[英]how do I build a protocol header and body over a tcp socket in C
我正在寫一個塔卡奇+客戶
我試圖編寫一個簡單的數據包發送到服務器,檢查了RFC頁面 ,發現協議需要在每個數據包中獲取此標頭:
+----------------+----------------+----------------+----------------+
|major | minor | | | |
|version| version| type | seq_no | flags |
+----------------+----------------+----------------+----------------+
| |
| session_id |
+----------------+----------------+----------------+----------------+
| |
| length |
+----------------+----------------+----------------+----------------+
現在我對此很陌生,我不確定如何構建此標頭,是否正在創建這樣的緩沖區足夠好?:
snprintf(buffer, sizeof(buffer), "%x%x%x%x%x",version,version,type,seq,flags,session_id,length);
然后以相同的方式獲取此緩沖區並將其附加到主體並發送:
send(socket,buffer,sizeof(buffer),0);
還是有另一種方式來完成整個數據包的構建?
您所擁有的根本無法產生正確的輸出!
以下是可移植的:
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
uint8_t* pack_uint8(uint8_t* dest, uint8_t src) {
*(dest++) = src;
return dest;
}
uint8_t* pack_uint32be(uint8_t* dest, uint32_t src) {
*(dest++) = src >> 24;
*(dest++) = (src >> 16) & 0xFF;
*(dest++) = (src >> 8) & 0xFF;
*(dest++) = src & 0xFF;
return dest;
}
uint8_t* build_packet(
uint8_t maj_version,
uint8_t min_version,
uint8_t type,
uint8_t seq,
uint8_t flags,
uint32_t session_id,
uint32_t body_length,
const uint8_t* body
) {
uint8_t* packet = malloc(12 + body_length);
uint8_t* p = packet;
p = pack_uint8(p, ( maj_version << 4 ) | min_version);
p = pack_uint8(p, type);
p = pack_uint8(p, seq);
p = pack_uint8(p, flags);
p = pack_uint32be(p, session_id);
p = pack_uint32be(p, body_length);
memcpy(p, body, body_length);
return packet;
}
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