Valgrind 使用 asprintf 报告内存泄漏

Question

这里有一段代码，基于一个简单的结构

在套接字上写入HTTP响应

void write_response(request *req, response *resp, int socket) {
  char *raw_resp;
  int bytes = 0;

  asprintf(&raw_resp, "HTTP/1.1 %d %s\r\n", resp->code, resp->reason_phrase);

  bytes += strlen(raw_resp);
  for (int i = 0; i < resp->header_count; i++) {
    asprintf(&raw_resp, "%s%s", raw_resp, resp->headers[i]);
    bytes += strlen(resp->headers[i]);
  }

  if (resp->content != NULL) {
    asprintf(&raw_resp, "%s\r\n", raw_resp);
    raw_resp = realloc(raw_resp, bytes + 2 + resp->content->size);
    memcpy(&raw_resp[strlen(raw_resp)], resp->content->data,
           resp->content->size);
    bytes += (resp->content->size + 2);
  }
  write(socket, raw_resp, bytes);
  free(raw_resp);
}

基本上，它首先添加 HTTP 请求行，然后是 headers，如果需要，最后是 body。

但是，valgrind 在前 2 个 asprintf 上报告 Invalid free() / delete / delete[] / realloc() 和 18 bytes in 1 blocks are definitely lost in loss record 2 of 4（内存泄漏），但奇怪的是在第 3 个上没有。

我用的 asprintf 对吗？

Answer 1

手册页是这样说的：

The functions asprintf() .... allocate a string...

以后

This pointer should be passed to free(3) to release the allocated storage when it is no longer needed.

每次新调用都会导致新分配。您似乎没有释放之前分配的字符串。

Answer 2

您的代码没有 free asprintf 分配的所有字符串。鉴于您如何使用 asprintf 执行动态字符串连接，修复此问题有点麻烦。请注意，您也不处理内存分配失败。您可以使用 asprintf return 值来检测并更新 bytes，而无需额外的 strlen() 调用。

/* return the number of bytes written or -1 in case of error */
int write_response(request *req, response *resp, int socket) {
    char *raw_resp, *new_p;
    int bytes;

    bytes = asprintf(&raw_resp, "HTTP/1.1 %d %s\r\n", resp->code, resp->reason_phrase);
    if (bytes < 0)
        return -1;

    for (int i = 0; i < resp->header_count; i++) {
        bytes = asprintf(&new_p, "%s%s", raw_resp, resp->headers[i]);
        free(raw_resp);
        raw_resp = newp;
        if (bytes < 0)
            return -1;
    }

    if (resp->content != NULL) {
        bytes = asprintf(&new_p, "%s\r\n", raw_resp);
        free(raw_resp);
        raw_resp = newp;
        if (bytes < 0)
            return -1;
        new_p = realloc(raw_resp, bytes + resp->content->size);
        if (new_p == NULL) {
            free(raw_resp);
            return -1;
        }
        raw_resp = new_p;
        memcpy(raw_resp + bytes, resp->content->data, resp->content->size);
        bytes += resp->content->size;
    }
    bytes = write(socket, raw_resp, bytes);
    free(raw_resp);
    return bytes;
}

备注：

使用asprintf执行字符串连接分配似乎效率低下，只需使用strlen、realloc和memcpy.
asprintf() 是 non-standard，并非在所有平台上都可用。
除非要求您发出对 write 的单个调用，否则单独编写内容可能更有效，以避免额外调用 realloc()大量内存。
在初始阶段用 snprintf 和 strlen 计算 headers 的长度并分配 space 对于 headers 直接分配到完整大小，或者如果低于使用本地数组的合理阈值 (4K) 甚至不分配。

这是修改后的版本：

int write_response(request *req, response *resp, int socket) {
    char buffer[4096];
    char *raw_resp, *allocated = NULL;
    int bytes, pos;

    bytes = snprintf(NULL, 0, "HTTP/1.1 %d %s\r\n", resp->code, resp->reason_phrase);
    for (int i = 0; i < resp->header_count; i++)
        bytes += strlen(resp->headers[i]);
    if (resp->content != NULL)
        bytes += 2 + resp->content->size;

    /* need an extra byte for `snprintf` null terminator 
       if no headers and no contents */
    if (bytes < sizeof(buffer)) {
        raw_resp = buffer;
    } else {
        raw_resp = allocated = malloc(bytes + 1): 
        if (raw_resp == NULL)
            return -1;
    }
    pos = snprintf(raw_resp, bytes, "HTTP/1.1 %d %s\r\n", resp->code, resp->reason_phrase);
    for (int i = 0; i < resp->header_count; i++) {
        int len = strlen(resp->headers[i]);
        memcpy(raw_resp + pos, resp->headers[i], len);
        pos += len;
    }

    if (resp->content != NULL) {
        raw_resp[pos++] = '\r';
        raw_resp[pos++] = '\n';
        memcpy(raw_resp + pos, resp->content->data, resp->content->size);
        pos += resp->content->size;
    }
    bytes = write(socket, raw_resp, bytes);
    free(allocated);
    return bytes;
}

Answer 3

你缺少自由，你不需要 asprintf 除了第一次

可以是：

void write_response(request *req, response *resp, int socket) {
  char * buff;
  int len;

  len = asprintf(&buff, "HTTP/1.1 %d %s\r\n", resp->code, resp->reason_phrase);
  if (len == -1)
    .. error management

  for (int i = 0; i < resp->header_count; i++) {
    size_t hlen = strlen(resp->headers[i]);

    buff = realloc(buff, len + hlen + 1);
    if (buff == NULL)
      ... error management
    strcpy(buff + len, resp->headers[i]);
    len += hlen;
  }

  if (resp->content != NULL) {
    buff = realloc(buff, len + 2 + resp->content->size);
    if (buff == NULL)
      ... error management
    buff[len] = '\r';
    buff[len + 1] = '\n';
    memcpy(len + 2, resp->content->data, resp->content->size);
    len += resp->content->size + 2;
  }
  if (write(socket, buff, len) != len)
    ... error management
  free(buff);
}

Valgrind 使用 asprintf 报告内存泄漏

Valgrind reports memory leak with asprintf

c

linux

valgrind