Windows® Internals, Sixth Edition, Part 1

When downloading files, BITS writes the file to a temporary hidden file in the destination directory. Of course, BITS will impersonate the user to ensure that file-system security and quotas are enforced properly. When the application calls the IBackgroundCopyJob::Complete method (or the Complete-BitsTransfer cmdlet in PowerShell), BITS renames the temporary files to their destination names, and the files are available to the client. If there is already a file in the destination directory with the same name, BITS overwrites the file.

When uploading files, by default, BITS does not allow overwriting an existing file. When the transfer is finished and BITS would overwrite the file, an error is returned to the client. To allow overwrites, set the BITSAllowOverwrites property to True in the Internet Information Services (IIS) metabase using PowerShell or Windows Management Instrumentation (WMI) scripting.

The BITS server is a server-side component that lets you configure an IIS server to allow BITS clients to perform file transfers to IIS virtual directories. Upon completion of a file upload, the BITS server can notify a web application of the new file’s presence (via an HTTP POST message) so the web application can process the uploaded files.

The BITS server extends IIS to support throttled, restartable uploads of files. To make use of the upload feature, you must create an IIS virtual directory on the server where you want the clients to upload their files. BITS adds properties to the IIS metabase for the virtual directory you create and uses these properties to determine how to upload the files.

For security reasons, BITS will not permit uploading files to a virtual directory that has scripting and execute permissions enabled. If you upload a file to a virtual directory that has these permissions enabled, the job will fail. Also, BITS does not require the virtual directory to be write-enabled, so it is recommended that you turn off write access to the virtual directory; however, the user must have write access to the physical directory.

In some cases, the BITS Compact Server might be used instead of IIS. The Compact Server is intended for use by enterprise and small business customers that meet the following conditions:

The anticipated usage is a maximum of 25 URL groups, and each URL group supports up to three simultaneous file transfers

File transfers occur between systems in the same domain or mutually trusted domains

File transfers are not intended for Internet-facing clients

Figure 7-14 demonstrates how to load the BITS module within PowerShell, and some of the BITS PowerShell cmdlets.

Figure 7-15 demonstrates the use of the BITSAdmin tool, which is now deprecated in favor of PowerShell for managing and using BITS.

Figure 7-14. Using BITS from PowerShell

Figure 7-15. BitsAdmin tool

Figure 7-16 shows BITS messages written to the event log.

Figure 7-16. BITS messages in the event log

Peer-to-Peer Infrastructure

Peer-to-Peer Infrastructure is a set of APIs that cover different technologies to enhance the Windows networking stack by providing flexible peer-to-peer (P2P) support for applications and services. The P2P infrastructure covers four major technologies, shown in Figure 7-17.

Figure 7-17. Peer-to-peer architecture

Here are the major peer-to-peer components:

Peer-to-Peer Graphing. Allows applications to pass data between peers efficiently and reliably by using nodes and events.

Peer-to-Peer Namespace Provider. Enables serverless name resolution of peers and their services (described later in the Name Resolution section).

Peer-to-Peer Grouping. Combines graphing and namespace technologies to group and isolate services and/or peers into a defined group and uniquely identify it.

Peer-to-Peer Identity Manager. Enhances the services offered by the namespace provider to securely create, publish, and identify peer names, as well as to identify group members that are part of the grouping API.

The Peer-to-Peer Infrastructure in Windows is also paired with the Peer-to-Peer Collaboration Interface, which adds support for creating collaborative P2P applications (such as online games and group instant messaging) and supersedes the Real-Time Communications (RTC) architecture in earlier versions of Windows. It also provides presence capabilities through the People Near Me (PNM) architecture.

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