Resolve nsdata that contain illegal UTF-8 encoding

We often meet in the development of the NSData conversion to nsstring, or through nsjsonserialization parsing JSON scene, once NSData contains illegal UTF-8 encoding, then the result will be returned nil, but the result is not in line with our expectations, Because this is probably just a coding error, we would prefer to discard or replace the error code with an error character.
On Google to find a lap, some people have achieved such a method, but the individual feel that the writing is not rigorous, fault tolerance is not very good, simply write a bar, in strict accordance with RFC3629 standards.

UTF-8 is a variable length encoding, for different lengths of bytes have a fixed format, in the RFC3629 specification can only be up to four bytes, and the range has requirements, more relevant introduction please jump Wikipedia UTF-8 entry (jump address):

1 2 3 4

0xxxxxxx 10xxxxxx 10xxxxxx 10xxxxxx

According to this rule write a nsdata extension method, see the code:

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@implementationNSData (UTF8) - (NSData *) Utf8data { Save Results Nsmutabledata *resdata = [[Nsmutabledata alloc] Initwithcapacity:Self. length]; Invalid code substitution symbol (common?-?) NSData *replacement = [@ "?" datausingencoding:nsutf8stringencoding]; uint64_t index =0; Const uint8_t *bytes =Self. bytes; while (Index <Self. length) { uint8_t len =0; uint8_t header = Bytes[index]; Single byte if ((header&0x80) = =0) { Len =1; } 2 bytes (and cannot be c0,c1) Elseif ((header&0xE0) = =0XC0) { if (header! =0xC0 && Header! =0XC1) { Len =2; } } 3 bytes Elseif ((header&0xF0) = =0XE0) { Len =3; } 4 bytes (and cannot be f5,f6,f7) Elseif ((header&0xF8) = =0XF0) { if (header! =0xf5 && Header! =0xf6 && Header! =0XF7) { Len =4; } } Not recognized if (len = =0) { [Resdata appenddata:replacement]; index++; Continue } Detects valid data length (how many bytes are in the back of 10xxxxxx) uint8_t Validlen =1; while (Validlen < Len && Index+validlen <Self. length) { if ((Bytes[index+validlen) &0XC0)! =0x80 Break validlen++; //valid bytes equals the number of bytes required by the encoding to represent legal , otherwise illegal if (validlen = len) { [Resdata Appendbytes:bytes+index Length:len]; else [Resdata Appenddata:replacement]; //move subscript index + = Validlen; return resdata; @end

link on GitHub address: https://github.com/tanhaogg/THCategory

Resolve nsdata that contain illegal UTF-8 encoding