support/download: Add SFTP support

Add Secure File Transfer Program (SFTP) support using a simple wrapper.
SFTP is a common protocol used to transfer files securely between
enterprises, but it is not currently supported in Buildroot because all
of the packages are usually available via HTTP, git or some other
download method.

SFTP is similar to FTP but it preforms all operations over an encrypted
SSH transport using a specific protocol. This is unlike ftps, which is
traditional FTP over an SSL/TLS connection.

Signed-off-by: Thomas Preston <thomas.preston@codethink.co.uk>
Signed-off-by: Michael Drake <michael.drake@codethink.co.uk>
[Arnout:
 - update documentation with sftp everywhere scp is mentioned;
 - rename "verbose" variable to "quiet";
 - print the sftp command, similar to wget and scp helpers.
]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

Config.in

@@ -119,6 +119,10 @@ config BR2_SCP
 	string "Secure copy (scp) command"
 	default "scp"
 
+config BR2_SFTP
+	string "Secure file transfer (sftp) command"
+	default "sftp"
+
 config BR2_HG
 	string "Mercurial (hg) command"
 	default "hg"

docs/manual/adding-packages-generic.txt

@@ -256,7 +256,7 @@ not and can not work as people would expect it should:
   +scp://[user@]host:filepath+, and that filepath is relative to the
   user's home directory, so you may want to prepend the path with a
   slash for absolute paths:
-  +scp://[user@]host:/absolutepath+. +
+  +scp://[user@]host:/absolutepath+. The same goes for SFTP URLs. +
   If +HOST_LIBFOO_SITE+ is not specified, it defaults to
   +LIBFOO_SITE+.
   Examples: +
@@ -291,6 +291,8 @@ not and can not work as people would expect it should:
      +ftp://+.
   ** +scp+ for downloads of tarballs over SSH with scp. Used by
      default when +LIBFOO_SITE+ begins with +scp://+.
+  ** +sftp+ for downloads of tarballs over SSH with sftp. Used by
+     default when +LIBFOO_SITE+ begins with +sftp://+.
   ** +svn+ for retrieving source code from a Subversion repository.
      Used by default when +LIBFOO_SITE+ begins with +svn://+. When a
      +http://+ Subversion repository URL is specified in

docs/manual/prerequisite.txt

@@ -78,6 +78,7 @@ corresponding tool on the host system:
 ** +mercurial+
 ** +rsync+
 ** +scp+
+** +sftp+
 ** +subversion+
 
 * Java-related packages, if the Java Classpath needs to be built for

package/pkg-download.mk

@@ -15,6 +15,7 @@ export BZR := $(call qstrip,$(BR2_BZR))
 export GIT := $(call qstrip,$(BR2_GIT))
 export HG := $(call qstrip,$(BR2_HG))
 export SCP := $(call qstrip,$(BR2_SCP))
+export SFTP := $(call qstrip,$(BR2_SFTP))
 export LOCALFILES := $(call qstrip,$(BR2_LOCALFILES))
 
 # Version of the format of the archives we generate in the corresponding

support/download/dl-wrapper

@@ -88,7 +88,7 @@ main() {
         backend_urlencode="${uri%%+*}"
         backend="${backend_urlencode%|*}"
         case "${backend}" in
-            git|svn|cvs|bzr|file|scp|hg) ;;
+            git|svn|cvs|bzr|file|scp|hg|sftp) ;;
             *) backend="wget" ;;
         esac
         uri=${uri#*+}

support/download/sftp

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+# We want to catch any unexpected failure, and exit immediately
+set -e
+
+# Download helper for sftp, to be called from the download wrapper script
+#
+# Options:
+#   -q          Be quiet.
+#   -o FILE     Copy to local file FILE.
+#   -f FILE     Copy from remote file FILE.
+#   -u URI      Download file at URI.
+#
+# Environment:
+#   SFTP      : the sftp command to call
+
+quiet=
+while getopts "${BR_BACKEND_DL_GETOPTS}" OPT; do
+    case "${OPT}" in
+    q)  quiet=-q;;
+    o)  output="${OPTARG}";;
+    f)  filename="${OPTARG}";;
+    u)  uri="${OPTARG}";;
+    :)  printf "option '%s' expects a mandatory argument\n" "${OPTARG}"; exit 1;;
+    \?) printf "unknown option '%s'\n" "${OPTARG}" >&2; exit 1;;
+    esac
+done
+
+shift $((OPTIND-1)) # Get rid of our options
+
+# Caller needs to single-quote its arguments to prevent them from
+# being expanded a second time (in case there are spaces in them)
+_sftp() {
+    if [ -z "${quiet}" ]; then
+        printf '%s ' ${SFTP} "${@}"; printf '\n'
+    fi
+    # Note: please keep command below aligned with what is printed above
+    eval ${SFTP} "${@}"
+}
+
+_sftp ${quiet} "${@}" "'${uri}/${filename}'" "'${output}'"