Check UTF-8 encoding, and convert strings to UTF-8

Handle conversion errors properly by inserting � instead.  Add a binary
header to provide portable way to write binary literals (I like them) Also
add a test file.  ref #2404

src/utils/encoding.cpp

@@ -0,0 +1,139 @@
+#include <utils/encoding.hpp>
+#include <utils/binary.hpp>
+
+#include <utils/scopeguard.hpp>
+
+#include <assert.h>
+#include <string.h>
+#include <iconv.h>
+
+/**
+ * The UTF-8-encoded character used as a place holder when a character conversion fails.
+ * This is U+FFFD � "replacement character"
+ */
+static const char* invalid_char = "\xef\xbf\xbd";
+static const size_t invalid_char_len = 3;
+
+namespace utils
+{
+  /**
+   * Based on http://en.wikipedia.org/wiki/UTF-8#Description
+   */
+  bool is_valid_utf8(const char* s)
+  {
+    if (!s)
+      return false;
+
+    const unsigned char* str = reinterpret_cast<const unsigned char*>(s);
+
+    while (*str)
+      {
+        // 4 bytes:  11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+        if ((str[0] & 11111000_b) == 11110000_b)
+          {
+            if (!str[1] || !str[2] || !str[3]
+                || ((str[1] & 11000000_b) != 10000000_b)
+                || ((str[2] & 11000000_b) != 10000000_b)
+                || ((str[3] & 11000000_b) != 10000000_b))
+              return false;
+            str += 4;
+          }
+        // 3 bytes:  1110xxx 10xxxxxx 10xxxxxx
+        else if ((str[0] & 11110000_b) == 11100000_b)
+          {
+            if (!str[1] || !str[2]
+                || ((str[1] & 11000000_b) != 10000000_b)
+                || ((str[2] & 11000000_b) != 10000000_b))
+              return false;
+            str += 3;
+          }
+        // 2 bytes:  110xxxxx 10xxxxxx
+        else if (((str[0]) & 11100000_b) == 11000000_b)
+          {
+            if (!str[1] ||
+                ((str[1] & 11000000_b) != 10000000_b))
+              return false;
+            str += 2;
+          }
+        // 1 byte:  0xxxxxxx
+        else if ((str[0] & 10000000_b) != 0)
+          return false;
+        else
+          str++;
+      }
+    return true;
+  }
+
+  std::string convert_to_utf8(const std::string& str, const char* charset)
+  {
+    std::string res;
+
+    const iconv_t cd = iconv_open("UTF-8", charset);
+    if (cd == (iconv_t)-1)
+      throw std::runtime_error("Cannot convert into UTF-8");
+
+    // Make sure cd is always closed when we leave this function
+    ScopeGuard sg([&]{ iconv_close(cd); });
+
+    // iconv will not attempt to modify this buffer, but it still requires
+    // a char**.
+    size_t inbytesleft = str.size();
+    char* inbuf_ptr = const_cast<char*>(str.c_str());
+
+    size_t outbytesleft = str.size() * 4;
+    char* outbuf = new char[outbytesleft];
+    char* outbuf_ptr = outbuf;
+
+    // Make sure outbuf is always deleted when we leave this function
+    sg.add_callback([&]{ delete[] outbuf; });
+
+    bool done = false;
+    while (done == false)
+      {
+        size_t error = iconv(cd, &inbuf_ptr, &inbytesleft, &outbuf_ptr, &outbytesleft);
+        if ((size_t)-1 == error)
+          {
+            switch (errno)
+              {
+              case EILSEQ:
+                // Invalid byte found. Insert a placeholder instead of the
+                // converted character, jump one byte and continue
+                memcpy(outbuf_ptr, invalid_char, invalid_char_len);
+                outbuf_ptr += invalid_char_len;
+                inbytesleft--;
+                inbuf_ptr++;
+                break;
+              case EINVAL:
+                // A multibyte sequence is not terminated, but we can't
+                // provide any more data, so we just add a placeholder to
+                // indicate that the character is not properly converted,
+                // and we stop the conversion
+                memcpy(outbuf_ptr, invalid_char, invalid_char_len);
+                outbuf_ptr += invalid_char_len;
+                outbuf_ptr++;
+                done = true;
+                break;
+              case E2BIG:
+                // This should never happen
+                done = true;
+              default:
+                // This should happen even neverer
+                done = true;
+                break;
+              }
+          }
+        else
+          {
+            // The conversion finished without any error, stop converting
+            done = true;
+          }
+      }
+    // Terminate the converted buffer, and copy that buffer it into the
+    // string we return
+    *outbuf_ptr = '\0';
+    res = outbuf;
+    return res;
+  }
+
+}
+