在基于 libevent 的 TCP 服務器開發中，處理消息邊界是常見需求。以下是兩種主流分包方案的完整實現：

一、基于 Content-Length 的分包方案

1.1 數據結構設計

typedef struct {struct bufferevent *bev;int content_length;  // 當前消息的預期長度int received_bytes;  // 已接收字節數char *buffer;        // 消息緩沖區size_t buffer_size;  // 緩沖區大小
} tcp_session_t;

1.2 核心處理邏輯

void read_cb(struct bufferevent *bev, void *arg) {tcp_session_t *session = (tcp_session_t *)arg;struct evbuffer *input = bufferevent_get_input(bev);// 階段1：讀取消息頭if (session->content_length == -1) {char *line = evbuffer_readln(input, NULL, EVBUFFER_EOL_CRLF);if (!line) return;  // 不完整的行// 解析Content-Lengthif (strstr(line, "Content-Length:") != NULL) {sscanf(line, "Content-Length: %d", &session->content_length);session->buffer = malloc(session->content_length + 1);}free(line);// 檢查是否到達頭部結束（空行）line = evbuffer_readln(input, NULL, EVBUFFER_EOL_CRLF);if (line && strlen(line) == 0) {free(line);if (session->content_length == -1) {// 沒有Content-Length的簡單消息session->content_length = evbuffer_get_length(input);}} else {return;  // 繼續等待頭部結束}}// 階段2：讀取消息體size_t avail = evbuffer_get_length(input);size_t need = session->content_length - session->received_bytes;size_t to_read = avail < need ? avail : need;evbuffer_remove(input, session->buffer + session->received_bytes, to_read);session->received_bytes += to_read;// 階段3：完整消息處理if (session->received_bytes == session->content_length) {session->buffer[session->content_length] = '\0';process_complete_message(session->buffer);// 重置狀態free(session->buffer);session->buffer = NULL;session->content_length = -1;session->received_bytes = 0;}
}

二、基于雙 CRLF 的分包方案

2.1 數據結構設計

typedef struct {struct bufferevent *bev;int header_complete;  // 頭部是否解析完成char *header;         // 消息頭緩沖區char *body;           // 消息體緩沖區size_t body_len;      // 消息體長度
} tcp_session_t;

2.2 核心處理邏輯

void read_cb(struct bufferevent *bev, void *arg) {tcp_session_t *session = (tcp_session_t *)arg;struct evbuffer *input = bufferevent_get_input(bev);// 階段1：解析消息頭if (!session->header_complete) {char *line = evbuffer_readln(input, NULL, EVBUFFER_EOL_CRLF);if (!line) return;if (session->header == NULL) {session->header = malloc(1024);session->header[0] = '\0';}// 空行表示頭部結束if (strlen(line) == 0) {session->header_complete = 1;free(line);// 檢查是否有消息體（如POST請求）const char *content_len = strstr(session->header, "Content-Length:");if (content_len) {sscanf(content_len, "Content-Length: %zu", &session->body_len);session->body