FTP
The ftp: prefix indicates that the
FTP protocol is used, as defined
in RFC959 or any successor. The port
number, if present, gives the port
of the FTP server if not the FTP
default.
User name and password
The syntax allows for the inclusion
of a user name and even a password
for those systems which do not use
the anonymous FTP convention. The
default, however, if no user or password
is supplied, will be to use that
convention, viz. that the user name
is "anonymous" and the password the
user's Internet-style mail address
.
Where possible, this mail address
should correspond to a usable mail
address for the user, and preferably
give a DNS host name which resolves
to the IP address of the client.
Note that servers currently vary
in their treatment of the anonymous
password.
Path
The FTP protocol allows for a sequence
of CWD commands (change working directory)
and a TYPE command prior to service
commands such as RETR (retrieve)
or NLIST (etc) which actually access
a file.
The arguments of any CWD commands
are successive segment parts of the
URL delimited by slash, and the final
segment is suitable as the filename
argument to the RETR command for
retrieval or the directory argument
to NLIST.
For some file systems (Unix in particular),
the "/" used to denote the hierarchical
structure of the URL corresponds
to the delimiter used to construct
a file name hierarchy, and thus,
the filename will look the same as
the URL path. This does NOT mean
that the URL is a Unix filename.
Note: Retrieving subsequent URLs
from the same host
There is no common hierarchical model
to the FTP protocol, so if a directory
change command has been given, it
is impossible in general to deduce
what sequence should be given to
navigate to another directory for
a second retrieval, if the paths
are different. The only reliable
algorithm is to disconnect and reestablish
the control connection.
The data content type of a file can
only, in the general FTP case, be
deduced from the name, normally the
suffix of the name. This is not standardized.
An alternative is for it to be transferred
in information outside the URL. A
suitable FTP transfer type (for example
binary "I" or text "A") must in
turn be deduced from the data content
type. It is recommended that conventions
for suffixes of public archives be
established, but it is outside the
scope of this standard.
An FTP URL may optionally specify
the FTP data transfer type by which
an object is to be retrieved. Most
of the methods correspond to the
FTP "Data Types" ASCII and IMAGE
for the retrieval of a document,
as specified in FTP by the TYPE command
. One method indicates directory
access.
The data type is specified by a suffix
to the URL. Possible suffixes are:
- ;type = <type-code>
- Use FTP type
as given to perform data transfer.
- /
- Use FTP directory list commands
to read directory
-
The type code is in the format defined
in RFC959 except that THE SPACE IS
OMITTED FROM THE URL.
Transfer Mode
Stream Mode is always used.