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The FrontPage Server Extensions Remote Protocol is used by client applications to display the contents of a site as a file system. The FrontPage Server Extensions Remote Protocol provides file uploading and downloading, directory creation and listing, basic file locking, and file movement on a web server by using a set of methods.
Each message from the client is in the form of an HTTP POST or GET ([RFC2616] sections 9.5 and 9.3) that includes a set of parameters, and each reply from the server returns a set of values as an HTML response ([RFC2854]). The method parameter defines what operation the server will perform in addition to the meanings of the other parameters and return values.
The client sends method call requests to the server, and the server sends return values to the client via HTML. The server never initiates any communication with the client. All communication is transported over HTTP or secure HTTP (HTTPS), as described in [RFC2616] section 9.1. Method calls are sent as HTTP POSTs, [RFC2616] section 4.2, with the method name and arguments as the message entity, and server responses are sent as a list in the message body, [RFC2616] section 4.2, of an HTTP response. All posts are made to one of several well-defined URLs on the server, which can be discovered by clients.
A protocol client initiates its communication with the server by requesting well-defined URLs for further communication, as specified in section 3.1.3.2.1, and determining the version of the server as specified in section 1.7.1. This protocol specifies no additional requirements on the HTTP protocol layer as described in [RFC2616] for maintaining state across request/responses. See [RFC2616] section 4.4 for more information about the determination of message length, and [RFC2616] section 8 for information about layering HTTP on top of the TCP protocol.
The following sequence diagram depicts a generic FrontPage Server Extensions conversation. A brief explanation of each message follows, and details are defined in sections 2 and 3.
Figure 1: A generic Microsoft FrontPage Server Extension message sequence
The HTTP OPTIONS request is sent to determine if the server supports the FrontPage Server Extensions Remote Protocol. If the response contains the MS-Author-Via header, as specified in section 3.1.3.1, the server supports the protocol. This value is often cached by clients.
The HTTP GET on _vti_inf.html will return information specifying the well-defined URLs to which the client can POST further method calls.
At this point, the client is prepared to start making method calls against the server. The first call is a server version request (see section 3.1.5.3.14) whereby the client negotiates a protocol version with the server.
The client can then call the url to web url (see section 3.1.5.3.16) if the site is a subsite, that is, one not located at the root of the server's namespace.
Next, the client can make an open service request (see section 3.1.5.3.10) on the site that it wants to open. This request is optional, but it will return information about the site's capabilities, such as support for version control.
The client can make any method calls against the server. The nature of any further client/server communication is determined by the specific needs of the client at the time.
To give an example of how the protocol is used in Windows, a user might type an HTTP URL into the address bar of a file browser. The file browser contacts the server to determine if it supports the FrontPage Server Extensions Remote Protocol. If so, the file browser uses the FrontPage Server Extensions Remote Protocol to list the contents of the directory that the user entered and to display the contents just as it would display files on the local hard disk.
The Windows SharePoint Services dialogview aspect of the FrontPage Server Extensions Remote Protocol is designed to allow a client to ask the server to provide an HTML rendering of its file structure. The client can then display this HTML rendering and navigate through it.
When using Windows SharePoint Services dialogview (see section 3.1.5.3.17.1), the sequence of messages is similar to that shown in the following figure. For a brief explanation of each message, see sections 2 and 3.
Figure 2: Windows SharePoint Services dialogview message sequence
The first three messages are used identically to those shown in the first figure in this section. The final HTTP GET returns the HTML that the client can use to display the site's file system. This GET is performed against a specific, well-known URL on the server (see section 3.1.3.2).