本文共 7116 字，大约阅读时间需要 23 分钟。
场景：
1. 下载过程中,遇设备突然断网，在使用libcurl提供的API时，出现阻塞不返回的情况，影响了后续的业务。
问题：
curl_easy_perform是阻塞的方式进行下载的, curl_easy_perform执行后,程序会在这里阻塞等待下载结束(成功结束或者失败结束).此时若正常下载一段时间后,进行网络中断, curl_easy_perform并不会返回失败,而是阻塞整个程序卡在这里,此时即使网络连接重新恢复, curl_easy_perform也无法恢复继续下载,导致整个程序出现”死机”状态.
之前提供的解决办法：
2.1在下载中,另起一个线程,若发现下载状态卡死(可以通过定期检查文件大小来实现),则从外部中断下载线程.此方法需另起线程,而且直接中断线程,会给整个程序带来不稳定.
2.2.下载过程中,设置超时时间为30秒, 30秒后若下载未完成就重新连接进行下载.
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3、我的解决办法（实际代码）：封装libcurl，设置超时时间，以及必要的变量控制
需要注意的设置项
curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 10L); //timeout for the connect phase
/* abort if slower than 1 bytes/sec during 6 seconds */curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, 1);
curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, 6);头文件：
typedef struct http_set_opt{ int timeout; const char *ca_file; const char *ca_path; const char *content_type; const char *digest_value; const char *token; void *write_func; void *write_data; void *progress_func; void *progress_data; const char *upload_file_path; void *read_func; void *read_data; int read_data_size;}http_set_opt_t;typedef int(*download_file_progress_cbk)(void *lpUserData, int64_t dltotal, int64_t dlnow);typedef struct http_download_param{ http_set_opt_t * http_set_opt; /* * request */ const char * serv_url; const char * store_path; /* * callback */ download_file_progress_cbk progress_cbk; void * progress_cbk_userdata; /* * attribute */ int running; // abort: < 0, running: 1 /* * defaults */ char defaults[16];}http_download_param_t;/*接口*/OpenSDK_API int Open_http_client_download_file(http_download_param_t*download_param);/*回调*/typedef struct { int(*Open_http_client_download_file)(http_download_param_t *download_param); }http_client_interface; CPP文件：
#include#include #include #include #include #include static size_t download_write_func(char *ptr, size_t size, size_t nmemb, void *userdata){ FILE *fp = (FILE *)userdata; if(fwrite(ptr, size, nmemb, fp) != (size*nmemb)) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: fwrite failed\n", __FILE__, __FUNCTION__, __LINE__); } return (size*nmemb);}/*回调*/static int http_client_download_file_progress(void *clientp, curl_off_t dltotal, curl_off_t dlnow, curl_off_t ultotal, curl_off_t ulnow){ http_download_param_t *download_param = (http_download_param_t *)clientp; if (download_param == NULL || download_param->running < 0) //特别注意running的使用，可以快速返回 return -1; if (download_param != NULL && download_param->progress_cbk != NULL){ int64_t totalSize = (int64_t)dltotal; int64_t downloadedSize = (int64_t)dlnow; download_param->progress_cbk(download_param->progress_cbk_userdata, totalSize, downloadedSize); } return 0;}/*实现*/int Open_http_client_download_file(http_download_param_t *download_param){ if (download_param->serv_url == NULL || download_param->store_path == NULL) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: argument for sky_http_client_download_file should not be NULL\n", __FILE__, __FUNCTION__, __LINE__); return -1; } if (download_param->progress_cbk == NULL) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: download progress callback func should not be NULL\n", __FILE__, __FUNCTION__, __LINE__); return -1; } long local_file_length = 0;// get_localfile_length(download_param->store_path); //fprintf(stderr, "local file length is: %ld\n", local_file_length); FILE *fp = fopen(download_param->store_path, "wb"); if (fp == NULL) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: can not open %s\n", __FILE__, __FUNCTION__, __LINE__, download_param->store_path); return -1; } CURL *curl = curl_easy_init(); if (curl == NULL) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: curl_easy_init failed\n", __FILE__, __FUNCTION__, __LINE__); fclose(fp); return -1; } download_param->running = 1; //注意赋值 /* 1: set http server url */ curl_easy_setopt(curl, CURLOPT_URL, download_param->serv_url); /* 2:set debug opt */#if HTTP_DEBUG curl_easy_setopt(curl, CURLOPT_VERBOSE, 1); curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, http_debug);#endif /* 3: set http request method */ curl_easy_setopt(curl, CURLOPT_HTTPGET, 1); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, download_write_func); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, http_client_download_file_progress); curl_easy_setopt(curl, CURLOPT_XFERINFODATA, download_param); curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);// curl_easy_setopt(curl, CURLOPT_RESUME_FROM_LARGE, local_file_length); /* abort if slower than 1 bytes/sec during 6 seconds */ /* 注意该此处的设置，断网等情况下的死锁 */ //timeout for the connect phase curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 10L); /* abort if slower than 1 bytes/sec during 6 seconds */ curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, 1L); curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, 6L); curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, 1L); curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, 6L); if (download_param->http_set_opt != NULL) { /* 4:set time out by user */ if (download_param->http_set_opt->timeout) { curl_easy_setopt(curl, CURLOPT_TIMEOUT, download_param->http_set_opt->timeout); } /* 5:set CA */ if (download_param->http_set_opt->ca_file) { curl_easy_setopt(curl, CURLOPT_CAINFO, download_param->http_set_opt->ca_file); } if (download_param->http_set_opt->ca_path) { curl_easy_setopt(curl, CURLOPT_CAPATH, download_param->http_set_opt->ca_path); curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 1); } } else { curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0); curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0); } /* 6:set no signal */ curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1); CURLcode ret_code = curl_easy_perform(curl); if (ret_code != CURLE_OK) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: curl_easy_perform failed, error code: %d\n", __FILE__, __FUNCTION__, __LINE__, ret_code); //LOG_WRITE(LOG_LEVEL_ERROR, "curl_easy_perform failed, error code: %d", ret_code); if (ret_code == CURLE_COULDNT_CONNECT || ret_code == CURLE_COULDNT_RESOLVE_HOST || ret_code == CURLE_COULDNT_RESOLVE_PROXY) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: network problem\n", __FILE__, __FUNCTION__, __LINE__); } else if (ret_code == CURLE_OPERATION_TIMEDOUT){ fprintf(stderr, "file:<%s> func:<%s> line:<%d>: curl_easy_perform time out\n", __FILE__, __FUNCTION__, __LINE__); } else if (ret_code == CURLE_SSL_CONNECT_ERROR) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: SSL connect error\n", __FILE__, __FUNCTION__, __LINE__); } else if (ret_code == CURLE_SSL_CACERT) { fprintf(stderr, "file:<%s> func:<%s> line:<%d>: CA file error\n", __FILE__, __FUNCTION__, __LINE__); } curl_easy_cleanup(curl); fclose(fp); return -1; } curl_easy_cleanup(curl); fclose(fp); return 0;}
以上为封装的文件下载过程，应用层在使用该接口的时候，需要根据实际的情况，给 http_download_param_t http_download对象先初始化，memset(&http_download, 0, sizeof(http_download))，在具体的情境下赋值，比如上层的业务突然关闭或者停止，需要将 http_download.running = -1; 这样就内部就能及时地返回结束，而不会使得上层调用 int result= Open_http_client_download_file(&http_download);接口时被阻塞，不返回；
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