consume: add Avro support

.gitignore

@@ -1,2 +1,3 @@
 /kt
 /quickfix
+hkt

README.md

@@ -38,19 +38,19 @@ $ hkt topic -filter news -partitions
 <details><summary>Produce messages</summary>
 
 ```sh
-$ echo 'Alice wins Oscar' | kt produce -topic actor-news -literal
+$ echo 'Alice wins Oscar' | hkt produce -topic actor-news -literal
 {
   "count": 1,
   "partition": 0,
   "startOffset": 0
 }
-$ echo 'Bob wins Oscar' | kt produce -tlsca myca.pem -tlscert myclientcert.pem -tlscertkey mycertkey.pem -topic actor-news -literal
+$ echo 'Bob wins Oscar' | hkt produce -tlsca myca.pem -tlscert myclientcert.pem -tlscertkey mycertkey.pem -topic actor-news -literal
 {
   "count": 1,
   "partition": 0,
   "startOffset": 0
 }
-$ for i in {6..9} ; do echo Bourne sequel $i in production. | kt produce -topic actor-news -literal ;done
+$ for i in {6..9} ; do echo Bourne sequel $i in production. | hkt produce -topic actor-news -literal ;done
 {
   "count": 1,
   "partition": 0,

common.go

@@ -284,40 +284,6 @@ func decoderForType(typ string) (func(m json.RawMessage) ([]byte, error), error)
 
 var nullJSON = json.RawMessage("null")
 
-func encoderForType(typ string) (func([]byte) (json.RawMessage, error), error) {
-	var enc func([]byte) string
-	switch typ {
-	case "json":
-		return func(data []byte) (json.RawMessage, error) {
-			if err := json.Unmarshal(data, new(json.RawMessage)); err != nil {
-				return nil, fmt.Errorf("invalid JSON value %q: %v", data, err)
-			}
-			return json.RawMessage(data), nil
-		}, nil
-	case "hex":
-		enc = hex.EncodeToString
-	case "base64":
-		enc = base64.StdEncoding.EncodeToString
-	case "string":
-		enc = func(data []byte) string {
-			return string(data)
-		}
-	default:
-		return nil, fmt.Errorf(`unsupported decoder %#v, only json, string, hex and base64 are supported`, typ)
-	}
-	return func(data []byte) (json.RawMessage, error) {
-		if data == nil {
-			return nullJSON, nil
-		}
-		data1, err := json.Marshal(enc(data))
-		if err != nil {
-			// marshaling a string cannot fail but be defensive.
-			return nil, err
-		}
-		return json.RawMessage(data1), nil
-	}, nil
-}
-
 func min(x, y int64) int64 {
 	if x < y {
 		return x

consume.go

@@ -3,6 +3,8 @@ package main
 import (
 	"bytes"
 	"context"
+	"encoding/base64"
+	"encoding/hex"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -13,12 +15,14 @@ import (
 	"time"
 
 	"github.com/Shopify/sarama"
+	"github.com/heetch/avro/avroregistry"
+	"github.com/linkedin/goavro/v2"
 )
 
 type consumeCmd struct {
 	commonFlags
+
 	topic          string
-	offsets        string
 	timeout        time.Duration
 	valueCodecType string
 	keyCodecType   string
@@ -33,6 +37,9 @@ type consumeCmd struct {
 	encodeKey     func([]byte) (json.RawMessage, error)
 	client        sarama.Client
 	consumer      sarama.Consumer
+
+	registryURL string
+	registry    *avroregistry.Registry
 }
 
 // consumedMessage defines the format that's used to
@@ -48,13 +55,15 @@ type consumedMessage struct {
 func (cmd *consumeCmd) addFlags(flags *flag.FlagSet) {
 	cmd.commonFlags.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), defaults to json.")
+	flags.StringVar(&cmd.valueCodecType, "valuecodec", "json", "Present message value as (json|string|hex|base64|avro), defaults to json.")
 	flags.StringVar(&cmd.keyCodecType, "keycodec", "string", "Present message key as (string|hex|base64), defaults to string.")
+	flags.StringVar(&cmd.registryURL, "registry", "", "The Avro schema registry server URL.")
 
 	flags.Usage = func() {
 		fmt.Fprintln(os.Stderr, "Usage: hkt consume [flags] TOPIC [OFFSETS]")
@@ -65,7 +74,8 @@ func (cmd *consumeCmd) addFlags(flags *flag.FlagSet) {
 
 func (cmd *consumeCmd) environFlags() map[string]string {
 	return map[string]string{
-		"brokers": "KT_BROKERS",
+		"brokers":  "KT_BROKERS",
+		"registry": "KT_REGISTRY",
 	}
 }
 
@@ -88,18 +98,28 @@ func (cmd *consumeCmd) run(args []string) error {
 		sarama.Logger = log.New(os.Stderr, "", log.LstdFlags)
 	}
 	var err error
-	cmd.encodeValue, err = encoderForType(cmd.valueCodecType)
+	if cmd.valueCodecType == "avro" {
+		if cmd.registryURL == "" {
+			return fmt.Errorf("-registry or $KT_REGISTRY is required for avro codec type")
+		}
+		cmd.registry, 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(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 = encoderForType(cmd.keyCodecType)
+	cmd.encodeKey, err = cmd.encoderForType(cmd.keyCodecType)
 	if err != nil {
 		return fmt.Errorf("bad -keycodec argument: %v", err)
 	}
+
 	offsets, err := parseOffsets(offsetsStr, time.Now())
 	if err != nil {
 		return err
@@ -108,16 +128,14 @@ func (cmd *consumeCmd) run(args []string) error {
 	if err != nil {
 		return fmt.Errorf("bad -partitioners argument: %v", err)
 	}
-	c, err := cmd.newClient()
+	cmd.client, err = cmd.newClient()
 	if err != nil {
 		return err
 	}
-	cmd.client = c
-	consumer, err := sarama.NewConsumerFromClient(cmd.client)
+	cmd.consumer, err = sarama.NewConsumerFromClient(cmd.client)
 	if err != nil {
 		return fmt.Errorf("cannot create kafka consumer: %v", err)
 	}
-	cmd.consumer = consumer
 	defer logClose("consumer", cmd.consumer)
 	cmd.allPartitions, err = cmd.consumer.Partitions(cmd.topic)
 	if err != nil {
@@ -145,10 +163,7 @@ func (cmd *consumeCmd) run(args []string) error {
 	if err != nil {
 		return fmt.Errorf("cannot resolve offsets: %v", err)
 	}
-	if err := cmd.consume(resolvedOffsets, limits); err != nil {
-		return err
-	}
-	return nil
+	return cmd.consume(resolvedOffsets, limits)
 }
 
 func (cmd *consumeCmd) newClient() (sarama.Client, error) {
@@ -291,6 +306,68 @@ func (cmd *consumeCmd) newConsumedMessage(m *sarama.ConsumerMessage) (consumedMe
 	return result, nil
 }
 
+func (cmd *consumeCmd) encoderForType(typ string) (func([]byte) (json.RawMessage, error), error) {
+	var enc func([]byte) string
+	switch typ {
+	case "json":
+		return func(data []byte) (json.RawMessage, error) {
+			if err := json.Unmarshal(data, new(json.RawMessage)); err != nil {
+				return nil, fmt.Errorf("invalid JSON value %q: %v", data, err)
+			}
+			return json.RawMessage(data), nil
+		}, nil
+	case "hex":
+		enc = hex.EncodeToString
+	case "base64":
+		enc = base64.StdEncoding.EncodeToString
+	case "string":
+		enc = func(data []byte) string {
+			return string(data)
+		}
+	case "avro":
+		return cmd.encodeAvro, nil
+	default:
+		return nil, fmt.Errorf(`unsupported decoder %#v, only json, string, hex, base64 and avro are supported`, typ)
+	}
+	return func(data []byte) (json.RawMessage, error) {
+		if data == nil {
+			return nullJSON, nil
+		}
+		data1, err := json.Marshal(enc(data))
+		if err != nil {
+			// marshaling a string cannot fail but be defensive.
+			return nil, err
+		}
+		return json.RawMessage(data1), nil
+	}, nil
+}
+
+func (cmd *consumeCmd) encodeAvro(data []byte) (json.RawMessage, error) {
+	dec := cmd.registry.Decoder()
+	id, body := dec.DecodeSchemaID(data)
+	if body == nil {
+		return nil, fmt.Errorf("cannot decode schema id")
+	}
+	// TODO: cache the schema
+	schema, err := dec.SchemaForID(context.Background(), id)
+	if err != nil {
+		return nil, fmt.Errorf("cannot get schema for id %d: %v", id, err)
+	}
+	codec, err := goavro.NewCodec(schema.String())
+	if err != nil {
+		return nil, fmt.Errorf("cannot create codec from schema %s", schema.String())
+	}
+	native, _, err := codec.NativeFromBinary(body)
+	if err != nil {
+		return nil, fmt.Errorf("cannot convert native from binary: %v", err)
+	}
+	textual, err := codec.TextualFromNative(nil, native)
+	if err != nil {
+		return nil, fmt.Errorf("cannot convert textual from native: %v", err)
+	}
+	return json.RawMessage(textual), 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.