Sometimes Fidonet is regarded as a text-only network. At least, Fidonet is notable for its very few means of transferring binary data. File echoes do not enjoy an audience comparable to that of traditional echo areas; file requests and attaches are almost never routed between nodes. In that somewhat harsh circumstances, however, several means of encoding and embedding the binary data inside text messages exist. Files (and sometimes whole directories of files) are packed to economize traffic; some of the resulting archives are encoded in text lines that are sent via text-only means of communication -- in echomail, in netmail.
That's why all the following Fidonet URL schemes must have some common method to designate, if necessary, an object inside packed (archive) file and/or embedded in some text. The <required-part> of their URL always ends with "/<object-path>", and so URLs are written as follows:
The character "/" always has its reserved meaning in <object-path> part of URL; this character plays the role of delimiter between parts of the path.
The <object-path> part of URL takes one of the following forms:
<object-name>
If <object-path> contains just a name of some object, the URL designates that object. The object itself is embedded or is contained inside the resource specified by the rest of URL:
<scheme>://<basic-required-part>?<optional-part>
<object-name>/
The named object itself is a container (e.g. packed archive). The URL designates the root directory of that container.
<object-name>/<needed-object>
The <object-name> is a container (e.g. a packed archive), and its root directory contains <needed-object>; the URL designates that <needed-object>. If <needed-object> is a directory (i.e. not a file), the <object-path> is equivalent to its following form, <object-name>/<needed-object>/
<object-name>/<needed-object>/
The <needed-object> inside <object-name> is either a container itself (e.g. a packed archive file) or a subdirectory inside <object-name> container. The URL designates the contents of <needed-object> container or directory. (If <needed-object> is a container with subdirectories, the URL designate the contents of its root directory.)
<object-name>/<elem1>/<elem2>/.../<elemN>/<needed-object> or <object-name>/<elem1>/<elem2>/.../<elemN>/<needed-object>/
The <object-name> contains a hierarchy as deep as N elements, they're either subdirectories or container objects (packed archive files, for example). It is necessary to enter those containers and browse into directories, one after another, in the given order. The innermost element contains the object <needed-object>. The URL designates either the object itself (if trailing slash is missing and <needed-object> is not a subdirectory) or its contents (if <needed-object> is a subdirectory, that directory's contents is designated; otherwise, <needed-object>/ means the root directory of <needed-object>).
7.1.1. The leading slash and the trailing slash -+---------------------------------------------
The leading slash of <object-path> is a mere delimiter between <basic-required-part> and <object-path>. If the <object-path> part of a URL is empty, its leading slash MUST be ignored by the program interpreting the URL. If the <object-path> part of a URL is empty, its leading slash MAY be omitted by the author of that URL, thus the following URLs are equivalent:
<scheme>://<basic-required-part>/?<optional-part>
<scheme>://<basic-required-part>?<optional-part>
However, the trailing slash of <object-path> has its own value, makes some real difference. For example, "example.zip" means the archive itself (a file that may be saved or sent, etc.), and "example.zip/" means the root directory of that archive (a container that may be browsed, updated, etc.)
The trailing slash of <object-path> MUST NOT be ignored.
7.1.2. Dealing with unknown containers -+------------------------------------
Sometimes an <object-path> designates an object inside such a container that certain Fidonet browsers are not able to open by themselves. This MAY happen when the archive format is unknown (or is known, but is newer than the supported one).
If the object is requested as a separate entity (for example, its URL is entered in the address line of a Fidonet browser, or the user follows a hyperlink specifying that URL), the browser MAY inform the user about the unknown container encountered, and suggest saving that container for possible manual analysis (after all, the user may have unpacker tools in his avail that are not yet integrated into a Fidonet browser, and may be willing to try them).
If the requested object is not a separate entity (for example, if it is just one of images on a hypertext page), if many such objects are requested at the same time and for the same purpose, then it would not be wise to flood the user with information about each of such obstacles concurrently encountered, and so the browser SHOULD follow its standard procedures prescribed for the state of error (display a "broken image" icon, or use an alternate object or an alternate text where it is provided).
7.2. "area://" scheme -+-------------------
Echomail is an important and powerful force in Fidonet. Echomail is, by definition, a broadcast medium. See echomail specifications in FTS-0004.
An echomail area is a shared base of messages that have common areatag (area identifier) and are distributed through Fidonet via hierarchical and/or p2p-alike connections between individual Fidonet systems (nodes and points).
Due to the immanent modularity of Fidonet software packages, echomail composer and echomail browser can be different programs (for example, the latter does not require read/write access to the area message base and is able to work through a read-only gate). The "echomail:" scheme (defined above) is designed to designate an action of a Fidonet echomail composer; the "area://" scheme, defined is this section, designates a resource that is located in an area message base.
The area URLs take the form:
area://<areatag>/<object-path>?<optional-part>
The character "/" has its literal meaning in the <optional-part> of URLs of this scheme. The character "/" has its reserved meaning in the required part of URL (<areatag>/<object-path>), playing the role of delimiter between parts of the path. If an <areatag>
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