qt5集成libcurl实现tftp和ftp的方法之二：实现tftp文件上传和下载

QT5本身对ftp和tftp的支持不太好，找了很多地方也没找到好用的方法，无奈之下只好使用开源的curl来实现。但是该怎么使用tftp一直没找到说明。在curl的doc下有一堆的examples，但是就是没有tftp的，但是文档里明明说实现了tftp啊？答案是人家感觉tftp太简单了，都懒得单独写个demo了，╮(╯▽╰)╭深深的被鄙视了。下面我就说一下该怎么使用tftp功能。

1.建立tftp测试环境

写代码过程中随时会出问题，一旦环境出了问题，一切都是白搭，所以首先建立tftp的测试环境，方法非常简单。为了减少意外，最好使用两台电脑（或者电脑+虚拟机，总之尽量隔离开），每个电脑安装一个tftpd程序，window自带该功能的，但是太麻烦，下载一个tftpd32.exe就行了。
打开其中一台电脑的tftp32.exe程序，选择“tftp server”端，当做服务器。然后在另一个电脑打开tftp32.exe之后选择“client（客户端）”选项，如下图所示：



注意这里的设置：
1.“current directory”是tftp的工作目录，该目录下的文件可以直接tftp传输，下载的文件也自动放在这里。
2.“server interface”是本机IP地址，这个要注意网卡和网段，选错的话会导致传输连接无法建立。
3.Host：服务器的IP地址，Port：端口，tftp默认都是69
4.LocalFile：本地文件，例如“ds.txt”。Remote File：服务器端文件名，例如“2.2”。注意这里的设置，如果是下载的话（Get模式），就是将服务器端的”2.2“文件保存到本地，名称为ds.txt。如果是上传的话（Put模式），就是将本地文件”ds.txt“上传到服务器，名称为”2.2“。如果重复操作，文件会被覆盖，因此这里要注意。
传输完成，会出现下面的界面：

2.curl实现文件下载

好了，上面测试成功的话，就可以用curl写代码了。过程就不细说了，直接上代码：

struct TftpFile {
const char *filename;
FILE *stream;
};

static size_t my_fwrite(void *buffer, size_t size, size_t nmemb,void *stream)
{
struct TftpFile *out=(struct TftpFile *)stream;
if(out && !out->stream) {
/* open file for writing */
out->stream=fopen(out->filename, "wb");
if(!out->stream)
return -1; /* failure, can't open file to write */
}

return fwrite(buffer, size, nmemb, out->stream);
}

int downloadFileFromServer(int deviceID,char* tftpurl,char*local)
{
CURL *curl;
CURLcode res;
struct TftpFile tftpfile={
local,
NULL
};

curl_global_init(CURL_GLOBAL_DEFAULT);

curl = curl_easy_init();
if(curl) {

curl_easy_setopt(curl, CURLOPT_URL,tftpurl);

curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, my_fwrite);

curl_easy_setopt(curl, CURLOPT_WRITEDATA, &tftpfile);

curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);

curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

res = curl_easy_perform(curl);

/* always cleanup */
curl_easy_cleanup(curl);

if(CURLE_OK != res) {
/* we failed */
fprintf(stderr, "curl told us %d\n", res);
}
}

if(tftpfile.stream)
fclose(tftpfile.stream); /* close the local file */

curl_global_cleanup();

return 0;
}

外部调用方法：

downloadFileFromServer();

执行的时候就可以发现程序将服务器端下的“tftps.cpp”保存到本地了。

3.实现文件上传

还是直接上代码;

/*upload*/
#define LOCAL_FILE      "D:/tmp/curl.c"
#define UPLOAD_FILE_AS  "uploading.txt"
#define REMOTE_URL      "tftp://192.168.1.110:69/uploading.txt"
#define RENAME_FILE_TO  "renamed.txt"

static size_t read_callback(void *ptr, size_t size, size_t nmemb, void *stream)
{
curl_off_t nread;
/* in real-world cases, this would probably get this data differently
as this fread() stuff is exactly what the library already would do
by default internally */
size_t retcode = fread(ptr, size, nmemb, (FILE*)stream);

nread = (curl_off_t)retcode;

fprintf(stderr, "*** We read %" CURL_FORMAT_CURL_OFF_T
" bytes from file\n", nread);
return retcode;
}
int tftpfileUpload()
{
CURL *curl;
CURLcode res;
FILE *hd_src;
struct stat file_info;
curl_off_t fsize;

struct curl_slist *headerlist=NULL;
static const char buf_1 [] =  UPLOAD_FILE_AS;
static const char buf_2 [] =  RENAME_FILE_TO;

/* get the file size of the local file */
if(stat(LOCAL_FILE, &file_info)) {
printf("Couldnt open '%s': %s\n", LOCAL_FILE, strerror(errno));
return 1;
}
fsize = (curl_off_t)file_info.st_size;

printf("Local file size: %" CURL_FORMAT_CURL_OFF_T " bytes.\n", fsize);

/* get a FILE * of the same file */
hd_src = fopen(LOCAL_FILE, "rb");

/* In windows, this will init the winsock stuff */
curl_global_init(CURL_GLOBAL_ALL);

/* get a curl handle */
curl = curl_easy_init();
if(curl) {

/* we want to use our own read function */
curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);

/* enable uploading */
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

/* specify target */
curl_easy_setopt(curl,CURLOPT_URL, REMOTE_URL);

/* pass in that last of FTP commands to run after the transfer */
curl_easy_setopt(curl, CURLOPT_POSTQUOTE, headerlist);

/* now specify which file to upload */
curl_easy_setopt(curl, CURLOPT_READDATA, hd_src);

/* Set the size of the file to upload (optional).  If you give a *_LARGE
option you MUST make sure that the type of the passed-in argument is a
curl_off_t. If you use CURLOPT_INFILESIZE (without _LARGE) you must
make sure that to pass in a type 'long' argument. */
curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE,
(curl_off_t)fsize);

/* Now run off and do what you've been told! */
res = curl_easy_perform(curl);
/* Check for errors */
if(res != CURLE_OK)
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));

/* clean up the FTP commands list */
curl_slist_free_all (headerlist);

/* always cleanup */
curl_easy_cleanup(curl);
}
fclose(hd_src); /* close the local file */

curl_global_cleanup();
return 0;
}

调用方法为

tftpfileUpload();

OK !就这么简单。