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STTS Wire Protocol

STTS implements its own custom wire protocol, that uses Bincode to encode and decode messages.

Message Format

Each message should be raw binary data, with the following header:

Field Type Description
type u8 The message type

Immediately following the header is the message payload.

String Encoding

Strings are encoded as follows:

Field Type Description
len u64 The length of the string
data u8 The string data (must be valid UTF-8!)

Boolean Encoding

Booleans are simply u8s, with 0 for false and 1 for true.

Client -> Server

Initialize Streaming

This message is sent by the client to initialize the streaming connection.

Type

0x00

Payload

Field Type Description
verbose bool Should the response include verbose data?
language String The language to use for the model.

Audio Data Packet

This message is sent to feed audio into the STT engine.

Do not send this message until you receive a "Initialization Complete" message. Any packets sent before that will be ignored.

Type

0x01

Payload

Field Type Description
data_len u32 The length of the audio data.
data i16 The audio data. This must be exactly data_len*2 bytes.

Finalize Streaming

This message is sent to signal the end of audio streaming, and will trigger a "STT Result Packet" to be sent.

Type

0x02

Payload

None

Close Connection

This message is sent to close the connection early, and will immediately trigger a close on the server side.

Type

0x03

Payload

None

Convert to Status

This message is sent when the client would like this connection to monitor the server status.

Type

0x04

Payload

None

Server -> Client

Initialization Complete

This message is sent by the server to signal that the streaming state has been initialized.

After this message is sent, you may send audio data packets.

Type

0x00

Payload

None

Initialization Failed

This message is sent by the server to signal that the streaming state has failed to initialize.

Immediately after the message is sent, the server will close the connection.

Type

0x01

Payload

Field Type Description
error String The error message.

STT Result Packet (normal)

This message is sent by the server to signal the end of speech to text processing.

Immediately after the message is sent, the server will close the connection.

Type

0x02

Payload

Field Type Description
result String The STT result.

STT Result Packet (verbose)

This is the same as the normal STT result message, but includes verbose data.

Just like the normal STT result message, the connection will be closed after this message is sent.

Type

0x03

Payload

Field Type Description
num_transcripts u32 The number of transcripts in the result. If this is 0, this is the only field that is sent.
main_transcript String The main transcript.
confidence f64 The confidence of the main transcript.

STT Result Failure

This message is sent when the STT engine fails to run the final result.

Type

0x04

Payload

Field Type Description
error i64 The error code.

Shutting Down

This message is sent by the server to signal that the server is shutting down.

Immediately after the message is sent, the server will close the connection.

Type

0x05

Payload

None

Status Connection Open

This message is sent after the client requests switching the connection into a status connection.

Type

0x06

Payload

Field Type Description
max_utilization f64 The maximum utilization of the server.
can_overload bool If true, and required, max_utilization can be ignored.

Status Connection Data

This message is sent every 5 seconds after a "Status Connection Open" message.

Type

0x07

Payload

Field Type Description
utilization f64 The current utilization of the server.

Fatal IO Error

This message is sent when the server encounters a fatal IO error.

Type

0xFD

Payload

Field Type Description
error String The Rust formatted error message.

Fatal User Error

This message is sent when the sender sends invalid data.

Type

0xFE

Payload

None

Fatal Unknown Error

This message is sent when the server encounters an unknown error.

Type

0xFF

Payload

None