c++ - curl 回调未返回相同数量的字节

Question

我在尝试使用 curl 获取 http 数据时遇到不一致的失败。

libcurl: (23) Failed writing body (23048858 != 16058)

它一直在失败，然后它开始工作了。现在又失败了。我四处寻找，大多数帖子要么归咎于回调，要么归咎于设置 curl 选项的顺序。我重新安排了选项，我没有发现回调有任何问题。事实上，当我调试回调时，输入参数与我实际获得的输出值相匹配。所以我不确定 23048858 这个值是从哪里来的。

来源

SwReceiver* SwReceiver::instance;

SwReceiver *SwReceiver::getInstance(
  std::string &address,
  std::string &key,
  std::string &options)
{
  if(!instance)
  {
    instance = new SwReceiver(address, key, options);
    return instance;
  }
}

SwReceiver::SwReceiver(
  std::string &address,
  std::string &key,
  std::string &options)
{
  curl_global_init(CURL_GLOBAL_ALL);
  data = curl_easy_init();
  if(data)
  {
    std::string addrstr = address + '/' + key + '/' + options;
    // std::cout << "Address = " << addrstr << std::endl;
    curl_easy_setopt(data, CURLOPT_URL, addrstr.c_str());
    curl_easy_setopt(data, CURLOPT_WRITEDATA, (void *)&chunk);
    curl_easy_setopt(data, CURLOPT_USERAGENT, "libcurl-agent/1.0");
    curl_easy_setopt(data, CURLOPT_ERRORBUFFER, errorBuffer);
    curl_easy_setopt(data, CURLOPT_WRITEFUNCTION, writeMemoryCallback);
    memset(errorBuffer, 0, sizeof(CURL_ERROR_SIZE));
    /* DEBUG */
    curl_easy_setopt(data, CURLOPT_VERBOSE, 1);

    runQuery();
  }
  else
  {
    //TODO add to error buffer
  }
}

SwReceiver::~SwReceiver()
{
  delete(instance);
  curl_easy_cleanup(data);
}

void SwReceiver::runQuery()
{
  result = curl_easy_perform(data);
  if(result != CURLE_OK)
  {
    size_t len = strlen(errorBuffer);
    fprintf(stderr, "\nlibcurl: (%d) ", result);
    if(len)
    {
      fprintf(stderr, "%s%s", errorBuffer,
        ((errorBuffer[len - 1] != '\n') ? "\n" : ""));
    }
    else
    {
      fprintf(stderr, "%s\n", curl_easy_strerror(result));
    }
  }
}

MemoryStruct *SwReceiver::getData()
{
  return &chunk;
}

size_t SwReceiver::writeMemoryCallback(
  void *contents, size_t size, size_t nmemb, void *userp)
{
  size_t realSize = size * nmemb;
  struct MemoryStruct *mem = (struct MemoryStruct *)userp;

  char *ptr = (char*)realloc(mem->memory, mem->size + realSize + 1);
  if(ptr == NULL)
  {
    //TODO This should write to the error buffer
    std::cout << "Not enought memory!\n";
    return 0;
  }

  mem->memory = ptr;
  memcpy(&(mem->memory[mem->size]), contents, realSize);
  mem->size += realSize;
  mem->memory[mem->size] = 0;
}

内存结构源

 struct MemoryStruct
{
  char * memory;
  size_t size;

  MemoryStruct()
  : memory((char*)malloc(1)),
  size(0)
  {

  }
};

由于尺寸原因，我没有发布标题。如果您觉得我应该发帖，请告诉我。

调试

(gdb)
(gdb) break 79
Breakpoint 1 at 0x40240c: file swreceiver.cpp, line 79.
(gdb) run
Starting program: /home/ubuntu/src/stickweather/stickweather
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff1de9700 (LWP 26989)]
[Thread 0x7ffff1de9700 (LWP 26989) exited]
*   Trying 34.193.12.42...
* Connected to api.darksky.net (34.193.12.42) port 443 (#0)
* ALPN, offering http/1.1
* Cipher selection: ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: /etc/ssl/certs
* SSL connection using TLSv1.2 / ECDHE-RSA-AES128-GCM-SHA256
* ALPN, server accepted to use http/1.1
* Server certificate:
*        subject: CN=darksky.net
*        start date: Apr 26 00:00:00 2019 GMT
*        expire date: May 26 12:00:00 2020 GMT
*        subjectAltName: api.darksky.net matched
*        issuer: C=US; O=Amazon; OU=Server CA 1B; CN=Amazon
*        SSL certificate verify ok.
> GET /forecast/<hidden>/37.8267,-122.4233 HTTP/1.1
Host: api.darksky.net
User-Agent: libcurl-agent/1.0
Accept: */*

< HTTP/1.1 200 OK
< Date: Tue, 22 Oct 2019 14:18:40 GMT
< Content-Type: application/json; charset=utf-8
< Content-Length: 28035
< Connection: keep-alive
< X-Authentication-Time: 687ms
< X-Forecast-API-Calls: 13
< Cache-Control: max-age=60
< Expires: Tue, 22 Oct 2019 14:19:39 +0000
< X-Response-Time: 333.671ms
< Vary: Accept-Encoding
<

Thread 1 "stickweather" hit Breakpoint 1, SwReceiver::writeMemoryCallback (contents=0x650be6, size=1, nmemb=16058,
    userp=0x635848) at swreceiver.cpp:82
82        size_t realSize = size * nmemb;

Answer 1

您的 writeMemoryCallback 不返回写入的字节数，在底部控件到达函数末尾时没有返回，因此在 x86 上它可能会返回垃圾。我怀疑这是其他值(value)的来源。

https://curl.haxx.se/libcurl/c/CURLOPT_WRITEFUNCTION.html