who: fix --lookup

This closes #2181.

`who --lookup` is failing with a runtime panic (double free).
Since `crate::dns-lookup` already includes a safe wrapper for `getaddrinfo`
I used this crate instead of further debugging the existing code in
utmpx::canon_host().

* It was neccessary to remove the version constraint for libc in uucore.

Cargo.lock

@@ -576,6 +576,18 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "dns-lookup"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "093d88961fd18c4ecacb8c80cd0b356463ba941ba11e0e01f9cf5271380b79dc"
+dependencies = [
+ "cfg-if 1.0.0",
+ "libc",
+ "socket2",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "dunce"
 version = "1.0.1"
@@ -1445,6 +1457,17 @@ dependencies = [
  "maybe-uninit",
 ]
 
+[[package]]
+name = "socket2"
+version = "0.3.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "122e570113d28d773067fab24266b66753f6ea915758651696b6e35e49f88d6e"
+dependencies = [
+ "cfg-if 1.0.0",
+ "libc",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "strsim"
 version = "0.8.0"
@@ -1820,11 +1843,9 @@ name = "uu_df"
 version = "0.0.6"
 dependencies = [
  "clap",
- "libc",
  "number_prefix",
  "uucore",
  "uucore_procs",
- "winapi 0.3.9",
 ]
 
 [[package]]
@@ -2407,8 +2428,6 @@ name = "uu_stat"
 version = "0.0.6"
 dependencies = [
  "clap",
- "libc",
- "time",
  "uucore",
  "uucore_procs",
 ]
@@ -2672,6 +2691,7 @@ name = "uucore"
 version = "0.0.8"
 dependencies = [
  "data-encoding",
+ "dns-lookup",
  "dunce",
  "getopts",
  "lazy_static",
@@ -2682,6 +2702,7 @@ dependencies = [
  "thiserror",
  "time",
  "wild",
+ "winapi 0.3.9",
 ]
 
 [[package]]

src/uu/pinky/src/pinky.rs

@@ -286,17 +286,10 @@ impl Pinky {
 
         print!(" {}", time_string(&ut));
 
-        if self.include_where && !ut.host().is_empty() {
-            let ut_host = ut.host();
-            let mut res = ut_host.splitn(2, ':');
-            let host = match res.next() {
-                Some(_) => ut.canon_host().unwrap_or_else(|_| ut_host.clone()),
-                None => ut_host.clone(),
-            };
-            match res.next() {
-                Some(d) => print!(" {}:{}", host, d),
-                None => print!(" {}", host),
-            }
+        let mut s = ut.host();
+        if self.include_where && !s.is_empty() {
+            s = safe_unwrap!(ut.canon_host());
+            print!(" {}", s);
         }
 
         println!();

src/uu/who/src/who.rs

@@ -548,20 +548,10 @@ impl Who {
             "  ?".into()
         };
 
-        let mut buf = vec![];
-        let ut_host = ut.host();
-        let mut res = ut_host.splitn(2, ':');
-        if let Some(h) = res.next() {
-            if self.do_lookup {
-                buf.push(ut.canon_host().unwrap_or_else(|_| h.to_owned()));
-            } else {
-                buf.push(h.to_owned());
-            }
+        let mut s = ut.host();
+        if self.do_lookup {
+            s = safe_unwrap!(ut.canon_host());
         }
-        if let Some(h) = res.next() {
-            buf.push(h.to_owned());
-        }
-        let s = buf.join(":");
         let hoststr = if s.is_empty() { s } else { format!("({})", s) };
 
         self.print_line(

src/uucore/Cargo.toml

@@ -16,6 +16,7 @@ edition = "2018"
 path="src/lib/lib.rs"
 
 [dependencies]
+dns-lookup = "1.0.5"
 dunce = "1.0.0"
 getopts = "<= 0.2.21"
 wild = "2.0.4"

src/uucore/src/lib/features/utmpx.rs

@@ -188,47 +188,40 @@ impl Utmpx {
 
     /// Canonicalize host name using DNS
     pub fn canon_host(&self) -> IOResult<String> {
-        const AI_CANONNAME: libc::c_int = 0x2;
         let host = self.host();
-        let host = host.split(':').next().unwrap();
-        let hints = libc::addrinfo {
-            ai_flags: AI_CANONNAME,
-            ai_family: 0,
-            ai_socktype: 0,
-            ai_protocol: 0,
-            ai_addrlen: 0,
-            ai_addr: ptr::null_mut(),
-            ai_canonname: ptr::null_mut(),
-            ai_next: ptr::null_mut(),
-        };
-        let c_host = CString::new(host).unwrap();
-        let mut res = ptr::null_mut();
-        let status = unsafe {
-            libc::getaddrinfo(
-                c_host.as_ptr(),
-                ptr::null(),
-                &hints as *const _,
-                &mut res as *mut _,
-            )
-        };
-        if status == 0 {
-            let info: libc::addrinfo = unsafe { ptr::read(res as *const _) };
-            // http://lists.gnu.org/archive/html/bug-coreutils/2006-09/msg00300.html
-            // says Darwin 7.9.0 getaddrinfo returns 0 but sets
-            // res->ai_canonname to NULL.
-            let ret = if info.ai_canonname.is_null() {
-                Ok(String::from(host))
-            } else {
-                Ok(unsafe { CString::from_raw(info.ai_canonname).into_string().unwrap() })
+
+        // TODO: change to use `split_once` when MSRV hits 1.52.0
+        // let (hostname, display) = host.split_once(':').unwrap_or((&host, ""));
+        let mut h = host.split(':');
+        let hostname = h.next().unwrap_or(&host);
+        let display = h.next().unwrap_or("");
+
+        if !hostname.is_empty() {
+            extern crate dns_lookup;
+            use dns_lookup::{getaddrinfo, AddrInfoHints};
+
+            const AI_CANONNAME: i32 = 0x2;
+            let hints = AddrInfoHints {
+                flags: AI_CANONNAME,
+                ..AddrInfoHints::default()
             };
-            unsafe {
-                libc::freeaddrinfo(res);
+            let sockets = getaddrinfo(Some(&hostname), None, Some(hints))
+                .unwrap()
+                .collect::<IOResult<Vec<_>>>()?;
+            for socket in sockets {
+                if let Some(ai_canonname) = socket.canonname {
+                    return Ok(if display.is_empty() {
+                        ai_canonname
+                    } else {
+                        format!("{}:{}", ai_canonname, display)
+                    });
+                }
             }
-            ret
-        } else {
-            Err(IOError::last_os_error())
         }
+
+        Ok(host.to_string())
     }
+
     pub fn iter_all_records() -> UtmpxIter {
         UtmpxIter
     }

tests/by-util/test_pinky.rs

@@ -98,6 +98,23 @@ fn test_short_format_q() {
     assert_eq!(v_actual, v_expect);
 }
 
+#[cfg(target_os = "linux")]
+#[test]
+fn test_no_flag() {
+    let scene = TestScenario::new(util_name!());
+
+    let actual = scene.ucmd().succeeds().stdout_move_str();
+    let expect = scene
+        .cmd_keepenv(util_name!())
+        .env("LANGUAGE", "C")
+        .succeeds()
+        .stdout_move_str();
+
+    let v_actual: Vec<&str> = actual.split_whitespace().collect();
+    let v_expect: Vec<&str> = expect.split_whitespace().collect();
+    assert_eq!(v_actual, v_expect);
+}
+
 #[cfg(target_os = "linux")]
 fn expected_result(args: &[&str]) -> String {
     TestScenario::new(util_name!())

tests/by-util/test_who.rs

@@ -162,7 +162,6 @@ fn test_users() {
 
 #[cfg(target_os = "linux")]
 #[test]
-#[ignore]
 fn test_lookup() {
     for opt in vec!["--lookup"] {
         new_ucmd!()