[__git] Keep repository up to date in subsequent runs.

This also ensure that tags and branch changes are supported.

Closes #819.

cdist/conf/type/__git/explorer/branch

@@ -0,0 +1,22 @@
+#!/bin/sh -e
+
+destination="/$__object_id"
+
+os="$(cat "$__global/explorer/os")"
+state_should="$(cat "$__object/parameter/state")"
+owner="$(cat "$__object/parameter/owner")"
+
+# If the user did not provide an owner, cdist defaults to root.
+git_user="${owner:-root}"
+
+# Only do something if we are not removing the repo and it is not the first run
+if [ "$state_should" = "present" ] && [ -d "$destination/.git" ]; then
+    # Whenever possible run git as non-root, see history of CVEs.
+    branch="$(su -m "$git_user" -c "git -C '$destination' rev-parse --abbrev-ref HEAD")"
+    if [ "$branch" != "HEAD" ]; then
+        echo $branch
+    else
+        # We are using tags
+        su -m "$git_user" -c "git -C '$destination' describe --always --tags --abbrev=0"
+    fi
+fi

cdist/conf/type/__git/explorer/needs-update

@@ -0,0 +1,27 @@
+#!/bin/sh -e
+
+destination="/$__object_id"
+
+os="$(cat "$__global/explorer/os")"
+state_should="$(cat "$__object/parameter/state")"
+branch_should="$(cat "$__object/parameter/branch")"
+owner="$(cat "$__object/parameter/owner")"
+
+# If the user did not provide an owner, cdist defaults to root.
+git_user="${owner:-root}"
+
+# Only do something if we are not removing the repo and it is not the first run
+if [ "$state_should" = "present" ] && [ -d "$destination/.git" ]; then
+    # First fetch the remote
+    # Whenever possible run git as non-root, see history of CVEs.
+    su -m "$git_user" -c "git -C '$destination' fetch -q"
+    head="$(su -m "$git_user" -c "git -C '$destination' rev-parse HEAD")"
+    # Try first to get the latest commit in the remote current branch,
+    # if it fails try to get the commit for the expected tag name
+    upstream="$(su -m "$git_user" -c "git -C '$destination' rev-parse @{u}" 2>/dev/null ||
+        su -m "$git_user" -c "git -C '$destination' rev-parse '${branch_should}^{}'")"
+    if [ "${head}" != "$upstream" ]; then
+        echo "YES"
+        exit
+    fi
+fi

cdist/conf/type/__git/gencode-remote

@@ -19,13 +19,15 @@
 #
 #
 
+branch_is=$(cat "$__object/explorer/branch")
 state_is=$(cat "$__object/explorer/state")
 owner_is=$(cat "$__object/explorer/owner")
 group_is=$(cat "$__object/explorer/group")
+needs_update=$(cat "$__object/explorer/needs-update")
 
 state_should=$(cat "$__object/parameter/state")
 
-branch=$(cat "$__object/parameter/branch")
+branch_should=$(cat "$__object/parameter/branch")
 
 source=$(cat "$__object/parameter/source")
 
@@ -47,10 +49,35 @@ fi
  && [ -z "$needs_chown" ] \
  && [ -n "$mode" ] && exit 0
 
+# Whenever possible run git as non-root, see history of CVEs.
+if [ -n "$owner" ]; then
+    git_user="$owner"
+else
+    git_user="root"
+fi
+
 case $state_should in
     present)
         if [ "$state_should" != "$state_is" ]; then
-            echo git clone --quiet "$recursive" "$shallow" --branch "$branch" "$source" "$destination"
+            if [ "$git_user" != "root" ]; then
+                # If we execute git as non-root, it is not obvious that we'll be able
+                # to create the output directory, so we have to ensure that.
+                cat << EOF
+if [ ! -d '$destination' ]; then
+    mkdir '$destination'
+fi
+chown '${owner}:${group}' '$destination'
+EOF
+            fi
+            # Actually clone the repository
+            su -m "$git_user" -c "git clone --quiet '$recursive' '$shallow' --branch '$branch' '$source' '$destination'"
+        elif [ "$branch_should" != "$branch_is" ]; then
+            # User has changed tag / branch, let's update that
+            echo su -m "$git_user" -c "git checkout '$branch_should'"
+        elif [ "$needs_update" = "YES" ]; then
+            # The remote has newer information than our repository.
+            # Fetch was done in the explorer, here we can just pull
+            echo su -m "$git_user" -c "git -C '$destination' pull"
         fi
         if [ -n "$needs_chown" ]; then
             echo chown -R "${owner}:${group}" "$destination"