Passing SFTP options when using SCP

[Damien Miller]

On Tue, 6 Dec 2022, Chris Rapier wrote:

> Hey all,
> 
> I might have missed this but is there any effective way of passing sftp
> options when using scp? For example, increasing the number of outstanding
> requests which would be the -R command line option in sftp.
> 
> For my purposes I'm mostly looking at sending different buffer (-B) and
> request (-R) options. Even better if there is a way to do that
> programmatically. For example, in sftp-client.c I can just change
> DEFAULT_NUM_REQUESTS to whatever value I like and every sftp transfer I
> initiate will use that.
> 
> Just curious. If there isn't I'll try to come up with a method and share it
> when I'm done.

There are no options to do this ATM and at least one of the option
letters that sftp uses already has meaning for sftp. These are
rarely used, so maybe it makes sent to put them behind a single
getopt chat that accepts multiple arguments.

diff --git a/scp.c b/scp.c
index c7194c2..4e50be1 100644
--- a/scp.c
+++ b/scp.c
@@ -150,6 +150,10 @@ char *ssh_program = _PATH_SSH_PROGRAM;
 pid_t do_cmd_pid = -1;
 pid_t do_cmd_pid2 = -1;
 
+/* SFTP copy parameters */
+size_t sftp_copy_buflen;
+size_t sftp_nrequests;
+
 /* Needed for sftp */
 volatile sig_atomic_t interrupted = 0;
 
@@ -419,7 +423,7 @@ int
 main(int argc, char **argv)
 {
 	int ch, fflag, tflag, status, n;
-	char **newargv, *argv0;
+	char **newargv, *argv0, *cp;
 	const char *errstr;
 	extern char *optarg;
 	extern int optind;
@@ -452,7 +456,7 @@ main(int argc, char **argv)
 
 	fflag = Tflag = tflag = 0;
 	while ((ch = getopt(argc, argv,
-	    "12346ABCTdfOpqRrstvD:F:J:M:P:S:c:i:l:o:")) != -1) {
+	    "12346ABCTdfOpqRrstvD:F:J:M:P:S:c:i:l:o:X:")) != -1) {
 		switch (ch) {
 		/* User-visible flags. */
 		case '1':
@@ -533,6 +537,23 @@ main(int argc, char **argv)
 			addargs(&remote_remote_args, "-q");
 			showprogress = 0;
 			break;
+		case 'X':
+			if (strncmp(optarg, "buffer=", 7) == 0) {
+				sftp_copy_buflen = strtol(optarg + 7, &cp, 10);
+				if (sftp_copy_buflen == 0 || *cp != '\0') {
+					fatal("Invalid buffer size \"%s\"",
+					     optarg);
+				}
+			} else if (strncmp(optarg, "nrequests=", 10) == 0) {
+				sftp_nrequests = strtol(optarg + 10, &cp, 10);
+				if (sftp_nrequests == 0 || *cp != '\0') {
+					fatal("Invalid number of requests "
+					    "\"%s\"", optarg);
+				}
+			} else {
+				fatal("Invalid -X option");
+			}
+			break;
 
 		/* Server options. */
 		case 'd':
@@ -941,7 +962,8 @@ do_sftp_connect(char *host, char *user, int port, char *sftp_direct,
 		    reminp, remoutp, pidp) < 0)
 			return NULL;
 	}
-	return do_init(*reminp, *remoutp, 32768, 64, limit_kbps);
+	return do_init(*reminp, *remoutp,
+	    sftp_copy_buflen, sftp_nrequests, limit_kbps);
 }
 
 void