Remove unreachable errors; add unit tests for coverage

build.rs

@@ -0,0 +1,16 @@
+fn main() -> Result<(), std::io::Error> {
+    let sample_table = std::fs::read_to_string(concat!(
+        env!("CARGO_MANIFEST_DIR"),
+        "/sample-tables/sample-table.txt"
+    ))?;
+
+    let sample_table = format!("const SAMPLE_TABLE: &str = {sample_table:?};\n");
+
+    let out_dir = std::env::var("OUT_DIR").expect("env OUT_DIR");
+    std::fs::write(
+        format!("{out_dir}/sample_table.rs"),
+        sample_table.as_bytes(),
+    )?;
+
+    Ok(())
+}

src/routing_table.rs

@@ -21,14 +21,10 @@ pub enum Error {
     NetstatFail(ExitStatus),
     #[error("netstat output not non-UTF-8")]
     NetstatUtf8(FromUtf8Error),
-    #[error("Unrecognized section name {0:?}")]
-    NetstatParseUnrecognizedSectionName(String),
-    #[error("{0:?} section missing headers")]
+    #[error("no headers follow {0:?} section marker")]
     NetstatParseNoHeaders(String),
     #[error("parsing route entry: {0}")]
     RouteEntryParse(#[from] crate::route_entry::Error),
-    #[error("CIDR first address neither V4 nor V6")]
-    CidrNotV4V6,
     #[error("route entry found before protocol (Internet/Internet6) found.")]
     EntryBeforeProto,
 }
@@ -67,9 +63,7 @@ impl RoutingTable {
                     proto = match section {
                         "Internet:" => Some(Protocol::V4),
                         "Internet6:" => Some(Protocol::V6),
-                        _ => {
-                            return Err(Error::NetstatParseUnrecognizedSectionName(section.into()))
-                        }
+                        _ => unreachable!(),
                     };
                     // Next line will contain the column headers
                     if let Some(line) = lines.next() {
@@ -88,7 +82,9 @@ impl RoutingTable {
                             if cidr.is_host_address() {
                                 let route = route.clone();
                                 let gws = if_router.entry(route.net_if).or_insert_with(Vec::new);
-                                gws.push(cidr.first_address().ok_or(Error::CidrNotV4V6)?);
+                                // The route parser doesn't produce `Any` CIDRs,
+                                // so there's always a first address.
+                                gws.push(cidr.first_address().unwrap_or_else(|| unreachable!()));
                             }
                         }
                         routes.push(route);
@@ -123,6 +119,10 @@ impl RoutingTable {
 }
 
 /// Execute `netstat -rn` and return the output
+///
+/// # Errors
+///
+/// Returns an error if command execution fails, or the output is not UTF-8
 pub async fn execute_netstat() -> Result<String, Error> {
     let output = Command::new(NETSTAT_PATH)
         .arg("-rn")
@@ -135,3 +135,91 @@ pub async fn execute_netstat() -> Result<String, Error> {
     }
     String::from_utf8(output.stdout).map_err(Error::NetstatUtf8)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::Error;
+    use crate::{Destination, Entity, RoutingTable};
+    use std::{process::ExitStatus, string::FromUtf8Error};
+
+    include!(concat!(env!("OUT_DIR"), "/sample_table.rs"));
+
+    #[tokio::test]
+    async fn coverage() {
+        let rt = RoutingTable::from_netstat_output(SAMPLE_TABLE).expect("parse routing table");
+        let _ = format!("{rt:?}");
+        let _ = format!(
+            "{:?}",
+            Error::NetstatExec(std::io::Error::from_raw_os_error(1))
+        );
+        let _ = format!("{:?}", Error::NetstatFail(ExitStatus::default()));
+        // This error is reachable only if the netstat command outputs invalid
+        // UTF-8.
+        let from_utf8err = String::from_utf8([0xa0, 0xa1].to_vec()).unwrap_err();
+        let _ = format!("{:?}", Error::NetstatUtf8(from_utf8err));
+    }
+
+    #[tokio::test]
+    #[cfg(target_os = "macos")]
+    async fn live_test() {
+        let _routing_table = RoutingTable::load_from_netstat()
+            .await
+            .expect("parse live routing table");
+    }
+
+    #[test]
+    fn good_table() {
+        let rt = RoutingTable::from_netstat_output(SAMPLE_TABLE).expect("parse routing table");
+        let entry = rt.find_route_entry("1.1.1.1".parse().unwrap());
+        dbg!(&entry);
+        assert!(entry.is_some());
+        let entry = entry.unwrap();
+        assert!(matches!(
+            entry.dest,
+            Destination {
+                entity: Entity::Default,
+                zone: None
+            }
+        ));
+        // Coverage of debug formatting
+        let _ = format!("{rt:?}");
+    }
+
+    #[test]
+    fn missing_headers() {
+        for section in ["", "6"] {
+            let input = format!("{SAMPLE_TABLE}Internet{section}:\n");
+            let result = RoutingTable::from_netstat_output(&input);
+            assert!(matches!(result, Err(Error::NetstatParseNoHeaders(_))));
+            // Coverage of debug formatting
+            let _ = format!("{:?}", result.unwrap_err());
+        }
+    }
+
+    #[test]
+    fn stray_entry() {
+        let input = format!("extra stuff\n{SAMPLE_TABLE}");
+        let result = RoutingTable::from_netstat_output(&input);
+        assert!(matches!(result, Err(Error::EntryBeforeProto)));
+        // Coverage of debug formatting
+        let _ = format!("{:?}", result.unwrap_err());
+    }
+
+    #[test]
+    fn bad_entry() {
+        let input = format!("{SAMPLE_TABLE}How now brown cow.\n");
+        let result = RoutingTable::from_netstat_output(&input);
+        dbg!(&result);
+        assert!(matches!(
+            result,
+            Err(Error::RouteEntryParse(
+                crate::route_entry::Error::ParseIPv4AddrBadInt {
+                    addr: _,
+                    err: std::num::ParseIntError { .. },
+                }
+            ))
+        ));
+        // Coverage of debug formatting
+        let _ = format!("{:?}", result.unwrap_err());
+    }
+}

tests/live.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::missing_panics_doc)]
+#![allow(clippy::missing_panics_doc, clippy::missing_errors_doc)]
 
 use anyhow::Result;
 use macos_routing_table::{execute_netstat, RoutingTable};