Indy Http Server with resume support - delphi

Question

I have written an indy http server, I want to serve file download with resume support. When I use IDM to download file, the download is single threaded:
Note that the Resume capability is Yes, but When I pause and resume the download, It starts form beginning.
My Indy Http Server is as:
void __fastcall TfrmMain::httpServerCommandGet(TIdContext *AContext,
TIdHTTPRequestInfo *ARequestInfo, TIdHTTPResponseInfo *AResponseInfo)
{
Beep(1000, 100);
string fileName = ExtractFileDir(Application->ExeName) + ARequestInfo->Document;
fileName = fileName.replace("/", "\\");
TFileStream *stream = new TFileStream(fileName, fmOpenRead | fmShareDenyNone);
int start = 0, end = 0;
string range = ARequestInfo->Range;
if(!range.empty())
{
int dash_pos = range.find("-");
start = range.substr(0, dash_pos).intValue();
end = range.substr(dash_pos + 1).intValue();
if(end == 0) // Endless Range: start-
end = stream->Size;
}
else
{
start = 0;
end = stream->Size;
}
OutputDebugStringW(string("ctx=[] start=[] end=[]") <<
IntToHex((int)AContext, 8) << start << end);
stream->Seek((__int64)start, soBeginning);
AResponseInfo->ContentStream = stream;
AResponseInfo->FreeContentStream = true;
AResponseInfo->ContentLength = stream->Size;
if(!range.empty())
{
AResponseInfo->ContentRangeStart = start;
AResponseInfo->ContentRangeEnd = end;
AResponseInfo->ResponseNo = 206;
AResponseInfo->ContentRangeInstanceLength = end + 1;
AResponseInfo->ContentLength = end - start + 1;
AResponseInfo->AcceptRanges = "bytes";
}
AResponseInfo->WriteHeader();
AResponseInfo->WriteContent();
}
any help would be appreciated.

Answer 1

The IdCustomHTTPServer unit has a TIdHTTPRangeStream helper class for this very purpose.
If the client requests a ranged download, create an instance of TIdHTTPRangeStream and pass it your intended TStream and the client's requested range, then assign it as the ContentStream to be sent. TIdHTTPRangeStream also has a ResponseCode property that you need to assign to the response's ResponseNo property.
For example:
void __fastcall TfrmMain::httpServerCommandGet(TIdContext *AContext, TIdHTTPRequestInfo *ARequestInfo, TIdHTTPResponseInfo *AResponseInfo)
{
// create file stream ...
// THTTPServer parses the ranges for you
if (ARequestInfo->Ranges->Count > 0)
{
if (ARequestInfo->Ranges->Count > 1)
{
AResponseInfo->ResponseNo = 416;
return;
}
TIdEntityRange *range = ARequestInfo->Ranges->Range[0];
TIdHTTPRangeStream *rstream = new TIdHTTPRangeStream(stream, range->StartPos, range->EndPos, true);
AResponseInfo->ResponseNo = rstream->ResponseCode;
AResponseInfo->ContentRangeStart = rstream->RangeStart;
AResponseInfo->ContentRangeEnd = rstream->RangeEnd;
AResponseInfo->ContentStream = rstream;
AResponseInfo->AcceptRanges = "bytes";
}
else
{
AResponseInfo->ContentStream = stream;
}
// no need to seek the target stream manually
// no need to set the ContentLength manually
// no need to call WriteHeader() and WriteContent() manually
//
// TIdHTTPServer handles all that for you internally!
}