Ensure curl is available and check its return code in SSH key deployment

bin/uncloud-init

@@ -1,7 +1,7 @@
 #!/bin/sh
 #
 # Initialize an uncloud VM. This script depends on:
-# curl grep getent (i.e. glibc) curl,dirname (i.e. coreutils)
+# curl grep getent (i.e. glibc) curl,dirname (i.e. coreutils) mktemp
 
 # TODO: complete other tasks even if one fail.
 # TODO: do not up ALL network interfaces.
@@ -65,7 +65,28 @@ deploy_ssh_authorized_keys () {
 			return
 	fi
 
-	curl "$UNCLOUD_METADATA_SERVER/fnux" --output "$authorized_keys_file"
+	if [ ! -x "$(command -v curl)" ]; then
+		echo "Could not find or execute curl. Exiting." >&2
+		exit 1
+	fi
+
+	if [ ! -x "$(command -v mktemp)" ]; then
+		echo "Could not find or execute mktemp. Exiting." >&2
+		exit 1
+	fi
+
+	curl_output=$(mktemp)
+	if curl "$UNCLOUD_METADATA_SERVER/fnux" --output "$curl_output"; then
+		echo "Something went wrong fetching the authorized_keys file from the \
+			metedata server." >&2
+		echo "CURL Output: $(cat "$curl_output")"
+		rm "$curl_output"
+		exit 1
+	fi
+
+	mv "$curl_output" "$authorized_keys_file"
+	echo "Deployed $(wc -l < "$authorized_keys_file") entries in \
+		$authorized_keys_file."
 }
 
 grow_root_partition () {