Download a html page using url with parameters [duplicate] - delphi

Question

There's a web services I want to call in my application, I can use it with importing the WSDL or by just use "HTTP GET" with the URL and parameters, so I prefer the later because it's simple thing.
I know I can use indy idhttp.get, to do the job, but this is very simple thing and I don't want to add complex indy code to my application.
UPDATE: sorry if I was not clear, I meant by "not to add complex indy code", that I don't want add indy components for just this simple task, and prefer more lighter way for that.

Answer 1

Calling a RESTful web service using Indy is pretty straight forward.
Add IdHTTP to your uses clause. Remember that IdHTTP needs the "HTTP://" prefix on your URLs.
function GetURLAsString(const aURL: string): string;
var
lHTTP: TIdHTTP;
begin
lHTTP := TIdHTTP.Create;
try
Result := lHTTP.Get(aURL);
finally
lHTTP.Free;
end;
end;

Answer 2

You could use the WinINet API like this:
uses WinInet;
function GetUrlContent(const Url: string): string;
var
NetHandle: HINTERNET;
UrlHandle: HINTERNET;
Buffer: array[0..1024] of Char;
BytesRead: dWord;
begin
Result := '';
NetHandle := InternetOpen('Delphi 5.x', INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
if Assigned(NetHandle) then
begin
UrlHandle := InternetOpenUrl(NetHandle, PChar(Url), nil, 0, INTERNET_FLAG_RELOAD, 0);
if Assigned(UrlHandle) then
{ UrlHandle valid? Proceed with download }
begin
FillChar(Buffer, SizeOf(Buffer), 0);
repeat
Result := Result + Buffer;
FillChar(Buffer, SizeOf(Buffer), 0);
InternetReadFile(UrlHandle, #Buffer, SizeOf(Buffer), BytesRead);
until BytesRead = 0;
InternetCloseHandle(UrlHandle);
end
else
{ UrlHandle is not valid. Raise an exception. }
raise Exception.CreateFmt('Cannot open URL %s', [Url]);
InternetCloseHandle(NetHandle);
end
else
{ NetHandle is not valid. Raise an exception }
raise Exception.Create('Unable to initialize Wininet');
end;
source: http://www.scalabium.com/faq/dct0080.htm
The WinINet API uses the same stuff InternetExplorer is using so you also get any connection and proxy settings set by InternetExplorer for free.

Answer 3

Actually code in accepted answer did't work for me. So I modified it a little bit so it actually returns String and gracefully closes everything after execution. Example returns retrieved data as UTF8String so it will work well for ASCII as well as for UTF8 pages.
uses WinInet;
function GetUrlContent(const Url: string): UTF8String;
var
NetHandle: HINTERNET;
UrlHandle: HINTERNET;
Buffer: array[0..1023] of byte;
BytesRead: dWord;
StrBuffer: UTF8String;
begin
Result := '';
NetHandle := InternetOpen('Delphi 2009', INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
if Assigned(NetHandle) then
try
UrlHandle := InternetOpenUrl(NetHandle, PChar(Url), nil, 0, INTERNET_FLAG_RELOAD, 0);
if Assigned(UrlHandle) then
try
repeat
InternetReadFile(UrlHandle, #Buffer, SizeOf(Buffer), BytesRead);
SetString(StrBuffer, PAnsiChar(#Buffer[0]), BytesRead);
Result := Result + StrBuffer;
until BytesRead = 0;
finally
InternetCloseHandle(UrlHandle);
end
else
raise Exception.CreateFmt('Cannot open URL %s', [Url]);
finally
InternetCloseHandle(NetHandle);
end
else
raise Exception.Create('Unable to initialize Wininet');
end;
Hope it helps for somebody like me who was looking for easy code how to retrieve page content in Delphi.
Cheers, Aldis :)

Answer 4

In newer Delphi versions it is better to use THTTPClient from System.Net.HttpClient unit, since it is standard and cross-platform. Simple example is
function GetURL(const AURL: string): string;
var
HttpClient: THttpClient;
HttpResponse: IHttpResponse;
begin
HttpClient := THTTPClient.Create;
try
HttpResponse := HttpClient.Get(AURL);
Result := HttpResponse.ContentAsString();
finally
HttpClient.Free;
end;
end;

Answer 5

If it's okay to download to a file, you can use TDownloadURL from the ExtActns unit. Much simpler than using WinInet directly.
procedure TMainForm.DownloadFile(URL: string; Dest: string);
var
dl: TDownloadURL;
begin
dl := TDownloadURL.Create(self);
try
dl.URL := URL;
dl.FileName := Dest;
dl.ExecuteTarget(nil); //this downloads the file
finally
dl.Free;
end;
end;
It's also possible to get progress notifications when using this. Simply assign an event handler to TDownloadURL's OnDownloadProgress event.

Answer 6

Using Windows HTTP API might be easy too.
procedure TForm1.Button1Click(Sender: TObject);
var http: variant;
begin
http:=createoleobject('WinHttp.WinHttpRequest.5.1');
http.open('GET', 'http://lazarus.freepascal.org', false);
http.send;
showmessage(http.responsetext);
end;
https://msdn.microsoft.com/ru-ru/library/windows/desktop/aa382925.aspx
http://forum.lazarus.freepascal.org/index.php?topic=14609.0
Save a file downloaded via WinHTTP to disk, using Delphi XE
How to use "WinHttp.WinHttpRequest.5.1" asynchronously?
http://www.delphigroups.info/2/4/217167.html
https://github.com/fabriciocolombo/delphi-rest-client-api/blob/master/src/HttpConnectionWinHttp.pas
In the code above I imply that COM was already initialized for the main VCL thread. Reportedly it might not be always the case for simplistic apps or for LCL apps. Also it would definitely not be the case for async (multithread) work.
Below is the snippet from a real code running. Note - the functionality is bonus. It is not required to work. So while I do issue requests, I do not care about their results, that result is ignored and dumped.
procedure TfmHaspList.YieldBlinkHTTP(const LED: boolean; const Key_Hardware_ID: cardinal);
var URL: WideString;
begin
URL := 'http://127.0.0.1:1947/action.html?blink' +
IfThen( LED, 'on', 'off') + '=' + IntToStr(Key_Hardware_ID);
TThread.CreateAnonymousThread(
procedure
var Request: OleVariant;
begin
// COM library initialization for the current thread
CoInitialize(nil);
try
// create the WinHttpRequest object instance
Request := CreateOleObject('WinHttp.WinHttpRequest.5.1');
// open HTTP connection with GET method in synchronous mode
Request.Open('GET', URL, False);
// set the User-Agent header value
// Request.SetRequestHeader('User-Agent', 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0');
// sends the HTTP request to the server, the Send method does not return
// until WinHTTP completely receives the response (synchronous mode)
Request.Send;
// // store the response into the field for synchronization
// FResponseText := Request.ResponseText;
// // execute the SynchronizeResult method within the main thread context
// Synchronize(SynchronizeResult);
finally
// release the WinHttpRequest object instance
Request := Unassigned;
// uninitialize COM library with all resources
CoUninitialize;
end;
end
).Start;
end;

Answer 7

Use the Synapse TCP/IP function in the HTTPSEND unit (HTTPGetText, HTTPGetBinary). It will do the HTTP pull for you and doesn't require any external DLL's other than Winsock. The latest SVN release works perfectly well in Delphi 2009. This uses blocking function calls, so no events to program.
Update: The units are very light, and are not component based. The latest version from SVN runs perfectly well in Delphi XE4 also.

Answer 8

If your application is Windows-only, I would suggest using WinSock. It's simple enough, allows to execute any HTTP request, can work both synchronously and asynchronously (using non-blocking WSASend/WSARecv with callbacks or good old send/recv in a dedicated thread).