metricdog: prepend scheme to https proxy value

reqwest does not support HTTPS_PROXY values that are not in URL format
(i.e. if there is no protocol scheme). On Bottlerocket we expect an
HTTPS_PROXY value with no scheme to be treated as http://.

Here we check the HTTPS_PROXY value, and if it has no scheme we reset
the value to prepend https://

sources/metricdog/src/metricdog.rs

@@ -140,6 +140,7 @@ impl Metricdog {
 
     fn send_get_request(url: Url, timeout_sec: Option<u64>) -> Result<()> {
         debug!("sending: {}", url.as_str());
+        fix_https_proxy_env();
         let client = Client::builder()
             .timeout(Duration::from_secs(
                 timeout_sec.unwrap_or(DEFAULT_TIMEOUT_SECONDS),
@@ -156,3 +157,30 @@ impl Metricdog {
         Ok(())
     }
 }
+
+/// reqwest needs a URL protocol scheme to be present, but other implementations assume
+/// `http://` as the scheme when none is present. We need to check the `HTTPS_PROXY` env and
+/// reset it with `http://` when no scheme is present. This can be removed when we are using
+/// reqwest >= 0.11.1
+// TODO - remove this workaround, see https://github.com/bottlerocket-os/bottlerocket/issues/1332
+fn fix_https_proxy_env() {
+    let proxy = match std::env::var("HTTPS_PROXY") {
+        Ok(s) if !s.is_empty() => s,
+        _ => return,
+    };
+
+    // try to parse it as a URL. if it works, a scheme is present
+    if Url::parse(&proxy).is_ok() {
+        return;
+    }
+
+    // since the URL could not be parsed, try parsing with http:// prepended
+    let proxy = format!("http://{}", proxy);
+
+    // use URL again to see if the proxy value is now valid
+    if Url::parse(&proxy).is_ok() {
+        debug!("Adding a scheme to HTTPS_PROXY: '{}'", proxy);
+        // success, so let's change the HTTPS_PROXY value for the sake of reqwest
+        std::env::set_var("HTTPS_PROXY", proxy);
+    }
+}