feat: introduce catalog api

crates/paimon/src/catalog/mod.rs

@@ -0,0 +1,212 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Catalog API for Apache Paimon.
+//!
+//! Design aligns with [Paimon Java Catalog](https://github.com/apache/paimon/blob/master/paimon-core/src/main/java/org/apache/paimon/catalog/Catalog.java)
+//! and follows API patterns from Apache Iceberg Rust.
+
+use std::collections::HashMap;
+use std::fmt;
+
+use serde::{Deserialize, Serialize};
+
+// ======================= Identifier ===============================
+
+/// Splitter for system table names (e.g. `table$snapshots`).
+#[allow(dead_code)]
+pub const SYSTEM_TABLE_SPLITTER: &str = "$";
+/// Prefix for branch in object name (e.g. `table$branch_foo`).
+#[allow(dead_code)]
+pub const SYSTEM_BRANCH_PREFIX: &str = "branch_";
+/// Default main branch name.
+#[allow(dead_code)]
+pub const DEFAULT_MAIN_BRANCH: &str = "main";
+/// Database value when the database is not known; [`Identifier::full_name`] returns only the object.
+pub const UNKNOWN_DATABASE: &str = "unknown";
+
+/// Identifies a catalog object (e.g. a table) by database and object name.
+///
+/// Corresponds to [org.apache.paimon.catalog.Identifier](https://github.com/apache/paimon/blob/master/paimon-api/src/main/java/org/apache/paimon/catalog/Identifier.java).
+/// The object name may be a table name or a qualified name like `table$branch_foo` or
+/// `table$snapshots` for system tables.
+#[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Identifier {
+    /// Database name.
+    database: String,
+    /// Object name (table name, or table$branch$system for system tables).
+    object: String,
+}
+
+impl Identifier {
+    /// Create an identifier from database and object name.
+    pub fn new(database: impl Into<String>, object: impl Into<String>) -> Self {
+        Self {
+            database: database.into(),
+            object: object.into(),
+        }
+    }
+
+    /// Database name.
+    pub fn database(&self) -> &str {
+        &self.database
+    }
+
+    /// Full object name (table name, or with branch/system suffix).
+    pub fn object(&self) -> &str {
+        &self.object
+    }
+
+    /// Full name: when database is [`UNKNOWN_DATABASE`], returns only the object;
+    /// otherwise returns `database.object`.
+    pub fn full_name(&self) -> String {
+        if self.database == UNKNOWN_DATABASE {
+            self.object.clone()
+        } else {
+            format!("{}.{}", self.database, self.object)
+        }
+    }
+}
+
+impl fmt::Display for Identifier {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.full_name())
+    }
+}
+
+impl fmt::Debug for Identifier {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Identifier")
+            .field("database", &self.database)
+            .field("object", &self.object)
+            .finish()
+    }
+}
+
+// ======================= Catalog trait ===============================
+
+use async_trait::async_trait;
+
+use crate::spec::{Schema, SchemaChange};
+use crate::table::Table;
+use crate::Result;
+
+/// Catalog API for reading and writing metadata (databases, tables) in Paimon.
+///
+/// Corresponds to [org.apache.paimon.catalog.Catalog](https://github.com/apache/paimon/blob/master/paimon-core/src/main/java/org/apache/paimon/catalog/Catalog.java).
+#[async_trait]
+pub trait Catalog: Send + Sync {
+    // ======================= database methods ===============================
+
+    /// List names of all databases in this catalog.
+    ///
+    /// # Errors
+    /// Implementations may return other errors (e.g. I/O or backend-specific).
+    async fn list_databases(&self) -> Result<Vec<String>>;
+
+    /// Create a database.
+    ///
+    /// * `ignore_if_exists` - if true, do nothing when the database already exists;
+    ///   if false, return [`crate::Error::DatabaseAlreadyExist`].
+    ///
+    /// # Errors
+    /// * [`crate::Error::DatabaseAlreadyExist`] - database already exists when `ignore_if_exists` is false.
+    async fn create_database(
+        &self,
+        name: &str,
+        ignore_if_exists: bool,
+        properties: HashMap<String, String>,
+    ) -> Result<()>;
+
+    /// Drop a database.
+    ///
+    /// * `ignore_if_not_exists` - if true, do nothing when the database does not exist.
+    /// * `cascade` - if true, delete all tables in the database then delete the database;
+    ///   if false, return [`crate::Error::DatabaseNotEmpty`] when not empty.
+    ///
+    /// # Errors
+    /// * [`crate::Error::DatabaseNotExist`] - database does not exist when `ignore_if_not_exists` is false.
+    /// * [`crate::Error::DatabaseNotEmpty`] - database is not empty when `cascade` is false.
+    async fn drop_database(
+        &self,
+        name: &str,
+        ignore_if_not_exists: bool,
+        cascade: bool,
+    ) -> Result<()>;
+
+    // ======================= table methods ===============================
+
+    /// Get table metadata for the given identifier.
+    ///
+    /// # Errors
+    /// * [`crate::Error::DatabaseNotExist`] - database in identifier does not exist.
+    /// * [`crate::Error::TableNotExist`] - table does not exist.
+    async fn get_table(&self, identifier: &Identifier) -> Result<Table>;
+
+    /// List table names in a database. System tables are not listed.
+    ///
+    /// # Errors
+    /// * [`crate::Error::DatabaseNotExist`] - database does not exist.
+    async fn list_tables(&self, database_name: &str) -> Result<Vec<String>>;
+
+    /// Create a table.
+    ///
+    /// * `ignore_if_exists` - if true, do nothing when the table already exists;
+    ///   if false, return [`crate::Error::TableAlreadyExist`].
+    ///
+    /// # Errors
+    /// * [`crate::Error::DatabaseNotExist`] - database in identifier does not exist.
+    /// * [`crate::Error::TableAlreadyExist`] - table already exists when `ignore_if_exists` is false.
+    async fn create_table(
+        &self,
+        identifier: &Identifier,
+        creation: Schema,
+        ignore_if_exists: bool,
+    ) -> Result<()>;
+
+    /// Drop a table. System tables cannot be dropped.
+    ///
+    /// # Errors
+    /// * [`crate::Error::TableNotExist`] - table does not exist when `ignore_if_not_exists` is false.
+    async fn drop_table(&self, identifier: &Identifier, ignore_if_not_exists: bool) -> Result<()>;
+
+    /// Rename a table.
+    ///
+    /// # Errors
+    /// * [`crate::Error::TableNotExist`] - source table does not exist when `ignore_if_not_exists` is false.
+    /// * [`crate::Error::TableAlreadyExist`] - target table already exists.
+    async fn rename_table(
+        &self,
+        from: &Identifier,
+        to: &Identifier,
+        ignore_if_not_exists: bool,
+    ) -> Result<()>;
+
+    /// Apply schema changes to a table.
+    ///
+    /// # Errors
+    /// * [`crate::Error::TableNotExist`] - table does not exist when `ignore_if_not_exists` is false.
+    /// * [`crate::Error::ColumnAlreadyExist`] - adding a column that already exists.
+    /// * [`crate::Error::ColumnNotExist`] - altering or dropping a column that does not exist.
+    async fn alter_table(
+        &self,
+        identifier: &Identifier,
+        changes: Vec<SchemaChange>,
+        ignore_if_not_exists: bool,
+    ) -> Result<()>;
+}

crates/paimon/src/error.rs

@@ -66,6 +66,24 @@ pub enum Error {
         display("Paimon hitting invalid file index format: {}", message)
     )]
     FileIndexFormatInvalid { message: String },
+
+    // ======================= catalog errors ===============================
+    #[snafu(display("Database {} already exists.", database))]
+    DatabaseAlreadyExist { database: String },
+    #[snafu(display("Database {} does not exist.", database))]
+    DatabaseNotExist { database: String },
+    #[snafu(display("Database {} is not empty.", database))]
+    DatabaseNotEmpty { database: String },
+    #[snafu(display("Table {} already exists.", full_name))]
+    TableAlreadyExist { full_name: String },
+    #[snafu(display("Table {} does not exist.", full_name))]
+    TableNotExist { full_name: String },
+    #[snafu(display("Column {} already exists in table {}.", column, full_name))]
+    ColumnAlreadyExist { full_name: String, column: String },
+    #[snafu(display("Column {} does not exist in table {}.", column, full_name))]
+    ColumnNotExist { full_name: String, column: String },
+    #[snafu(display("Invalid identifier: {}", message))]
+    IdentifierInvalid { message: String },
 }
 
 impl From<opendal::Error> for Error {

crates/paimon/src/lib.rs

@@ -19,6 +19,8 @@ mod error;
 pub use error::Error;
 pub use error::Result;
 
+pub mod catalog;
 pub mod file_index;
 pub mod io;
 pub mod spec;
+mod table;