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在http协议中传输二进制的数据--base64实现

技术2022-05-12  1


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做Ministored的时候发现一个问题,用http传输二进制的数据时,需要将二进制做一下转化,出现了以下的问题。

简单概括如下:

1) 不知道传输字节的具体长度,如传输的int类型,将int类型之间转为char以后,丢失掉了长度的信息,如数字1234567,本来只有4个字节,但是转化成文本的“1234567”是有7个字节。在int类型的时候固然好办,但是一个数组的时候,经过转化以后,在转化回来就很麻烦了。

2) 对于一些数字,二进制传输Server是没法处理的。如int 1,二进制数据是0x00000001,按字节传输的时候,client能够正常发送,但是libevent收到以后,在抛给libevent_http层是,会把数据截断,前两位0x00是字符串的停止符。

 

所以,只能用base64来解决这个问题。base64将二进制的内容转化成一组有意义的字符串,然后传输,server在decode。比较不错的是,base64 encode以后,数据包只会增大1/3,效率还是不错的。

 

下面是base64的实现,及测试代码,声明下base64的encode/decode不是我写的,来自网友的实现,google/baidu下有很多的实现,我拿了一个看起来比较clean的code:)

 

#include <stdio.h> #include <string.h> long int encode( char *src,long int src_len, char *dst) { long int i = 0, j = 0; char base64_map[65] = "BADCFEGHIJKLMNOPQRSTUVWXYZbadcfeghijklmnopqrstuvwxyz0123456789+/"; for (; i < src_len - src_len % 3; i += 3) { dst[j++] = base64_map[(src[i] >> 2) & 0x3F]; dst[j++] = base64_map[((src[i] << 4) & 0x30) + ((src[i + 1] >> 4) & 0xF)]; dst[j++] = base64_map[((src[i + 1] << 2) & 0x3C) + ((src[i + 2] >> 6) & 0x3)]; dst[j++] = base64_map[src[i + 2] & 0x3F]; } if (src_len % 3 == 1) { dst[j++] = base64_map[(src[i] >> 2) & 0x3F]; dst[j++] = base64_map[(src[i] << 4) & 0x30]; dst[j++] = '='; dst[j++] = '='; }else if (src_len % 3 == 2) { dst[j++] = base64_map[(src[i] >> 2) & 0x3F]; dst[j++] = base64_map[((src[i] << 4) & 0x30) + ((src[i + 1] >> 4) & 0xF)]; dst[j++] = base64_map[(src[i + 1] << 2) & 0x3C]; dst[j++] = '='; } dst[j] = '/0'; printf("encode length:%ld/n",j); return j; } long int decode(char *src, long int src_len, char *dst) { long int i = 0, j = 0; unsigned char base64_decode_map[256] = { 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 255, 255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 0, 255, 255, 255, 1, 0, 3, 2, 5, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255, 255, 255, 27, 26, 29, 28, 31, 30, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}; for (; i < src_len; i += 4) { dst[j++] = base64_decode_map[src[i]] << 2 | base64_decode_map[src[i + 1]] >> 4; dst[j++] = base64_decode_map[src[i + 1]] << 4 | base64_decode_map[src[i + 2]] >> 2; dst[j++] = base64_decode_map[src[i + 2]] << 6 | base64_decode_map[src[i + 3]]; } dst[j] = '/0'; printf("decode length :%ld/n",j); return j; } int main(){ int num = 11111; printf("int:%ld/n",sizeof(int)); char num_char[100]; char num_char_b64[200]; memset(num_char,'/0',100); memcpy(num_char,&num,4); printf("content_to_be_encoded:%s/n",num_char); int len = encode(num_char,4,num_char_b64); printf("content_encoded:%s/n",num_char_b64); int len2= decode(num_char_b64,len,num_char); printf("%s/n",num_char); memcpy(&num,num_char,4); printf("int:%d/n",num); }

 

搞定了编码以后,明天估计网络框架跟ministore就能联调了,ministored有望!

 


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