Command-line utility to convert protobuf-encoded messages to JSON and vice versa.

$ npm install -g protobuf2json

$ protobuf2json -h

  Usage: protobuf2json [options]

  Convert protobuf to JSON


  Options:

    -V, --version           output the version number
    -d, --directory <path>  path to base directory containing proto file and all its imports
    -p, --proto <path>      path to proto file relative to base directory
    -t, --type <name>       protobuf message type
    -m, --multi             multiple protobuf messages with prefixed signed 32-bit big endian message length
    -h, --help              output usage information

The protobuf-encoded message(s) is given as stdin. For example, suppose all of our proto files are in the protos directory. Inside the directory there is my_message.proto containing the MyMessage message. my_message.proto may import other proto files located inside the protos directory and subdirectories. The following command will decode the my_message.bin file containing a single protobuf-encoded MyMessage and emit the JSON to stdout:

$ protobuf2json -d protos -p my_message.proto -t MyMessage < my_message.bin

If multiple messages are combined in the input, each message must be prefixed with a signed, 32-bit big endian integer indicating the length of the message. A file in this encoding can be converted to JSON as follows:

$ protobuf2json -d protos -p my_message.proto -t MyMessage -m < my_messages.bin

$ json2protobuf -h

  Usage: json2protobuf [options]

  Convert JSON to protobuf


  Options:

    -V, --version           output the version number
    -d, --directory <path>  path to base directory containing proto file and all its imports
    -p, --proto <path>      path to proto file relative to base directory
    -t, --type <name>       protobuf message type
    -m, --multi             multiple JSON messages separated by newlines
    -h, --help              output usage information

The JSON message(s) is given as stdin. For example, suppose all of our proto files are in the protos directory. Inside the directory there is my_message.proto containing the MyMessage message. my_message.proto may import other proto files located inside the protos directory and subdirectories. The following command will encode the my_message.json file containing a single MyMessage in JSON form and emit the encoded protobuf to stdout:

$ json2protobuf -d protos -p my_message.proto -t MyMessage < my_message.json

If multiple JSON messages are combined in the input, each message must be a single line, and terminated by a newline. A file in this encoding can be converted to protobuf as follows:

$ json2protobuf -d protos -p my_message.proto -t MyMessage -m < my_messages.json

This utility can be used with kafkacat to publish protobuf-encoded messages to Kafka topics, and to examine the contents of Kafka topics containing protobuf-encoded messages.

To publish a protobuf-encoded message to Kafka:

$ json2protobuf -d protos -p my_message.proto -t MyMessage < my_message.json | kafkacat -P -b <broker> -t <topic> -D \t

To print the contents of a protobuf-encoded Kafka topic to stdout:

$ kafkacat -C -b <broker> -t <topic> -e -o beginning -f '%R%s' | protobuf2json -d protos -p my_message.proto -t MyMessage -m

Note the use of the -f '%R%s' argument to kafkacat to produce length-prefixed message output and the -m argument to protobuf2json to support multiple messages as input.