Deduplicate UBJSON/BJData length-type error message

The "expected length type specification" parse error was built with an
identical if/else block in both get_ubjson_string() and
get_ubjson_size_value(), each branching on the input format to pick the
marker list. Extract a single unexpected_length_type_message() helper that
selects the markers via a ternary and appends the caller-supplied infix,
removing four near-duplicate message strings and centralizing the marker
list. Error messages are unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tv6SnfYbcx8y3y4PrECcto

include/nlohmann/detail/input/binary_reader.hpp

@@ -1869,6 +1869,24 @@ class binary_reader
         return true;
     }
 
+    /*!
+    @brief create the error message for a missing/invalid length-type marker
+
+    Used both when reading a UBJSON/BJData string and when reading an optimized
+    container size. The accepted markers depend on the input format, and the
+    size variant appends " after '#'" via @a infix.
+
+    @param[in] last_token  the offending byte as returned by get_token_string()
+    @param[in] infix       extra context inserted after the marker list
+    @return the formatted error message
+    */
+    std::string unexpected_length_type_message(const std::string& last_token, const char* infix) const
+    {
+        return concat("expected length type specification (",
+                      input_format == input_format_t::bjdata ? "U, i, u, I, m, l, M, L" : "U, i, I, l, L",
+                      ")", infix, "; last byte: 0x", last_token);
+    }
+
     /*!
     @brief reads a UBJSON string
 
@@ -1961,17 +1979,8 @@ class binary_reader
                 break;
         }
         auto last_token = get_token_string();
-        std::string message;
-
-        if (input_format != input_format_t::bjdata)
-        {
-            message = "expected length type specification (U, i, I, l, L); last byte: 0x" + last_token;
-        }
-        else
-        {
-            message = "expected length type specification (U, i, u, I, m, l, M, L); last byte: 0x" + last_token;
-        }
-        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format, message, "string"), nullptr));
+        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
+                                exception_message(input_format, unexpected_length_type_message(last_token, ""), "string"), nullptr));
     }
 
     /*!
@@ -2250,17 +2259,8 @@ class binary_reader
                 break;
         }
         auto last_token = get_token_string();
-        std::string message;
-
-        if (input_format != input_format_t::bjdata)
-        {
-            message = "expected length type specification (U, i, I, l, L) after '#'; last byte: 0x" + last_token;
-        }
-        else
-        {
-            message = "expected length type specification (U, i, u, I, m, l, M, L) after '#'; last byte: 0x" + last_token;
-        }
-        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read, exception_message(input_format, message, "size"), nullptr));
+        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
+                                exception_message(input_format, unexpected_length_type_message(last_token, " after '#'"), "size"), nullptr));
     }
 
     /*!

include/nlohmann/detail/output/output_adapters.hpp

@@ -13,7 +13,6 @@
 #include <iterator> // back_inserter
 #include <memory> // shared_ptr, make_shared
 #include <string> // basic_string
-#include <utility> // move
 #include <vector> // vector
 
 #ifndef JSON_NO_IO
@@ -119,72 +118,6 @@ class output_string_adapter : public output_adapter_protocol<CharType>
     StringType& str;
 };
 
-/// @brief non-virtual output sink writing into a std::vector
-///
-/// Unlike output_vector_adapter, this sink is not part of the virtual
-/// output_adapter_protocol hierarchy: it is passed to binary_writer by value as
-/// a template parameter, so write_character()/write_characters() are ordinary
-/// (inlinable) calls with no vtable lookup and no shared_ptr. It is used for the
-/// common `to_cbor`/`to_msgpack`/... into a std::vector.
-template<typename CharType, typename AllocatorType = std::allocator<CharType>>
-class output_vector_sink
-{
-  public:
-    explicit output_vector_sink(std::vector<CharType, AllocatorType>& vec) noexcept
-        : v(vec)
-    {}
-
-    void write_character(CharType c)
-    {
-        v.push_back(c);
-    }
-
-    // no JSON_HEDLEY_NON_NULL here: binary_writer legitimately passes a null
-    // pointer with length 0 for empty strings/binary values. Appending an empty
-    // range is a no-op; the type-erased path tolerates this via the (unattributed)
-    // virtual base, and the concrete sink must do the same.
-    void write_characters(const CharType* s, std::size_t length)
-    {
-        v.insert(v.end(), s, s + length);
-    }
-
-  private:
-    std::vector<CharType, AllocatorType>& v;
-};
-
-/// @brief output sink forwarding to a type-erased output adapter
-///
-/// Wraps the polymorphic output_adapter_t so the same binary_writer template can
-/// also target arbitrary adapters (output streams, strings, user-provided
-/// adapters) via the `output_adapter`-based overloads. Each write still goes
-/// through one virtual call, exactly as before; only the concrete sinks above
-/// avoid it.
-template<typename CharType>
-class output_adapter_sink
-{
-  public:
-    explicit output_adapter_sink(output_adapter_t<CharType> adapter)
-        : oa(std::move(adapter))
-    {
-        JSON_ASSERT(oa);
-    }
-
-    void write_character(CharType c)
-    {
-        oa->write_character(c);
-    }
-
-    // no JSON_HEDLEY_NON_NULL: forwards (null, 0) for empty payloads, exactly as
-    // the type-erased path already did before this sink existed
-    void write_characters(const CharType* s, std::size_t length)
-    {
-        oa->write_characters(s, length);
-    }
-
-  private:
-    output_adapter_t<CharType> oa = nullptr;
-};
-
 template<typename CharType, typename StringType = std::basic_string<CharType>>
 class output_adapter
 {

include/nlohmann/json.hpp

@@ -140,7 +140,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     friend ::nlohmann::detail::serializer<basic_json>;
     template<typename BasicJsonType>
     friend class ::nlohmann::detail::iter_impl;
-    template<typename BasicJsonType, typename CharType, typename OutputSinkType>
+    template<typename BasicJsonType, typename CharType>
     friend class ::nlohmann::detail::binary_writer;
     template<typename BasicJsonType, typename InputType, typename SAX>
     friend class ::nlohmann::detail::binary_reader;
@@ -4327,9 +4327,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_cbor(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_reserve_hint(j));
-        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
-            detail::output_vector_sink<std::uint8_t>(result)).write_cbor(j);
+        to_cbor(j, result);
         return result;
     }
 
@@ -4352,9 +4350,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_msgpack(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_reserve_hint(j));
-        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
-            detail::output_vector_sink<std::uint8_t>(result)).write_msgpack(j);
+        to_msgpack(j, result);
         return result;
     }
 
@@ -4379,9 +4375,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             const bool use_type = false)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_reserve_hint(j));
-        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
-            detail::output_vector_sink<std::uint8_t>(result)).write_ubjson(j, use_size, use_type);
+        to_ubjson(j, result, use_size, use_type);
         return result;
     }
 
@@ -4409,9 +4403,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             const bjdata_version_t version = bjdata_version_t::draft2)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_reserve_hint(j));
-        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
-            detail::output_vector_sink<std::uint8_t>(result)).write_ubjson(j, use_size, use_type, true, true, version);
+        to_bjdata(j, result, use_size, use_type, version);
         return result;
     }
 
@@ -4438,9 +4430,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_bson(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_reserve_hint(j));
-        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
-            detail::output_vector_sink<std::uint8_t>(result)).write_bson(j);
+        to_bson(j, result);
         return result;
     }