Modify XML encoder to hex-encode invalid UTF-8 sequences

There are still some holes, e.g. we leave surrogate pairs be
even though they are not a part of valid UTF-8, but this might
be for the better -- WTF-8 does support surrogate pairs inside
text.

Closes #1207

include/internal/catch_xmlwriter.cpp

@@ -7,51 +7,145 @@
 
 #include "catch_xmlwriter.h"
 
+#include "catch_enforce.h"
+
 #include <iomanip>
 
+using uchar = unsigned char;
+
 namespace Catch {
 
+namespace {
+
+    size_t trailingBytes(unsigned char c) {
+        if ((c & 0xE0) == 0xC0) {
+            return 2;
+        }
+        if ((c & 0xF0) == 0xE0) {
+            return 3;
+        }
+        if ((c & 0xF8) == 0xF0) {
+            return 4;
+        }
+        CATCH_INTERNAL_ERROR("Invalid multibyte utf-8 start byte encountered");
+    }
+
+    uint32_t headerValue(unsigned char c) {
+        if ((c & 0xE0) == 0xC0) {
+            return c & 0x1F;
+        }
+        if ((c & 0xF0) == 0xE0) {
+            return c & 0x0F;
+        }
+        if ((c & 0xF8) == 0xF0) {
+            return c & 0x07;
+        }
+        CATCH_INTERNAL_ERROR("Invalid multibyte utf-8 start byte encountered");
+    }
+
+    void hexEscapeChar(std::ostream& os, unsigned char c) {
+        os << "\\x"
+            << std::uppercase << std::hex << std::setfill('0') << std::setw(2)
+            << static_cast<int>(c);
+    }
+
+} // anonymous namespace
+
     XmlEncode::XmlEncode( std::string const& str, ForWhat forWhat )
     :   m_str( str ),
         m_forWhat( forWhat )
     {}
 
     void XmlEncode::encodeTo( std::ostream& os ) const {
-
         // Apostrophe escaping not necessary if we always use " to write attributes
         // (see: http://www.w3.org/TR/xml/#syntax)
 
-        for( std::size_t i = 0; i < m_str.size(); ++ i ) {
+        for( std::size_t idx = 0; idx < m_str.size(); ++ idx ) {
-            char c = m_str[i];
+            uchar c = m_str[idx];
-            switch( c ) {
+            switch (c) {
-                case '<':   os << "&lt;"; break;
+            case '<':   os << "&lt;"; break;
-                case '&':   os << "&amp;"; break;
+            case '&':   os << "&amp;"; break;
 
-                case '>':
+            case '>':
-                    // See: http://www.w3.org/TR/xml/#syntax
+                // See: http://www.w3.org/TR/xml/#syntax
-                    if( i > 2 && m_str[i-1] == ']' && m_str[i-2] == ']' )
+                if (idx > 2 && m_str[idx - 1] == ']' && m_str[idx - 2] == ']')
-                        os << "&gt;";
+                    os << "&gt;";
-                    else
+                else
-                        os << c;
+                    os << c;
+                break;
+
+            case '\"':
+                if (m_forWhat == ForAttributes)
+                    os << "&quot;";
+                else
+                    os << c;
+                break;
+
+            default:
+                // Check for control characters and invalid utf-8
+
+                // Escape control characters in standard ascii
+                // see http://stackoverflow.com/questions/404107/why-are-control-characters-illegal-in-xml-1-0
+                if (c < 0x09 || (c > 0x0D && c < 0x20) || c == 0x7F) {
+                    hexEscapeChar(os, c);
                     break;
+                }
 
-                case '\"':
+                // Plain ASCII: Write it to stream
-                    if( m_forWhat == ForAttributes )
+                if (c < 0x7F) {
-                        os << "&quot;";
+                    os << c;
-                    else
-                        os << c;
                     break;
+                }
 
-                default:
+                // UTF-8 territory
-                    // Escape control chars - based on contribution by @espenalb in PR #465 and
+                // Check if the encoding is valid and if it is not, hex escape bytes.
-                    // by @mrpi PR #588
+                // Important: We do not check the exact decoded values for validity, only the encoding format
-                    if ( ( c >= 0 && c < '\x09' ) || ( c > '\x0D' && c < '\x20') || c=='\x7F' ) {
+                // First check that this bytes is a valid lead byte:
-                        // see http://stackoverflow.com/questions/404107/why-are-control-characters-illegal-in-xml-1-0
+                // This means that it is not encoded as 1111 1XXX
-                        os << "\\x" << std::uppercase << std::hex << std::setfill('0') << std::setw(2)
+                // Or as 10XX XXXX
-                           << static_cast<int>( c );
+                if (c <  0xC0 ||
-                    }
+                    c >= 0xF8) {
-                    else
+                    hexEscapeChar(os, c);
-                        os << c;
+                    break;
+                }
+
+                auto encBytes = trailingBytes(c);
+                // Are there enough bytes left to avoid accessing out-of-bounds memory?
+                if (idx + encBytes - 1 >= m_str.size()) {
+                    hexEscapeChar(os, c);
+                    break;
+                }
+                // The header is valid, check data
+                // The next encBytes bytes must together be a valid utf-8
+                // This means: bitpattern 10XX XXXX and the extracted value is sane (ish)
+                bool valid = true;
+                uint32_t value = headerValue(c);
+                for (std::size_t n = 1; n < encBytes; ++n) {
+                    uchar nc = m_str[idx + n];
+                    valid &= ((nc & 0xC0) == 0x80);
+                    value = (value << 6) | (nc & 0x3F);
+                }
+
+                if (
+                    // Wrong bit pattern of following bytes
+                    (!valid) ||
+                    // Overlong encodings
+                    (value < 0x80) ||
+                    (0x80 <= value && value < 0x800   && encBytes > 2) ||
+                    (0x800 < value && value < 0x10000 && encBytes > 3) ||
+                    // Encoded value out of range
+                    (value >= 0x110000)
+                    ) {
+                    hexEscapeChar(os, c);
+                    break;
+                }
+
+                // If we got here, this is in fact a valid(ish) utf-8 sequence
+                for (std::size_t n = 0; n < encBytes; ++n) {
+                    os << m_str[idx + n];
+                }
+                idx += encBytes - 1;
+                break;
             }
         }
     }

projects/SelfTest/Baselines/compact.sw.approved.txt

@@ -905,6 +905,48 @@ Xml.tests.cpp:<line number>: passed: encode( stringWithQuotes, Catch::XmlEncode:
 "don't &quot;quote&quot; me on that"
 Xml.tests.cpp:<line number>: passed: encode( "[/x01]" ) == "[//x01]" for: "[/x01]" == "[/x01]"
 Xml.tests.cpp:<line number>: passed: encode( "[/x7F]" ) == "[//x7F]" for: "[/x7F]" == "[/x7F]"
+Xml.tests.cpp:<line number>: passed: encode(u8"Here be 👾") == u8"Here be 👾" for: "Here be 👾" == "Here be 👾"
+Xml.tests.cpp:<line number>: passed: encode(u8"šš") == u8"šš" for: "šš" == "šš"
+Xml.tests.cpp:<line number>: passed: encode("/xDF/xBF") == "/xDF/xBF" for: "߿" == "߿"
+Xml.tests.cpp:<line number>: passed: encode("/xE0/xA0/x80") == "/xE0/xA0/x80" for: "ࠀ" == "ࠀ"
+Xml.tests.cpp:<line number>: passed: encode("/xED/x9F/xBF") == "/xED/x9F/xBF" for: "퟿" == "퟿"
+Xml.tests.cpp:<line number>: passed: encode("/xEE/x80/x80") == "/xEE/x80/x80" for: "" == ""
+Xml.tests.cpp:<line number>: passed: encode("/xEF/xBF/xBF") == "/xEF/xBF/xBF" for: "￿" == "￿"
+Xml.tests.cpp:<line number>: passed: encode("/xF0/x90/x80/x80") == "/xF0/x90/x80/x80" for: "𐀀" == "𐀀"
+Xml.tests.cpp:<line number>: passed: encode("/xF4/x8F/xBF/xBF") == "/xF4/x8F/xBF/xBF" for: "􏿿" == "􏿿"
+Xml.tests.cpp:<line number>: passed: encode("Here /xFF be 👾") == u8"Here //xFF be 👾" for: "Here /xFF be 👾" == "Here /xFF be 👾"
+Xml.tests.cpp:<line number>: passed: encode("/xFF") == "//xFF" for: "/xFF" == "/xFF"
+Xml.tests.cpp:<line number>: passed: encode("/xC5/xC5/xA0") == u8"//xC5Š" for: "/xC5Š" == "/xC5Š"
+Xml.tests.cpp:<line number>: passed: encode("/xF4/x90/x80/x80") == u8"//xF4//x90//x80//x80" for: "/xF4/x90/x80/x80" == "/xF4/x90/x80/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xC0/x80") == u8"//xC0//x80" for: "/xC0/x80" == "/xC0/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF0/x80/x80/x80") == u8"//xF0//x80//x80//x80" for: "/xF0/x80/x80/x80" == "/xF0/x80/x80/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xC1/xBF") == u8"//xC1//xBF" for: "/xC1/xBF" == "/xC1/xBF"
+Xml.tests.cpp:<line number>: passed: encode("/xE0/x9F/xBF") == u8"//xE0//x9F//xBF" for: "/xE0/x9F/xBF" == "/xE0/x9F/xBF"
+Xml.tests.cpp:<line number>: passed: encode("/xF0/x8F/xBF/xBF") == u8"//xF0//x8F//xBF//xBF" for: "/xF0/x8F/xBF/xBF" == "/xF0/x8F/xBF/xBF"
+Xml.tests.cpp:<line number>: passed: encode("/xED/xA0/x80") == "/xED/xA0/x80" for: "<22><><EFBFBD>" == "<22><><EFBFBD>"
+Xml.tests.cpp:<line number>: passed: encode("/xED/xAF/xBF") == "/xED/xAF/xBF" for: "<22><><EFBFBD>" == "<22><><EFBFBD>"
+Xml.tests.cpp:<line number>: passed: encode("/xED/xB0/x80") == "/xED/xB0/x80" for: "<22><><EFBFBD>" == "<22><><EFBFBD>"
+Xml.tests.cpp:<line number>: passed: encode("/xED/xBF/xBF") == "/xED/xBF/xBF" for: "<22><><EFBFBD>" == "<22><><EFBFBD>"
+Xml.tests.cpp:<line number>: passed: encode("/x80") == u8"//x80" for: "/x80" == "/x80"
+Xml.tests.cpp:<line number>: passed: encode("/x81") == u8"//x81" for: "/x81" == "/x81"
+Xml.tests.cpp:<line number>: passed: encode("/xBC") == u8"//xBC" for: "/xBC" == "/xBC"
+Xml.tests.cpp:<line number>: passed: encode("/xBF") == u8"//xBF" for: "/xBF" == "/xBF"
+Xml.tests.cpp:<line number>: passed: encode("/xF5/x80/x80/x80") == u8"//xF5//x80//x80//x80" for: "/xF5/x80/x80/x80" == "/xF5/x80/x80/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF6/x80/x80/x80") == u8"//xF6//x80//x80//x80" for: "/xF6/x80/x80/x80" == "/xF6/x80/x80/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF7/x80/x80/x80") == u8"//xF7//x80//x80//x80" for: "/xF7/x80/x80/x80" == "/xF7/x80/x80/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xDE") == u8"//xDE" for: "/xDE" == "/xDE"
+Xml.tests.cpp:<line number>: passed: encode("/xDF") == u8"//xDF" for: "/xDF" == "/xDF"
+Xml.tests.cpp:<line number>: passed: encode("/xE0") == u8"//xE0" for: "/xE0" == "/xE0"
+Xml.tests.cpp:<line number>: passed: encode("/xEF") == u8"//xEF" for: "/xEF" == "/xEF"
+Xml.tests.cpp:<line number>: passed: encode("/xF0") == u8"//xF0" for: "/xF0" == "/xF0"
+Xml.tests.cpp:<line number>: passed: encode("/xF4") == u8"//xF4" for: "/xF4" == "/xF4"
+Xml.tests.cpp:<line number>: passed: encode("/xE0/x80") == u8"//xE0//x80" for: "/xE0/x80" == "/xE0/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xE0/xBF") == u8"//xE0//xBF" for: "/xE0/xBF" == "/xE0/xBF"
+Xml.tests.cpp:<line number>: passed: encode("/xE1/x80") == u8"//xE1//x80" for: "/xE1/x80" == "/xE1/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF0/x80") == u8"//xF0//x80" for: "/xF0/x80" == "/xF0/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF4/x80") == u8"//xF4//x80" for: "/xF4/x80" == "/xF4/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF0/x80/x80") == u8"//xF0//x80//x80" for: "/xF0/x80/x80" == "/xF0/x80/x80"
+Xml.tests.cpp:<line number>: passed: encode("/xF4/x80/x80") == u8"//xF4//x80//x80" for: "/xF4/x80/x80" == "/xF4/x80/x80"
 ToStringVector.tests.cpp:<line number>: passed: Catch::Detail::stringify( empty ) == "{  }" for: "{  }" == "{  }"
 ToStringVector.tests.cpp:<line number>: passed: Catch::Detail::stringify( oneValue ) == "{ 42 }" for: "{ 42 }" == "{ 42 }"
 ToStringVector.tests.cpp:<line number>: passed: Catch::Detail::stringify( twoValues ) == "{ 42, 250 }" for: "{ 42, 250 }" == "{ 42, 250 }"

projects/SelfTest/Baselines/console.std.approved.txt

@@ -1084,6 +1084,6 @@ due to unexpected exception with message:
   Why would you throw a std::string?
 
 ===============================================================================
-test cases:  202 | 149 passed |  49 failed |  4 failed as expected
+test cases:  203 | 150 passed |  49 failed |  4 failed as expected
-assertions: 1015 | 887 passed | 107 failed | 21 failed as expected
+assertions: 1057 | 929 passed | 107 failed | 21 failed as expected
 

projects/SelfTest/Baselines/console.sw.approved.txt

@@ -7112,6 +7112,305 @@ PASSED:
 with expansion:
   "[\x7F]" == "[\x7F]"
 
+-------------------------------------------------------------------------------
+XmlEncode: UTF-8
+  Valid utf-8 strings
+-------------------------------------------------------------------------------
+Xml.tests.cpp:<line number>
+...............................................................................
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode(u8"Here be 👾") == u8"Here be 👾" )
+with expansion:
+  "Here be 👾" == "Here be 👾"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode(u8"šš") == u8"šš" )
+with expansion:
+  "šš" == "šš"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xDF\xBF") == "\xDF\xBF" )
+with expansion:
+  "߿" == "߿"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xE0\xA0\x80") == "\xE0\xA0\x80" )
+with expansion:
+  "ࠀ" == "ࠀ"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xED\x9F\xBF") == "\xED\x9F\xBF" )
+with expansion:
+  "퟿" == "퟿"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xEE\x80\x80") == "\xEE\x80\x80" )
+with expansion:
+  "" == ""
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xEF\xBF\xBF") == "\xEF\xBF\xBF" )
+with expansion:
+  "￿" == "￿"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF0\x90\x80\x80") == "\xF0\x90\x80\x80" )
+with expansion:
+  "𐀀" == "𐀀"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF4\x8F\xBF\xBF") == "\xF4\x8F\xBF\xBF" )
+with expansion:
+  "􏿿" == "􏿿"
+
+-------------------------------------------------------------------------------
+XmlEncode: UTF-8
+  Invalid utf-8 strings
+  Various broken strings
+-------------------------------------------------------------------------------
+Xml.tests.cpp:<line number>
+...............................................................................
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("Here \xFF be 👾") == u8"Here \\xFF be 👾" )
+with expansion:
+  "Here \xFF be 👾" == "Here \xFF be 👾"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xFF") == "\\xFF" )
+with expansion:
+  "\xFF" == "\xFF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xC5\xC5\xA0") == u8"\\xC5Š" )
+with expansion:
+  "\xC5Š" == "\xC5Š"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF4\x90\x80\x80") == u8"\\xF4\\x90\\x80\\x80" )
+with expansion:
+  "\xF4\x90\x80\x80" == "\xF4\x90\x80\x80"
+
+-------------------------------------------------------------------------------
+XmlEncode: UTF-8
+  Invalid utf-8 strings
+  Overlong encodings
+-------------------------------------------------------------------------------
+Xml.tests.cpp:<line number>
+...............................................................................
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xC0\x80") == u8"\\xC0\\x80" )
+with expansion:
+  "\xC0\x80" == "\xC0\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF0\x80\x80\x80") == u8"\\xF0\\x80\\x80\\x80" )
+with expansion:
+  "\xF0\x80\x80\x80" == "\xF0\x80\x80\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xC1\xBF") == u8"\\xC1\\xBF" )
+with expansion:
+  "\xC1\xBF" == "\xC1\xBF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xE0\x9F\xBF") == u8"\\xE0\\x9F\\xBF" )
+with expansion:
+  "\xE0\x9F\xBF" == "\xE0\x9F\xBF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF0\x8F\xBF\xBF") == u8"\\xF0\\x8F\\xBF\\xBF" )
+with expansion:
+  "\xF0\x8F\xBF\xBF" == "\xF0\x8F\xBF\xBF"
+
+-------------------------------------------------------------------------------
+XmlEncode: UTF-8
+  Invalid utf-8 strings
+  Surrogate pairs
+-------------------------------------------------------------------------------
+Xml.tests.cpp:<line number>
+...............................................................................
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xED\xA0\x80") == "\xED\xA0\x80" )
+with expansion:
+  "<22><><EFBFBD>" == "<22><><EFBFBD>"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xED\xAF\xBF") == "\xED\xAF\xBF" )
+with expansion:
+  "<22><><EFBFBD>" == "<22><><EFBFBD>"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xED\xB0\x80") == "\xED\xB0\x80" )
+with expansion:
+  "<22><><EFBFBD>" == "<22><><EFBFBD>"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xED\xBF\xBF") == "\xED\xBF\xBF" )
+with expansion:
+  "<22><><EFBFBD>" == "<22><><EFBFBD>"
+
+-------------------------------------------------------------------------------
+XmlEncode: UTF-8
+  Invalid utf-8 strings
+  Invalid start byte
+-------------------------------------------------------------------------------
+Xml.tests.cpp:<line number>
+...............................................................................
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\x80") == u8"\\x80" )
+with expansion:
+  "\x80" == "\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\x81") == u8"\\x81" )
+with expansion:
+  "\x81" == "\x81"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xBC") == u8"\\xBC" )
+with expansion:
+  "\xBC" == "\xBC"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xBF") == u8"\\xBF" )
+with expansion:
+  "\xBF" == "\xBF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF5\x80\x80\x80") == u8"\\xF5\\x80\\x80\\x80" )
+with expansion:
+  "\xF5\x80\x80\x80" == "\xF5\x80\x80\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF6\x80\x80\x80") == u8"\\xF6\\x80\\x80\\x80" )
+with expansion:
+  "\xF6\x80\x80\x80" == "\xF6\x80\x80\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF7\x80\x80\x80") == u8"\\xF7\\x80\\x80\\x80" )
+with expansion:
+  "\xF7\x80\x80\x80" == "\xF7\x80\x80\x80"
+
+-------------------------------------------------------------------------------
+XmlEncode: UTF-8
+  Invalid utf-8 strings
+  Missing continuation byte(s)
+-------------------------------------------------------------------------------
+Xml.tests.cpp:<line number>
+...............................................................................
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xDE") == u8"\\xDE" )
+with expansion:
+  "\xDE" == "\xDE"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xDF") == u8"\\xDF" )
+with expansion:
+  "\xDF" == "\xDF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xE0") == u8"\\xE0" )
+with expansion:
+  "\xE0" == "\xE0"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xEF") == u8"\\xEF" )
+with expansion:
+  "\xEF" == "\xEF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF0") == u8"\\xF0" )
+with expansion:
+  "\xF0" == "\xF0"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF4") == u8"\\xF4" )
+with expansion:
+  "\xF4" == "\xF4"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xE0\x80") == u8"\\xE0\\x80" )
+with expansion:
+  "\xE0\x80" == "\xE0\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xE0\xBF") == u8"\\xE0\\xBF" )
+with expansion:
+  "\xE0\xBF" == "\xE0\xBF"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xE1\x80") == u8"\\xE1\\x80" )
+with expansion:
+  "\xE1\x80" == "\xE1\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF0\x80") == u8"\\xF0\\x80" )
+with expansion:
+  "\xF0\x80" == "\xF0\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF4\x80") == u8"\\xF4\\x80" )
+with expansion:
+  "\xF4\x80" == "\xF4\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF0\x80\x80") == u8"\\xF0\\x80\\x80" )
+with expansion:
+  "\xF0\x80\x80" == "\xF0\x80\x80"
+
+Xml.tests.cpp:<line number>:
+PASSED:
+  CHECK( encode("\xF4\x80\x80") == u8"\\xF4\\x80\\x80" )
+with expansion:
+  "\xF4\x80\x80" == "\xF4\x80\x80"
+
 -------------------------------------------------------------------------------
 array<int, N> -> toString
 -------------------------------------------------------------------------------
@@ -8598,6 +8897,6 @@ Misc.tests.cpp:<line number>:
 PASSED:
 
 ===============================================================================
-test cases:  202 | 136 passed |  62 failed |  4 failed as expected
+test cases:  203 | 137 passed |  62 failed |  4 failed as expected
-assertions: 1029 | 887 passed | 121 failed | 21 failed as expected
+assertions: 1071 | 929 passed | 121 failed | 21 failed as expected
 

projects/SelfTest/Baselines/junit.sw.approved.txt

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuitesloose text artifact
 >
-  <testsuite name="<exe-name>" errors="17" failures="105" tests="1030" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="105" tests="1072" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <testcase classname="<exe-name>.global" name="# A test name that starts with a #" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="#1005: Comparing pointer to int and long (NULL can be either on various systems)" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="#1027" time="{duration}"/>
@@ -706,6 +706,12 @@ Exception.tests.cpp:<line number>
     <testcase classname="<exe-name>.global" name="XmlEncode/string with quotes" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="XmlEncode/string with control char (1)" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="XmlEncode/string with control char (x7F)" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="XmlEncode: UTF-8/Valid utf-8 strings" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="XmlEncode: UTF-8/Invalid utf-8 strings/Various broken strings" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="XmlEncode: UTF-8/Invalid utf-8 strings/Overlong encodings" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="XmlEncode: UTF-8/Invalid utf-8 strings/Surrogate pairs" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="XmlEncode: UTF-8/Invalid utf-8 strings/Invalid start byte" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="XmlEncode: UTF-8/Invalid utf-8 strings/Missing continuation byte(s)" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="array&lt;int, N> -> toString" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="atomic if" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="boolean member" time="{duration}"/>

projects/SelfTest/Baselines/xml.sw.approved.txt

@@ -7881,7 +7881,7 @@ Message from section two
     <TestCase name="X/level/1/b" tags="[Tricky]" filename="projects/<exe-name>/UsageTests/Tricky.tests.cpp" >
       <OverallResult success="true"/>
     </TestCase>
-    <TestCase name="XmlEncode" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+    <TestCase name="XmlEncode" tags="[XML]" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
       <Section name="normal string" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
         <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
           <Original>
@@ -7994,6 +7994,378 @@ Message from section two
       </Section>
       <OverallResult success="true"/>
     </TestCase>
+    <TestCase name="XmlEncode: UTF-8" tags="[UTF-8][XML]" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+      <Section name="Valid utf-8 strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode(u8"Here be 👾") == u8"Here be 👾"
+          </Original>
+          <Expanded>
+            "Here be 👾" == "Here be 👾"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode(u8"šš") == u8"šš"
+          </Original>
+          <Expanded>
+            "šš" == "šš"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xDF\xBF") == "\xDF\xBF"
+          </Original>
+          <Expanded>
+            "߿" == "߿"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xE0\xA0\x80") == "\xE0\xA0\x80"
+          </Original>
+          <Expanded>
+            "ࠀ" == "ࠀ"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xED\x9F\xBF") == "\xED\x9F\xBF"
+          </Original>
+          <Expanded>
+            "퟿" == "퟿"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xEE\x80\x80") == "\xEE\x80\x80"
+          </Original>
+          <Expanded>
+            "" == ""
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xEF\xBF\xBF") == "\xEF\xBF\xBF"
+          </Original>
+          <Expanded>
+            "￿" == "￿"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xF0\x90\x80\x80") == "\xF0\x90\x80\x80"
+          </Original>
+          <Expanded>
+            "𐀀" == "𐀀"
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Original>
+            encode("\xF4\x8F\xBF\xBF") == "\xF4\x8F\xBF\xBF"
+          </Original>
+          <Expanded>
+            "􏿿" == "􏿿"
+          </Expanded>
+        </Expression>
+        <OverallResults successes="9" failures="0" expectedFailures="0"/>
+      </Section>
+      <Section name="Invalid utf-8 strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+        <Section name="Various broken strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("Here \xFF be 👾") == u8"Here \\xFF be 👾"
+            </Original>
+            <Expanded>
+              "Here \xFF be 👾" == "Here \xFF be 👾"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xFF") == "\\xFF"
+            </Original>
+            <Expanded>
+              "\xFF" == "\xFF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xC5\xC5\xA0") == u8"\\xC5Š"
+            </Original>
+            <Expanded>
+              "\xC5Š" == "\xC5Š"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF4\x90\x80\x80") == u8"\\xF4\\x90\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF4\x90\x80\x80" == "\xF4\x90\x80\x80"
+            </Expanded>
+          </Expression>
+          <OverallResults successes="4" failures="0" expectedFailures="0"/>
+        </Section>
+        <OverallResults successes="4" failures="0" expectedFailures="0"/>
+      </Section>
+      <Section name="Invalid utf-8 strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+        <Section name="Overlong encodings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xC0\x80") == u8"\\xC0\\x80"
+            </Original>
+            <Expanded>
+              "\xC0\x80" == "\xC0\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF0\x80\x80\x80") == u8"\\xF0\\x80\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF0\x80\x80\x80" == "\xF0\x80\x80\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xC1\xBF") == u8"\\xC1\\xBF"
+            </Original>
+            <Expanded>
+              "\xC1\xBF" == "\xC1\xBF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xE0\x9F\xBF") == u8"\\xE0\\x9F\\xBF"
+            </Original>
+            <Expanded>
+              "\xE0\x9F\xBF" == "\xE0\x9F\xBF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF0\x8F\xBF\xBF") == u8"\\xF0\\x8F\\xBF\\xBF"
+            </Original>
+            <Expanded>
+              "\xF0\x8F\xBF\xBF" == "\xF0\x8F\xBF\xBF"
+            </Expanded>
+          </Expression>
+          <OverallResults successes="5" failures="0" expectedFailures="0"/>
+        </Section>
+        <OverallResults successes="5" failures="0" expectedFailures="0"/>
+      </Section>
+      <Section name="Invalid utf-8 strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+        <Section name="Surrogate pairs" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xED\xA0\x80") == "\xED\xA0\x80"
+            </Original>
+            <Expanded>
+              "<22><><EFBFBD>" == "<22><><EFBFBD>"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xED\xAF\xBF") == "\xED\xAF\xBF"
+            </Original>
+            <Expanded>
+              "<22><><EFBFBD>" == "<22><><EFBFBD>"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xED\xB0\x80") == "\xED\xB0\x80"
+            </Original>
+            <Expanded>
+              "<22><><EFBFBD>" == "<22><><EFBFBD>"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xED\xBF\xBF") == "\xED\xBF\xBF"
+            </Original>
+            <Expanded>
+              "<22><><EFBFBD>" == "<22><><EFBFBD>"
+            </Expanded>
+          </Expression>
+          <OverallResults successes="4" failures="0" expectedFailures="0"/>
+        </Section>
+        <OverallResults successes="4" failures="0" expectedFailures="0"/>
+      </Section>
+      <Section name="Invalid utf-8 strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+        <Section name="Invalid start byte" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\x80") == u8"\\x80"
+            </Original>
+            <Expanded>
+              "\x80" == "\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\x81") == u8"\\x81"
+            </Original>
+            <Expanded>
+              "\x81" == "\x81"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xBC") == u8"\\xBC"
+            </Original>
+            <Expanded>
+              "\xBC" == "\xBC"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xBF") == u8"\\xBF"
+            </Original>
+            <Expanded>
+              "\xBF" == "\xBF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF5\x80\x80\x80") == u8"\\xF5\\x80\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF5\x80\x80\x80" == "\xF5\x80\x80\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF6\x80\x80\x80") == u8"\\xF6\\x80\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF6\x80\x80\x80" == "\xF6\x80\x80\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF7\x80\x80\x80") == u8"\\xF7\\x80\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF7\x80\x80\x80" == "\xF7\x80\x80\x80"
+            </Expanded>
+          </Expression>
+          <OverallResults successes="7" failures="0" expectedFailures="0"/>
+        </Section>
+        <OverallResults successes="7" failures="0" expectedFailures="0"/>
+      </Section>
+      <Section name="Invalid utf-8 strings" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+        <Section name="Missing continuation byte(s)" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xDE") == u8"\\xDE"
+            </Original>
+            <Expanded>
+              "\xDE" == "\xDE"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xDF") == u8"\\xDF"
+            </Original>
+            <Expanded>
+              "\xDF" == "\xDF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xE0") == u8"\\xE0"
+            </Original>
+            <Expanded>
+              "\xE0" == "\xE0"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xEF") == u8"\\xEF"
+            </Original>
+            <Expanded>
+              "\xEF" == "\xEF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF0") == u8"\\xF0"
+            </Original>
+            <Expanded>
+              "\xF0" == "\xF0"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF4") == u8"\\xF4"
+            </Original>
+            <Expanded>
+              "\xF4" == "\xF4"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xE0\x80") == u8"\\xE0\\x80"
+            </Original>
+            <Expanded>
+              "\xE0\x80" == "\xE0\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xE0\xBF") == u8"\\xE0\\xBF"
+            </Original>
+            <Expanded>
+              "\xE0\xBF" == "\xE0\xBF"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xE1\x80") == u8"\\xE1\\x80"
+            </Original>
+            <Expanded>
+              "\xE1\x80" == "\xE1\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF0\x80") == u8"\\xF0\\x80"
+            </Original>
+            <Expanded>
+              "\xF0\x80" == "\xF0\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF4\x80") == u8"\\xF4\\x80"
+            </Original>
+            <Expanded>
+              "\xF4\x80" == "\xF4\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF0\x80\x80") == u8"\\xF0\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF0\x80\x80" == "\xF0\x80\x80"
+            </Expanded>
+          </Expression>
+          <Expression success="true" type="CHECK" filename="projects/<exe-name>/IntrospectiveTests/Xml.tests.cpp" >
+            <Original>
+              encode("\xF4\x80\x80") == u8"\\xF4\\x80\\x80"
+            </Original>
+            <Expanded>
+              "\xF4\x80\x80" == "\xF4\x80\x80"
+            </Expanded>
+          </Expression>
+          <OverallResults successes="13" failures="0" expectedFailures="0"/>
+        </Section>
+        <OverallResults successes="13" failures="0" expectedFailures="0"/>
+      </Section>
+      <OverallResult success="true"/>
+    </TestCase>
     <TestCase name="array&lt;int, N> -> toString" tags="[array][containers][toString]" filename="projects/<exe-name>/UsageTests/ToStringVector.tests.cpp" >
       <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/UsageTests/ToStringVector.tests.cpp" >
         <Original>
@@ -9469,7 +9841,7 @@ loose text artifact
       </Section>
       <OverallResult success="true"/>
     </TestCase>
-    <OverallResults successes="887" failures="122" expectedFailures="21"/>
+    <OverallResults successes="929" failures="122" expectedFailures="21"/>
   </Group>
-  <OverallResults successes="887" failures="121" expectedFailures="21"/>
+  <OverallResults successes="929" failures="121" expectedFailures="21"/>
 </Catch>

projects/SelfTest/IntrospectiveTests/Xml.tests.cpp

@@ -1,5 +1,4 @@
 #include "catch.hpp"
-
 #include "internal/catch_xmlwriter.h"
 
 #include <sstream>
@@ -10,7 +9,7 @@ inline std::string encode( std::string const& str, Catch::XmlEncode::ForWhat for
     return oss.str();
 }
 
-TEST_CASE( "XmlEncode" ) {
+TEST_CASE( "XmlEncode", "[XML]" ) {
     SECTION( "normal string" ) {
         REQUIRE( encode( "normal string" ) == "normal string" );
     }
@@ -39,3 +38,75 @@ TEST_CASE( "XmlEncode" ) {
         REQUIRE( encode( "[\x7F]" ) == "[\\x7F]" );
     }
 }
+
+// Thanks to Peter Bindels (dascandy) for some of the tests
+TEST_CASE("XmlEncode: UTF-8", "[XML][UTF-8]") {
+    SECTION("Valid utf-8 strings") {
+        CHECK(encode(u8"Here be 👾") == u8"Here be 👾");
+        CHECK(encode(u8"šš") == u8"šš");
+
+        CHECK(encode("\xDF\xBF")         == "\xDF\xBF"); // 0x7FF
+        CHECK(encode("\xE0\xA0\x80")     == "\xE0\xA0\x80"); // 0x800
+        CHECK(encode("\xED\x9F\xBF")     == "\xED\x9F\xBF"); // 0xD7FF
+        CHECK(encode("\xEE\x80\x80")     == "\xEE\x80\x80"); // 0xE000
+        CHECK(encode("\xEF\xBF\xBF")     == "\xEF\xBF\xBF"); // 0xFFFF
+        CHECK(encode("\xF0\x90\x80\x80") == "\xF0\x90\x80\x80"); // 0x10000
+        CHECK(encode("\xF4\x8F\xBF\xBF") == "\xF4\x8F\xBF\xBF"); // 0x10FFFF
+    }
+    SECTION("Invalid utf-8 strings") {
+        SECTION("Various broken strings") {
+            CHECK(encode("Here \xFF be 👾") == u8"Here \\xFF be 👾");
+            CHECK(encode("\xFF") == "\\xFF");
+            CHECK(encode("\xC5\xC5\xA0") == u8"\\xC5Š");
+            CHECK(encode("\xF4\x90\x80\x80") == u8"\\xF4\\x90\\x80\\x80"); // 0x110000 -- out of unicode range
+        }
+
+        SECTION("Overlong encodings") {
+            CHECK(encode("\xC0\x80") == u8"\\xC0\\x80"); // \0
+            CHECK(encode("\xF0\x80\x80\x80") == u8"\\xF0\\x80\\x80\\x80"); // Super-over-long \0
+            CHECK(encode("\xC1\xBF") == u8"\\xC1\\xBF"); // ASCII char as UTF-8 (0x7F)
+            CHECK(encode("\xE0\x9F\xBF") == u8"\\xE0\\x9F\\xBF"); // 0x7FF
+            CHECK(encode("\xF0\x8F\xBF\xBF") == u8"\\xF0\\x8F\\xBF\\xBF"); // 0xFFFF
+        }
+
+        // Note that we actually don't modify surrogate pairs, as we do not do strict checking
+        SECTION("Surrogate pairs") {
+            CHECK(encode("\xED\xA0\x80") == "\xED\xA0\x80"); // Invalid surrogate half 0xD800
+            CHECK(encode("\xED\xAF\xBF") == "\xED\xAF\xBF"); // Invalid surrogate half 0xDBFF
+            CHECK(encode("\xED\xB0\x80") == "\xED\xB0\x80"); // Invalid surrogate half 0xDC00
+            CHECK(encode("\xED\xBF\xBF") == "\xED\xBF\xBF"); // Invalid surrogate half 0xDFFF
+        }
+
+        SECTION("Invalid start byte") {
+            CHECK(encode("\x80") == u8"\\x80");
+            CHECK(encode("\x81") == u8"\\x81");
+            CHECK(encode("\xBC") == u8"\\xBC");
+            CHECK(encode("\xBF") == u8"\\xBF");
+            // Out of range
+            CHECK(encode("\xF5\x80\x80\x80") == u8"\\xF5\\x80\\x80\\x80");
+            CHECK(encode("\xF6\x80\x80\x80") == u8"\\xF6\\x80\\x80\\x80");
+            CHECK(encode("\xF7\x80\x80\x80") == u8"\\xF7\\x80\\x80\\x80");
+        }
+
+        SECTION("Missing continuation byte(s)") {
+            // Missing first continuation byte
+            CHECK(encode("\xDE") == u8"\\xDE");
+            CHECK(encode("\xDF") == u8"\\xDF");
+            CHECK(encode("\xE0") == u8"\\xE0");
+            CHECK(encode("\xEF") == u8"\\xEF");
+            CHECK(encode("\xF0") == u8"\\xF0");
+            CHECK(encode("\xF4") == u8"\\xF4");
+
+            // Missing second continuation byte
+            CHECK(encode("\xE0\x80") == u8"\\xE0\\x80");
+            CHECK(encode("\xE0\xBF") == u8"\\xE0\\xBF");
+            CHECK(encode("\xE1\x80") == u8"\\xE1\\x80");
+            CHECK(encode("\xF0\x80") == u8"\\xF0\\x80");
+            CHECK(encode("\xF4\x80") == u8"\\xF4\\x80");
+
+            // Missing third continuation byte
+            CHECK(encode("\xF0\x80\x80") == u8"\\xF0\\x80\\x80");
+            CHECK(encode("\xF4\x80\x80") == u8"\\xF4\\x80\\x80");
+        }
+    }
+}