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Date:      Wed, 28 Mar 2007 14:52:27 -0700
From:      Nate Lawson <nate@root.org>
To:        current@FreeBSD.org
Cc:        =?ISO-8859-1?Q?Dag-Erling_Sm=F8rgrav?= <des@des.no>
Subject:   libfetch ftp patch for less latency
Message-ID:  <460AE39B.4070706@root.org>

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To speed up pkg_add and other ftp command channel performance over slow
links, change this:

>>> PWD
<<< 257 "/"
>>> CWD pub
<<< 250 Directory successfully changed.
>>> CWD FreeBSD
<<< 250 Directory successfully changed.
>>> CWD ports
<<< 250 Directory successfully changed.
>>> CWD amd64
<<< 250 Directory successfully changed.
>>> CWD packages-6-stable
<<< 250 Directory successfully changed.
>>> CWD Latest
<<< 250 Directory successfully changed.
>>> MODE S

Into this:

>>> PWD
<<< 257 "/"
>>> CWD pub/FreeBSD/ports/amd64/packages-6-stable/Latest
<<< 250 Directory successfully changed.

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.

-- 
Nate

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===================================================================
RCS file: /home/ncvs/src/lib/libfetch/ftp.c,v
--- ftp.c	22 Jul 2006 06:01:58 -0000	1.91.2.1
+++ ftp.c	28 Mar 2007 20:42:58 -0000
@@ -267,6 +267,7 @@
 	char pwd[PATH_MAX];
 	int e, i, len;
 
+	/* If no slashes in name, no need to change dirs. */
 	if ((end = strrchr(file, '/')) == NULL)
 		return (0);
 	if ((e = _ftp_cmd(conn, "PWD")) != FTP_WORKING_DIRECTORY ||
@@ -276,7 +277,8 @@
 	}
 	for (;;) {
 		len = strlen(pwd);
-		/* look for a common prefix */
+
+		/* Look for a common prefix between PWD and dir to fetch. */
 		for (i = 0; i <= len && i <= end - file; ++i)
 			if (pwd[i] != file[i])
 				break;
@@ -284,6 +286,7 @@
 		DEBUG(fprintf(stderr, "have: [%.*s|%s]\n", i, pwd, pwd + i));
 		DEBUG(fprintf(stderr, "want: [%.*s|%s]\n", i, file, file + i));
 #endif
+		/* Keep going up a dir until we have a matching prefix. */
 		if (pwd[i] == '\0' && (file[i - 1] == '/' || file[i] == '/'))
 			break;
 		if ((e = _ftp_cmd(conn, "CDUP")) != FTP_FILE_ACTION_OK ||
@@ -293,6 +296,21 @@
 			return (-1);
 		}
 	}
+
+	/* Skip leading slashes, even "////". */
+	for (beg = file + i; beg < end && *beg == '/'; ++beg, ++i)
+		/* nothing */ ;
+
+	/* If there is no trailing dir, we're already there. */
+	if (beg >= end)
+		return (0);
+
+	/* Change to the directory all in one chunk (e.g., foo/bar/baz). */
+	e = _ftp_cmd(conn, "CWD %.*s", (int)(end - beg), beg);
+	if (e == FTP_FILE_ACTION_OK)
+		return (0);
+
+	/* That didn't work so go back to legacy behavior (multiple CWDs). */
 	for (beg = file + i; beg < end; beg = file + i + 1) {
 		while (*beg == '/')
 			++beg, ++i;

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