refactor body formatting

Author: problame

src/main.rs

@@ -176,20 +176,32 @@ fn main() {
         .map(|os_str| os_str.to_string_lossy().to_string())
         .unwrap_or("???".to_string());
 
-    let invocation_ctx = {
-        let mut out = String::new();
+    let subject = format!("{sender}@{hostname}: {summary}");
+
+    let body = (|| {
+        let mut body = String::new();
+        writeln!(
+            &mut body,
+            "A process on host {hostname:?} invoked the sendmail binary."
+        )?;
+        writeln!(
+            &mut body,
+            "The original message is attached inline to this wrapper message."
+        )?;
+        writeln!(&mut body)?;
+        writeln!(&mut body, "Invocation args: {args}")?;
+        writeln!(&mut body)?;
         writeln!(
-            &mut out,
+            &mut body,
             "uid:{} gid:{} euid:{} egid:{}",
             users::get_current_uid(),
             users::get_current_gid(),
             users::get_effective_uid(),
             users::get_effective_gid()
-        )
-        .unwrap();
+        )?;
         let mut display_or_none = |what, value: Option<OsString>| {
             writeln!(
-                &mut out,
+                &mut body,
                 "{what}: {}",
                 value
                     .as_ref()
@@ -202,28 +214,19 @@ fn main() {
         display_or_none("groupname", users::get_current_groupname());
         display_or_none("effective username", users::get_effective_username());
         display_or_none("effective groupname", users::get_effective_groupname());
-        writeln!(&mut out).unwrap();
-        writeln!(&mut out, "hostname: {}", whoami::hostname()).unwrap();
-        writeln!(&mut out, "device name: {}", whoami::devicename()).unwrap();
-        writeln!(&mut out, "distro: {}", whoami::distro()).unwrap();
-        writeln!(&mut out, "platform: {}", whoami::platform()).unwrap();
-        out
-    };
-
-    let subject = format!("{sender}@{hostname}: {summary}");
-    let body = format!(
-        r#"A process on host {hostname:?} invoked the sendmail binary.
-The original message is attached inline to this wrapper message.
-
-Invocation args: {args}
-
-{invocation_ctx}
-
-(This message was generated by forwad-as-attachment-mta)
-
-
-"#
-    );
+        writeln!(&mut body)?;
+        writeln!(&mut body, "hostname: {}", whoami::hostname())?;
+        writeln!(&mut body, "device name: {}", whoami::devicename())?;
+        writeln!(&mut body, "distro: {}", whoami::distro())?;
+        writeln!(&mut body, "platform: {}", whoami::platform())?;
+        writeln!(&mut body)?;
+        writeln!(
+            &mut body,
+            "This message was generated by forwad-as-attachment-mta"
+        )?;
+        std::result::Result::<_, std::fmt::Error>::Ok(body)
+    })()
+    .expect("this is all in-memory and we don't expect formatting to fail");
 
     let envelope = Envelope::new(
         Some(config.sender_email.clone()),