+// Notes on UTF-8:
+// 0xxxxxxx represents a 7-bit ASCII value from 0x00 to 0x7F
+// 10xxxxxx is a continuation byte of a multi-byte character
+// 110xxxxx is the first byte of a 2-byte character (11 effective bits; values 0x 80 - 0x 800-1)
+// 1110xxxx is the first byte of a 3-byte character (16 effective bits; values 0x 800 - 0x 10000-1)
+// 11110xxx is the first byte of a 4-byte character (21 effective bits; values 0x 10000 - 0x 200000-1)
+// 111110xx is the first byte of a 5-byte character (26 effective bits; values 0x 200000 - 0x 4000000-1)
+// 1111110x is the first byte of a 6-byte character (31 effective bits; values 0x4000000 - 0x80000000-1)
+//
+// UTF-16 surrogate pairs are used in UTF-16 to encode values larger than 0xFFFF.
+// Although UTF-16 surrogate pairs are not supposed to appear in legal UTF-8, we want to be defensive
+// about that too. (See <http://www.unicode.org/faq/utf_bom.html#34>, "What are surrogates?")
+// The first of pair is a UTF-16 value in the range 0xD800-0xDBFF (11101101 1010xxxx 10xxxxxx in UTF-8),
+// and the second is a UTF-16 value in the range 0xDC00-0xDFFF (11101101 1011xxxx 10xxxxxx in UTF-8).
+
+mDNSexport mDNSu32 TruncateUTF8ToLength(mDNSu8 *string, mDNSu32 length, mDNSu32 max)
+ {
+ if (length > max)
+ {
+ mDNSu8 c1 = string[max]; // First byte after cut point
+ mDNSu8 c2 = (max+1 < length) ? string[max+1] : 0xB0; // Second byte after cut point
+ length = max; // Trim length down
+ while (length > 0)
+ {
+ // Check if the byte right after the chop point is a UTF-8 continuation byte,
+ // or if the character right after the chop point is the second of a UTF-16 surrogate pair.
+ // If so, then we continue to chop more bytes until we get to a legal chop point.
+ mDNSBool continuation = ((c1 & 0xC0) == 0x80);
+ mDNSBool secondsurrogate = (c1 == 0xED && (c2 & 0xF0) == 0xB0);
+ if (!continuation && !secondsurrogate) break;
+ c2 = c1;
+ c1 = string[--length];
+ }
+ // Having truncated characters off the end of our string, also cut off any residual white space
+ while (length > 0 && string[length-1] <= ' ') length--;
+ }
+ return(length);
+ }
+
projects / apple / mdnsresponder.git / blobdiff