A COM component offering Internet download utilities

Download source files - 78 Kb

Sample Image - MyInetUtils.jpg

Introduction

A year ago I wanted to create a large multi-download program. I implemented the visual interface in VB6 and the actual download functionality in an ATL COM component. I used the URL monikers and specifically the CBindStatusCallback ATL class to implement downloading. Unfortunately the documentation for URL monikers is poor and I have only scratched the surface of this subject. I have not yet succeeded in implementing suspend and resume of downloads. The component also includes some other useful functions for cache access, URL and resolving of paths. I hope you'll find it useful. The figure above shows a small VB6 program that simultaneously downloads 3 files from the Microsoft download site.

Below there is a brief listing of the interface methods. In the source code zip file, you'll find also an HtmlHelp, created with my 'Automatic HTMLHelp Documentation' tool.

Object AsyncDownloader

Name	Type	Explanation
Interface IAsyncDownloader
AbortDownload	Method	Abort downloading (does not work)
ConcurrentDownloads	Property Get/Let	Number of concurrent downloads
DownloadedBytes	Property Get	Downloaded bytes yet
MaxBytes	Property Get	Maximum bytes to download
RequestDownload	Method	Request Download
ResumeDownload	Method	Resume Download (does not work)
Status	Property Get	Status of download (in progress, etc.)
SuspendDownload	Method	Suspend Download (does not work)
Event Interface _IAsyncDownloaderEvents
OnData	Event	Data arrived
OnFinish	Event	Finished downloading
OnStart	Event	Started downloading

Object CacheUtils

Name	Type	Explanation
Interface ICacheUtils
CrackUrl	Method	Crack Url into a UrlComponents object (host,path,etc.)
DownloadToFile	Method	Download URL To local file
MakeSureDirectoryPathExists	Method	Make Sure Directory Path Exists
PathCombine	Method	Combine paths
SaveURLfileFromCacheToLocalfile	Method	Save URL file From Cache To Local file
UrlCombine	Method	Url Combine

Object UrlComponents

Name	Type	Explanation
Interface IUrlComponents
ExtraInfo	Property Get/Let	ExtraInfo
FullURL	Property Get/Let	FullURL
HostName	Property Get/Let	HostName
Password	Property Get/Let	Password
Port	Property Get/Let	Port
Scheme	Property Get/Let	Scheme
UrlPath	Property Get/Let	UrlPath
UserName	Property Get/Let	UserName

Object PathUtils

Name	Type	Explanation
Interface IPathUtils
GetFullPathName	Method	Get Full PathName
GetModuleFileName	Method	Get Module FileName
GetShortPathName	Method	Get Short PathName
MakeSureDirectoryPathExists	Method	Make Sure Directory Path Exists
PathCanonicalize	Method	Path Canonicalize
PathCombine	Method	Path Combine
PathCommonPrefix	Method	Path Common Prefix
PathFindFileName	Method	Path Find FileName
PathIsDirectory	Method	Path Is Directory
PathIsFileSpec	Method	Path Is File Spec
PathIsPrefix	Method	Path Is Prefix
PathIsRelative	Method	Path Is Relative
PathIsRoot	Method	Path Is Root
PathIsSameRoot	Method	Path Is Same Root
PathIsUNC	Method	Path Is UNC
PathIsURL	Method	Path Is URL
PathMatchSpec	Method	Path Match Spec
PathQuoteSpaces	Method	Path Quote Spaces
PathRelativePathTo	Method	Path Relative Path To
PathRemoveArgs	Method	Path Remove Args
PathRemoveBackslash	Method	Path Remove Backslash
PathRemoveBlanks	Method	Path Remove Blanks
PathRemoveExtension	Method	Path Remove Extension
PathRemoveFileSpec	Method	Path Remove File Spec
PathRenameExtension	Method	Path Rename Extension
UrlCombine	Method	Url Combine

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Philipos Sakellaropoulos

Web Developer

Greece

Member

Software developer and Microsoft Trainer, Athens, Greece (MCT, MCSD.net, MCSE 2003, MCDBA 2000,MCTS, MCITP, MCIPD).

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Undefined behavior?

Humberto

7:19 18 Aug '06

In CacheUtils.cpp you have these lines (examples in MSDN Library do the same): `lpCacheEntry = LPINTERNET_CACHE_ENTRY_INFO(new char[dwEntrySize]); ... lpszOut = new char[dwStreamSize]; ... delete (lpCacheEntry); delete (lpszOut);` Using plain delete in objects that are allocated using new[] results in undefined behavior. Right?
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Is it possible to get images from Database?

Bill Murray

10:03 23 Nov '03

I am just wondering because the solution I am working on uses images that are stored in a database (existing app). I would, ideally, like to be able to pull the images out of the database and resample as a thumbnail.
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Save to file

Supay

5:25 25 Sep '03

Where is saved the files of you vb sample?
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Re: Save to file

Philipos Sakellaropoulos

11:16 29 Sep '03

Supay wrote: Where is saved the files of you vb sample? Good question..but i am not sure! I think you must use the SaveURLfileFromCacheToLocalfile function after finishing downloading. --- Remember yourself !! --------
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How to download a file again without copying from cache ?

piggybank

19:07 1 Jun '03

hi thanks a lot for your article and com :') I wonder how to download a file again for getting last version? and what's meaning the param 'Force' of method RequestDownlaod ? could you please provide a method like 'SaveURLfileFromCacheToLocalfile' as 'ClearURLfileFromCache' ? thanks very much ) piggybank@CN
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I did it with DeleteUrlCacheEntry()

piggybank

21:00 1 Jun '03

thanks again x)
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Run in browser

johndue

17:17 24 Apr '03

If any one know how to make this component work with events in javascript please let me know. Thanks
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Resume

Todd Smith

15:17 23 Dec '02

The default CBindStatusCallback implementation is setting the BINDF_GETNEWESTVERSION and BINDF_NOWRITECACHE flags in GetBindInfo() which disables resume I beleive.

I think you'd have to tap into the IHttpNegotiate interface and add a resume header in BeginningTransaction().

I looked into this before and found it easier to just write my own downloader from scratch using Winsock. ATL didn't gain me anything but trouble Frown | :(