Download a file from a FTP Server

{**************************************************************}
The following function shows how to connect to a ftp server
and download a file.

Specify the Host, User, Password, Port, Ftp-Directory,
File on Ftp, the local file.

You need a TProgressBar to show the progress and a TLabel to
show some progress informations.

Note: The functions from wininet.dll are used.

{**************************************************************}

uses
WinInet, ComCtrls;

function FtpDownloadFile(strHost, strUser, strPwd: string;
Port: Integer; ftpDir, ftpFile, TargetFile: string; ProgressBar: TProgressBar): Boolean;

function FmtFileSize(Size: Integer): string;
begin
if Size >= $F4240 then
Result := Format('%.2f', [Size / $F4240]) + ' Mb'
else
if Size < 1000 then
Result := IntToStr(Size) + ' bytes'
else
Result := Format('%.2f', [Size / 1000]) + ' Kb';
end;

const
READ_BUFFERSIZE = 4096; // or 256, 512, ...
var
hNet, hFTP, hFile: HINTERNET;
buffer: array[0..READ_BUFFERSIZE - 1] of Char;
bufsize, dwBytesRead, fileSize: DWORD;
sRec: TWin32FindData;
strStatus: string;
LocalFile: File;
bSuccess: Boolean;
begin
Result := False;

{ Open an internet session }
hNet := InternetOpen('Program_Name', // Agent
INTERNET_OPEN_TYPE_PRECONFIG, // AccessType
nil, // ProxyName
nil, // ProxyBypass
0); // or INTERNET_FLAG_ASYNC / INTERNET_FLAG_OFFLINE

{
Agent contains the name of the application or
entity calling the Internet functions
}

{ See if connection handle is valid }
if hNet = nil then
begin
ShowMessage('Unable to get access to WinInet.Dll');
Exit;
end;

{ Connect to the FTP Server }
hFTP := InternetConnect(hNet, // Handle from InternetOpen
PChar(strHost), // FTP server
port, // (INTERNET_DEFAULT_FTP_PORT),
PChar(StrUser), // username
PChar(strPwd), // password
INTERNET_SERVICE_FTP, // FTP, HTTP, or Gopher?
0, // flag: 0 or INTERNET_FLAG_PASSIVE
0);// User defined number for callback

if hFTP = nil then
begin
InternetCloseHandle(hNet);
ShowMessage(Format('Host "%s" is not available',[strHost]));
Exit;
end;

{ Change directory }
bSuccess := FtpSetCurrentDirectory(hFTP, PChar(ftpDir));

if not bSuccess then
begin
InternetCloseHandle(hFTP);
InternetCloseHandle(hNet);
ShowMessage(Format('Cannot set directory to %s.',[ftpDir]));
Exit;
end;

{ Read size of file }
if FtpFindFirstFile(hFTP, PChar(ftpFile), sRec, 0, 0) <> nil then
begin
fileSize := sRec.nFileSizeLow;
// fileLastWritetime := sRec.lastWriteTime
end else
begin
InternetCloseHandle(hFTP);
InternetCloseHandle(hNet);
ShowMessage(Format('Cannot find file ',[ftpFile]));
Exit;
end;

{ Open the file }
hFile := FtpOpenFile(hFTP, // Handle to the ftp session
PChar(ftpFile), // filename
GENERIC_READ, // dwAccess
FTP_TRANSFER_TYPE_BINARY, // dwFlags
0); // This is the context used for callbacks.

if hFile = nil then
begin
InternetCloseHandle(hFTP);
InternetCloseHandle(hNet);
Exit;
end;

{ Create a new local file }
AssignFile(LocalFile, TargetFile);
{$i-}
Rewrite(LocalFile, 1);
{$i+}

if IOResult <> 0 then
begin
InternetCloseHandle(hFile);
InternetCloseHandle(hFTP);
InternetCloseHandle(hNet);
Exit;
end;

dwBytesRead := 0;
bufsize := READ_BUFFERSIZE;

while (bufsize > 0) do
begin
Application.ProcessMessages;

if not InternetReadFile(hFile,
@buffer, // address of a buffer that receives the data
READ_BUFFERSIZE, // number of bytes to read from the file
bufsize) then Break; // receives the actual number of bytes read

if (bufsize > 0) and (bufsize <= READ_BUFFERSIZE) then
BlockWrite(LocalFile, buffer, bufsize);
dwBytesRead := dwBytesRead + bufsize;

{ Show Progress }
ProgressBar.Position := Round(dwBytesRead * 100 / fileSize);
Form1.Label1.Caption := Format('%s of %s / %d %%',[FmtFileSize(dwBytesRead),FmtFileSize(fileSize) ,ProgressBar.Position]);
end;

CloseFile(LocalFile);

InternetCloseHandle(hFile);
InternetCloseHandle(hFTP);
InternetCloseHandle(hNet);
Result := True;
end;