Also submitted upstream https://github.com/microsoft/cpprestsdk/pull/1829
Cpprestsdk is using a lot of unsigned types like uint8_t with C++ streams, this
seems to be fine with msvc/win32 and at least for now with gcc. This patch will
provide a char_traits type to the streams types other than std::char_traits if
needed. This is detected via template specialisations. Google & AIs will probably
suggest adding a std::char_traits<unsingned char> implementation, but I think that
is very innappropriate in a library for use by applications.
--- a/Release/include/cpprest/streams.h	(revision 0b1ce318a757bbfb89bdb0fffb61ca4e38dc3b33)
+++ b/Release/include/cpprest/streams.h	(revision 32b322b564e5e540ff02393ffe3bd3bade8d299c)
@@ -16,6 +16,7 @@
 #define CASA_STREAMS_H
 
 #include "cpprest/astreambuf.h"
+#include "cpprest/details/char_traits.h"
 #include <iosfwd>
 #include <cstdio>
 
@@ -60,30 +61,95 @@
     concurrency::streams::streambuf<CharType> m_buffer;
 };
 
-template<typename CharType>
+template<typename CharType, class Traits = typename utility::CanUseStdCharTraits<CharType>::TraitsType>
 struct Value2StringFormatter
 {
+    struct SanitizeInput
+    {
+        const std::basic_string<char> &operator () (const std::basic_string<char> &input)
+        {
+            return input;
+        }
+        template <class InputTraits> std::basic_string<char> operator () (const std::basic_string<unsigned char, InputTraits> &input)
+        {
+            return {reinterpret_cast<const char *>(input.c_str()), input.size()};
+        }
+        const char *operator () (const char *input) {
+            return input;
+        }
+        const char *operator () (const unsigned char *input)
+        {
+            return reinterpret_cast<const char *>(input);
+        }
+        template <class T> T operator () (T input)
+        {
+            return input;
+        }
+    };
+    struct GenerateFormatOutput
+    {
+        std::basic_string<CharType,Traits> &&operator() (std::basic_string<CharType,Traits> &&result)
+        {
+            return std::move(result);
+        }
+        std::basic_string<CharType,Traits> operator() (const std::basic_string<char> &intermediate)
+        {
+            return {reinterpret_cast<const CharType *>(intermediate.c_str()), intermediate.size()};
+        }
+    };
     template<typename T>
-    static std::basic_string<CharType> format(const T& val)
+    static std::basic_string<CharType, Traits> format(const T& val)
     {
-        std::basic_ostringstream<CharType> ss;
+        typename std::conditional<
+            sizeof(CharType) == 1,
+            std::basic_ostringstream<char>,
+            std::basic_ostringstream<typename std::make_signed<CharType>::type>
+        >::type ss;
+        SanitizeInput sanitizer;
+        ss << sanitizer(val);
+        typename std::conditional<
+            sizeof(CharType) == 1,
+            std::basic_string<char>,
+            std::basic_string<typename std::make_signed<CharType>::type>
+        >::type str = ss.str();
+        GenerateFormatOutput generateFormatOutput;
+        return generateFormatOutput(std::move(str));
+    }
+};
+
+template<class Traits, typename T>
+struct Value2StringFormatterUint8Format
+{
+    std::basic_string<uint8_t, Traits> operator () (const T& val)
+    {
+        std::basic_ostringstream<char> ss;
         ss << val;
-        return ss.str();
+        return reinterpret_cast<const uint8_t*>(ss.str().c_str());
+    }
+};
+
+template <class Traits>
+struct Value2StringFormatterUint8Format<Traits, std::basic_string<uint8_t,Traits>>
+{
+    std::basic_string<uint8_t, Traits> operator () (
+        const std::basic_string<uint8_t, typename utility::CanUseStdCharTraits<uint8_t>::TraitsType>& val)
+    {
+        Value2StringFormatterUint8Format<Traits,std::basic_string<char>> format;
+        return format(reinterpret_cast<const std::basic_string<char>&>(val));
     }
 };
 
 template<>
 struct Value2StringFormatter<uint8_t>
 {
-    template<typename T>
-    static std::basic_string<uint8_t> format(const T& val)
+    template <typename T, class Traits = typename utility::CanUseStdCharTraits<uint8_t>::TraitsType>
+    static std::basic_string<uint8_t, Traits> format(const T& val)
     {
-        std::basic_ostringstream<char> ss;
-        ss << val;
-        return reinterpret_cast<const uint8_t*>(ss.str().c_str());
+        Value2StringFormatterUint8Format<Traits, T> format;
+        return format(val);
     }
 
-    static std::basic_string<uint8_t> format(const utf16string& val)
+    static std::basic_string<uint8_t, typename utility::CanUseStdCharTraits<uint8_t>::TraitsType> format(const utf16string& val)
     {
         return format(utility::conversions::utf16_to_utf8(val));
     }
@@ -262,7 +328,7 @@
     /// Write the specified string to the output stream.
     /// </summary>
     /// <param name="str">Input string.</param>
-    pplx::task<size_t> print(const std::basic_string<CharType>& str) const
+    pplx::task<size_t> print(const std::basic_string<CharType,traits>& str) const
     {
         pplx::task<size_t> result;
         if (!_verify_and_return_task(details::_out_stream_msg, result)) return result;
@@ -273,7 +339,7 @@
         }
         else
         {
-            auto sharedStr = std::make_shared<std::basic_string<CharType>>(str);
+            auto sharedStr = std::make_shared<std::basic_string<CharType,traits>>(str);
             return helper()->m_buffer.putn_nocopy(sharedStr->c_str(), sharedStr->size()).then([sharedStr](size_t size) {
                 return size;
             });
@@ -294,7 +360,7 @@
         if (!_verify_and_return_task(details::_out_stream_msg, result)) return result;
         // TODO in the future this could be improved to have Value2StringFormatter avoid another unnecessary copy
         // by putting the string on the heap before calling the print string overload.
-        return print(details::Value2StringFormatter<CharType>::format(val));
+        return print(details::Value2StringFormatter<CharType, traits>::format(val));
     }
 
     /// <summary>
--- a/Release/include/cpprest/astreambuf.h	(revision d17f091b5a753b33fb455e92b590fc9f4e921119)
+++ b/Release/include/cpprest/astreambuf.h	(revision 4188ad89b2cf2e8de3cc3513adcf400fbfdc5ce7)
@@ -15,6 +15,7 @@
 
 #include "cpprest/asyncrt_utils.h"
 #include "cpprest/details/basic_types.h"
+#include "cpprest/details/char_traits.h"
 #include "pplx/pplxtasks.h"
 #include <atomic>
 #include <cstring>
@@ -56,55 +57,28 @@
 /// <typeparam name="_CharType">
 /// The data type of the basic element of the stream.
 /// </typeparam>
+namespace detail
+{
 template<typename _CharType>
-struct char_traits : std::char_traits<_CharType>
+struct char_traits : utility::CanUseStdCharTraits<_CharType>::TraitsType
 {
     /// <summary>
     /// Some synchronous functions will return this value if the operation
     /// requires an asynchronous call in a given situation.
     /// </summary>
     /// <returns>An <c>int_type</c> value which implies that an asynchronous call is required.</returns>
-    static typename std::char_traits<_CharType>::int_type requires_async()
+    static typename utility::CanUseStdCharTraits<_CharType>::TraitsType::int_type requires_async()
     {
-        return std::char_traits<_CharType>::eof() - 1;
+        return utility::CanUseStdCharTraits<_CharType>::TraitsType::eof() - 1;
     }
+};
+}
+template<typename _CharType> struct char_traits : detail::char_traits<_CharType> {
 };
 #if !defined(_WIN32)
-template<>
-struct char_traits<unsigned char> : private std::char_traits<char>
-{
-public:
-    typedef unsigned char char_type;
-
-    using std::char_traits<char>::eof;
-    using std::char_traits<char>::int_type;
-    using std::char_traits<char>::off_type;
-    using std::char_traits<char>::pos_type;
-
-    static size_t length(const unsigned char* str)
-    {
-        return std::char_traits<char>::length(reinterpret_cast<const char*>(str));
-    }
-
-    static void assign(unsigned char& left, const unsigned char& right) { left = right; }
-    static unsigned char* assign(unsigned char* left, size_t n, unsigned char value)
-    {
-        return reinterpret_cast<unsigned char*>(
-            std::char_traits<char>::assign(reinterpret_cast<char*>(left), n, static_cast<char>(value)));
-    }
-
-    static unsigned char* copy(unsigned char* left, const unsigned char* right, size_t n)
-    {
-        return reinterpret_cast<unsigned char*>(
-            std::char_traits<char>::copy(reinterpret_cast<char*>(left), reinterpret_cast<const char*>(right), n));
-    }
-
-    static unsigned char* move(unsigned char* left, const unsigned char* right, size_t n)
-    {
-        return reinterpret_cast<unsigned char*>(
-            std::char_traits<char>::move(reinterpret_cast<char*>(left), reinterpret_cast<const char*>(right), n));
-    }
-
+template <> struct char_traits<unsigned char> : detail::char_traits<unsigned char> {
+    typedef typename std::char_traits<char>::int_type int_type;
+    static int_type eof() { return std::char_traits<char>::eof(); }
     static int_type requires_async() { return eof() - 1; }
 };
 #endif
new file mode 100644
--- /dev/null	(revision 4188ad89b2cf2e8de3cc3513adcf400fbfdc5ce7)
+++ b/Release/include/cpprest/details/char_traits.h	(revision 4188ad89b2cf2e8de3cc3513adcf400fbfdc5ce7)
@@ -0,0 +1,102 @@
+//
+// Created by sigsegv on 6/28/25.
+//
+
+#ifndef CPPRESTSDK_ROOT_CHAR_TRAITS_H
+#define CPPRESTSDK_ROOT_CHAR_TRAITS_H
+
+#include <type_traits>
+#include <string>
+
+namespace utility {
+
+namespace detail {
+
+template <typename T> struct IntTypeFor {
+    typedef typename std::conditional<std::is_unsigned<T>::value, unsigned long long int, long long int>::type type;
+};
+template <> struct IntTypeFor<char> {
+    typedef typename std::char_traits<char>::int_type type;
+};
+template <> struct IntTypeFor<unsigned char> {
+    typedef typename std::make_unsigned<typename std::char_traits<char>::int_type>::type type;
+};
+
+template <typename T> class DetailCharTraits
+{
+public:
+    using char_type  = T;
+    using int_type   = typename IntTypeFor<T>::type;
+    using off_type   = std::streamoff;
+    using pos_type   = std::streampos;
+    using state_type = mbstate_t;
+
+    static void assign(char_type& r, const char_type& a) noexcept { r = a; }
+    static char_type to_char_type(int_type c) noexcept { return char_type(c); }
+    static int_type  to_int_type(char_type c) noexcept { return c; }
+    static bool eq(char_type a, char_type b) noexcept { return a == b; }
+    static bool lt(char_type a, char_type b) noexcept { return a <  b; }
+    static int compare(const char_type* s1,const char_type* s2,size_t n){
+        for (; n--; ++s1, ++s2) {
+            if (!eq(*s1, *s2))
+                return lt(*s1,*s2)?-1:1;
+        }
+        return 0;
+    }
+    static size_t length(const char_type* s){
+        const char_type* p = s;
+        while (*p)
+            ++p;
+        return size_t(p - s);
+    }
+    static const char_type* find(const char_type* s,size_t n,const char_type& a){
+        for (; n--; ++s)
+        {
+            if (eq(*s, a))
+                return s;
+            return nullptr;
+        }
+    }
+    static char_type* move (char_type* r,const char_type* s,size_t n){
+        return (char_type*)memmove(r, s, n * sizeof(char_type));
+    }
+    static char_type* copy (char_type* r,const char_type* s,size_t n){
+        return (char_type*)memcpy (r, s, n * sizeof(char_type));
+    }
+    static char_type* assign(char_type* r,size_t n,char_type a){
+        if (sizeof(char_type) == 1)
+        {
+            return (char_type*)memset(r, a, n);
+        }
+        else
+        {
+            for (char_type *s = r; n--; ++s)
+            {
+                *s = a;
+            }
+        }
+    }
+    static int_type  eof() noexcept { return ~0u; }
+    static int_type  not_eof(int_type c) noexcept { return c == eof() ? 0 : c; }
+};
+
+template <typename T, typename = bool> struct CanUseStdCharTraits : public std::false_type
+{
+public:
+    typedef DetailCharTraits<T> TraitsType;
+};
+
+template <typename T> struct CanUseStdCharTraits<T, decltype(std::char_traits<T>::eq(std::declval<T>(), std::declval<T>()))> : public std::true_type
+{
+public:
+    typedef std::char_traits<T> TraitsType;
+};
+
+}
+
+template <typename T> struct CanUseStdCharTraits : detail::CanUseStdCharTraits<typename std::remove_const<typename std::remove_reference<T>::type>::type> {
+};
+
+}
+
+#endif // CPPRESTSDK_ROOT_CHAR_TRAITS_H
--- a/Release/tests/functional/streams/memstream_tests.cpp	(revision d17f091b5a753b33fb455e92b590fc9f4e921119)
+++ b/Release/tests/functional/streams/memstream_tests.cpp	(revision 6df13a8c0417ef700c0f164bcd0686ad46f66fd9)
@@ -8,6 +8,7 @@
  *
  * =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
  ****/
+#include "cpprest/details/char_traits.h"
 #include "stdafx.h"
 #if defined(__cplusplus_winrt)
 #include <wrl.h>
@@ -32,7 +33,7 @@
 {
     VERIFY_IS_TRUE(wbuf.can_write());
 
-    std::basic_string<typename StreamBufferType::char_type> s;
+    std::basic_string<typename StreamBufferType::char_type,typename utility::CanUseStdCharTraits<typename StreamBufferType::char_type>::TraitsType> s;
     s.push_back((typename StreamBufferType::char_type)0);
     s.push_back((typename StreamBufferType::char_type)1);
     s.push_back((typename StreamBufferType::char_type)2);
@@ -137,7 +138,7 @@
 {
     VERIFY_IS_TRUE(wbuf.can_write());
 
-    std::basic_string<typename StreamBufferType::char_type> s;
+    std::basic_string<typename StreamBufferType::char_type,typename utility::CanUseStdCharTraits<typename StreamBufferType::char_type>::TraitsType> s;
     s.push_back((typename StreamBufferType::char_type)0);
     s.push_back((typename StreamBufferType::char_type)1);
     s.push_back((typename StreamBufferType::char_type)2);
@@ -169,7 +170,7 @@
 
     typedef concurrency::streams::rawptr_buffer<CharType> StreamBufferType;
 
-    std::basic_string<CharType> s;
+    std::basic_string<CharType,typename CanUseStdCharTraits<CharType>::TraitsType> s;
     s.push_back((CharType)0);
     s.push_back((CharType)1);
     s.push_back((CharType)2);
@@ -198,7 +199,7 @@
     typedef concurrency::streams::container_buffer<CollectionType> StreamBufferType;
     typedef typename concurrency::streams::container_buffer<CollectionType>::char_type CharType;
 
-    std::basic_string<CharType> s;
+    std::basic_string<CharType, typename utility::CanUseStdCharTraits<CharType>::TraitsType> s;
     s.push_back((CharType)0);
     s.push_back((CharType)1);
     s.push_back((CharType)2);
@@ -553,7 +554,7 @@
     VERIFY_IS_TRUE(rwbuf.can_read());
     VERIFY_IS_TRUE(rwbuf.can_write());
     VERIFY_IS_FALSE(rwbuf.is_eof());
-    std::basic_string<typename StreamBufferType::char_type> s;
+    std::basic_string<typename StreamBufferType::char_type, typename utility::CanUseStdCharTraits<typename StreamBufferType::char_type>::TraitsType> s;
     s.push_back((typename StreamBufferType::char_type)0);
     s.push_back((typename StreamBufferType::char_type)1);
     s.push_back((typename StreamBufferType::char_type)2);
@@ -684,7 +685,7 @@
     VERIFY_IS_TRUE(rwbuf.can_write());
 
     // Write 4 characters
-    std::basic_string<typename StreamBufferType::char_type> s;
+    std::basic_string<typename StreamBufferType::char_type, typename utility::CanUseStdCharTraits<typename StreamBufferType::char_type>::TraitsType> s;
     s.push_back((typename StreamBufferType::char_type)0);
     s.push_back((typename StreamBufferType::char_type)1);
     s.push_back((typename StreamBufferType::char_type)2);
@@ -726,7 +727,7 @@
     VERIFY_IS_TRUE(rwbuf.can_write());
 
     // Write 4 characters
-    std::basic_string<typename StreamBufferType::char_type> s;
+    std::basic_string<typename StreamBufferType::char_type, typename utility::CanUseStdCharTraits<typename StreamBufferType::char_type>::TraitsType> s;
     s.push_back((typename StreamBufferType::char_type)0);
     s.push_back((typename StreamBufferType::char_type)1);
     s.push_back((typename StreamBufferType::char_type)2);
--- a/Release/tests/functional/streams/stdstream_tests.cpp	(revision d17f091b5a753b33fb455e92b590fc9f4e921119)
+++ b/Release/tests/functional/streams/stdstream_tests.cpp	(revision 6df13a8c0417ef700c0f164bcd0686ad46f66fd9)
@@ -13,6 +13,7 @@
 #include "cpprest/filestream.h"
 #include "cpprest/producerconsumerstream.h"
 #include "cpprest/rawptrstream.h"
+#include "cpprest/details/char_traits.h"
 
 #if (!defined(_WIN32) || !defined(CPPREST_EXCLUDE_WEBSOCKETS)) && !defined(__cplusplus_winrt)
 #include <boost/interprocess/streams/bufferstream.hpp>
@@ -303,7 +304,8 @@
 
         const std::streamsize iterations = 100;
 
-        const std::string the_alphabet("abcdefghijklmnopqrstuvwxyz");
+        const char *the_alphabet_characters = "abcdefghijklmnopqrstuvwxyz";
+        const std::basic_string<uint8_t,typename utility::CanUseStdCharTraits<uint8_t>::TraitsType> the_alphabet(reinterpret_cast<const uint8_t *>(the_alphabet_characters));
 
         auto writer = pplx::create_task([ostream, iterations, the_alphabet]() {
             auto os = ostream;
@@ -341,7 +343,8 @@
 
         const std::streamsize iterations = 100;
 
-        const std::string the_alphabet("abcdefghijklmnopqrstuvwxyz");
+        const char *the_alphabet_chars = "abcdefghijklmnopqrstuvwxyz";
+        const std::basic_string<uint8_t,typename CanUseStdCharTraits<uint8_t>::TraitsType> the_alphabet(reinterpret_cast<const uint8_t *>(the_alphabet_chars));
 
         auto writer = pplx::create_task([ostream, iterations, the_alphabet]() {
             auto os = ostream;