feat(windows): add ExpandString for environment variable expansion

Implement ExpandString struct to handle Windows environment variable expansion
with proper error handling. Also reorganize windows-sys dependencies and improve
icon loading error messages.

wfassoc/Cargo.toml

@@ -9,11 +9,12 @@ license = "SPDX:MIT"
 [dependencies]
 thiserror = { workspace = true }
 windows-sys = { version = "0.60.2", features = [
-    "Win32_Security",
-    "Win32_System_SystemServices",
     "Win32_UI_Shell",
     "Win32_UI_WindowsAndMessaging",
+    "Win32_Security",
+    "Win32_System_Environment",
     "Win32_System_Registry",
+    "Win32_System_SystemServices",
 ] }
 winreg = { version = "0.55.0", features = ["transactions"] }
 widestring = "1.2.1"

wfassoc/src/extra/windows.rs

@@ -2,20 +2,139 @@
 //! These features are not implemented in any crates (as I known scope)
 //! and should be manually implemented for our file association use.
 
+use regex::Regex;
+use std::fmt::Display;
 use std::path::Path;
+use std::str::FromStr;
+use std::sync::LazyLock;
 use thiserror::Error as TeError;
-use widestring::WideCString;
+use widestring::{WideCStr, WideCString, WideChar};
 use windows_sys::Win32::UI::Shell::ExtractIconExW;
 use windows_sys::Win32::UI::WindowsAndMessaging::{DestroyIcon, HICON};
 
+// region: Expand String
+
+/// Error occurs when creating Expand String.
+#[derive(Debug, TeError)]
+#[error("given string is not an expand string")]
+pub struct BadExpandStrError {}
+
+impl BadExpandStrError {
+    fn new() -> Self {
+        Self {}
+    }
+}
+
+/// Error occurs when expand Expand String
+#[derive(Debug, TeError)]
+#[error("error occurs when expanding expand string")]
+pub enum ExpandEnvVarError {
+    /// Given string has embedded NUL.
+    EmbeddedNul(#[from] widestring::error::ContainsNul<WideChar>),
+    /// Error occurs when executing Win32 expand function.
+    ExpandFunction,
+    /// Error occurs when int type casting.
+    BadIntCast(#[from] std::num::TryFromIntError),
+    /// Integeral arithmatic downflow.
+    Underflow,
+    /// The C-format string is invalid.
+    BadString(#[from] widestring::error::NulError<WideChar>),
+    /// The encoding of string is invalid.
+    BadEncoding(#[from] widestring::error::Utf16Error),
+    /// Some environment vairable are not expanded.
+    NoEnvVar,
+}
+
+/// The struct representing an Expand String,
+/// which contain environment variable in string,
+/// like `%LOCALAPPDATA%\SomeApp.exe`.
+pub struct ExpandString {
+    inner: String,
+}
+
+impl ExpandString {
+    const VAR_RE: LazyLock<Regex> = LazyLock::new(|| Regex::new(r"%[a-zA-Z0-9_]+%").unwrap());
+}
+
+impl ExpandString {
+    /// Create a new expand string
+    pub fn new(s: &str) -> Result<Self, BadExpandStrError> {
+        Self::from_str(s)
+    }
+
+    /// Expand the variables located in this string
+    /// and produce the final usable string.
+    pub fn expand_string(&self) -> Result<String, ExpandEnvVarError> {
+        use windows_sys::Win32::System::Environment::ExpandEnvironmentStringsW;
+
+        // Fetch the size of expand result
+        let source = WideCString::from_str(self.inner.as_str())?;
+        let size = unsafe {
+            ExpandEnvironmentStringsW(source.as_ptr(), Default::default(), 0)
+        };
+        if size == 0 {
+            return Err(ExpandEnvVarError::ExpandFunction)
+        }
+        let size_no_nul = size.checked_sub(1).ok_or(ExpandEnvVarError::Underflow)?;
+
+        // Allocate buffer for it.
+        let len: usize = size.try_into()?;
+        let len_no_nul = len.checked_sub(1).ok_or(ExpandEnvVarError::Underflow)?;
+        let mut buffer= vec![0; len];
+        // Receive result
+        let size = unsafe {
+            ExpandEnvironmentStringsW(source.as_ptr(), buffer.as_mut_ptr(), size_no_nul)
+        };
+        if size == 0 {
+            return Err(ExpandEnvVarError::ExpandFunction)
+        }
+
+        // Cast result as Rust string
+        let wstr = unsafe { WideCStr::from_ptr(buffer.as_ptr(), len_no_nul)? };
+        let rv = wstr.to_string()?;
+
+        // If the final string still has environment variable,
+        // we think we fail to expand it.
+        if Self::VAR_RE.is_match(rv.as_str()) {
+            Err(ExpandEnvVarError::NoEnvVar)
+        } else {
+            Ok(rv)
+        }
+    }
+}
+
+impl Display for ExpandString {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.inner)
+    }
+}
+
+impl FromStr for ExpandString {
+    type Err = BadExpandStrError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if Self::VAR_RE.is_match(s) {
+            Ok(Self {
+                inner: s.to_string(),
+            })
+        } else {
+            Err(BadExpandStrError::new())
+        }
+    }
+}
+
+// endregion
+
 // region: Icon
 
 /// Error occurs when loading icon.
 #[derive(Debug, TeError)]
 #[error("error occurs when loading icon")]
 pub enum LoadIconError {
-    EmbeddedNul(#[from] widestring::error::ContainsNul<widestring::WideChar>),
-    Other,
+    /// Given path has embedded NUL.
+    EmbeddedNul(#[from] widestring::error::ContainsNul<WideChar>),
+    /// Error occurs when executing Win32 extract function.
+    ExtractIcon,
 }
 
 /// The size kind of loaded icon
@@ -50,13 +169,13 @@ impl Icon {
         };
 
         if rv != 1 || icon.is_null() {
-            Err(LoadIconError::Other)
+            Err(LoadIconError::ExtractIcon)
         } else {
             Ok(Self { icon })
         }
     }
 
-    pub fn from_raw(hicon: HICON) -> Self {
+    pub unsafe fn from_raw(hicon: HICON) -> Self {
         Self { icon: hicon }
     }