Don't allocate memory to handle obs-fold

CHANGELOG.md

@@ -1,3 +1,9 @@
+Version 55:
+
+* Don't allocate memory to handle obs-fold
+
+--------------------------------------------------------------------------------
+
 Version 54:
 
 * static_buffer coverage

include/beast/http/basic_parser.hpp

@@ -60,6 +60,9 @@ namespace http {
 
     @tparam Derived The derived class type. This is part of the
     Curiously Recurring Template Pattern interface.
+
+    @note If the parser encounters a field value with obs-fold
+    longer than 4 kilobytes in length, an error is generated.
 */
 template<bool isRequest, class Derived>
 class basic_parser
@@ -68,6 +71,9 @@ class basic_parser
     template<bool OtherIsRequest, class OtherDerived>
     friend class basic_parser;
 
+    // limit on the size of the obs-fold buffer
+    static std::size_t constexpr max_obs_fold = 4096;
+
     // Message will be complete after reading header
     static unsigned constexpr flagSkipBody              = 1<<  0;
 

include/beast/http/error.hpp

@@ -115,7 +115,10 @@ enum class error
     bad_transfer_encoding,
 
     /// The chunk syntax is invalid.
-    bad_chunk
+    bad_chunk,
+
+    /// An obs-fold exceeded an internal limit.
+    bad_obs_fold
 };
 
 } // http

include/beast/http/fields.hpp

@@ -40,12 +40,11 @@ namespace http {
     as a `std::multiset`; there will be a separate value for each occurrence
     of the field name.
 
-    @note Meets the requirements of @b Fields
+    Meets the requirements of @b Fields
 */
 template<class Allocator>
 class basic_fields
 {
-private:
     using off_t = std::uint16_t;
 
 public:

include/beast/http/impl/basic_parser.ipp

@@ -8,6 +8,7 @@
 #ifndef BEAST_HTTP_IMPL_BASIC_PARSER_IPP
 #define BEAST_HTTP_IMPL_BASIC_PARSER_IPP
 
+#include <beast/core/static_string.hpp>
 #include <beast/core/type_traits.hpp>
 #include <beast/core/detail/ci_char_traits.hpp>
 #include <beast/core/detail/clamp.hpp>
@@ -701,25 +702,34 @@ parse_fields(char const*& p,
                 if(ec)
                     return;
             }
-            std::string s;
-            if(p != term)
+            // https://stackoverflow.com/questions/686217/maximum-on-http-header-values
+            static_string<max_obs_fold> s;
+            try
             {
-                s.append(p, term - 2);
-                p = term;
-                for(;;)
+                if(p != term)
                 {
-                    if(*p != ' ' && *p != '\t')
-                        break;
-                    s.push_back(' ');
-                    detail::skip_ows(p, term - 2);
-                    term = find_eol(p, last, ec);
-                    if(ec)
-                        return;
-                    if(p != term - 2)
-                        s.append(p, term - 2);
+                    s.append(p, term - 2);
                     p = term;
+                    for(;;)
+                    {
+                        if(*p != ' ' && *p != '\t')
+                            break;
+                        s.push_back(' ');
+                        detail::skip_ows(p, term - 2);
+                        term = find_eol(p, last, ec);
+                        if(ec)
+                            return;
+                        if(p != term - 2)
+                            s.append(p, term - 2);
+                        p = term;
+                    }
                 }
             }
+            catch(std::length_error const&)
+            {
+                ec = error::bad_obs_fold;
+                return;
+            }
             auto const f = string_to_field(name);
             string_view const value{s.data(), s.size()};
             do_field(f, value, ec);

include/beast/http/impl/error.ipp

@@ -56,6 +56,7 @@ public:
         case error::bad_content_length: return "bad Content-Length";
         case error::bad_transfer_encoding: return "bad Transfer-Encoding";
         case error::bad_chunk: return "bad chunk";
+        case error::bad_obs_fold: return "bad obs-fold";
         }
     }