[编程点滴]C++编写下载工具

由于软件里面需要一个下载功能, 就从<C++编程艺术>里面把代码搞出来, 做了一个Unicode版本的下载功能(为了跟软件和谐一点点..).

原理挺简单的, 基本就是用WinINet里面的函数, 详细的就不说了.

对于ANSI版本的字符串函数对应的Unicode版本, 可以参见这个链接.

推荐一下<C++编程艺术>这本书, 虽然很基础..

还是上代码吧~~

//dl.h
#include <iostream>
#include <windows.h>
#include <wininet.h>
#include <fstream>
#include <cstdio>

using namespace std;

const int MAX_ERRMSG_SIZE = 80;
const int MAX_FILENAME_SIZE = 512;
const int BUF_SIZE = 1024;

// A class for downloading files from the Internet.
class Download
{
public:
    static bool ishttp(TCHAR *url);
    static bool httpverOK(HINTERNET hIurl);
    static bool getfname(TCHAR *url, TCHAR *fname);
    static unsigned long openfile(TCHAR *url, bool reload,
                                  ofstream &fout);
public:
    static bool download(TCHAR *url, bool restart = false,
                         void (*update)(unsigned long, unsigned long) = NULL);
};

//dl.cpp
#include "dl.h"
#include <tchar.h>

bool Download::download(TCHAR *url, bool reload,
                        void (*update)(unsigned long, unsigned long))
{
    ofstream fout;           // output stream
    unsigned char buf[BUF_SIZE]; // input buffer
    unsigned long numrcved;  // number of bytes read
    unsigned long filelen;   // length of file on disk
    HINTERNET hIurl, hInet;  // Internet handles
    unsigned long contentlen;// length of content
    unsigned long len;       // length of contentlen
    unsigned long total = 0; // running total of bytes received
    TCHAR header[80];         // holds Range header

    if(!ishttp(url))
        return FALSE;

    filelen = openfile(url, reload, fout);

    // See if Internet connection available.
    if(InternetAttemptConnect(0) != ERROR_SUCCESS)
    {
        return FALSE;
    }

    // Open Internet connection.
    hInet = InternetOpen(TEXT("downloader"),
                         INTERNET_OPEN_TYPE_DIRECT,
                         NULL, NULL,  0);

    if(hInet == NULL)return FALSE;

    // Construct header requesting range of data.
    swprintf(header, TEXT("Range:bytes=%d-"), filelen);
    /*printf("%s\n", header);*/

    // Open the URL and request range.
    hIurl = InternetOpenUrl(hInet, url,
                            header, -1,
                            INTERNET_FLAG_NO_CACHE_WRITE, 0);

    if(hIurl == NULL)
    {
        return FALSE;
    }

    // Confirm that HTTP/1.1 or greater is supported.
    if(!httpverOK(hIurl))
        return FALSE;

    // Get content length.
    len = sizeof(contentlen);
    if(!HttpQueryInfo(hIurl,
                      HTTP_QUERY_CONTENT_LENGTH |
                      HTTP_QUERY_FLAG_NUMBER,
                      &contentlen, &len, NULL))
    {

        printf("File or content length not found.\n");
    }

    // If existing file (if any) is not complete,
    // then finish downloading.
    if(filelen != contentlen && contentlen)
        do
        {
            // Read a buffer of info.
            if(!InternetReadFile(hIurl, &buf,
                                 BUF_SIZE, &numrcved))
            {
                printf("Error occurred during download.\n");
            }

            // Write buffer to disk.
            fout.write((const char *) buf, numrcved);
            if(!fout.good())
            {
                printf("Error writing file.\n");
            }

            total += numrcved; // update running total

            // Call update function, if specified.
            if(update && numrcved > 0)
                update(contentlen + filelen, total + filelen);

        }
        while(numrcved > 0);
    else if(update)
        update(filelen, filelen);

    fout.close();
    InternetCloseHandle(hIurl);
    InternetCloseHandle(hInet);

    return true;
}

// Return true if HTTP version of 1.1 or greater.
bool Download::httpverOK(HINTERNET hIurl)
{
    TCHAR str[80] = {0};
    unsigned long len = 79;

    // Get HTTP version.
    if(!HttpQueryInfo(hIurl, HTTP_QUERY_VERSION, &str, &len, NULL))
        return false;
    TCHAR *p = wcschr(str, TEXT('/'));

    p++;
    if(*p == TEXT('0')) return false; // can use HTTP 0.x

    // Now, find start of minor HTTP version number.
    p = wcschr(str, TEXT('.'));
    p++;

    // Convert to int.
    int minorVerNum = _tstoi(p);

    if(minorVerNum > 0) return true;
    return false;
}

// Extract the filename from the URL.  Return false if
// the filename cannot be found.
bool Download::getfname(TCHAR *url, TCHAR *fname)
{
    TCHAR *p = wcsrchr(url, TEXT('/'));
    if(p && (wcslen(p) < MAX_FILENAME_SIZE))
    {
        p++;
        wcscpy(fname, p);
        return true;
    }
    else
        return false;
}

//返回的值是文件的大小, 用户后来展现进度用...
unsigned long Download::openfile(TCHAR *url,
                                 bool reload,
                                 ofstream &fout)
{
    TCHAR fname[MAX_FILENAME_SIZE];

    if(!getfname(url, fname))
        return 0;
    if(!reload)
        fout.open(fname, ios::binary | ios::out |
                  ios::app | ios::ate);
    else
        fout.open(fname, ios::binary | ios::out |
                  ios::trunc);
    if(!fout)
        return 0;
    return fout.tellp();
}

bool Download::ishttp(TCHAR *url)
{
    TCHAR str[5] = TEXT("");
    wcsncpy(str, url, 4);
    for(TCHAR *p = str; *p; p++) *p = towlower(*p);
    return !wcscmp(TEXT("http"), str);
}

//main.cpp
#include <iostream>
#include "dl.h"

// This function displays the download progress as a percentage.
void showprogress(unsigned long total, unsigned long part)
{
    int val = (int) ((double) part / total * 100);
    cout << val << "%" << endl;
}

int main(int argc, char *argv[])
{
    TCHAR url[] =
        TEXT("http://zeq2.com/SVN/Source/Tools/MinGW/include/ddk/ntddk.h");

    bool reload = false;

    if(argc == 2 && !strcmp(argv[1], "reload"))
        reload = true;

    cout << "Beginning download.\n";
    if(Download::download(url, reload, showprogress))
        cout << "Download Complete\n";
    return 0;
}