Implement pg_stat_gssapi & pg_backend_pid() (#185)

Implement the pg_stat_gssapi table, which will always contain a single
record showing only the current user.   Also, implement pg_backend_pid
function.

Both of these always use `BACKEND_PID` as the pid, which is currently
hard coded to 1.

These additions help towards making pgadmin startup queries run.

Author: mjgarton

datafusion-postgres/src/pg_catalog.rs

@@ -4,7 +4,8 @@ use std::sync::Arc;
 
 use async_trait::async_trait;
 use datafusion::arrow::array::{
-    as_boolean_array, ArrayRef, AsArray, BooleanBuilder, RecordBatch, StringArray, StringBuilder,
+    as_boolean_array, ArrayRef, AsArray, BooleanBuilder, Int32Builder, RecordBatch, StringArray,
+    StringBuilder,
 };
 use datafusion::arrow::datatypes::{DataType, Field, Int32Type, SchemaRef};
 use datafusion::arrow::ipc::reader::FileReader;
@@ -32,6 +33,7 @@ pub mod pg_get_expr_udf;
 pub mod pg_namespace;
 pub mod pg_replication_slot;
 pub mod pg_settings;
+pub mod pg_stat_gssapi;
 pub mod pg_tables;
 pub mod pg_views;
 
@@ -100,6 +102,7 @@ const PG_CATALOG_VIEW_PG_SETTINGS: &str = "pg_settings";
 const PG_CATALOG_VIEW_PG_VIEWS: &str = "pg_views";
 const PG_CATALOG_VIEW_PG_MATVIEWS: &str = "pg_matviews";
 const PG_CATALOG_VIEW_PG_TABLES: &str = "pg_tables";
+const PG_CATALOG_VIEW_PG_STAT_GSSAPI: &str = "pg_stat_gssapi";
 const PG_CATALOG_VIEW_PG_STAT_USER_TABLES: &str = "pg_stat_user_tables";
 const PG_CATALOG_VIEW_PG_REPLICATION_SLOTS: &str = "pg_replication_slots";
 
@@ -339,6 +342,13 @@ impl<C: CatalogInfo> SchemaProvider for PgCatalogSchemaProvider<C> {
                     vec![table],
                 )?)))
             }
+            PG_CATALOG_VIEW_PG_STAT_GSSAPI => {
+                let table = Arc::new(pg_stat_gssapi::PgStatGssApiTable::new());
+                Ok(Some(Arc::new(StreamingTable::try_new(
+                    Arc::clone(table.schema()),
+                    vec![table],
+                )?)))
+            }
             PG_CATALOG_VIEW_PG_TABLES => {
                 let table = Arc::new(pg_tables::PgTablesTable::new(self.catalog_list.clone()));
                 Ok(Some(Arc::new(StreamingTable::try_new(
@@ -1162,6 +1172,25 @@ pub fn create_pg_encoding_to_char_udf() -> ScalarUDF {
     )
 }
 
+pub fn create_pg_backend_pid_udf() -> ScalarUDF {
+    let func = move |_args: &[ColumnarValue]| {
+        let mut builder = Int32Builder::new();
+        builder.append_value(BACKEND_PID);
+        let array: ArrayRef = Arc::new(builder.finish());
+        Ok(ColumnarValue::Array(array))
+    };
+
+    create_udf(
+        "pg_backend_pid",
+        vec![],
+        DataType::Int32,
+        Volatility::Stable,
+        Arc::new(func),
+    )
+}
+
+const BACKEND_PID: i32 = 1;
+
 /// Install pg_catalog and postgres UDFs to current `SessionContext`
 pub fn setup_pg_catalog(
     session_context: &SessionContext,
@@ -1207,6 +1236,7 @@ pub fn setup_pg_catalog(
     session_context.register_udf(create_pg_relation_is_publishable_udf());
     session_context.register_udf(create_pg_get_statisticsobjdef_columns_udf());
     session_context.register_udf(create_pg_encoding_to_char_udf());
+    session_context.register_udf(create_pg_backend_pid_udf());
 
     Ok(())
 }

datafusion-postgres/src/pg_catalog/pg_stat_gssapi.rs

@@ -0,0 +1,65 @@
+use datafusion::arrow::array::{ArrayRef, BooleanArray, Int32Array, RecordBatch, StringArray};
+use datafusion::arrow::datatypes::{DataType, Field, Schema, SchemaRef};
+use datafusion::error::Result;
+use datafusion::execution::{SendableRecordBatchStream, TaskContext};
+use datafusion::physical_plan::stream::RecordBatchStreamAdapter;
+use datafusion::physical_plan::streaming::PartitionStream;
+use std::sync::Arc;
+
+use crate::pg_catalog::BACKEND_PID;
+
+#[derive(Debug, Clone)]
+pub(crate) struct PgStatGssApiTable {
+    schema: SchemaRef,
+}
+
+impl PgStatGssApiTable {
+    pub(crate) fn new() -> Self {
+        let schema = Arc::new(Schema::new(vec![
+            Field::new("pid", DataType::Int32, true),
+            Field::new("gss_authenticated", DataType::Boolean, false),
+            Field::new("principal", DataType::Utf8, true),
+            Field::new("encrypted", DataType::Boolean, false),
+            Field::new("credentials_delegated", DataType::Boolean, false),
+        ]));
+
+        Self { schema }
+    }
+
+    /// Generate record batches based on the current state of the catalog
+    async fn get_data(this: Self) -> Result<RecordBatch> {
+        let pid = vec![BACKEND_PID];
+        let gss_authenticated = vec![false];
+        let principal: Vec<Option<String>> = vec![None];
+        let encrypted = vec![false];
+        let credentials_delegated = vec![false];
+
+        // Create Arrow arrays from the collected data
+        let arrays: Vec<ArrayRef> = vec![
+            Arc::new(Int32Array::from(pid)),
+            Arc::new(BooleanArray::from(gss_authenticated)),
+            Arc::new(StringArray::from(principal)),
+            Arc::new(BooleanArray::from(encrypted)),
+            Arc::new(BooleanArray::from(credentials_delegated)),
+        ];
+
+        // Create a record batch
+        let batch = RecordBatch::try_new(this.schema.clone(), arrays)?;
+
+        Ok(batch)
+    }
+}
+
+impl PartitionStream for PgStatGssApiTable {
+    fn schema(&self) -> &SchemaRef {
+        &self.schema
+    }
+
+    fn execute(&self, _ctx: Arc<TaskContext>) -> SendableRecordBatchStream {
+        let this = self.clone();
+        Box::pin(RecordBatchStreamAdapter::new(
+            this.schema.clone(),
+            futures::stream::once(async move { PgStatGssApiTable::get_data(this).await }),
+        ))
+    }
+}