Factor out Consumer from the roomserver (#50)

src/github.com/matrix-org/dendrite/cmd/dendrite-roomserver/main.go

@@ -2,16 +2,18 @@ package main
 
 import (
 	"fmt"
-	"github.com/matrix-org/dendrite/roomserver/input"
-	"github.com/matrix-org/dendrite/roomserver/query"
-	"github.com/matrix-org/dendrite/roomserver/storage"
-	"github.com/prometheus/client_golang/prometheus"
-	sarama "gopkg.in/Shopify/sarama.v1"
 	"net/http"
 	_ "net/http/pprof"
 	"os"
 	"strconv"
 	"strings"
+
+	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/roomserver/input"
+	"github.com/matrix-org/dendrite/roomserver/query"
+	"github.com/matrix-org/dendrite/roomserver/storage"
+	"github.com/prometheus/client_golang/prometheus"
+	sarama "gopkg.in/Shopify/sarama.v1"
 )
 
 var (
@@ -43,10 +45,13 @@ func main() {
 	}
 
 	consumer := input.Consumer{
-		Consumer:             kafkaConsumer,
+		ContinualConsumer: common.ContinualConsumer{
+			Topic:          inputRoomEventTopic,
+			Consumer:       kafkaConsumer,
+			PartitionStore: db,
+		},
 		DB:                   db,
 		Producer:             kafkaProducer,
-		InputRoomEventTopic:  inputRoomEventTopic,
 		OutputRoomEventTopic: outputRoomEventTopic,
 	}
 

src/github.com/matrix-org/dendrite/common/consumers.go

@@ -0,0 +1,108 @@
+package common
+
+import (
+	"fmt"
+
+	sarama "gopkg.in/Shopify/sarama.v1"
+)
+
+// A PartitionOffset is the offset into a partition of the input log.
+type PartitionOffset struct {
+	// The ID of the partition.
+	Partition int32
+	// The offset into the partition.
+	Offset int64
+}
+
+// A PartitionStorer has the storage APIs needed by the consumer.
+type PartitionStorer interface {
+	// PartitionOffsets returns the offsets the consumer has reached for each partition.
+	PartitionOffsets(topic string) ([]PartitionOffset, error)
+	// SetPartitionOffset records where the consumer has reached for a partition.
+	SetPartitionOffset(topic string, partition int32, offset int64) error
+}
+
+// A ContinualConsumer continually consumes logs even across restarts. It requires a PartitionStorer to
+// remember the offset it reached.
+type ContinualConsumer struct {
+	// The kafkaesque topic to consume events from.
+	// This is the name used in kafka to identify the stream to consume events from.
+	Topic string
+	// A kafkaesque stream consumer providing the APIs for talking to the event source.
+	// The interface is taken from a client library for Apache Kafka.
+	// But any equivalent event streaming protocol could be made to implement the same interface.
+	Consumer sarama.Consumer
+	// A thing which can load and save partition offsets for a topic.
+	PartitionStore PartitionStorer
+	// ProcessMessage is a function which will be called for each message in the log. Return an error to
+	// stop processing messages. See ErrShutdown for specific control signals.
+	ProcessMessage func(msg *sarama.ConsumerMessage) error
+	// ShutdownCallback is called when ProcessMessage returns ErrShutdown, after the partition has been saved.
+	// It is optional.
+	ShutdownCallback func()
+}
+
+// ErrShutdown can be returned from ContinualConsumer.ProcessMessage to stop the ContinualConsumer.
+var ErrShutdown = fmt.Errorf("shutdown")
+
+// Start starts the consumer consuming.
+// Starts up a goroutine for each partition in the kafka stream.
+// Returns nil once all the goroutines are started.
+// Returns an error if it can't start consuming for any of the partitions.
+func (c *ContinualConsumer) Start() error {
+	offsets := map[int32]int64{}
+
+	partitions, err := c.Consumer.Partitions(c.Topic)
+	if err != nil {
+		return err
+	}
+	for _, partition := range partitions {
+		// Default all the offsets to the beginning of the stream.
+		offsets[partition] = sarama.OffsetOldest
+	}
+
+	storedOffsets, err := c.PartitionStore.PartitionOffsets(c.Topic)
+	if err != nil {
+		return err
+	}
+	for _, offset := range storedOffsets {
+		// We've already processed events from this partition so advance the offset to where we got to.
+		offsets[offset.Partition] = offset.Offset
+	}
+
+	var partitionConsumers []sarama.PartitionConsumer
+	for partition, offset := range offsets {
+		pc, err := c.Consumer.ConsumePartition(c.Topic, partition, offset)
+		if err != nil {
+			for _, p := range partitionConsumers {
+				p.Close()
+			}
+			return err
+		}
+		partitionConsumers = append(partitionConsumers, pc)
+	}
+	for _, pc := range partitionConsumers {
+		go c.consumePartition(pc)
+	}
+
+	return nil
+}
+
+// consumePartition consumes the room events for a single partition of the kafkaesque stream.
+func (c *ContinualConsumer) consumePartition(pc sarama.PartitionConsumer) {
+	defer pc.Close()
+	for message := range pc.Messages() {
+		msgErr := c.ProcessMessage(message)
+		// Advance our position in the stream so that we will start at the right position after a restart.
+		if err := c.PartitionStore.SetPartitionOffset(c.Topic, message.Partition, message.Offset); err != nil {
+			panic(fmt.Errorf("the ContinualConsumer failed to SetPartitionOffset: %s", err))
+		}
+		// Shutdown if we were told to do so.
+		if msgErr == ErrShutdown {
+			if c.ShutdownCallback != nil {
+				c.ShutdownCallback()
+			}
+			return
+		}
+	}
+}

src/github.com/matrix-org/dendrite/common/partition_offset_table.go

@@ -1,9 +1,6 @@
-package storage
+package common
 
-import (
-	"database/sql"
-	"github.com/matrix-org/dendrite/roomserver/types"
-)
+import "database/sql"
 
 const partitionOffsetsSchema = `
 -- The offsets that the server has processed up to.
@@ -26,32 +23,37 @@ const upsertPartitionOffsetsSQL = "" +
 	" ON CONFLICT ON CONSTRAINT topic_partition_unique" +
 	" DO UPDATE SET partition_offset = $3"
 
-type partitionOffsetStatements struct {
+// PartitionOffsetStatements represents a set of statements that can be run on a partition_offsets table.
+type PartitionOffsetStatements struct {
 	selectPartitionOffsetsStmt *sql.Stmt
 	upsertPartitionOffsetStmt  *sql.Stmt
 }
 
-func (s *partitionOffsetStatements) prepare(db *sql.DB) (err error) {
+// Prepare converts the raw SQL statements into prepared statements.
+func (s *PartitionOffsetStatements) Prepare(db *sql.DB) (err error) {
 	_, err = db.Exec(partitionOffsetsSchema)
 	if err != nil {
 		return
 	}
-
-	return statementList{
-		{&s.selectPartitionOffsetsStmt, selectPartitionOffsetsSQL},
-		{&s.upsertPartitionOffsetStmt, upsertPartitionOffsetsSQL},
-	}.prepare(db)
+	if s.selectPartitionOffsetsStmt, err = db.Prepare(selectPartitionOffsetsSQL); err != nil {
+		return
+	}
+	if s.upsertPartitionOffsetStmt, err = db.Prepare(upsertPartitionOffsetsSQL); err != nil {
+		return
+	}
+	return
 }
 
-func (s *partitionOffsetStatements) selectPartitionOffsets(topic string) ([]types.PartitionOffset, error) {
+// SelectPartitionOffsets returns all the partition offsets for the given topic.
+func (s *PartitionOffsetStatements) SelectPartitionOffsets(topic string) ([]PartitionOffset, error) {
 	rows, err := s.selectPartitionOffsetsStmt.Query(topic)
 	if err != nil {
 		return nil, err
 	}
 	defer rows.Close()
-	var results []types.PartitionOffset
+	var results []PartitionOffset
 	for rows.Next() {
-		var offset types.PartitionOffset
+		var offset PartitionOffset
 		if err := rows.Scan(&offset.Partition, &offset.Offset); err != nil {
 			return nil, err
 		}
@@ -59,7 +61,8 @@ func (s *partitionOffsetStatements) selectPartitionOffsets(topic string) ([]type
 	return results, nil
 }
 
-func (s *partitionOffsetStatements) upsertPartitionOffset(topic string, partition int32, offset int64) error {
+// UpsertPartitionOffset updates or inserts the partition offset for the given topic.
+func (s *PartitionOffsetStatements) UpsertPartitionOffset(topic string, partition int32, offset int64) error {
 	_, err := s.upsertPartitionOffsetStmt.Exec(topic, partition, offset)
 	return err
 }

src/github.com/matrix-org/dendrite/roomserver/input/consumer.go

@@ -4,19 +4,17 @@ package input
 import (
 	"encoding/json"
 	"fmt"
-	"github.com/matrix-org/dendrite/roomserver/api"
-	"github.com/matrix-org/dendrite/roomserver/types"
-	sarama "gopkg.in/Shopify/sarama.v1"
 	"sync/atomic"
+
+	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	sarama "gopkg.in/Shopify/sarama.v1"
 )
 
 // A ConsumerDatabase has the storage APIs needed by the consumer.
 type ConsumerDatabase interface {
 	RoomEventDatabase
-	// PartitionOffsets returns the offsets the consumer has reached for each partition.
-	PartitionOffsets(topic string) ([]types.PartitionOffset, error)
-	// SetPartitionOffset records where the consumer has reached for a partition.
-	SetPartitionOffset(topic string, partition int32, offset int64) error
+	common.PartitionStorer
 }
 
 // An ErrorLogger handles the errors encountered by the consumer.
@@ -31,16 +29,10 @@ type ErrorLogger interface {
 // The events needed to construct the state at the event should already be stored on the roomserver.
 // If the event is not valid then it will be discarded and an error will be logged.
 type Consumer struct {
-	// A kafkaesque stream consumer providing the APIs for talking to the event source.
-	// The interface is taken from a client library for Apache Kafka.
-	// But any equivalent event streaming protocol could be made to implement the same interface.
-	Consumer sarama.Consumer
+	ContinualConsumer common.ContinualConsumer
 	// The database used to store the room events.
 	DB       ConsumerDatabase
 	Producer sarama.SyncProducer
-	// The kafkaesque topic to consume room events from.
-	// This is the name used in kafka to identify the stream to consume events from.
-	InputRoomEventTopic string
 	// The kafkaesque topic to output new room events to.
 	// This is the name used in kafka to identify the stream to write events to.
 	OutputRoomEventTopic string
@@ -75,79 +67,42 @@ func (c *Consumer) WriteOutputRoomEvent(output api.OutputRoomEvent) error {
 // Returns nil once all the goroutines are started.
 // Returns an error if it can't start consuming for any of the partitions.
 func (c *Consumer) Start() error {
-	offsets := map[int32]int64{}
+	c.ContinualConsumer.ProcessMessage = c.processMessage
+	c.ContinualConsumer.ShutdownCallback = c.shutdown
+	return c.ContinualConsumer.Start()
+}
 
-	partitions, err := c.Consumer.Partitions(c.InputRoomEventTopic)
-	if err != nil {
-		return err
-	}
-	for _, partition := range partitions {
-		// Default all the offsets to the beginning of the stream.
-		offsets[partition] = sarama.OffsetOldest
-	}
-
-	storedOffsets, err := c.DB.PartitionOffsets(c.InputRoomEventTopic)
-	if err != nil {
-		return err
-	}
-	for _, offset := range storedOffsets {
-		// We've already processed events from this partition so advance the offset to where we got to.
-		offsets[offset.Partition] = offset.Offset
-	}
-
-	var partitionConsumers []sarama.PartitionConsumer
-	for partition, offset := range offsets {
-		pc, err := c.Consumer.ConsumePartition(c.InputRoomEventTopic, partition, offset)
-		if err != nil {
-			for _, p := range partitionConsumers {
-				p.Close()
-			}
-			return err
+func (c *Consumer) processMessage(message *sarama.ConsumerMessage) error {
+	var input api.InputRoomEvent
+	if err := json.Unmarshal(message.Value, &input); err != nil {
+		// If the message is invalid then log it and move onto the next message in the stream.
+		c.logError(message, err)
+	} else {
+		if err := processRoomEvent(c.DB, c, input); err != nil {
+			// If there was an error processing the message then log it and
+			// move onto the next message in the stream.
+			// TODO: If the error was due to a problem talking to the database
+			// then we shouldn't move onto the next message and we should either
+			// retry processing the message, or panic and kill ourselves.
+			c.logError(message, err)
 		}
-		partitionConsumers = append(partitionConsumers, pc)
 	}
-	for _, pc := range partitionConsumers {
-		go c.consumePartition(pc)
+	// Update the number of processed messages using atomic addition because it is accessed from multiple goroutines.
+	processed := atomic.AddInt64(&c.processed, 1)
+	// Check if we should stop processing.
+	// Note that since we have multiple goroutines it's quite likely that we'll overshoot by a few messages.
+	// If we try to stop processing after M message and we have N goroutines then we will process somewhere
+	// between M and (N + M) messages because the N goroutines could all try to process what they think will be the
+	// last message. We could be more careful here but this is good enough for getting rough benchmarks.
+	if c.StopProcessingAfter != nil && processed >= int64(*c.StopProcessingAfter) {
+		return common.ErrShutdown
 	}
-
 	return nil
 }
 
-// consumePartition consumes the room events for a single partition of the kafkaesque stream.
-func (c *Consumer) consumePartition(pc sarama.PartitionConsumer) {
-	defer pc.Close()
-	for message := range pc.Messages() {
-		var input api.InputRoomEvent
-		if err := json.Unmarshal(message.Value, &input); err != nil {
-			// If the message is invalid then log it and move onto the next message in the stream.
-			c.logError(message, err)
-		} else {
-			if err := processRoomEvent(c.DB, c, input); err != nil {
-				// If there was an error processing the message then log it and
-				// move onto the next message in the stream.
-				// TODO: If the error was due to a problem talking to the database
-				// then we shouldn't move onto the next message and we should either
-				// retry processing the message, or panic and kill ourselves.
-				c.logError(message, err)
-			}
-		}
-		// Advance our position in the stream so that we will start at the right position after a restart.
-		if err := c.DB.SetPartitionOffset(c.InputRoomEventTopic, message.Partition, message.Offset); err != nil {
-			c.logError(message, err)
-		}
-		// Update the number of processed messages using atomic addition because it is accessed from multiple goroutines.
-		processed := atomic.AddInt64(&c.processed, 1)
-		// Check if we should stop processing.
-		// Note that since we have multiple goroutines it's quite likely that we'll overshoot by a few messages.
-		// If we try to stop processing after M message and we have N goroutines then we will process somewhere
-		// between M and (N + M) messages because the N goroutines could all try to process what they think will be the
-		// last message. We could be more careful here but this is good enough for getting rough benchmarks.
-		if c.StopProcessingAfter != nil && processed >= int64(*c.StopProcessingAfter) {
-			if c.ShutdownCallback != nil {
-				c.ShutdownCallback(fmt.Sprintf("Stopping processing after %d messages", c.processed))
-			}
-			return
-		}
+func (c *Consumer) shutdown() {
+	if c.ShutdownCallback != nil {
+		c.ShutdownCallback(fmt.Sprintf("Stopping processing after %d messages", c.processed))
 	}
 }
 

src/github.com/matrix-org/dendrite/roomserver/storage/sql.go

@@ -2,10 +2,12 @@ package storage
 
 import (
 	"database/sql"
+
+	"github.com/matrix-org/dendrite/common"
 )
 
 type statements struct {
-	partitionOffsetStatements
+	common.PartitionOffsetStatements
 	eventTypeStatements
 	eventStateKeyStatements
 	roomStatements
@@ -19,7 +21,7 @@ type statements struct {
 func (s *statements) prepare(db *sql.DB) error {
 	var err error
 
-	if err = s.partitionOffsetStatements.prepare(db); err != nil {
+	if err = s.PartitionOffsetStatements.Prepare(db); err != nil {
 		return err
 	}
 

src/github.com/matrix-org/dendrite/roomserver/storage/storage.go

@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	// Import the postgres database driver.
 	_ "github.com/lib/pq"
+	"github.com/matrix-org/dendrite/common"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@@ -28,13 +29,13 @@ func Open(dataSourceName string) (*Database, error) {
 }
 
 // PartitionOffsets implements input.ConsumerDatabase
-func (d *Database) PartitionOffsets(topic string) ([]types.PartitionOffset, error) {
-	return d.statements.selectPartitionOffsets(topic)
+func (d *Database) PartitionOffsets(topic string) ([]common.PartitionOffset, error) {
+	return d.statements.SelectPartitionOffsets(topic)
 }
 
 // SetPartitionOffset implements input.ConsumerDatabase
 func (d *Database) SetPartitionOffset(topic string, partition int32, offset int64) error {
-	return d.statements.upsertPartitionOffset(topic, partition, offset)
+	return d.statements.UpsertPartitionOffset(topic, partition, offset)
 }
 
 // StoreEvent implements input.EventDatabase

src/github.com/matrix-org/dendrite/roomserver/types/types.go

@@ -5,14 +5,6 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 )
 
-// A PartitionOffset is the offset into a partition of the input log.
-type PartitionOffset struct {
-	// The ID of the partition.
-	Partition int32
-	// The offset into the partition.
-	Offset int64
-}
-
 // EventTypeNID is a numeric ID for an event type.
 type EventTypeNID int64