Handle EmptyQueryResponse (#500)

Sources/PostgresNIO/New/Connection State Machine/ExtendedQueryStateMachine.swift

@@ -10,7 +10,8 @@ struct ExtendedQueryStateMachine {
         case parameterDescriptionReceived(ExtendedQueryContext)
         case rowDescriptionReceived(ExtendedQueryContext, [RowDescription.Column])
         case noDataMessageReceived(ExtendedQueryContext)
-
+        case emptyQueryResponseReceived
+
         /// A state that is used if a noData message was received before. If a row description was received `bufferingRows` is
         /// used after receiving a `bindComplete` message
         case bindCompleteReceived(ExtendedQueryContext)
@@ -122,7 +123,7 @@ struct ExtendedQueryStateMachine {
                 return .forwardStreamError(.queryCancelled, read: true)
             }
 
-        case .commandComplete, .error, .drain:
+        case .commandComplete, .emptyQueryResponseReceived, .error, .drain:
             // the stream has already finished.
             return .wait
 
@@ -229,6 +230,7 @@ struct ExtendedQueryStateMachine {
              .messagesSent,
              .parseCompleteReceived,
              .parameterDescriptionReceived,
+             .emptyQueryResponseReceived,
              .bindCompleteReceived,
              .streaming,
              .drain,
@@ -268,6 +270,7 @@ struct ExtendedQueryStateMachine {
              .parseCompleteReceived,
              .parameterDescriptionReceived,
              .noDataMessageReceived,
+             .emptyQueryResponseReceived,
              .rowDescriptionReceived,
              .bindCompleteReceived,
              .commandComplete,
@@ -285,7 +288,7 @@ struct ExtendedQueryStateMachine {
             case .unnamed(_, let eventLoopPromise), .executeStatement(_, let eventLoopPromise):
                 return self.avoidingStateMachineCoW { state -> Action in
                     state = .commandComplete(commandTag: commandTag)
-                    let result = QueryResult(value: .noRows(commandTag), logger: context.logger)
+                    let result = QueryResult(value: .noRows(.tag(commandTag)), logger: context.logger)
                     return .succeedQuery(eventLoopPromise, with: result)
                 }
 
@@ -309,6 +312,7 @@ struct ExtendedQueryStateMachine {
              .parseCompleteReceived,
              .parameterDescriptionReceived,
              .noDataMessageReceived,
+             .emptyQueryResponseReceived,
              .rowDescriptionReceived,
              .commandComplete,
              .error:
@@ -319,7 +323,22 @@ struct ExtendedQueryStateMachine {
     }
 
     mutating func emptyQueryResponseReceived() -> Action {
-        preconditionFailure("Unimplemented")
+        guard case .bindCompleteReceived(let queryContext) = self.state else {
+            return self.setAndFireError(.unexpectedBackendMessage(.emptyQueryResponse))
+        }
+
+        switch queryContext.query {
+        case .unnamed(_, let eventLoopPromise),
+             .executeStatement(_, let eventLoopPromise):
+            return self.avoidingStateMachineCoW { state -> Action in
+                state = .emptyQueryResponseReceived
+                let result = QueryResult(value: .noRows(.emptyResponse), logger: queryContext.logger)
+                return .succeedQuery(eventLoopPromise, with: result)
+            }
+
+        case .prepareStatement(_, _, _, _):
+            return self.setAndFireError(.unexpectedBackendMessage(.emptyQueryResponse))
+        }
     }
 
     mutating func errorReceived(_ errorMessage: PostgresBackendMessage.ErrorResponse) -> Action {
@@ -336,7 +355,7 @@ struct ExtendedQueryStateMachine {
             return self.setAndFireError(error)
         case .streaming, .drain:
             return self.setAndFireError(error)
-        case .commandComplete:
+        case .commandComplete, .emptyQueryResponseReceived:
             return self.setAndFireError(.unexpectedBackendMessage(.error(errorMessage)))
         case .error:
             preconditionFailure("""
@@ -382,6 +401,7 @@ struct ExtendedQueryStateMachine {
              .parseCompleteReceived,
              .parameterDescriptionReceived,
              .noDataMessageReceived,
+             .emptyQueryResponseReceived,
              .rowDescriptionReceived,
              .bindCompleteReceived:
             preconditionFailure("Requested to consume next row without anything going on.")
@@ -405,6 +425,7 @@ struct ExtendedQueryStateMachine {
              .parseCompleteReceived,
              .parameterDescriptionReceived,
              .noDataMessageReceived,
+             .emptyQueryResponseReceived,
              .rowDescriptionReceived,
              .bindCompleteReceived:
             return .wait
@@ -449,6 +470,7 @@ struct ExtendedQueryStateMachine {
             }
         case .initialized,
              .commandComplete,
+             .emptyQueryResponseReceived,
              .drain,
              .error:
             // we already have the complete stream received, now we are waiting for a
@@ -495,7 +517,7 @@ struct ExtendedQueryStateMachine {
                 return .forwardStreamError(error, read: true)
             }
 
-        case .commandComplete, .error:
+        case .commandComplete, .emptyQueryResponseReceived, .error:
             preconditionFailure("""
                 This state must not be reached. If the query `.isComplete`, the
                 ConnectionStateMachine must not send any further events to the substate machine.
@@ -507,7 +529,7 @@ struct ExtendedQueryStateMachine {
 
     var isComplete: Bool {
         switch self.state {
-        case .commandComplete, .error:
+        case .commandComplete, .emptyQueryResponseReceived, .error:
             return true
 
         case .noDataMessageReceived(let context), .rowDescriptionReceived(let context, _):

Sources/PostgresNIO/New/PSQLRowStream.swift

@@ -3,7 +3,7 @@ import Logging
 
 struct QueryResult {
     enum Value: Equatable {
-        case noRows(String)
+        case noRows(PSQLRowStream.StatementSummary)
         case rowDescription([RowDescription.Column])
     }
 
@@ -16,25 +16,30 @@ struct QueryResult {
 final class PSQLRowStream: @unchecked Sendable {
     private typealias AsyncSequenceSource = NIOThrowingAsyncSequenceProducer<DataRow, Error, AdaptiveRowBuffer, PSQLRowStream>.Source
 
+    enum StatementSummary: Equatable {
+        case tag(String)
+        case emptyResponse
+    }
+
     enum Source {
         case stream([RowDescription.Column], PSQLRowsDataSource)
-        case noRows(Result<String, Error>)
+        case noRows(Result<StatementSummary, Error>)
     }
 
     let eventLoop: EventLoop
     let logger: Logger
-    
+
     private enum BufferState {
         case streaming(buffer: CircularBuffer<DataRow>, dataSource: PSQLRowsDataSource)
-        case finished(buffer: CircularBuffer<DataRow>, commandTag: String)
+        case finished(buffer: CircularBuffer<DataRow>, summary: StatementSummary)
         case failure(Error)
     }
-    
+
     private enum DownstreamState {
         case waitingForConsumer(BufferState)
         case iteratingRows(onRow: (PostgresRow) throws -> (), EventLoopPromise<Void>, PSQLRowsDataSource)
         case waitingForAll([PostgresRow], EventLoopPromise<[PostgresRow]>, PSQLRowsDataSource)
-        case consumed(Result<String, Error>)
+        case consumed(Result<StatementSummary, Error>)
         case asyncSequence(AsyncSequenceSource, PSQLRowsDataSource, onFinish: @Sendable () -> ())
     }
 
@@ -52,9 +57,9 @@ final class PSQLRowStream: @unchecked Sendable {
         case .stream(let rowDescription, let dataSource):
             self.rowDescription = rowDescription
             bufferState = .streaming(buffer: .init(), dataSource: dataSource)
-        case .noRows(.success(let commandTag)):
+        case .noRows(.success(let summary)):
             self.rowDescription = []
-            bufferState = .finished(buffer: .init(), commandTag: commandTag)
+            bufferState = .finished(buffer: .init(), summary: summary)
         case .noRows(.failure(let error)):
             self.rowDescription = []
             bufferState = .failure(error)
@@ -98,12 +103,12 @@ final class PSQLRowStream: @unchecked Sendable {
             self.downstreamState = .asyncSequence(source, dataSource, onFinish: onFinish)
             self.executeActionBasedOnYieldResult(yieldResult, source: dataSource)
 
-        case .finished(let buffer, let commandTag):
+        case .finished(let buffer, let summary):
             _ = source.yield(contentsOf: buffer)
             source.finish()
             onFinish()
-            self.downstreamState = .consumed(.success(commandTag))
-            
+            self.downstreamState = .consumed(.success(summary))
+
         case .failure(let error):
             source.finish(error)
             self.downstreamState = .consumed(.failure(error))
@@ -190,12 +195,12 @@ final class PSQLRowStream: @unchecked Sendable {
             dataSource.request(for: self)
             return promise.futureResult
 
-        case .finished(let buffer, let commandTag):
+        case .finished(let buffer, let summary):
             let rows = buffer.map {
                 PostgresRow(data: $0, lookupTable: self.lookupTable, columns: self.rowDescription)
             }
 
-            self.downstreamState = .consumed(.success(commandTag))
+            self.downstreamState = .consumed(.success(summary))
             return self.eventLoop.makeSucceededFuture(rows)
 
         case .failure(let error):
@@ -247,8 +252,8 @@ final class PSQLRowStream: @unchecked Sendable {
             }
 
             return promise.futureResult
-            
-        case .finished(let buffer, let commandTag):
+
+        case .finished(let buffer, let summary):
             do {
                 for data in buffer {
                     let row = PostgresRow(
@@ -259,7 +264,7 @@ final class PSQLRowStream: @unchecked Sendable {
                     try onRow(row)
                 }
 
-                self.downstreamState = .consumed(.success(commandTag))
+                self.downstreamState = .consumed(.success(summary))
                 return self.eventLoop.makeSucceededVoidFuture()
             } catch {
                 self.downstreamState = .consumed(.failure(error))
@@ -292,7 +297,7 @@ final class PSQLRowStream: @unchecked Sendable {
 
         case .waitingForConsumer(.finished), .waitingForConsumer(.failure):
             preconditionFailure("How can new rows be received, if an end was already signalled?")
-            
+
         case .iteratingRows(let onRow, let promise, let dataSource):
             do {
                 for data in newRows {
@@ -347,25 +352,25 @@ final class PSQLRowStream: @unchecked Sendable {
     private func receiveEnd(_ commandTag: String) {
         switch self.downstreamState {
         case .waitingForConsumer(.streaming(buffer: let buffer, _)):
-            self.downstreamState = .waitingForConsumer(.finished(buffer: buffer, commandTag: commandTag))
-            
-        case .waitingForConsumer(.finished), .waitingForConsumer(.failure):
+            self.downstreamState = .waitingForConsumer(.finished(buffer: buffer, summary: .tag(commandTag)))
+
+        case .waitingForConsumer(.finished), .waitingForConsumer(.failure), .consumed(.success(.emptyResponse)):
             preconditionFailure("How can we get another end, if an end was already signalled?")
 
         case .iteratingRows(_, let promise, _):
-            self.downstreamState = .consumed(.success(commandTag))
+            self.downstreamState = .consumed(.success(.tag(commandTag)))
             promise.succeed(())
 
         case .waitingForAll(let rows, let promise, _):
-            self.downstreamState = .consumed(.success(commandTag))
+            self.downstreamState = .consumed(.success(.tag(commandTag)))
             promise.succeed(rows)
 
         case .asyncSequence(let source, _, let onFinish):
-            self.downstreamState = .consumed(.success(commandTag))
+            self.downstreamState = .consumed(.success(.tag(commandTag)))
             source.finish()
             onFinish()
 
-        case .consumed:
+        case .consumed(.success(.tag)), .consumed(.failure):
             break
         }
     }
@@ -375,7 +380,7 @@ final class PSQLRowStream: @unchecked Sendable {
         case .waitingForConsumer(.streaming):
             self.downstreamState = .waitingForConsumer(.failure(error))
 
-        case .waitingForConsumer(.finished), .waitingForConsumer(.failure):
+        case .waitingForConsumer(.finished), .waitingForConsumer(.failure), .consumed(.success(.emptyResponse)):
             preconditionFailure("How can we get another end, if an end was already signalled?")
 
         case .iteratingRows(_, let promise, _):
@@ -391,7 +396,7 @@ final class PSQLRowStream: @unchecked Sendable {
             consumer.finish(error)
             onFinish()
 
-        case .consumed:
+        case .consumed(.success(.tag)), .consumed(.failure):
             break
         }
     }
@@ -413,10 +418,15 @@ final class PSQLRowStream: @unchecked Sendable {
     }
 
     var commandTag: String {
-        guard case .consumed(.success(let commandTag)) = self.downstreamState else {
+        guard case .consumed(.success(let consumed)) = self.downstreamState else {
             preconditionFailure("commandTag may only be called if all rows have been consumed")
         }
-        return commandTag
+        switch consumed {
+        case .tag(let tag):
+            return tag
+        case .emptyResponse:
+            return ""
+        }
     }
 }
 

Sources/PostgresNIO/New/PostgresChannelHandler.swift

@@ -550,9 +550,9 @@ final class PostgresChannelHandler: ChannelDuplexHandler {
             )
             self.rowStream = rows
 
-        case .noRows(let commandTag):
+        case .noRows(let summary):
             rows = PSQLRowStream(
-                source: .noRows(.success(commandTag)),
+                source: .noRows(.success(summary)),
                 eventLoop: context.channel.eventLoop,
                 logger: result.logger
             )

Sources/PostgresNIO/PostgresDatabase+Query.swift

@@ -73,10 +73,7 @@ public struct PostgresQueryMetadata: Sendable {
 
     init?(string: String) {
         let parts = string.split(separator: " ")
-        guard parts.count >= 1 else {
-            return nil
-        }
-        switch parts[0] {
+        switch parts.first {
         case "INSERT":
             // INSERT oid rows
             guard parts.count == 3 else {

Tests/IntegrationTests/PSQLIntegrationTests.swift

@@ -123,6 +123,25 @@ final class IntegrationTests: XCTestCase {
         XCTAssertEqual(foo, "hello")
     }
 
+    func testQueryNothing() throws {
+        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
+        defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }
+        let eventLoop = eventLoopGroup.next()
+
+        var conn: PostgresConnection?
+        XCTAssertNoThrow(conn = try PostgresConnection.test(on: eventLoop).wait())
+        defer { XCTAssertNoThrow(try conn?.close().wait()) }
+
+        var _result: PostgresQueryResult?
+        XCTAssertNoThrow(_result = try conn?.query("""
+            -- Some comments
+            """, logger: .psqlTest).wait())
+
+        let result = try XCTUnwrap(_result)
+        XCTAssertEqual(result.rows, [])
+        XCTAssertEqual(result.metadata.command, "")
+    }
+
     func testDecodeIntegers() {
         let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
         defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }

Tests/PostgresNIOTests/New/Connection State Machine/ExtendedQueryStateMachineTests.swift

@@ -20,7 +20,7 @@ class ExtendedQueryStateMachineTests: XCTestCase {
         XCTAssertEqual(state.parameterDescriptionReceived(.init(dataTypes: [.int8])), .wait)
         XCTAssertEqual(state.noDataReceived(), .wait)
         XCTAssertEqual(state.bindCompleteReceived(), .wait)
-        XCTAssertEqual(state.commandCompletedReceived("DELETE 1"), .succeedQuery(promise, with: .init(value: .noRows("DELETE 1"), logger: logger)))
+        XCTAssertEqual(state.commandCompletedReceived("DELETE 1"), .succeedQuery(promise, with: .init(value: .noRows(.tag("DELETE 1")), logger: logger)))
         XCTAssertEqual(state.readyForQueryReceived(.idle), .fireEventReadyForQuery)
     }
 
@@ -77,7 +77,25 @@ class ExtendedQueryStateMachineTests: XCTestCase {
         XCTAssertEqual(state.commandCompletedReceived("SELECT 2"), .forwardStreamComplete([row5, row6], commandTag: "SELECT 2"))
         XCTAssertEqual(state.readyForQueryReceived(.idle), .fireEventReadyForQuery)
     }
-
+
+    func testExtendedQueryWithNoQuery() {
+        var state = ConnectionStateMachine.readyForQuery()
+
+        let logger = Logger.psqlTest
+        let promise = EmbeddedEventLoop().makePromise(of: PSQLRowStream.self)
+        promise.fail(PSQLError.uncleanShutdown) // we don't care about the error at all.
+        let query: PostgresQuery = "-- some comments"
+        let queryContext = ExtendedQueryContext(query: query, logger: logger, promise: promise)
+
+        XCTAssertEqual(state.enqueue(task: .extendedQuery(queryContext)), .sendParseDescribeBindExecuteSync(query))
+        XCTAssertEqual(state.parseCompleteReceived(), .wait)
+        XCTAssertEqual(state.parameterDescriptionReceived(.init(dataTypes: [.int8])), .wait)
+        XCTAssertEqual(state.noDataReceived(), .wait)
+        XCTAssertEqual(state.bindCompleteReceived(), .wait)
+        XCTAssertEqual(state.emptyQueryResponseReceived(), .succeedQuery(promise, with: .init(value: .noRows(.emptyResponse), logger: logger)))
+        XCTAssertEqual(state.readyForQueryReceived(.idle), .fireEventReadyForQuery)
+    }
+
     func testReceiveTotallyUnexpectedMessageInQuery() {
         var state = ConnectionStateMachine.readyForQuery()