Ftp的断点下载实现

思路：首先获取本地临时文件的大小，在通过FTp的REST命令获取远程文件的偏移，然后再RETR命令在偏移处下载。while循环对比本地文件和远程文件的字节大小，如此

不断的反复以上过程，直到远程文件字节和本地文件字节一样，退出循环，下载完成。

 1    long remote_file_size = m_ftp->getFileLength(remoteFileName.toStdString());
 2     long recvSize = 0;
 3
 4     if (remote_file_size == -1 )
 5     {
 6         return false;
 7     }
 8
 9     int conn_count = 10;
10
11     while (conn_count != 0 && local_file_size != remote_file_size)
12     {
13         recvSize = m_ftp->Get2(remoteFileName.toStdString(), tmp_save_file_name.toStdString(), local_file_size);
14         if (recvSize <= 0)
15         {
16             msleep(50);
17             if (!reConnect())
18             {
19                 break;
20             }
21             conn_count--;
22         }
23
24         local_file_size = getLocalFileSize(tmp_save_file_name);
25     }

1 FTP_API CFTP::Get2(const std::string &strRemoteFile, const std::string &strLocalFile, const int pos)
2 {
3     return downLoad2(strRemoteFile, strLocalFile, pos);
4 }

 1 FTP_API CFTP::downLoad2(const std::string &strRemoteFile, const std::string& strLocalFile, const int pos /*= 0*/, const unsigned int length /*= 0*/)
 2 {
 3     assert(length >= 0);
 4
 5     FILE *file = NULL;
 6     unsigned long nDataLen = FTP_DEFAULT_BUFFER;
 7     char strPos[MAX_PATH] = { 0 };
 8     int data_fd = socket(AF_INET, SOCK_STREAM, 0);
 9
10     assert(data_fd != -1);
11
12     if ((length != 0) && (length < nDataLen))
13     {
14         nDataLen = length;
15     }
16     char *dataBuf = new char[nDataLen];
17     if (dataBuf == NULL)
18     {
19         return -1;
20     }
21     memset(dataBuf, 0, sizeof(dataBuf));
22
23     //assert(dataBuf != NULL);
24
25     sprintf(strPos, "%d", pos);
26
27     if (createDataLink(data_fd) < 0)
28     {
29         trace("@@@@ Create Data Link error!!!\n");
30         return -1;
31     }
32
33
34     std::string strCmdLine = parseCommand(FTP_COMMAND_DOWNLOAD_POS, strPos);//param 1 为REST命令
35     if (Send(m_cmdSocket, strCmdLine) < 0)
36     {
37         return -1;
38     }
39     trace("@@@@Response: %s\n", serverResponse(m_cmdSocket).c_str());
40
41
42     strCmdLine = parseCommand(FTP_COMMAND_DOWNLOAD_FILE, strRemoteFile);//param 1为RETR命令
43
44     if (Send(m_cmdSocket, strCmdLine) < 0)
45     {
46         return -1;
47     }
48
49     std::string strResponse = serverResponse(m_cmdSocket);
50     trace("@@@@Response: %s\n", strResponse.c_str());
51
52     file = createLocalFile2(std::string(strLocalFile));
53     assert(file != NULL);
54
55     int len = 0;
56     int nReceiveLen = 0;
57     while ((len = getData(data_fd, dataBuf, nDataLen)) > 0)
58     {
59         nReceiveLen += len;
60
61         int num = fwrite(dataBuf, 1, len, file);
62         memset(dataBuf, 0, sizeof(dataBuf));
63
64
65         trace("Num:%d, nReceiveLen:%d\n", num, nReceiveLen);
66
67     }
68
69     Close(data_fd);
70     fclose(file);
71     delete[]dataBuf;
72
73     return nReceiveLen;
74
75 }

references:

http://blog.chinaunix.net/uid-7377299-id-112977.html