feat: add two registry utility functions

wfassoc/src/lowlevel.rs

@@ -16,10 +16,14 @@ pub enum Error {
     NoPrivilege,
     #[error("given registry key is inexistant")]
     InexistantKey,
+
     #[error("registry operation error: {0}")]
     BadRegOp(#[from] std::io::Error),
     #[error("{0}")]
+    BadSoleSubKey(#[from] regext::OnlySubKeyError),
+    #[error("{0}")]
     UnexpectedBlankKey(#[from] regext::BlankPathError),
+
     #[error("{0}")]
     LoadIconRc(#[from] concept::LoadIconRcError),
     #[error("{0}")]

wfassoc/src/win32/regext.rs

@@ -7,6 +7,7 @@ use thiserror::Error as TeError;
 use windows_sys::Win32::Foundation::ERROR_FILE_NOT_FOUND;
 use windows_sys::Win32::System::Registry::REG_SAM_FLAGS;
 use winreg::RegKey;
+use winreg::enums::RegType;
 use winreg::types::FromRegValue;
 
 // region: Extra Operations
@@ -60,6 +61,57 @@ pub fn try_get_value<T: FromRegValue, N: AsRef<OsStr>>(
     }
 }
 
+/// The error occurs when fetching the name of only subkey.
+#[derive(Debug, TeError)]
+pub enum OnlySubKeyError {
+    #[error("registry operation error: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[error("there is no any subkey in given RegKey")]
+    NoSubKey,
+    #[error("there is more than one subkey in given RegKey")]
+    TooManySubKey,
+}
+
+/// Get the name of only subkey in given key.
+///
+/// This is usually used for ShellVerb fetching.
+pub fn get_sole_subkey_name(regkey: &RegKey) -> Result<String, OnlySubKeyError> {
+    let mut subkey_enumerator = regkey.enum_keys();
+
+    // Get first one.
+    let rv = match subkey_enumerator.next() {
+        Some(key) => key?,
+        None => return Err(OnlySubKeyError::NoSubKey),
+    };
+
+    // Check whether there is second one.
+    match subkey_enumerator.next() {
+        Some(_) => Err(OnlySubKeyError::TooManySubKey),
+        None => Ok(rv),
+    }
+}
+
+/// Get the name list of all "string" subkeys in given key.
+/// 
+/// This is usually used for "OpenWithProgIds" subkey.
+pub fn get_all_string_subkey_names(regkey: &RegKey) -> std::io::Result<Vec<String>> {
+    regkey
+        .enum_values()
+        .filter_map(|item| match item {
+            Ok((key, value)) => {
+                // Check subkey type.
+                if value.vtype == RegType::REG_SZ {
+                    Some(Ok(key))
+                } else {
+                    None
+                }
+            }
+            Err(err) => Some(Err(err)),
+        })
+        .collect::<Result<Vec<_>, _>>()
+}
+
 // endregion
 
 // region: Blank Path Guard