Implement XBPS_DISTFILES_MIRROR (second try)

The idea is to remove some burden from the original download
locations for distfiles by specifying one or more mirror locations.

+ Works with http:// or ftp:// mirrors for all $XBPS_CHROOT_CMD variants
+ Works with file:// mirrors together with uchroot and proot

xbps-src

@@ -351,6 +351,32 @@ read_pkg() {
     setup_pkg $XBPS_TARGET_PKG $XBPS_CROSS_BUILD
 }
 
+setup_distfiles_mirror() {
+    local mirror scheme path
+
+    # Scheme file:// mirror locations only work with uchroot or proot
+    for mirror in $XBPS_DISTFILES_MIRROR; do
+        scheme="file"
+        if [[ "$mirror" == *://* ]]; then
+            scheme="${mirror%%://*}"
+            path="${mirror#${scheme}://}"
+        else
+            path="$mirror"
+        fi
+        [ "$scheme" != "file" ] && continue
+        if [ "$XBPS_CHROOT_CMD" == "uchroot" -o "$XBPS_CHROOT_CMD" == "proot" ]; then
+            if [ ! -d "$path" ]; then
+                msg_warn "Invalid path in XBPS_DISTFILES_MIRROR ($mirror)\n"
+                continue
+            fi
+            mkdir -p "$XBPS_MASTERDIR/$path"
+            XBPS_CHROOT_CMD_ARGS+=" -b $path:$path"
+        else
+            msg_warn "File URLs ($mirror) don't work with '$XBPS_CHROOT_CMD'\n"
+        fi
+    done
+}
+
 readonly XBPS_VERSION_REQ="0.46"
 readonly XBPS_VERSION=$(xbps-uhelper -V|awk '{print $2}')
 readonly XBPS_SRC_VERSION="113"
@@ -516,7 +542,7 @@ export XBPS_SHUTILSDIR XBPS_CROSSPFDIR XBPS_TRIGGERSDIR \
     XBPS_SKIP_REMOTEREPOS XBPS_CROSS_BUILD XBPS_PKG_OPTIONS \
     XBPS_CONFIG_FILE XBPS_KEEP_ALL XBPS_HOSTDIR XBPS_MASTERDIR \
     XBPS_SRC_VERSION XBPS_DESTDIR XBPS_MACHINE XBPS_TEMP_MASTERDIR \
-    XBPS_BINPKG_EXISTS XBPS_LIBEXECDIR XBPS_DISTDIR
+    XBPS_BINPKG_EXISTS XBPS_LIBEXECDIR XBPS_DISTDIR XBPS_DISTFILES_MIRROR
 
 for i in REPOSITORY DESTDIR BUILDDIR SRCDISTDIR; do
     eval val="\$XBPS_$i"
@@ -571,6 +597,9 @@ check_build_requirements
 
 if [ -z "$IN_CHROOT" ]; then
     trap 'exit_func' INT TERM
+    if [ -n "$XBPS_DISTFILES_MIRROR" ]; then
+        setup_distfiles_mirror
+    fi
 fi
 
 #