Bug 1893406 - Always provide a valid installation time in WER crash r…

…eports a=RyanVM

Original Revision: https://phabricator.services.mozilla.com/D209234

Differential Revision: https://phabricator.services.mozilla.com/D211825

toolkit/crashreporter/mozwer-rust/lib.rs

@@ -12,7 +12,7 @@
  use serde_json::ser::to_writer;
  use std::convert::TryInto;
  use std::ffi::OsString;
- use std::fs::{read_to_string, DirBuilder, File};
+ use std::fs::{read_to_string, DirBuilder, File, OpenOptions};
  use std::io::{BufRead, BufReader, Write};
  use std::mem::{size_of, transmute, zeroed};
  use std::os::windows::ffi::{OsStrExt, OsStringExt};
@@ -442,8 +442,7 @@
          let install_time = ApplicationInformation::get_install_time(
              &crash_reports_dir,
              &application_data.build_id,
-         )
-         .unwrap_or("0".to_string());
+         );
 
          Ok(ApplicationInformation {
              install_path,
@@ -514,10 +513,29 @@
          }
      }
 
-     fn get_install_time(crash_reports_path: &Path, build_id: &str) -> Result<String, ()> {
+     fn get_install_time(crash_reports_path: &Path, build_id: &str) -> String {
          let file_name = "InstallTime".to_owned() + build_id;
          let file_path = crash_reports_path.join(file_name);
-         read_to_string(file_path).map_err(|_e| ())
+
+         // If the file isn't present we'll attempt to atomically create it and
+         // populate it. This code essentially matches the corresponding code in
+         // nsExceptionHandler.cpp SetupExtraData().
+         if let Ok(mut file) = OpenOptions::new()
+             .create_new(true)
+             .write(true)
+             .open(&file_path)
+         {
+             // SAFETY: No risks in calling `time()` with a null pointer.
+             let _ = write!(&mut file, "{}", unsafe { time(null_mut()) }.to_string());
+         }
+
+         // As a last resort, if we can't read the file we fall back to the
+         // current time. This might cause us to overstate the number of users
+         // affected by a crash, but given it's very unlikely to hit this particular
+         // path it won't be a problem.
+         //
+         // SAFETY: No risks in calling `time()` with a null pointer.
+         read_to_string(&file_path).unwrap_or(unsafe { time(null_mut()) }.to_string())
      }
  }