Use the PDF's existence to avoid sending duplicate emails

If the PDF is already on disk, it's a good sign that we've already sent
the email, so skip in that case.

To make the signal a bit more reliable, make writing the PDF to disk
the last action taken, in case sending the email fails.

Cargo.toml

@@ -16,6 +16,5 @@ ureq = { version = "*", features = ["cookies"] }
 codegen-units = 1
 lto = true
 opt-level = "z"
-panic = "abort"
 strip = true
 

src/main.rs

@@ -30,7 +30,9 @@ fn get_link(agent: ureq::Agent) -> Option<String> {
 fn main() {
     let mut args = std::env::args().skip(1);
 
-    let to: String = args.next().expect("Provide To: on the command line");
+    let to: String = args
+        .next()
+        .expect("Usage: MS_USER=... MS_PASS=... msme <to-address> [bcc-address]...");
     let bcc: Vec<String> = args.collect();
 
     let username = std::env::var("MS_USER").expect("Please set MS_USER envvar");
@@ -55,6 +57,11 @@ fn main() {
         .rsplit_once('/')
         .expect("Couldn't parse filename from link");
 
+    if std::path::Path::new(filename).exists() {
+        println!("We already have {}, skipping", filename);
+        return;
+    }
+
     let mut buf: Vec<u8> = vec![];
     {
         println!("Downloading PDF...");
@@ -65,8 +72,6 @@ fn main() {
             .into_reader()
             .read_to_end(&mut buf) // TODO: would be better to stream the bytes
             .expect("Couldn't read bytes from server");
-
-        std::fs::write(filename, &buf).expect("Couldn't create file");
     }
 
     println!("Sending email...");
@@ -96,5 +101,7 @@ fn main() {
 
     sendmail.wait().expect("Sendmail execution failed");
 
+    println!("Saving file...");
+    std::fs::write(filename, &buf).expect("Couldn't create file");
     println!("OK!");
 }