在http協議中傳輸二進制的數據--base64實現

做Ministored的時候發現一個問題，用http傳輸二進制的數據時，需要將二進制做一下轉化，出現了以下的問題。

簡單概括如下：

1) 不知道傳輸字節的具體長度，如傳輸的int類型，將int類型之間轉爲char以後，丟失掉了長度的信息，如數字1234567，本來只有4個字節，但是轉化成文本的“1234567”是有7個字節。在int類型的時候固然好辦，但是一個數組的時候，經過轉化以後，在轉化回來就很麻煩了。

2) 對於一些數字，二進制傳輸Server是沒法處理的。如int 1,二進制數據是0x00000001，按字節傳輸的時候，client能夠正常發送，但是libevent收到以後，在拋給libevent_http層是，會把數據截斷，前兩位0x00是字符串的停止符。

 

所以，只能用base64來解決這個問題。base64將二進制的內容轉化成一組有意義的字符串，然後傳輸，server在decode。比較不錯的是，base64 encode以後，數據包只會增大1/3，效率還是不錯的。

 

下面是base64的實現，及測試代碼，聲明下base64的encode/decode不是我寫的，來自網友的實現，google/baidu下有很多的實現，我拿了一個看起來比較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); }

 

搞定了編碼以後，明天估計網絡框架跟ministore就能聯調了，ministored有望！