check using subtraction: ensure `n` does not
-            // exceed the remaining capacity `max_size() - size()`.
-            if (req.body.size() >= req.body.max_size() ||
-                n > req.body.max_size() - req.body.size()) {
+            // Limit decompressed body size to payload_max_length_ to protect
+            // against "zip bomb" attacks where a small compressed payload
+            // decompresses to a massive size.
+            if (req.body.size() + n > payload_max_length_ ||
+                req.body.size() + n > req.body.max_size()) {
               return false;
             }
             req.body.append(buf, n);

test/test.cc

@@ -14101,3 +14101,52 @@ TEST(Issue2318Test, EmptyHostString) {
     EXPECT_EQ(httplib::Error::Connection, res.error());
   }
 }
+
+#ifdef CPPHTTPLIB_ZLIB_SUPPORT
+TEST(ZipBombProtectionTest, DecompressedSizeExceedsLimit) {
+  Server svr;
+
+  // Set a small payload limit (1KB)
+  svr.set_payload_max_length(1024);
+
+  svr.Post("/test", [&](const Request &req, Response &res) {
+    res.set_content("Body size: " + std::to_string(req.body.size()),
+                    "text/plain");
+  });
+
+  auto listen_thread = std::thread([&]() { svr.listen(HOST, PORT); });
+  auto se = detail::scope_exit([&] {
+    svr.stop();
+    listen_thread.join();
+  });
+
+  svr.wait_until_ready();
+
+  // Create data that compresses well but exceeds limit when decompressed
+  // 8KB of repeated null bytes compresses to a very small size
+  std::string original_data(8 * 1024, '\0');
+
+  // Compress the data using gzip
+  std::string compressed_data;
+  detail::gzip_compressor compressor;
+  compressor.compress(original_data.data(), original_data.size(), true,
+                      [&](const char *data, size_t size) {
+                        compressed_data.append(data, size);
+                        return true;
+                      });
+
+  // Verify compression worked (compressed should be much smaller)
+  ASSERT_LT(compressed_data.size(), original_data.size());
+  ASSERT_LT(compressed_data.size(), 1024u); // Compressed fits in limit
+
+  // Send compressed data with Content-Encoding: gzip
+  Client cli(HOST, PORT);
+  Headers headers = {{"Content-Encoding", "gzip"}};
+  auto res =
+      cli.Post("/test", headers, compressed_data, "application/octet-stream");
+
+  // Server should reject because decompressed size (8KB) exceeds limit (1KB)
+  ASSERT_TRUE(res);
+  EXPECT_EQ(StatusCode::BadRequest_400, res->status);
+}
+#endif