kvdb: add postgres

kvdb/postgres/db.go

@@ -0,0 +1,241 @@
+// +build kvdb_postgres
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"io"
+	"sync"
+	"time"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	_ "github.com/jackc/pgx/v4/stdlib"
+)
+
+const (
+	// kvTableName is the name of the table that will contain all the kv
+	// pairs.
+	kvTableName = "kv"
+)
+
+// KV stores a key/value pair.
+type KV struct {
+	key string
+	val string
+}
+
+// db holds a reference to the postgres connection connection.
+type db struct {
+	// cfg is the postgres connection config.
+	cfg *Config
+
+	// prefix is the table name prefix that is used to simulate namespaces.
+	// We don't use schemas because at least sqlite does not support that.
+	prefix string
+
+	// ctx is the overall context for the database driver.
+	//
+	// TODO: This is an anti-pattern that is in place until the kvdb
+	// interface supports a context.
+	ctx context.Context
+
+	// db is the underlying database connection instance.
+	db *sql.DB
+
+	// lock is the global write lock that ensures single writer.
+	lock sync.RWMutex
+
+	// table is the name of the table that contains the data for all
+	// top-level buckets that have keys that cannot be mapped to a distinct
+	// sql table.
+	table string
+}
+
+// Enforce db implements the walletdb.DB interface.
+var _ walletdb.DB = (*db)(nil)
+
+// newPostgresBackend returns a db object initialized with the passed backend
+// config. If postgres connection cannot be estabished, then returns error.
+func newPostgresBackend(ctx context.Context, config *Config, prefix string) (
+	*db, error) {
+
+	if prefix == "" {
+		return nil, errors.New("empty postgres prefix")
+	}
+
+	dbConn, err := sql.Open("pgx", config.Dsn)
+	if err != nil {
+		return nil, err
+	}
+
+	// Compose system table names.
+	table := fmt.Sprintf(
+		"%s_%s", prefix, kvTableName,
+	)
+
+	// Execute the create statements to set up a kv table in postgres. Every
+	// row points to the bucket that it is one via its parent_id field. A
+	// NULL parent_id means that the key belongs to the upper-most bucket in
+	// this table. A constraint on parent_id is enforcing referential
+	// integrity.
+	//
+	// Furthermore there is a <table>_p index on parent_id that is required
+	// for the foreign key constraint.
+	//
+	// Finally there are unique indices on (parent_id, key) to prevent the
+	// same key being present in a bucket more than once (<table>_up and
+	// <table>_unp). In postgres, a single index wouldn't enforce the unique
+	// constraint on rows with a NULL parent_id. Therefore two indices are
+	// defined.
+	_, err = dbConn.ExecContext(ctx, `
+CREATE SCHEMA IF NOT EXISTS public;
+CREATE TABLE IF NOT EXISTS public.`+table+`
+(
+    key bytea NOT NULL,
+    value bytea,
+    parent_id bigint,
+    id bigserial PRIMARY KEY,
+    sequence bigint,
+    CONSTRAINT `+table+`_parent FOREIGN KEY (parent_id)
+        REFERENCES public.`+table+` (id)
+        ON UPDATE NO ACTION
+        ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS `+table+`_p
+    ON public.`+table+` (parent_id);
+
+CREATE UNIQUE INDEX IF NOT EXISTS `+table+`_up
+    ON public.`+table+`
+    (parent_id, key) WHERE parent_id IS NOT NULL;
+
+CREATE UNIQUE INDEX IF NOT EXISTS `+table+`_unp 
+    ON public.`+table+` (key) WHERE parent_id IS NULL;
+`)
+	if err != nil {
+		_ = dbConn.Close()
+
+		return nil, err
+	}
+
+	backend := &db{
+		cfg:    config,
+		prefix: prefix,
+		ctx:    ctx,
+		db:     dbConn,
+		table:  table,
+	}
+
+	return backend, nil
+}
+
+// getTimeoutCtx gets a timeout context for database requests.
+func (db *db) getTimeoutCtx() (context.Context, func()) {
+	if db.cfg.Timeout == time.Duration(0) {
+		return db.ctx, func() {}
+	}
+
+	return context.WithTimeout(db.ctx, db.cfg.Timeout)
+}
+
+// getPrefixedTableName returns a table name for this prefix (namespace).
+func (db *db) getPrefixedTableName(table string) string {
+	return fmt.Sprintf("%s_%s", db.prefix, table)
+}
+
+// catchPanic executes the specified function. If a panic occurs, it is returned
+// as an error value.
+func catchPanic(f func() error) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			err = r.(error)
+			log.Criticalf("Caught unhandled error: %v", err)
+		}
+	}()
+
+	err = f()
+
+	return
+}
+
+// View opens a database read transaction and executes the function f with the
+// transaction passed as a parameter. After f exits, the transaction is rolled
+// back. If f errors, its error is returned, not a rollback error (if any
+// occur). The passed reset function is called before the start of the
+// transaction and can be used to reset intermediate state. As callers may
+// expect retries of the f closure (depending on the database backend used), the
+// reset function will be called before each retry respectively.
+func (db *db) View(f func(tx walletdb.ReadTx) error, reset func()) error {
+	return db.executeTransaction(
+		func(tx walletdb.ReadWriteTx) error {
+			return f(tx.(walletdb.ReadTx))
+		},
+		reset, true,
+	)
+}
+
+// Update opens a database read/write transaction and executes the function f
+// with the transaction passed as a parameter. After f exits, if f did not
+// error, the transaction is committed. Otherwise, if f did error, the
+// transaction is rolled back. If the rollback fails, the original error
+// returned by f is still returned. If the commit fails, the commit error is
+// returned. As callers may expect retries of the f closure, the reset function
+// will be called before each retry respectively.
+func (db *db) Update(f func(tx walletdb.ReadWriteTx) error, reset func()) (err error) {
+	return db.executeTransaction(f, reset, false)
+}
+
+// executeTransaction creates a new read-only or read-write transaction and
+// executes the given function within it.
+func (db *db) executeTransaction(f func(tx walletdb.ReadWriteTx) error,
+	reset func(), readOnly bool) error {
+
+	reset()
+
+	tx, err := newReadWriteTx(db, readOnly)
+	if err != nil {
+		return err
+	}
+
+	err = catchPanic(func() error { return f(tx) })
+	if err != nil {
+		if rollbackErr := tx.Rollback(); rollbackErr != nil {
+			log.Errorf("Error rolling back tx: %v", rollbackErr)
+		}
+
+		return err
+	}
+
+	return tx.Commit()
+}
+
+// PrintStats returns all collected stats pretty printed into a string.
+func (db *db) PrintStats() string {
+	return "stats not supported by Postgres driver"
+}
+
+// BeginReadWriteTx opens a database read+write transaction.
+func (db *db) BeginReadWriteTx() (walletdb.ReadWriteTx, error) {
+	return newReadWriteTx(db, false)
+}
+
+// BeginReadTx opens a database read transaction.
+func (db *db) BeginReadTx() (walletdb.ReadTx, error) {
+	return newReadWriteTx(db, true)
+}
+
+// Copy writes a copy of the database to the provided writer. This call will
+// start a read-only transaction to perform all operations.
+// This function is part of the walletdb.Db interface implementation.
+func (db *db) Copy(w io.Writer) error {
+	return errors.New("not implemented")
+}
+
+// Close cleanly shuts down the database and syncs all data.
+// This function is part of the walletdb.Db interface implementation.
+func (db *db) Close() error {
+	return db.db.Close()
+}