Add SystemExt::distribution_id()

SystemExt::name() returns human-readable distribution name,
but there is no machine-readable alternative.

SystemExt::distribution_id() returns os-release.ID, or
std::env::consts::OS if os-release.ID is unavailable.
Fallback behaviour is consistent with the os-release.ID
specification on Linux.

See also
- https://www.freedesktop.org/software/systemd/man/os-release.html#ID=
- https://doc.rust-lang.org/std/env/consts/constant.OS.html

Closes #843.

src/apple/system.rs

@@ -605,6 +605,10 @@ impl SystemExt for System {
             }
         }
     }
+
+    fn distribution_id(&self) -> String {
+        std::env::consts::OS.to_owned()
+    }
 }
 
 impl Default for System {

src/freebsd/system.rs

@@ -361,6 +361,10 @@ impl SystemExt for System {
     fn os_version(&self) -> Option<String> {
         self.system_info.get_os_release()
     }
+
+    fn distribution_id(&self) -> String {
+        std::env::consts::OS.to_owned()
+    }
 }
 
 impl Default for System {

src/lib.rs

@@ -344,6 +344,8 @@ mod test {
                 .long_os_version()
                 .expect("Failed to get long OS version")
                 .is_empty());
+
+            assert!(!s.distribution_id().is_empty());
         }
     }
 

src/linux/system.rs

@@ -697,6 +697,21 @@ impl SystemExt for System {
     fn os_version(&self) -> Option<String> {
         get_system_info_android(InfoType::OsVersion)
     }
+
+    #[cfg(not(target_os = "android"))]
+    fn distribution_id(&self) -> String {
+        get_system_info_linux(
+            InfoType::DistributionID,
+            Path::new("/etc/os-release"),
+            Path::new(""),
+        )
+        .unwrap_or_else(|| std::env::consts::OS.to_owned())
+    }
+
+    #[cfg(target_os = "android")]
+    fn distribution_id(&self) -> String {
+        std::env::consts::OS.to_owned()
+    }
 }
 
 impl Default for System {
@@ -722,6 +737,9 @@ enum InfoType {
     /// - Linux: The distributions name
     Name,
     OsVersion,
+    /// Machine-parseable ID of a distribution, see
+    /// https://www.freedesktop.org/software/systemd/man/os-release.html#ID=
+    DistributionID,
 }
 
 #[cfg(not(target_os = "android"))]
@@ -732,6 +750,7 @@ fn get_system_info_linux(info: InfoType, path: &Path, fallback_path: &Path) -> O
         let info_str = match info {
             InfoType::Name => "NAME=",
             InfoType::OsVersion => "VERSION_ID=",
+            InfoType::DistributionID => "ID=",
         };
 
         for line in reader.lines().flatten() {
@@ -750,6 +769,10 @@ fn get_system_info_linux(info: InfoType, path: &Path, fallback_path: &Path) -> O
     let info_str = match info {
         InfoType::OsVersion => "DISTRIB_RELEASE=",
         InfoType::Name => "DISTRIB_ID=",
+        InfoType::DistributionID => {
+            // lsb-release is inconsistent with os-release and unsupported.
+            return None;
+        }
     };
     for line in reader.lines().flatten() {
         if let Some(stripped) = line.strip_prefix(info_str) {
@@ -765,6 +788,10 @@ fn get_system_info_android(info: InfoType) -> Option<String> {
     let name: &'static [u8] = match info {
         InfoType::Name => b"ro.product.model\0",
         InfoType::OsVersion => b"ro.build.version.release\0",
+        InfoType::DistributionID => {
+            // Not supported.
+            return None;
+        }
     };
 
     let mut value_buffer = vec![0u8; libc::PROP_VALUE_MAX as usize];
@@ -798,6 +825,7 @@ mod test {
     fn lsb_release_fallback_android() {
         assert!(get_system_info_android(InfoType::OsVersion).is_some());
         assert!(get_system_info_android(InfoType::Name).is_some());
+        assert!(get_system_info_android(InfoType::DistributionID) == Some("android".to_owned()));
     }
 
     #[test]
@@ -844,6 +872,10 @@ DISTRIB_DESCRIPTION="Ubuntu 20.10"
             get_system_info_linux(InfoType::Name, &tmp1, Path::new("")),
             Some("Ubuntu".to_owned())
         );
+        assert_eq!(
+            get_system_info_linux(InfoType::DistributionID, &tmp1, Path::new("")),
+            Some("ubuntu".to_owned())
+        );
 
         // Check for the "fallback" path: "/etc/lsb-release"
         assert_eq!(
@@ -854,5 +886,9 @@ DISTRIB_DESCRIPTION="Ubuntu 20.10"
             get_system_info_linux(InfoType::Name, Path::new(""), &tmp2),
             Some("Ubuntu".to_owned())
         );
+        assert_eq!(
+            get_system_info_linux(InfoType::DistributionID, Path::new(""), &tmp2),
+            None
+        );
     }
 }

src/traits.rs

@@ -1235,6 +1235,22 @@ pub trait SystemExt: Sized + Debug + Default + Send + Sync {
     /// ```
     fn long_os_version(&self) -> Option<String>;
 
+    /// Returns the distribution id as defined by os-release,
+    /// or OS-name if unavailable.
+    /// See also
+    /// - https://www.freedesktop.org/software/systemd/man/os-release.html#ID=
+    /// - https://doc.rust-lang.org/std/env/consts/constant.OS.html
+    ///
+    /// **Important**: this information is computed every time this function is called.
+    ///
+    /// ```no_run
+    /// use sysinfo::{System, SystemExt};
+    ///
+    /// let s = System::new();
+    /// println!("Distribution ID: {:?}", s.distribution_id());
+    /// ```
+    fn distribution_id(&self) -> String;
+
     /// Returns the system hostname based off DNS
     ///
     /// **Important**: this information is computed every time this function is called.

src/windows/system.rs

@@ -496,6 +496,10 @@ impl SystemExt for System {
         };
         Some(format!("{} ({})", major, build_number))
     }
+
+    fn distribution_id(&self) -> String {
+        std::env::consts::OS.to_owned()
+    }
 }
 
 impl Default for System {