Merge pull request #138 from iVanlIsh/main

Update HOWTO.md

HOWTO.md

@@ -21,24 +21,46 @@ It can be controlled in a variety of ways:
 
 ## Preflight requests
 
-PNA preflight requests are available in Chrome starting in version 98 behind
-a pair of command-line flags:
+PNA preflight requests are available in Chrome starting in version 98 under warning-mode.
+It can be switched between enforcing-mode and warning-mode in following ways:
 
-1. `--enable-features=PrivateNetworkAccessSendPreflights`
-2. `--enable-features=PrivateNetworkAccessRespectPreflightResults`
+* the command-line flags: `--enable-features=PrivateNetworkAccessRespectPreflightResults`
+* the `chrome://` flag: `chrome://flags/#private-network-access-respect-preflight-results`
 
-The former configures Chrome to send preflight requests ahead of private network
-requests, but not does require the response to be successful. The latter enables
-enforcement: if the preflight request fails, then the request is not sent.
+Chrome is sending preflight requests ahead of private network requests, but does 
+not require the response to be successful. The flag above enables enforcement: 
+if the preflight request fails, then the request is not sent.
 
-See [here](https://www.chromium.org/developers/how-tos/run-chromium-with-flags)
-for instructions on setting command-line flags.
+### Navigations and Workers
 
-You can then test your own web app, or use a test page like
-https://private-network-access-test.glitch.me/.
+PNA preflight requests are also available for navigations and workers under the 
+following command-line flags:
+* `--enable-features=PrivateNetworkAccessForNavigations`
+* `--enable-features=PrivateNetworkAccessForWorkers`
+* `--enable-features=PrivateNetworkAccessForNavigationsWarningOnly`
+* `--enable-features=PrivateNetworkAccessForWorkersWarningOnly`
 
-Errors should manifest as CORS errors in the DevTools console, and as "Blocked
-requests" in the DevTools network panel.
+The first two flags enable the features under warning-mode. The second two flags
+works only when the first two are enabled and enables the enforcement of the 
+features.
+
+The second two flags can also be set by the `chrome://` flag:
+* `chrome://flags/#private-network-access-ignore-navigation-errors`
+* `chrome://flags/#private-network-access-ignore-worker-errors`
+
+### Reducing timeout
+
+In the ideal world, private servers will reply to the preflight requrests no 
+matter with or without the correct headers. However, there are several real life 
+cases that some servers would just drop the requests they do not understand and 
+Chrome will wait forever until a TCP timeout.
+
+In this case, Chrome provides an extra timeout limit, which is 200ms, to limit 
+the influence for websites and server haven't yet migrate with Private Network
+Access Preflights and do not reply to preflight requests.
+
+This extra timeout limit can be turned off by using the `chrome://` flag 
+`chrome://flags/#private-network-access-preflight-short-timeout`.
 
 ## Permission Prompt
 
@@ -51,8 +73,17 @@ It can be controlled in a variety of ways:
 * the [origin
   trial](https://developer.chrome.com/origintrials/#/view_trial/1367968386813788161)
 
-You can then test your own web app, or use a test page like
-https://private-network-access-permission-test.glitch.me/.
+See the [explainer](/permission_prompt/explainer.md) and [walk through doc](https://docs.google.com/document/d/1W70cFFaBGWd0EeOOMxJh9zkmxZ903vKUaGjyF-w7HcY/edit#heading=h.qof2sn5s8r89) for more details.
 
+## Moreover
 
-See the [explainer](/permission_prompt/explainer.md) and [walk through doc](https://docs.google.com/document/d/1W70cFFaBGWd0EeOOMxJh9zkmxZ903vKUaGjyF-w7HcY/edit#heading=h.qof2sn5s8r89) for more details.
+See [here](https://www.chromium.org/developers/how-tos/run-chromium-with-flags)
+for instructions on setting command-line flags.
+
+You can then test your own web app, or use a test page like
+https://private-network-access-test.glitch.me/ or 
+https://private-network-access-permission-test.glitch.me/ for the permission 
+prompt.
+
+Errors should manifest as CORS errors in the DevTools console, and as "Blocked
+requests" in the DevTools network panel.