consume.go

package main

import (
	"bytes"
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"os"
	"sort"
	"sync"
	"time"

	"github.com/Shopify/sarama"
	"github.com/heetch/avro/avroregistry"
)

type consumeCmd struct {
	commonFlags
	coder

	timeout        time.Duration
	valueCodecType string
	keyCodecType   string
	pretty         bool
	follow         bool
	keyStr         string
	partitioners   []string

	allPartitions []int32
	key           []byte // This holds the raw version of keyStr.
	encodeValue   func([]byte) (json.RawMessage, error)
	encodeKey     func([]byte) (json.RawMessage, error)
	client        sarama.Client
	consumer      sarama.Consumer
}

// consumedMessage defines the format that's used to
// print messages to the standard output.
type consumedMessage struct {
	Partition int32           `json:"partition"`
	Offset    int64           `json:"offset"`
	Key       json.RawMessage `json:"key,omitempty"`
	Value     json.RawMessage `json:"value,omitempty"`
	Time      *time.Time      `json:"time,omitempty"`
}

func (cmd *consumeCmd) addFlags(flags *flag.FlagSet) {
	cmd.commonFlags.addFlags(flags)
	cmd.coder.addFlags(flags)
	cmd.partitioners = []string{"sarama"}

	flags.Var(listFlag{&cmd.partitioners}, "partitioners", "Comma-separated list of partitioners to consider when using the key flag. See below for details")
	flags.DurationVar(&cmd.timeout, "timeout", time.Duration(0), "Timeout after not reading messages (default 0 to disable).")
	flags.StringVar(&cmd.keyStr, "key", "", "Print only messages with this key. Note: this relies on the producer using one of the partitioning algorithms specified with the -partitioners argument")
	flags.BoolVar(&cmd.pretty, "pretty", true, "Control output pretty printing.")
	flags.BoolVar(&cmd.follow, "f", false, "Follow topic by waiting new messages (default is to stop at end of topic)")
	flags.StringVar(&cmd.valueCodecType, "valuecodec", "json", "Present message value as (json|string|hex|base64|avro|none), defaults to json.")
	flags.StringVar(&cmd.keyCodecType, "keycodec", "string", "Present message key as (string|hex|base64), defaults to string.")

	flags.Usage = func() {
		fmt.Fprintln(os.Stderr, "Usage: hkt consume [flags] TOPIC [OFFSETS]")
		flags.PrintDefaults()
		fmt.Fprintln(os.Stderr, consumeDocString)
	}
}

func (cmd *consumeCmd) environFlags() map[string]string {
	return map[string]string{
		"brokers":  ENV_BROKERS,
		"registry": ENV_REGISTRY,
	}
}

func (cmd *consumeCmd) run(args []string) error {
	if len(args) < 1 {
		return fmt.Errorf("consume: no topic specified in first argument")
	}
	if len(args) > 2 {
		return fmt.Errorf("unexpected extra arguments to consume command")
	}
	cmd.topic = args[0]
	if cmd.topic == "" {
		return fmt.Errorf("empty topic name")
	}
	offsetsStr := "all"
	if len(args) > 1 {
		offsetsStr = args[1]
	}
	if cmd.verbose {
		sarama.Logger = log.New(os.Stderr, "", log.LstdFlags)
	}
	var err error
	if cmd.valueCodecType == "avro" {
		if cmd.registryURL == "" {
			return fmt.Errorf("-registry or $%s required for avro codec type", ENV_REGISTRY)
		}
		cmd.avroRegistry, err = avroregistry.New(avroregistry.Params{ServerURL: cmd.registryURL})
		if err != nil {
			return fmt.Errorf("cannot make Avro registry client: %v", err)
		}
	}
	cmd.encodeValue, err = cmd.encoderForType("value", cmd.valueCodecType)
	if err != nil {
		return fmt.Errorf("bad -valuecodec argument: %v", err)
	}
	if cmd.keyCodecType == "json" {
		// JSON for keys is not a good idea.
		return fmt.Errorf("JSON key codec not supported")
	}
	cmd.encodeKey, err = cmd.encoderForType("key", cmd.keyCodecType)
	if err != nil {
		return fmt.Errorf("bad -keycodec argument: %v", err)
	}

	offsets, err := parseOffsets(offsetsStr, time.Now())
	if err != nil {
		return err
	}
	partitioners, err := parseConsumerPartitioners(cmd.partitioners, partitioners["sarama"])
	if err != nil {
		return fmt.Errorf("bad -partitioners argument: %v", err)
	}
	cmd.client, err = cmd.newClient()
	if err != nil {
		return err
	}
	cmd.consumer, err = sarama.NewConsumerFromClient(cmd.client)
	if err != nil {
		return fmt.Errorf("cannot create kafka consumer: %v", err)
	}
	defer logClose("consumer", cmd.consumer)
	cmd.allPartitions, err = cmd.consumer.Partitions(cmd.topic)
	if err != nil {
		return err
	}
	if cmd.keyStr != "" {
		cmd.key, err = cmd.keyBytes(cmd.keyStr)
		if err != nil {
			return fmt.Errorf("invalid -key argument %q: %v", cmd.keyStr, err)
		}
		keyPartitions, err := partitioners.partitionsForKey(cmd.key, cmd.allPartitions)
		if err != nil {
			return fmt.Errorf("cannot determine partitions for key: %v", err)
		}
		if cmd.verbose {
			if len(keyPartitions) == len(cmd.allPartitions) {
				fmt.Fprintf(os.Stderr, "consuming all partitions\n")
			} else {
				fmt.Fprintf(os.Stderr, "consuming partitions %v from %v\n", keyPartitions, cmd.allPartitions)
			}
		}
		cmd.allPartitions = keyPartitions
	}

	resolvedOffsets, limits, err := cmd.resolveOffsets(context.TODO(), offsets)
	if err != nil {
		return fmt.Errorf("cannot resolve offsets: %v", err)
	}
	return cmd.consume(resolvedOffsets, limits)
}

func (cmd *consumeCmd) newClient() (sarama.Client, error) {
	cfg, err := cmd.saramaConfig("consume")
	if err != nil {
		return nil, err
	}
	client, err := sarama.NewClient(cmd.brokers(), cfg)
	if err != nil {
		return nil, fmt.Errorf("cannot create kafka client: %v", err)
	}
	return client, nil
}

func (cmd *consumeCmd) consume(partitions map[int32]resolvedInterval, limits map[int32]int64) error {
	// Make a slice of consume partitions so we can easily divide it up for merging.
	// We merge messages up to the partition limits; beyond the limits
	// we produce messages in order.
	consumerChans := make([]<-chan *sarama.ConsumerMessage, 0, len(partitions))
	out := newPrinter(cmd.pretty)
	var wg sync.WaitGroup
	wg.Add(len(partitions))
	for p, interval := range partitions {
		p, interval := p, interval
		if interval.end > limits[p] {
			interval.end = limits[p]
		}

		outc := make(chan *sarama.ConsumerMessage)
		go func() {
			defer wg.Done()
			defer close(outc)
			if err := cmd.consumePartition(outc, p, interval); err != nil {
				warningf("cannot consume partition %v: %v", p, err)
			}
		}()
		consumerChans = append(consumerChans, outc)
	}
	allMsgs := mergeConsumers(consumerChans...)
	for m := range allMsgs {
		if m1, err := cmd.newConsumedMessage(m); err != nil {
			warningf("invalid message in partition %d, offset %d: %v", m.Partition, m.Offset, err)
		} else {
			out.print(m1)
		}
	}
	wg.Wait()
	// We've got to the end of all partitions; now print messages
	// as soon as they arrive.
	outc := make(chan *sarama.ConsumerMessage)
	for p, interval := range partitions {
		p, interval := p, interval
		if interval.end <= limits[p] {
			// We've already consumed all the required messages, so
			// no need to consume this partition any more.
			continue
		}
		wg.Add(1)
		interval.start = limits[p]
		go func() {
			defer wg.Done()
			if err := cmd.consumePartition(outc, p, interval); err != nil {
				warningf("cannot consume partition %v: %v", p, err)
			}
		}()
	}
	go func() {
		wg.Wait()
		close(outc)
	}()
	for m := range outc {
		if m1, err := cmd.newConsumedMessage(m); err != nil {
			warningf("invalid message in partition %d, offset %d: %v", m.Partition, m.Offset, err)
		} else {
			out.print(m1)
		}
	}
	return nil
}

func (cmd *consumeCmd) consumePartition(out chan<- *sarama.ConsumerMessage, partition int32, interval resolvedInterval) error {
	if interval.start >= interval.end {
		return nil
	}
	pc, err := cmd.consumer.ConsumePartition(cmd.topic, partition, interval.start)
	if err != nil {
		return fmt.Errorf("failed to consume partition %v: %v", partition, err)
	}
	defer logClose(fmt.Sprintf("partition consumer %v", partition), pc)
	var timer *time.Timer
	var timeout <-chan time.Time
	if cmd.timeout > 0 {
		timer = time.NewTimer(cmd.timeout)
		timeout = timer.C
	}
	for {
		if timer != nil {
			if !timer.Stop() {
				<-timer.C
			}
			timer.Reset(cmd.timeout)
		}
		select {
		case <-timeout:
			return fmt.Errorf("consuming from partition %v timed out after %s", partition, cmd.timeout)
		case err := <-pc.Errors():
			return fmt.Errorf("partition %v consumer encountered error %s", partition, err)
		case msg, ok := <-pc.Messages():
			if !ok {
				return fmt.Errorf("unexpected closed messages chan")
			}
			if cmd.key == nil || bytes.Equal(msg.Key, cmd.key) {
				out <- msg
			}
			if interval.end > 0 && msg.Offset >= interval.end-1 {
				return nil
			}
		}
	}
}

func (cmd *consumeCmd) newConsumedMessage(m *sarama.ConsumerMessage) (consumedMessage, error) {
	key, err := cmd.encodeKey(m.Key)
	if err != nil {
		return consumedMessage{}, fmt.Errorf("invalid key: %v", err)
	}
	value, err := cmd.encodeValue(m.Value)
	if err != nil {
		return consumedMessage{}, fmt.Errorf("invalid value: %v", err)
	}
	result := consumedMessage{
		Partition: m.Partition,
		Offset:    m.Offset,
		Key:       key,
		Value:     value,
	}
	if !m.Timestamp.IsZero() {
		t := m.Timestamp.UTC()
		result.Time = &t
	}
	return result, nil
}

// mergeConsumers merges all the given channels in timestamp order
// until all existing messages have been received; it then produces
// messages as soon as they're received.
func mergeConsumers(chans ...<-chan *sarama.ConsumerMessage) <-chan *sarama.ConsumerMessage {
	switch len(chans) {
	case 0:
		// Shouldn't happen but be defensive.
		c := make(chan *sarama.ConsumerMessage)
		close(c)
		return c
	case 1:
		return chans[0]
	case 2:
		c0, c1 := chans[0], chans[1]
		out := make(chan *sarama.ConsumerMessage, 1)
		go mergeMessages([2]<-chan *sarama.ConsumerMessage{c0, c1}, out)
		return out
	default:
		n := len(chans) / 2
		return mergeConsumers(
			mergeConsumers(chans[0:n]...),
			mergeConsumers(chans[n:]...),
		)
	}
}

// merge merges two message channels in timestamp order,
// writing the result to out, which is closed when both
// input channels are closed.
func mergeMessages(cs [2]<-chan *sarama.ConsumerMessage, out chan<- *sarama.ConsumerMessage) {
	defer close(out)

	var msgs [2]*sarama.ConsumerMessage
	// get returns a message from cs[i], reading
	// from the channel if a message isn't already available.
	// If the channel is closed, it sets it to nil.
	get := func(i int) *sarama.ConsumerMessage {
		if msgs[i] != nil {
			return msgs[i]
		}
		m, ok := <-cs[i]
		msgs[i] = m
		if !ok {
			cs[i] = nil
		}
		return m
	}
	for cs[0] != nil && cs[1] != nil {
		if m0, m1 := get(0), get(1); m0 != nil && m1 != nil {
			if m0.Timestamp.Before(m1.Timestamp) {
				out <- m0
				msgs[0] = nil
			} else {
				out <- m1
				msgs[1] = nil
			}
		}
	}
	// One or both of the channels has been closed.
	var c <-chan *sarama.ConsumerMessage
	for i := range cs {
		if msgs[i] != nil {
			// There's a message remaining in the other channel; send it.
			out <- msgs[i]
		}
		if cs[i] != nil {
			c = cs[i]
		}
	}
	if c != nil {
		// Read the rest of the messages from the remaining unclosed channel.
		for m := range c {
			out <- m
		}
	}
}

type consumerPartitioners struct {
	all          bool
	partitioners []func(key []byte, numPartitions int) (int, error)
}

func parseConsumerPartitioners(ps []string, defaultPartitioner sarama.PartitionerConstructor) (*consumerPartitioners, error) {
	var cp consumerPartitioners
	for _, p := range ps {
		switch p {
		case "all":
			cp.all = true
		case "murmur2", "sarama", "std":
			cp.partitioners = append(cp.partitioners, partitionerFunc(partitioners[p]))
		default:
			return nil, fmt.Errorf("unknown partitioner %q", p)
		}
	}
	if cp.all {
		// No point in having any explicit partitioners if
		cp.partitioners = nil
	} else if len(cp.partitioners) == 0 {
		cp.partitioners = append(cp.partitioners, partitionerFunc(defaultPartitioner))
	}
	return &cp, nil
}

func partitionerFunc(makePartitioner sarama.PartitionerConstructor) func(key []byte, partitionSize int) (int, error) {
	if makePartitioner == nil {
		panic("bad partitioner (internal consistency error)")
	}
	// Note: all known partitioners ignore the topic argument to the constructor.
	// Why would a partitioner ever behave differently depending on the topic name anyway?!
	p := makePartitioner("")
	return func(key []byte, numPartitions int) (int, error) {
		// Note: the only partitioners we use ignore all fields except the key.
		n, err := p.Partition(&sarama.ProducerMessage{
			Key: sarama.ByteEncoder(key),
		}, int32(numPartitions))
		return int(n), err
	}
}

func (cmd *consumeCmd) keyBytes(key string) ([]byte, error) {
	dec, err := cmd.decoderForType("key", cmd.keyCodecType)
	if err != nil {
		// Shouldn't be able to happen, but be defensive.
		return nil, err
	}
	data, err := json.Marshal(key)
	if err != nil {
		// Shouldn't be able to happen, but be defensive.
		return nil, err
	}
	return dec(json.RawMessage(data))
}

// partitionsForKey returns the partitions that the given key may be found in, given the key itself
// and the list of all current partition ids.
func (cp *consumerPartitioners) partitionsForKey(key []byte, allPartitions []int32) ([]int32, error) {
	if len(allPartitions) == 0 {
		return nil, fmt.Errorf("no partitions found")
	}
	if cp.all {
		return allPartitions, nil
	}
	partitions := make(map[int32]bool)
	for _, pf := range cp.partitioners {
		choice, err := pf(key, len(allPartitions))
		if err != nil {
			return nil, err
		}
		if choice < 0 || choice >= len(allPartitions) {
			return nil, fmt.Errorf("invalid partition choice - broken partitioner")
		}
		partitions[allPartitions[choice]] = true
	}
	chosen := make([]int32, 0, len(partitions))
	for p := range partitions {
		chosen = append(chosen, p)
	}
	sort.Slice(chosen, func(i, j int) bool {
		return chosen[i] < chosen[j]
	})
	return chosen, nil
}

var consumeDocString = fmt.Sprintf(`
The consume command reads messages from a Kafka topic and prints them
to the standard output.

If the OFFSETS argument isn't provided, it defaults to "all" (all messages from
the topic are returned).

The messages will be printed as a stream of JSON objects in the following form:

	{
		// The partition ID holding the message.
		partition: int
		// The offset of the message within the partition
		offset: int
		// The key of the message (optional)
		key?: string
		// The value of the message (encoded according to the -valuecodec flag)
		value: null | string | {...}
		// The timestamp of the message in RFC3339 format.
		time?: string
	}

For example:

	{"partition":0,"key":"k1","value":{"foo":1234},"time":"2019-10-08T01:01:01Z"}

The value for -brokers can also be set with the environment variable %s.
The value supplied on the command line takes precedence over the environment variable.

KEY SEARCH

When the -key flag is specified, the "all" name for all partitions (see
in OFFSETS below) refers instead to all the partitions that may contain
messages with the specified key. Only messages with the specified key
will be printed.

Since clients, not Kafka itself, are responsible for choosing the
partition for a message, this means that hkt must read all partitions that
clients may have chosen. This is specified with the "-partitioners" flag,
which should be set to all the possible partitioners used by producers
to the topic. Possible partitioners are:

	murmur2 - used by default on Java clients
	sarama - used by default with the Sarama Go client. (Default)
	std - used by Java clients
	all - all partitions will be tried

As the number of partitions can change over time, this technique will
only work correctly if they haven't changed over the range of messages
being selected.

For example:

	hkt consume -key foo -partitioners sarama,std

will print only messages with key "foo" produced by Go and Java clients
across the current partition size.

OFFSETS

Offsets can be specified as a comma-separated list of intervals, each of which
is of the form:

  partition[=[start]:[end]]

For example:

	3=100:300,5=43:67

would consume from offset 100 to offset 300 inclusive in partition 3,
and from 43 to 67 in partition 5.

If the second part of an interval is omitted, there is no upper bound
to the interval unless an imprecise timestamp is used (see below).

The default is to consume from the oldest offset on every partition for
the given topic.

 - partition is the numeric identifier for a partition. You can use "all" to
   specify a default interval for all partitions.

 - start is the included offset or time where consumption should start;
   it defaults to "oldest".

 - end is the included offset or time where consumption should end;
   it defaults to "newest" when the -f flag isn't provided, or the
   maximum possible offset if it is.

An offset may be specified as:

- an absolute position as a decimal number (for example "400")

- "oldest", meaning the start of the available messages for the partition.

- "newest", meaning the newest available message in the partition.

- a timestamp enclosed in square brackets (see below).

A timestamp specifies the offset of the next message found after the
specified time. It may be specified as:

- an RFC3339 time, for example "[2019-09-12T14:49:12Z]")
- an ISO8601 date, for example "[2019-09-12]"
- a month, for example "[2019-09]"
- a year, for example "[2019]"
- a minute within the current day, for example "[14:49]"
- a second within the current day, for example "[14:49:12]"
- an hour within the current day, in 12h format, for example "[2pm]".

When a timestamp is specified with seconds precision, a timestamp
represents an exact moment; otherwise it represents the implied precision
of the timestamp (a year represents the whole of that year; a month
represents the whole month, etc).

The UTC time zone will be used unless the -local flag is provided.

When a non-precise timestamp is used as the start of an offset range,
the earliest time in the range is used; when it's used as the end of a
range, the latest time is used. So, for example:

	all=[2019]:[2020]

asks for all partitions from the start of 2019 to the very end of 2020.
If there is only one offset expression with no colon, the implied range
is used, so for example:

	all=[2019-09-12]

will ask for all messages on September 12th 2019.
To ask for all messages starting at a non-precise timestamp,
you can use an empty expression as the second part of the range.
For example:

	all=[2019-09-12]:

will ask for all messages from the start of 2019-09-12 up until the current time.

An absolute offset may also be combined with a relative offset with "+" or "-".
For example:

	all=newest-1000:

will request the latest thousand messages.

	all=oldest+1000:oldest+2000

will request the second thousand messages stored.  The absolute offset
may be omitted; it defaults to "newest" for "-" and "oldest" for "+",
so the previous two examples may be abbreviated to the following:

	all=-1000
	all=+1000:+2000

Relative offsets are based on numeric values and will not take skipped
offsets (e.g. due to compaction) into account.

A relative offset may also be specified as duration, meaning all
messages within that time period. The syntax is that accepted by Go's
time.ParseDuration function, for example:

	3.5s - three and a half seconds
	1s400ms - 1.4 seconds

So, for example:

	all=1000-5m:1000+5m

will ask for all messages in the 10 minute interval around the message
with offset 1000.

Note that if a message with that offset doesn't exist (because of
compaction, for example), the first message found after that offset will
be used for the timestamp.

More examples:

To consume messages from partition 0 between offsets 10 and 20 (inclusive).

  0=10:20

To define an interval for all partitions use -1 as the partition identifier:

  all=2:10

You can also override the offsets for a single partition, in this case 2:

  all=1-10,2=5-10

To consume from multiple partitions:

  0=4:,2=1:10,6

This would consume messages from three partitions:

  - Anything from partition 0 starting at offset 4.
  - Messages between offsets 1 and 10 from partition 2.
  - Anything from partition 6.

To start at the latest offset for each partition:

  all=newest:

Or shorter:

  newest:

To consume the last 10 messages:

  newest-10:

To skip the first 15 messages starting with the oldest offset:

  oldest+10:

In both cases you can omit "newest" and "oldest":

  -10:

and

  +10:

Will achieve the same as the two examples above.
`, ENV_BROKERS)