Re: libfetch ftp patch for less latency

On Thursday 29 March 2007 01:53:33 pm Rui Paulo wrote:
Nate Lawson wrote:
To speed up pkg_add and other ftp command channel performance over slow
links, change this:
[...]
All ftp servers I've ever seen support a full path when changing down
dirs. This might be a DOS ftp server thing however. In any case, if
there is an error to the all-in-one CWD, the code reverts back to legacy
behavior of multiple CWDs.

Yes, I think this behavior is acceptable. If the pathname fails it only
adds one more CWD, but reduces the time on the successful cases (which
are many if you consider the Ports collection).

Dag-Erling Smørgrav wrote:
> No. This is a violation of the FTP protocol.
> [...]
> When the all-in-one CWD fails, you're SOL. You have no idea what
> state the server is in, and you have to start over.

About the possible violation of the RFC, I quote:

pathname

Pathname is defined to be the character string which must be
input to a file system by a user in order to identify a file.
Pathname normally contains device and/or directory names, and
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
file name specification. FTP does not yet specify a standard
^^^^^^^^^^^^^^^^^^^^^^^
pathname convention. Each user must follow the file naming
conventions of the file systems involved in the transfer.


CHANGE WORKING DIRECTORY (CWD)

This command allows the user to work with a different
directory or dataset for file storage or retrieval without
altering his login or accounting information. Transfer
parameters are similarly unchanged. The argument is a
pathname specifying a directory or other system dependent
^^^^^^^^
file group designator.


I'm not sure why you consider this a violation of the protocol.
Also, considering the reply codes to the CWD command, only 421 seems to
change the server state.

Have you seen servers that change their state by issuing giving invalid
arguments to the CWD command ?

http://www.freebsd.org/cgi/query-pr.cgi?pr=83278

In this case IIRC, the problem was the leading / as the path fetched was
supposed to be relative to the user's home directory, but instead fetch sent
an absolute path and failed.

See also http://www.ietf.org/rfc/rfc1738.txt which is the RFC for URLs and
explains exactly how the <url-path> for ftp URLs should be interpreted:

<quote from="rfc1738">
3.2.2. FTP url-path

The url-path of a FTP URL has the following syntax:

<cwd1>/<cwd2>/.../<cwdN>/<name>;type=<typecode>

Where <cwd1> through <cwdN> and <name> are (possibly encoded) strings
and <typecode> is one of the characters "a", "i", or "d". The part
";type=<typecode>" may be omitted. The <cwdx> and <name> parts may be
empty. The whole url-path may be omitted, including the "/"
delimiting it from the prefix containing user, password, host, and
port.

The url-path is interpreted as a series of FTP commands as follows:

Each of the <cwd> elements is to be supplied, sequentially, as the
argument to a CWD (change working directory) command.

If the typecode is "d", perform a NLST (name list) command with
<name> as the argument, and interpret the results as a file
directory listing.

Otherwise, perform a TYPE command with <typecode> as the argument,
and then access the file whose name is <name> (for example, using
the RETR command.)

Within a name or CWD component, the characters "/" and ";" are
reserved and must be encoded. The components are decoded prior to
their use in the FTP protocol. In particular, if the appropriate FTP
sequence to access a particular file requires supplying a string
containing a "/" as an argument to a CWD or RETR command, it is
necessary to encode each "/".

For example, the URL <URL:ftp://myname@xxxxxxxx/%2Fetc/motd> is
interpreted by FTP-ing to "host.dom", logging in as "myname"
(prompting for a password if it is asked for), and then executing
"CWD /etc" and then "RETR motd". This has a different meaning from
<URL:ftp://myname@xxxxxxxx/etc/motd> which would "CWD etc" and then
"RETR motd"; the initial "CWD" might be executed relative to the
default directory for "myname". On the other hand,
<URL:ftp://myname@xxxxxxxx//etc/motd>, would "CWD " with a null
argument, then "CWD etc", and then "RETR motd".
</quote>

--
John Baldwin
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