Try find port type in parent device

CHANGELOG.md

@@ -10,6 +10,8 @@ project adheres to [Semantic Versioning](https://semver.org/).
 
 * Add `IntoRawHandle` implementation for `COMPort`
   [#199](https://github.com/serialport/serialport-rs/pull/199)
+* Add MODALIAS as additional source of information for USB devices on Linux
+  [#170](https://github.com/serialport/serialport-rs/pull/170)
 
 ### Changed
 ### Fixed

src/posix/enumerate.rs

@@ -1,7 +1,10 @@
 use cfg_if::cfg_if;
 
-#[cfg(all(target_os = "linux", not(target_env = "musl"), feature = "libudev"))]
-use std::ffi::OsStr;
+cfg_if! {
+    if #[cfg(all(target_os = "linux", not(target_env = "musl"), feature = "libudev"))]{
+        use std::ffi::OsStr;
+    }
+}
 
 cfg_if! {
     if #[cfg(any(target_os = "ios", target_os = "macos"))] {
@@ -174,10 +177,98 @@ fn port_type(d: &libudev::Device) -> Result<SerialPortType> {
                 Ok(SerialPortType::PciPort)
             }
         }
+        None => find_usb_interface_from_parents(d.parent())
+            .and_then(get_modalias_from_device)
+            .as_deref()
+            .and_then(parse_modalias)
+            .map_or(Ok(SerialPortType::Unknown), |port_info| {
+                Ok(SerialPortType::UsbPort(port_info))
+            }),
         _ => Ok(SerialPortType::Unknown),
     }
 }
 
+#[cfg(all(target_os = "linux", not(target_env = "musl"), feature = "libudev"))]
+fn find_usb_interface_from_parents(parent: Option<libudev::Device>) -> Option<libudev::Device> {
+    let mut p = parent?;
+
+    // limit the query depth
+    for _ in 1..4 {
+        match p.devtype() {
+            None => match p.parent() {
+                None => break,
+                Some(x) => p = x,
+            },
+            Some(s) => {
+                if s.to_str()? == "usb_interface" {
+                    break;
+                } else {
+                    match p.parent() {
+                        None => break,
+                        Some(x) => p = x,
+                    }
+                }
+            }
+        }
+    }
+
+    Some(p)
+}
+
+#[cfg(all(target_os = "linux", not(target_env = "musl"), feature = "libudev"))]
+fn get_modalias_from_device(d: libudev::Device) -> Option<String> {
+    Some(
+        d.property_value("MODALIAS")
+            .and_then(OsStr::to_str)?
+            .to_owned(),
+    )
+}
+
+//  MODALIAS = usb:v303Ap1001d0101dcEFdsc02dp01ic02isc02ip00in00
+//  v    303A  (device vendor)
+//  p    1001  (device product)
+//  d    0101  (bcddevice)
+//  dc     EF  (device class)
+//  dsc    02  (device subclass)
+//  dp     01  (device protocol)
+//  ic     02  (interface class)
+//  isc    02  (interface subclass)
+//  ip     00  (interface protocol)
+//  in     00  (interface number)
+#[cfg(all(target_os = "linux", not(target_env = "musl"), feature = "libudev"))]
+fn parse_modalias(moda: &str) -> Option<UsbPortInfo> {
+    // Find the start of the string, will start with "usb:"
+    let mod_start = moda.find("usb:v")?;
+
+    // Tail to update while searching.
+    let mut mod_tail = moda.get(mod_start + 5..)?;
+
+    // The next four characters should be hex values of the vendor.
+    let vid = mod_tail.get(..4)?;
+    mod_tail = mod_tail.get(4..)?;
+
+    // The next portion we care about is the device product ID.
+    let pid_start = mod_tail.find('p')?;
+    let pid = mod_tail.get(pid_start + 1..pid_start + 5)?;
+
+    Some(UsbPortInfo {
+        vid: u16::from_str_radix(vid, 16).ok()?,
+        pid: u16::from_str_radix(pid, 16).ok()?,
+        serial_number: None,
+        manufacturer: None,
+        product: None,
+        // Only attempt to find the interface if the feature is enabled.
+        #[cfg(feature = "usbportinfo-interface")]
+        interface: mod_tail.get(pid_start + 4..).and_then(|mod_tail| {
+            mod_tail.find("in").and_then(|i_start| {
+                mod_tail
+                    .get(i_start + 2..i_start + 4)
+                    .and_then(|interface| u8::from_str_radix(interface, 16).ok())
+            })
+        }),
+    })
+}
+
 #[cfg(any(target_os = "ios", target_os = "macos"))]
 fn get_parent_device_by_type(
     device: io_object_t,
@@ -598,3 +689,17 @@ cfg_if! {
         }
     }
 }
+
+#[cfg(all(target_os = "linux", not(target_env = "musl"), feature = "libudev"))]
+#[test]
+fn parser_modalias() {
+    const MODALIAS: &str = "usb:v303Ap1001d0101dcEFdsc02dp01ic02isc02ip00in0C";
+
+    let port_info = parse_modalias(MODALIAS).expect("parse failed");
+
+    assert_eq!(port_info.vid, 0x303A, "vendor parse invalid");
+    assert_eq!(port_info.pid, 0x1001, "product parse invalid");
+
+    #[cfg(feature = "usbportinfo-interface")]
+    assert_eq!(port_info.interface, Some(0x0C), "interface parse invalid");
+}