feat: make set/show a hook implementation (#209)

* feat: make set/show a hook implementation

* feat: implment extended query part

* refactor: avoid duplicate testing code

* chore: resolve lint issue

Author: sunng87

datafusion-postgres/src/client.rs

@@ -0,0 +1,54 @@
+use pgwire::api::ClientInfo;
+
+// Metadata keys for session-level settings
+const METADATA_STATEMENT_TIMEOUT: &str = "statement_timeout_ms";
+const METADATA_TIMEZONE: &str = "timezone";
+
+/// Get statement timeout from client metadata
+pub fn get_statement_timeout<C>(client: &C) -> Option<std::time::Duration>
+where
+    C: ClientInfo + ?Sized,
+{
+    client
+        .metadata()
+        .get(METADATA_STATEMENT_TIMEOUT)
+        .and_then(|s| s.parse::<u64>().ok())
+        .map(std::time::Duration::from_millis)
+}
+
+/// Set statement timeout in client metadata
+pub fn set_statement_timeout<C>(client: &mut C, timeout: Option<std::time::Duration>)
+where
+    C: ClientInfo + ?Sized,
+{
+    let metadata = client.metadata_mut();
+    if let Some(duration) = timeout {
+        metadata.insert(
+            METADATA_STATEMENT_TIMEOUT.to_string(),
+            duration.as_millis().to_string(),
+        );
+    } else {
+        metadata.remove(METADATA_STATEMENT_TIMEOUT);
+    }
+}
+
+/// Get statement timeout from client metadata
+pub fn get_timezone<C>(client: &C) -> Option<&str>
+where
+    C: ClientInfo + ?Sized,
+{
+    client.metadata().get(METADATA_TIMEZONE).map(|s| s.as_str())
+}
+
+/// Set statement timeout in client metadata
+pub fn set_timezone<C>(client: &mut C, timezone: Option<&str>)
+where
+    C: ClientInfo + ?Sized,
+{
+    let metadata = client.metadata_mut();
+    if let Some(timezone) = timezone {
+        metadata.insert(METADATA_TIMEZONE.to_string(), timezone.to_string());
+    } else {
+        metadata.remove(METADATA_TIMEZONE);
+    }
+}