+static int is_rfc2047_special(char ch)
+{
+ return ((ch & 0x80) || (ch == '=') || (ch == '?') || (ch == '_'));
+}
+
+static int add_rfc2047(char *buf, const char *line, int len)
+{
+ char *bp = buf;
+ int i, needquote;
+ static const char q_utf8[] = "=?utf-8?q?";
+
+ for (i = needquote = 0; !needquote && i < len; i++) {
+ unsigned ch = line[i];
+ if (ch & 0x80)
+ needquote++;
+ if ((i + 1 < len) &&
+ (ch == '=' && line[i+1] == '?'))
+ needquote++;
+ }
+ if (!needquote)
+ return sprintf(buf, "%.*s", len, line);
+
+ memcpy(bp, q_utf8, sizeof(q_utf8)-1);
+ bp += sizeof(q_utf8)-1;
+ for (i = 0; i < len; i++) {
+ unsigned ch = line[i];
+ if (is_rfc2047_special(ch)) {
+ sprintf(bp, "=%02X", ch);
+ bp += 3;
+ }
+ else if (ch == ' ')
+ *bp++ = '_';
+ else
+ *bp++ = ch;
+ }
+ memcpy(bp, "?=", 2);
+ bp += 2;
+ return bp - buf;
+}
+