"crow::multipart::message throws when the boundary is empty or malformed

CMakeLists.txt

@@ -101,6 +101,7 @@ if(CROW_AMALGAMATE)
 		include/crow/ci_map.h
 		include/crow/common.h
 		include/crow/compression.h
+		include/crow/exceptions.h
 		include/crow/http_connection.h
 		include/crow/http_parser_merged.h
 		include/crow/http_request.h

include/crow/exceptions.h

@@ -0,0 +1,14 @@
+#pragma once
+#include <stdexcept>
+
+namespace crow
+{
+    struct bad_request : public std::runtime_error
+    {
+        bad_request(const std::string& what_arg)
+            : std::runtime_error(what_arg) {}
+
+        bad_request(const char* what_arg)
+            : std::runtime_error(what_arg) {}
+    };
+}

include/crow/http_request.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <stdexcept>
 #ifdef CROW_USE_BOOST
 #include <boost/asio.hpp>
 #else

include/crow/multipart.h

@@ -7,6 +7,7 @@
 #include "crow/http_request.h"
 #include "crow/returnable.h"
 #include "crow/ci_map.h"
+#include "crow/exceptions.h"
 
 namespace crow
 {
@@ -147,8 +148,14 @@ namespace crow
               boundary(get_boundary(get_header_value("Content-Type")))
             {
                 if (!boundary.empty())
+                {
                     content_type = "multipart/form-data; boundary=" + boundary;
-                parse_body(req.body);
+                    parse_body(req.body);
+                }
+                else
+                {
+                    throw bad_request("Empty boundary in multipart message");
+                }
             }
 
         private:
@@ -178,8 +185,8 @@ namespace crow
                     size_t found = body.find(delimiter);
                     if (found == std::string::npos)
                     {
-                        // did not find delimiter; probably an ill-formed body; ignore the rest
-                        break;
+                        // did not find delimiter; probably an ill-formed body; throw to indicate the issue to user
+                        throw bad_request("Unable to find delimiter in multipart message. Probably ill-formed body");
                     }
                     std::string section = body.substr(0, found);
 

include/crow/routing.h

@@ -1813,6 +1813,11 @@ namespace crow // NOTE: Already documented in "crow/app.h"
             {
                 throw;
             }
+            catch (const bad_request& e)
+            {
+                res = response (400);
+                res.body = e.what();
+            }
             catch (const std::exception& e)
             {
                 CROW_LOG_ERROR << "An uncaught exception occurred: " << e.what();

tests/unittest.cpp

@@ -2510,6 +2510,54 @@ TEST_CASE("multipart")
 
         CHECK(test_string == res.body);
     }
+
+    //Test against empty boundary
+    {
+        request req;
+        response res;
+        req.url = "/multipart";
+        req.add_header("Content-Type", "multipart/form-data; boundary=");
+        req.body = test_string;
+
+        app.handle_full(req, res);
+
+        CHECK(res.code == 400);
+        CHECK(res.body == "Empty boundary in multipart message");
+
+    }
+
+    //Boundary that differs from actual boundary
+    {
+        const char alphabet[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        std::random_device dev;
+        std::mt19937 rng(dev());
+        std::uniform_int_distribution<std::mt19937::result_type> dist(0, sizeof(alphabet) - 2);
+        std::uniform_int_distribution<std::mt19937::result_type> boundary_sizes(1, 50);
+        std::array<std::string, 100> test_boundaries;
+
+        for (auto& boundary : test_boundaries)
+        {
+            const size_t boundary_size = boundary_sizes(rng);
+            boundary.reserve(boundary_size);
+            for (size_t idx = 0; idx < boundary_size; idx++)
+                boundary.push_back(alphabet[dist(rng)]);
+        }
+
+        for (const auto& boundary : test_boundaries)
+        {
+            request req;
+            response res;
+
+            req.url = "/multipart";
+            req.add_header("Content-Type", "multipart/form-data; boundary=" + boundary);
+            req.body = test_string;
+
+            app.handle_full(req, res);
+
+            CHECK(res.code == 400);
+            CHECK(res.body == "Unable to find delimiter in multipart message. Probably ill-formed body");
+        }
+    }
 } // multipart
 
 TEST_CASE("multipart_view")