Add escape for systemd service in installer script

[yangsheng6810]

Among all the characters that are allowed in a URL, both the percentage sign "%" and the single quotation mark "'" needs escaping when written as a environment variable in a systemd service file. While the single quotation mark may be rare, the percentage sign is widely used to escape characters in a URL. This is especially common in proxy setting, where username and password may contain special characters that need percentage escaping. This patch applies the following replacements:

  % -> %%
  ' -> \'

[thufschmitt]

Could systemd-escape be used instead? Since this is a systemd install, I imagine it's fine to assume that it's present and that would make the logic more robust and future-proof

[yangsheng6810]

Actually that was what I tried first, and unfortunately the answer is a "NO". systemd-escape is intended for escaping things to be included in unit names, a totally different scenario. For example

$ systemd-escape /mnt/some-dir
-mnt-some\x2ddir
$ systemd-escape http://127.0.0.1:8080
http:--127.0.0.1:8080

And the escaped URL is no longer valid.

Just another thought: while a single quote is technically legal in a URL according to RFC3986, it is rarely used in real life. It may be a good idea not to support it, to guard against potential escaping bugs. I do not expect someone to use a proxy with single quote somewhere in its URL. Should it happen, I would expect it already being escaped as "%27" in HTTP_PROXY.

[thufschmitt]

Actually that was what I tried first, and unfortunately the answer is a "NO". systemd-escape is intended for escaping things to be included in unit names, a totally different scenario.

Argh, too bad.

Just another thought: while a single quote is technically legal in a URL according to RFC3986, it is rarely used in real life. It may be a good idea not to support it, to guard against potential escaping bugs.

I don't have a strong opinion here, but I think supporting it is a good idea. It's edge-casy and all, but should work OK