Make usergen a bit more useful

So far, usergen printed a JSON object over standard output that had to
be manually copied into db.json. Now, this step is done automatically,
thanks to jq(1). OTOH, user directory is now also created by usergen.

README.md

@@ -43,6 +43,7 @@ to `slcl`. If required, encryption should be done before uploading e.g.: using
 - [`dynstr`](https://gitea.privatedns.org/xavi92/dynstr)
 (provided as a `git` submodule).
 - `xxd` (for [`usergen`](usergen) only).
+- `jq` (for [`usergen`](usergen) only).
 - CMake (optional).
 
 ### Ubuntu / Debian

usergen

@@ -2,8 +2,29 @@
 
 set -e
 
+usage()
+{
+    echo "$0 <dir>"
+}
+
+if [ $# != 1 ]; then
+    usage >&2
+    exit 1
+fi
+
+DIR=$1
+
 echo Username: >&2
 read -r USER
+
+DB="$DIR/db.json"
+
+if jq '.users[].name' "$DB" | grep -q $USER
+then
+    echo User $USER already in $DB >&2
+    exit 1
+fi
+
 echo Password: >&2
 read -r PWD
 echo "Quota, in MiB (leave empty for unlimited quota):" >&2
@@ -23,12 +44,23 @@ do
 done
 
 echo >&2
-cat <<-EOF
+TMP=$(mktemp)
+
+cleanup()
 {
-    "name": "$USER",
-    "password": "$PWD",
-    "salt": "$SALT",
-    "key": "$KEY",
-    "quota": "$QUOTA"
+    rm -f $TMP
 }
-EOF
+
+trap cleanup EXIT
+
+jq ".users += [
+{
+    \"name\": \"$USER\",
+    \"password\": \"$PWD\",
+    \"salt\": \"$SALT\",
+    \"key\": \"$KEY\",
+    \"quota\": \"$QUOTA\"
+}]" "$DB" > $TMP
+
+mv $TMP "$DB"
+mkdir "$DIR/user/$USER"