support/download/dl-wrapper: add concept of download post-processing

In order to support package managers such as Cargo (Rust) or Go, we
want to run some custom logic after the main download, but before
packing the tarball and checking the hash.

To implement this, this commit introduces a concept of download
post-processing: if -p <something> is passed to the dl-wrapper, then
support/download/<something>-post-process will be called.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[yann.morin.1998@free.fr:
  - double-quote variable expansion when calling post-process script
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

support/download/dl-wrapper

@@ -25,7 +25,7 @@ main() {
     local -a uris
 
     # Parse our options; anything after '--' is for the backend
-    while getopts ":c:d:D:o:n:N:H:lrf:u:q" OPT; do
+    while getopts ":c:d:D:o:n:N:H:lrf:u:qp:" OPT; do
         case "${OPT}" in
         c)  cset="${OPTARG}";;
         d)  dl_dir="${OPTARG}";;
@@ -38,6 +38,7 @@ main() {
         r)  recurse="-r";;
         f)  filename="${OPTARG}";;
         u)  uris+=( "${OPTARG}" );;
+        p)  post_process="${OPTARG}";;
         q)  quiet="-q";;
         :)  error "option '%s' expects a mandatory argument\n" "${OPTARG}";;
         \?) error "unknown option '%s'\n" "${OPTARG}";;
@@ -136,6 +137,12 @@ main() {
             continue
         fi
 
+        if [ -n "${post_process}" ] ; then
+            "${OLDPWD}/support/download/${post_process}-post-process" \
+                -o "${tmpf}" \
+                -n "${raw_base_name}"
+        fi
+
         # cd back to free the temp-dir, so we can remove it later
         cd "${OLDPWD}"