Add QUtil::hex_decode

include/qpdf/QUtil.hh

@@ -104,6 +104,14 @@ namespace QUtil
     QPDF_DLL
     std::string hex_encode(std::string const&);
 
+    // Returns a string that is the result of decoding the input
+    // string. The input string may consist of mixed case hexadecimal
+    // digits. Any characters that are not hexadecimal digits will be
+    // silently ignored. If there are an odd number of hexadecimal
+    // digits, a trailing 0 will be assumed.
+    QPDF_DLL
+    std::string hex_decode(std::string const&);
+
     // Set stdin, stdout to binary mode
     QPDF_DLL
     void binary_stdout();

libqpdf/QUtil.cc

@@ -290,6 +290,50 @@ QUtil::hex_encode(std::string const& input)
     return result;
 }
 
+std::string
+QUtil::hex_decode(std::string const& input)
+{
+    std::string result;
+    size_t pos = 0;
+    for (std::string::const_iterator p = input.begin(); p != input.end(); ++p)
+    {
+        char ch = *p;
+        bool skip = false;
+        if ((*p >= 'A') && (*p <= 'F'))
+        {
+            ch -= 'A';
+            ch += 10;
+        }
+        else if ((*p >= 'a') && (*p <= 'f'))
+        {
+            ch -= 'a';
+            ch += 10;
+        }
+        else if ((*p >= '0') && (*p <= '9'))
+        {
+            ch -= '0';
+        }
+        else
+        {
+            skip = true;
+        }
+        if (! skip)
+        {
+            if (pos == 0)
+            {
+                result.push_back(ch << 4);
+                pos = 1;
+            }
+            else
+            {
+                result.back() += ch;
+                pos = 0;
+            }
+        }
+    }
+    return result;
+}
+
 void
 QUtil::binary_stdout()
 {

libtests/qutil.cc

@@ -247,6 +247,44 @@ void read_lines_from_file_test()
     }
 }
 
+void assert_hex_encode(std::string const& input, std::string const& expected)
+{
+    std::string actual = QUtil::hex_encode(input);
+    if (expected != actual)
+    {
+        std::cout << "hex encode " << input
+                  << ": expected = " << expected
+                  << "; actual = " << actual
+                  << std::endl;
+    }
+}
+
+void assert_hex_decode(std::string const& input, std::string const& expected)
+{
+    std::string actual = QUtil::hex_decode(input);
+    if (expected != actual)
+    {
+        std::cout << "hex encode " << input
+                  << ": expected = " << expected
+                  << "; actual = " << actual
+                  << std::endl;
+    }
+}
+
+void hex_encode_decode_test()
+{
+    std::cout << "begin hex encode/decode\n";
+    assert_hex_encode("", "");
+    assert_hex_encode("Potato", "506f7461746f");
+    std::string with_null("a\367" "00w");
+    with_null[3] = '\0';
+    assert_hex_encode(with_null, "61f7300077");
+    assert_hex_decode("", "");
+    assert_hex_decode("61F7-3000-77", with_null);
+    assert_hex_decode("41455", "AEP");
+    std::cout << "end hex encode/decode\n";
+}
+
 int main(int argc, char* argv[])
 {
     try
@@ -266,6 +304,8 @@ int main(int argc, char* argv[])
 	same_file_test();
 	std::cout << "----" << std::endl;
 	read_lines_from_file_test();
+	std::cout << "----" << std::endl;
+	hex_encode_decode_test();
     }
     catch (std::exception& e)
     {