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schema_registry_decode

Automatically decodes and validates messages with schemas from a Confluent Schema Registry service.

This processor uses the Franz Kafka Schema Registry client.

  • Common

  • Advanced

processor:
  label: ""
  schema_registry_decode:
    avro:
      raw_unions: false # No default (optional)
      preserve_logical_types: false
      translate_kafka_connect_types: false
      store_schema_metadata: "" # No default (optional)
    protobuf:
      use_proto_names: false
      use_enum_numbers: false
      emit_unpopulated: false
      emit_default_values: false
      serialize_to_json: true
    json:
      coerce_data: false
    cache_duration: 10m
    url: "" # No default (required)
    default_schema_id: 0 # No default (optional)
processor:
  label: ""
  schema_registry_decode:
    avro:
      raw_unions: false # No default (optional)
      preserve_logical_types: false
      translate_kafka_connect_types: false
      mapping: "" # No default (optional)
      store_schema_metadata: "" # No default (optional)
    protobuf:
      use_proto_names: false
      use_enum_numbers: false
      emit_unpopulated: false
      emit_default_values: false
      serialize_to_json: true
    json:
      coerce_data: false
    cache_duration: 10m
    url: "" # No default (required)
    default_schema_id: 0 # No default (optional)
    oauth:
      enabled: false
      consumer_key: ""
      consumer_secret: ""
      access_token: ""
      access_token_secret: ""
    basic_auth:
      enabled: false
      username: ""
      password: ""
    jwt:
      enabled: false
      private_key_file: ""
      signing_method: ""
      claims: {}
      headers: {}
    tls:
      skip_cert_verify: false
      enable_renegotiation: false
      root_cas: ""
      root_cas_file: ""
      client_certs: []

Decodes messages automatically from a schema stored within a Confluent Schema Registry service by extracting a schema ID from the message and obtaining the associated schema from the registry. If a message fails to match against the schema then it will remain unchanged and the error can be caught using error-handling methods.

Avro, Protobuf and JSON schemas are supported, all are capable of expanding from schema references as of v4.22.0.

Avro JSON format

By default, this processor expects documents formatted as Avro JSON when decoding with Avro schemas. In this format, the value of a union is encoded in JSON as follows:

  • If the union’s type is null, it is encoded as a JSON null.

  • Otherwise, the union is encoded as a JSON object with one name/value pair. The name is the type’s name, and the value is the recursively-encoded value. The user-specified name is used for Avro’s named types (record, fixed, or enum). For other types, the type name is used.

For example, the union schema ["null","string","Transaction"], where Transaction is a record name, would encode:

  • null as a JSON null

  • The string "a" as {"string": "a"}

  • A Transaction instance as {"Transaction": {…​}}, where {…​} indicates the JSON encoding of a Transaction instance

Alternatively, you can create documents in standard/raw JSON format by setting the field avro.raw_unions to true.

Protobuf format

This processor decodes Protobuf messages to JSON documents. For more information about the JSON mapping of Protobuf messages, see the Protocol Buffers documentation.

Metadata

This processor also adds the following metadata to each outgoing message:

schema_id: the ID of the schema in the schema registry that was associated with the message.

Fields

avro

Configuration for how to decode schemas that are of type AVRO.

Type: object

avro.mapping

Define a custom mapping to apply to the JSON representation of Avro schemas. You can use mappings to convert custom types emitted by other tools, such as Debezium, into standard Avro types.

Type: string

# Examples:
mapping: |

  map isDebeziumTimestampType {
    root = this.type == "long" && this."connect.name" == "io.debezium.time.Timestamp" && !this.exists("logicalType")
  }
  map debeziumTimestampToAvroTimestamp {
    let mapped_fields = this.fields.or([]).map_each(item -> item.apply("debeziumTimestampToAvroTimestamp"))
    root = match {
      this.type == "record" => this.assign({"fields": $mapped_fields})
      this.type.type() == "array" => this.assign({"type": this.type.map_each(item -> item.apply("debeziumTimestampToAvroTimestamp"))})
      # Add a logical type so that it's decoded as a timestamp instead of a long.
      this.type.type() == "object" && this.type.apply("isDebeziumTimestampType") => this.merge({"type":{"logicalType": "timestamp-millis"}})
      _ => this
    }
  }
  root = this.apply("debeziumTimestampToAvroTimestamp")

avro.preserve_logical_types

Choose whether to:

  • Transform logical types into their primitive type (default). For example, decimals become raw bytes and timestamps become plain integers.

  • Preserve logical types.

Set to true to preserve logical types, which keeps decimal types as numbers in Bloblang and timestamps as time values.

Type: bool

Default: false

avro.raw_unions

Whether Avro messages should be decoded into normal JSON (JSON that meets the expectations of regular internet JSON) rather than Avro JSON.

If set to false (default), Avro messages are decoded as Avro JSON.

For example, the union schema ["null","string","Transaction"], where Transaction is a record name, would be decoded as:

  • A null as a JSON null

  • The string "a" as {"string": "a"}

  • A Transaction instance as {"Transaction": {…​}}, where {…​} indicates the JSON encoding of a Transaction instance.

If set to true, Avro messages are decoded as standard JSON.

For example, the same union schema ["null","string","Transaction"] is decoded as:

  • A null as JSON null

  • The string "a" as "a"

  • A Transaction instance as {…​}, where {…​} indicates the JSON encoding of a Transaction instance.

Type: bool

avro.store_schema_metadata

Optionally store the schema used to decode messages as a metadata field under the given name. This field can later be referenced in other components such as a parquet_encode processor in order to automatically infer their schema.

Type: string

avro.translate_kafka_connect_types

Only valid if preserve_logical_types is true. This decodes various Kafka Connect types into their bloblang equivalents when not representable by standard logical types according to the Avro standard.

Types that are currently translated:

Table 1. Debezium Custom Temporal Types
Type Name Bloblang Type Description

io.debezium.time.Date

timestamp

Date without time (days since epoch)

io.debezium.time.Timestamp

timestamp

Timestamp without timezone (milliseconds since epoch)

io.debezium.time.MicroTimestamp

timestamp

Timestamp with microsecond precision

io.debezium.time.NanoTimestamp

timestamp

Timestamp with nanosecond precision

io.debezium.time.ZonedTimestamp

timestamp

Timestamp with timezone (ISO-8601 format)

io.debezium.time.Year

timestamp at January 1st at 00:00:00

Year value

io.debezium.time.Time

timestamp at the unix epoch

Time without date (milliseconds past midnight)

io.debezium.time.MicroTime

timestamp at the unix epoch

Time with microsecond precision

io.debezium.time.NanoTime

timestamp at the unix epoch

Time with nanosecond precision

Type: bool

Default: false

basic_auth

Configure basic authentication for requests from this component.

Type: object

basic_auth.enabled

Whether to use basic authentication in requests.

Type: bool

Default: false

basic_auth.password

The password to use for authentication. Used together with username for basic authentication.

This field contains sensitive information that usually shouldn’t be added to a configuration directly. For more information, see Manage Secrets before adding it to your configuration.

Type: string

Default: ""

basic_auth.username

The username of the account credentials to authenticate as. Used together with password for basic authentication.

Type: string

Default: ""

cache_duration

The duration after which a cached schema is considered stale and is removed from the cache.

Type: string

Default: 10m

# Examples:
cache_duration: 1h

# ---

cache_duration: 5m

default_schema_id

This schema ID is used when a message’s schema header cannot be read (ErrBadHeader). If this value is not set, schema header errors are returned.

This configuration does not work with protobuf schemas.

You can also use the with_schema_registry_header bloblang function to add a schema ID to messages.

Type: int

json

Configuration for how to decode schemas that are of type JSON.

Type: object

json.coerce_data

Whether decoded values should be coerced to match the types declared in the JSON Schema. By default JSON Schema decoding only validates the message and leaves it untouched, which means numbers are later interpreted as floating point (double) and date-time values as strings. When set to true the decoder rebuilds the message so that values match the schema: integer fields become 64-bit integers, number fields stay floating point, string fields with format: date-time become timestamps, and any default values declared in the schema are applied to absent fields. This is useful for downstream components that infer their schema from the decoded values, such as the iceberg outputs, which will then create bigint columns for integer fields rather than double. Note that, unlike the default behavior, this is no longer a read-only operation: the message contents are transformed. Because coercion is stricter than validation, a message that passes validation may still fail coercion (for example an integer that overflows a 64-bit value, or a date-time string that is not valid RFC 3339), in which case the error can be caught using error handling methods.

Type: bool

Default: false

jwt

Beta

Configure JSON Web Token (JWT) authentication. This feature is in beta and may change in future releases. JWTs provide secure, stateless authentication between services.

Type: object

jwt.claims

A map of claims to include in the JWT. Claims pass the identity of the authenticated entity to the service provider.

Type: object

Default: {}

jwt.enabled

Whether to use JWT authentication in requests.

Type: bool

Default: false

jwt.headers

Additional key-value pairs to include in the JWT header (optional). These headers provide extra metadata for JWT processing.

Type: object

Default: {}

jwt.private_key_file

Path to a file containing the PEM-encoded private key using PKCS#1 or PKCS#8 format. The private key must be compatible with the algorithm specified in the signing_method field.

Type: string

Default: ""

jwt.signing_method

The cryptographic algorithm used to sign the JWT. Supported algorithms are RS256, RS384, RS512, and EdDSA. This algorithm must be compatible with the private key specified in the private_key_file field.

Type: string

Default: ""

oauth

Configure OAuth version 1.0 authentication for secure API access.

Type: object

oauth.access_token

The value used to gain access to the protected resources on behalf of the user.

Type: string

Default: ""

oauth.access_token_secret

The secret that establishes ownership of the access_token in OAuth 1.0 authentication.

This field contains sensitive information that usually shouldn’t be added to a configuration directly. For more information, see Manage Secrets before adding it to your configuration.

Type: string

Default: ""

oauth.consumer_key

The value used to identify this component or client to the service provider.

Type: string

Default: ""

oauth.consumer_secret

The secret that establishes ownership of the consumer key in OAuth 1.0 authentication.

This field contains sensitive information that usually shouldn’t be added to a configuration directly. For more information, see Manage Secrets before adding it to your configuration.

Type: string

Default: ""

oauth.enabled

Whether to enable OAuth version 1.0 authentication for requests.

Type: bool

Default: false

protobuf

Configuration for how to decode schemas that are of type PROTOBUF.

Type: object

protobuf.emit_default_values

Whether to emit default-valued primitive fields, empty lists, and empty maps. emit_unpopulated takes precedence over emit_default_values

Type: bool

Default: false

protobuf.emit_unpopulated

Whether to emit unpopulated fields. It does not emit unpopulated oneof fields or unpopulated extension fields.

Type: bool

Default: false

protobuf.serialize_to_json

If messages should be serialized to JSON bytes. If false then the message is kept in decoded form, which means that 64 bit integers are not converted to strings and types for bytes and google.protobuf.Timestamp are preserved (as they are not serialized to JSON strings).

Type: bool

Default: true

protobuf.use_enum_numbers

Emits enum values as numbers.

Type: bool

Default: false

protobuf.use_proto_names

Use proto field name instead of lowerCamelCase name.

Type: bool

Default: false

tls

Configure Transport Layer Security (TLS) settings to secure network connections. This includes options for standard TLS as well as mutual TLS (mTLS) authentication where both client and server authenticate each other using certificates. Key configuration options include client_certs for mTLS authentication, root_cas/root_cas_file for custom certificate authorities, and skip_cert_verify for development environments.

Type: object

tls.client_certs[]

A list of client certificates for mutual TLS (mTLS) authentication. Configure this field to enable mTLS, authenticating the client to the server with these certificates.

Certificate pairing rules: For each certificate item, provide either:

  • Inline PEM data using both cert and key or

  • File paths using both cert_file and key_file.

Mixing inline and file-based values within the same item is not supported.

Type: array<object>

Default: []

# Examples:
client_certs:
  - cert: foo
    key: bar


# ---

client_certs:
  - cert_file: ./example.pem
    key_file: ./example.key

tls.client_certs[].cert

The plaintext certificate to use for TLS authentication. Must be paired with the corresponding private key in the key field when using inline PEM data for mTLS client certificates.

Type: string

Default: ""

tls.client_certs[].cert_file

The path to a file containing the certificate to use for TLS authentication. Must be paired with the corresponding private key file in the key_file field when using file-based configuration for mTLS client certificates.

Type: string

Default: ""

tls.client_certs[].key

Private key for mTLS client certificate as inline PEM data. Must correspond to the client certificate specified in the cert field. Use this field together with cert when providing certificate data inline rather than through files.

This field contains sensitive information that usually shouldn’t be added to a configuration directly. For more information, see Manage Secrets before adding it to your configuration.

Type: string

Default: ""

tls.client_certs[].key_file

Path to private key file for mTLS client certificate in PEM format. Must correspond to the client certificate specified in the cert_file field. Use this field together with cert_file when loading certificate data from files.

Type: string

Default: ""

tls.client_certs[].password

The password to use for the private key (specified in the key or key_file fields), if it is password-protected. The PKCS#1 and PKCS#8 formats are supported. Supports environment variable interpolation for secure password management.

The pbeWithMD5AndDES-CBC algorithm is obsolete and not supported for the PKCS#8 format. This algorithm does not authenticate the ciphertext, making it vulnerable to padding oracle attacks that can let an attacker recover the plaintext.

This field contains sensitive information that usually shouldn’t be added to a configuration directly. For more information, see Manage Secrets before adding it to your configuration.

Type: string

Default: ""

# Examples:
password: foo

# ---

password: ${KEY_PASSWORD}

tls.enable_renegotiation

Whether to allow the remote server to repeatedly request renegotiation. Enable this option if you’re seeing the error message local error: tls: no renegotiation.

Type: bool

Default: false

tls.root_cas

Specify a root certificate authority to use (optional). This is a string that represents a certificate chain from the parent-trusted root certificate, through possible intermediate signing certificates, to the host certificate. Use either this field for inline certificate data or root_cas_file for file-based certificate loading.

This field contains sensitive information that usually shouldn’t be added to a configuration directly. For more information, see Manage Secrets before adding it to your configuration.

Type: string

Default: ""

# Examples:
root_cas: |-
  -----BEGIN CERTIFICATE-----
  ...
  -----END CERTIFICATE-----

tls.root_cas_file

Specify the path to a root certificate authority file (optional). This is a file, often with a .pem extension, which contains a certificate chain from the parent-trusted root certificate, through possible intermediate signing certificates, to the host certificate. Use either this field for file-based certificate loading or root_cas for inline certificate data.

Type: string

Default: ""

# Examples:
root_cas_file: ./root_cas.pem

tls.skip_cert_verify

Whether to skip server-side certificate verification. Set to true only for testing environments as this reduces security by disabling certificate validation. When using self-signed certificates or in development, this may be necessary, but should never be used in production. Consider using root_cas or root_cas_file to specify trusted certificates instead of disabling verification entirely.

Type: bool

Default: false

url

The base URL of the schema registry service.

Type: string