objective c - A string that eats up whatever is in front? -

i know weird question have string inside rkresponse (from restkit) eating whatever add after it.

i want know inside "response.bodyasstring" causes behavior.

this code:

    nslog(@"--- refreshfriendslist callback ---");      nslog(@"status code: %i",response.statuscode);     nslog(@"response contents: 54321%@12345",response.bodyasstring);      nslog(@"response contents length: %@",response.contentlength);      if ([response isok])     {         nslog(@"response ok");           nslog(@"length %lu",(unsigned long)response.bodyasstring.length);         nslog(@"trimmed lenght %lu",(unsigned long)[response.bodyasstring stringbytrimmingcharactersinset:[nscharacterset whitespaceandnewlinecharacterset]].length);          nslog(@"is empty? %@",[response.bodyasstring isequaltostring:@""]?@"yes":@"no");       .      .      . 

and output:

2013-09-04 15:26:31.958 appname[5658:707] --- refreshfriendslist callback --- 2013-09-04 15:26:31.965 appname[5658:707] status code: 200 2013-09-04 15:26:31.980 appname[5658:707] response contents: 54321 2013-09-04 15:26:31.986 appname[5658:707] response contents length: 4 2013-09-04 15:26:31.990 appname[5658:707] response ok 2013-09-04 15:26:31.997 appname[5658:707] length 4 2013-09-04 15:26:32.002 appname[5658:707] trimmed lenght 4 2013-09-04 15:26:32.014 appname[5658:707] empty? no 

as can see later 12345 disappeared , have no idea why, neither why length of string 4.

the server should returning empty string created having found no results

jsonobject friendsandfamilyinfo = manager.getfriendsandfamilylist(userid);  if (friendsandfamilyinfo != null) {      resp.getwriter().print(friendsandfamilyinfo.tostring());      resp.setstatus(200); } else {      resp.getwriter().print("error");      resp.setstatus(500); } 

update:

this when print response raw data:

2013-09-04 15:47:59.930 appname[5701:707] response data: <007b007d> 

and how restkit coverts data string:

- (nsstring *)bodyasstring {     return [[[nsstring alloc] initwithdata:self.body encoding:[self bodyencoding]] autorelease]; } 

this looks encoding problem: output

appname[5701:707] response data: <007b007d> 

one can see returned data string {} in utf-16 (big-endian) encoding. if converted nsstring using e.g. utf-8 or ascii encoding first character of converted string nul character.

then in

nslog(@"response contents: 54321%@12345",response.bodyasstring); 

the nul character acts string terminator.

it explain why length of string 4: each byte of data converted 1 unicode.

example:

uint8_t bytes[] = { 0x00, 0x7b, 0x00, 0x7d }; nsdata *data = [nsdata datawithbytes:bytes length:sizeof(bytes)]; nslog(@"%@", data); // output: <007b007d> nsstring *str = [[nsstring alloc] initwithdata:data encoding:nsutf8stringencoding]; nslog(@"contents: >>>%@<<<",str); // output: contents: >>> nslog(@"length: %d",[str length]); // output: 4 

but if correct encoding used:

nsstring *str = [[nsstring alloc] initwithdata:data encoding:nsutf16bigendianstringencoding]; nslog(@"contents: >>>%@<<<",str); // output: contents: >>>{}<<< nslog(@"length: %d",[str length]); // output: 2