所谓大端数据就是数据的高字节保存在内存的低地址中,而数据的低字节保存在内存的高地址中,这样的存储模式有点儿类似于把数据当作字符串顺序处理:地址由小向大增加,而数据从高位往低位放;这和我们的阅读习惯一致。
所谓的小端数据就是数据的高字节保存在内存的高地址中,而数据的低字节保存在内存的低地址中,这种存储模式将地址的高低和数据位权有效地结合起来,高地址部分权值高,低地址部分权值低。(简单的来说就是反过来存放数据了)
数据补位,是指在将数据按照8个字节一段进行加密或解密得到一段8个字节的密文或者明文,最后一段不足8个字节,按照需求补足8个字节(通常补00或者FF,根据实际要求不同)进行计算,之后按照顺序将计算所得的数据连在一起即可。
假设要发送一段这样的数据(16进制数据):
| head | cmdlen(2字节) | cmd | playloadLen (4 字节) | playload
这段数据的内容大概是包含了:我有一个头部标记,然后用头部之后的两个字节作为描述何种命令的长度,然后接上的是何种命令,然后接上了附带信息的长度(4个字节),然后是附带信息。
需要发送的信息为:| https(头部) | len | openStream | len2 | {@"速度与激情.h264",@"fileName"}
// // CtpTools.m // NetworkTest // // Created by 飞天江郎 on 10/11/2016. // Copyright ? 2016 EzioChen. All rights reserved. // //普通字符串转换为十六进制的。 + (NSString *)hexStringFromString:(NSString *)string { NSData *myD = [string dataUsingEncoding:NSUTF8StringEncoding]; Byte *bytes = (Byte *)[myD bytes]; //下面是Byte 转换为16进制。 NSString *hexStr=@""; for(int i=0;i<[myD length];i++) { NSString *newHexStr = [NSString stringWithFormat:@"%x",bytes[i]&0xff];///16进制数 if([newHexStr length]==1) hexStr = [NSString stringWithFormat:@"%@0%@",hexStr,newHexStr]; else hexStr = [NSString stringWithFormat:@"%@%@",hexStr,newHexStr]; } return hexStr; } //编写一个NSData类型数据 +(NSMutableData*)HexStringToData:(NSString*)str { NSString *command = str; command = [command stringByReplacingOccurrencesOfString:@" " withString:@""]; NSMutableData *commandToSend= [[NSMutableData alloc] init]; unsigned char whole_byte; char byte_chars[3] = {'/0','/0','/0'}; int i; for (i=0; i < [command length]/2; i++) { byte_chars[0] = [command characterAtIndex:i*2]; byte_chars[1] = [command characterAtIndex:i*2+1]; whole_byte = strtol(byte_chars, NULL, 16); [commandToSend appendBytes:&whole_byte length:1]; } return commandToSend; } //补位的方法 +(NSString*)addString:(NSString*)string Length:(NSInteger)length OnString:(NSString*)str { NSMutableString * nullStr = [[NSMutableString alloc] initWithString:@""]; if ((length-str.length)> 0) { for (int i = 0; i< (length-str.length); i++) { [nullStr appendString:string]; } } return [NSString stringWithFormat:@"%@%@",nullStr,str]; } //把整型转化为16进制的,然后在补位,转换成大端数据 +(NSString *)intToHexString:(NSInteger)number length:(NSInteger)len { NSString *result = [self addString:@"0" Length:len OnString:[self ToHex:(unsigned int)number]]; NSData *data = [self HexStringToData:result]; NSData *lastData = [self dataTransfromBigOrSmall:data]; result = [self dataChangeToString:lastData]; return result; } //把int 变成 16进制的字符串 +(NSString *)ToHex:(unsigned int)number { NSString * result = [NSString stringWithFormat:@"%x",number]; if (result.length<2) { result = [NSString stringWithFormat:@"0%x",number]; } return [result uppercaseString]; } //把data(十六进制)转化为为十进制整型 +(NSInteger)dataToInt:(NSData *)data { NSInteger temp; double sum = 0.0; NSString * string = [self dataChangeToString:data]; NSInteger length = string.length; for (int i = 0 ; i < length; i++) { NSString * tempStr = [string substringWithRange:NSMakeRange(i, 1)]; int tempInt = [self StringToInt:tempStr]; double tempDouble = tempInt * pow(16.0, (double)(length-1-i)); sum = sum + tempDouble; } temp = (NSInteger)sum; return temp; } //大小端数据转换(其实还有更简便的方法,不过看起来这个方法是最直观的) +(NSData *)dataTransfromBigOrSmall:(NSData *)data{ NSString *tmpStr = [self dataChangeToString:data]; NSMutableArray *tmpArra = [NSMutableArray array]; for (int i = 0 ;i" withString:@""]; string = [string stringByReplacingOccurrencesOfString:@" " withString:@""]; return string; } +(int)StringToInt:(NSString*)string{ int temp; temp = [string intValue]; if ([string isEqual:@"a"]||[string isEqual:@"A"]) { temp = 10; }else if ([string isEqual:@"b"]||[string isEqual:@"B"]) { temp = 11; }else if ([string isEqual:@"c"]||[string isEqual:@"C"]) { temp = 12; }else if ([string isEqual:@"d"]||[string isEqual:@"D"]) { temp = 13; }else if ([string isEqual:@"e"]||[string isEqual:@"E"]) { temp = 14; }else if ([string isEqual:@"f"]||[string isEqual:@"F"]) { temp = 15; } return temp; } //hexString 转换成 String + (NSString *)stringFromHexString:(NSString *)hexString { char *myBuffer = (char *)malloc((int)[hexString length] / 2 + 1); bzero(myBuffer, [hexString length] / 2 + 1); for (int i = 0; i < [hexString length] - 1; i += 2) { unsigned int anInt; NSString * hexCharStr = [hexString substringWithRange:NSMakeRange(i, 2)]; NSScanner * scanner = [[NSScanner alloc] initWithString:hexCharStr]; [scanner scanHexInt:&anInt]; myBuffer[i / 2] = (char)anInt; } NSString *unicodeString = [NSString stringWithCString:myBuffer encoding:4]; return unicodeString; }
NSString *headStr = @"https"; NSString *playload = @"{/"fileName/":/"速度与激情.h264/"}"; NSString *cmd = @"openStream"; NSString *headHex = [self hexStringFromString:headStr]; NSString *cmdHex = [self hexStringFromString:cmd]; NSString *cmdLen = [self intToHexString:cmdHex.length/2 length:4]; NSString *playloadHex = [self hexStringFromString:playload]; NSString *playloadHexLen = [self intToHexString:playloadHex.length/2 length:8];NSString *allHexStr = [self stringWithFormat:@"%@%@%@%@%@",headHex,cmdLen,cmdHex,playloadHexLen,playloadHex]; NSData *lastData = [self HexStringToData:allHexStr]; NSLog(@"lastData=>%@",lastData);
最后打印出的Data,就是对应数据的16进制标准格式了。
其实还有一些可优化的地方,仔细的观察下每次的Data组装,然后你就会发现NSData本来就已经是16进制的,而大小端的转换其实还有跟简单的转换比方说是这种:
#include#define ntohs(x) __DARWIN_OSSwapInt16(x) #define htons(x) __DARWIN_OSSwapInt16(x) #define ntohl(x) __DARWIN_OSSwapInt32(x) #define htonl(x) __DARWIN_OSSwapInt32(x)
这里写成这样完全是方便理解。