Add status-reporting transcoders to QUtil

ChangeLog

@@ -14,6 +14,11 @@
 	the first bug in qpdf's history that could result in silent loss
 	of data when processing a correct input file. Fixes #276.
 
+2019-01-14  Jay Berkenbilt  <ejb@ql.org>
+
+	* Add versions of utf8 to single-byte character transcoders that
+	return a success code.
+
 2019-01-13  Jay Berkenbilt  <ejb@ql.org>
 
 	* Add several more string transcoding and analysis methods to

include/qpdf/QUtil.hh

@@ -178,6 +178,22 @@ namespace QUtil
     std::string utf8_to_pdf_doc(
         std::string const& utf8, char unknown_char = '?');
 
+    // These versions return true if the conversion was successful and
+    // false if any unrepresentable characters were found and had to
+    // be substituted with the unknown character.
+    QPDF_DLL
+    bool utf8_to_ascii(
+        std::string const& utf8, std::string& ascii, char unknown_char = '?');
+    QPDF_DLL
+    bool utf8_to_win_ansi(
+        std::string const& utf8, std::string& win, char unknown_char = '?');
+    QPDF_DLL
+    bool utf8_to_mac_roman(
+        std::string const& utf8, std::string& mac, char unknown_char = '?');
+    QPDF_DLL
+    bool utf8_to_pdf_doc(
+        std::string const& utf8, std::string& pdfdoc, char unknown_char = '?');
+
     // Convert a UTF-16 big-endian encoded string to UTF-8.
     // Unrepresentable code points are converted to U+FFFD.
     QPDF_DLL

libqpdf/QUtil.cc

@@ -1705,11 +1705,12 @@ unsigned long get_next_utf8_codepoint(
     return codepoint;
 }
 
-static std::string
-transcode_utf8(std::string const& utf8_val, encoding_e encoding,
-               char unknown)
+static bool
+transcode_utf8(std::string const& utf8_val, std::string& result,
+               encoding_e encoding, char unknown)
 {
-    std::string result;
+    bool okay = true;
+    result.clear();
     if (encoding == e_utf16)
     {
         result += "\xfe\xff";
@@ -1721,6 +1722,7 @@ transcode_utf8(std::string const& utf8_val, encoding_e encoding,
         unsigned long codepoint = get_next_utf8_codepoint(utf8_val, i, error);
         if (error)
         {
+            okay = false;
             if (encoding == e_utf16)
             {
                 result += "\xff\xfd";
@@ -1768,11 +1770,21 @@ transcode_utf8(std::string const& utf8_val, encoding_e encoding,
             }
             if (ch == '\0')
             {
+                okay = false;
                 ch = static_cast<unsigned char>(unknown);
             }
             result.append(1, ch);
         }
     }
+    return okay;
+}
+
+static std::string
+transcode_utf8(std::string const& utf8_val, encoding_e encoding,
+               char unknown)
+{
+    std::string result;
+    transcode_utf8(utf8_val, result, encoding, unknown);
     return result;
 }
 
@@ -1806,6 +1818,34 @@ QUtil::utf8_to_pdf_doc(std::string const& utf8, char unknown_char)
     return transcode_utf8(utf8, e_pdfdoc, unknown_char);
 }
 
+bool
+QUtil::utf8_to_ascii(std::string const& utf8, std::string& ascii,
+                     char unknown_char)
+{
+    return transcode_utf8(utf8, ascii, e_ascii, unknown_char);
+}
+
+bool
+QUtil::utf8_to_win_ansi(std::string const& utf8, std::string& win,
+                        char unknown_char)
+{
+    return transcode_utf8(utf8, win, e_winansi, unknown_char);
+}
+
+bool
+QUtil::utf8_to_mac_roman(std::string const& utf8, std::string& mac,
+                         char unknown_char)
+{
+    return transcode_utf8(utf8, mac, e_macroman, unknown_char);
+}
+
+bool
+QUtil::utf8_to_pdf_doc(std::string const& utf8, std::string& pdfdoc,
+                       char unknown_char)
+{
+    return transcode_utf8(utf8, pdfdoc, e_pdfdoc, unknown_char);
+}
+
 bool
 QUtil::is_utf16(std::string const& val)
 {

libtests/qutil.cc

@@ -292,6 +292,22 @@ void transcoding_test()
     check_analyze("pi != 22/7", false, false, false);
     check_analyze(std::string("\xfe\xff\00\x51", 4), true, false, true);
     std::cout << "analysis done" << std::endl;
+    std::string input1("a\302\277b");
+    std::string input2("a\317\200b");
+    std::string input3("ab");
+    std::string output;
+    assert(! QUtil::utf8_to_ascii(input1, output));
+    assert(! QUtil::utf8_to_ascii(input2, output));
+    assert(QUtil::utf8_to_ascii(input3, output));
+    assert(QUtil::utf8_to_win_ansi(input1, output));
+    assert(! QUtil::utf8_to_win_ansi(input2, output));
+    assert(QUtil::utf8_to_win_ansi(input3, output));
+    assert(QUtil::utf8_to_mac_roman(input1, output));
+    assert(! QUtil::utf8_to_mac_roman(input2, output));
+    assert(QUtil::utf8_to_mac_roman(input3, output));
+    assert(QUtil::utf8_to_pdf_doc(input1, output));
+    assert(! QUtil::utf8_to_pdf_doc(input2, output));
+    assert(QUtil::utf8_to_pdf_doc(input3, output));
 }
 
 void print_whoami(char const* str)