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feat(kei-tts + kei-stt): TTS/STT abstractions with 4+3 backends

Browse source 
Two parallel atomars in the kei-buddy phase-1 plan. Mirror each other's
architecture: trait + feature-gated backend modules + env-driven dispatch
+ wiremock tests for HTTP backends + subprocess-error test for local.

## kei-tts (text-to-speech)
LOC: 959 across 15 files (largest src/lib.rs 121).
Trait `TtsBackend` + 4 backends behind feature flags:
  * elevenlabs — POST api.elevenlabs.io/v1/text-to-speech/{voice}/stream
  * openai     — POST api.openai.com/v1/audio/speech (tts-1, tts-1-hd)
  * google     — POST texttospeech.googleapis.com/v1/text:synthesize
                 (Wavenet voices, base64 audioContent)
  * piper      — local subprocess to piper-tts binary, raw PCM out
Default features: ["piper"]. all-backends feature gates the rest.
`from_env()` reads KEI_TTS_BACKEND (default piper). Returns Box<dyn TtsBackend>.
Tests: 9 passed (env routing + 3 wiremock backends + piper subprocess error).

## kei-stt (speech-to-text)
LOC: 935 across 13 files (largest whisper_local.rs 181).
Trait `SttBackend` + 3 backends:
  * whisper-local  — subprocess to `whisper` CLI / faster-whisper,
                     reads JSON output, parses segments
  * deepgram       — POST api.deepgram.com/v1/listen (Token auth header,
                     raw audio body, parses words → Segments)
  * openai-whisper — POST api.openai.com/v1/audio/transcriptions
                     (multipart file + model=whisper-1 +
                      response_format=verbose_json)
Default features: ["whisper-local"]. all-backends gates the rest.
`from_env()` reads KEI_STT_BACKEND (default whisper-local).
Tests: 10 passed + 1 doc-test (env routing + 5 wiremock + 2 JSON parsers
+ 1 subprocess error + 1 auth-header check).

## Common architecture decisions
  * `with_base_url(url)` constructor on each HTTP backend for wiremock
    testability — same pattern as kei-llm-router and kei-notify-telegram.
  * `tempfile` crate added to kei-stt for whisper-local audio scratch.
  * `base64 = { version = "0.22", optional = true }` in kei-tts for
    Google's base64-encoded audioContent.

## Verify-before-commit (RULE 0.13 §)
  * cargo check -p kei-tts (default + all-backends): PASS
  * cargo check -p kei-stt (default + all-backends): PASS
  * cargo test -p kei-tts --features all-backends --lib: 9/0
  * cargo test -p kei-stt --features all-backends --lib: 10/0
  * cargo check --workspace: PASS

STATUS-TRUTH from both agents: shipped=functional, stubs=0,
behaviour-verified=yes.

## Follow-up (deferred, non-blocking)
  * Real backend verification needs API keys for ElevenLabs / OpenAI /
    Google / Deepgram and piper-tts binary + .onnx model on PATH.
  * whisper-local language_detected always None — whisper CLI JSON
    schema differs across versions, parse heuristic to be added.
  * faster-whisper has different JSON schema from openai-whisper;
    current parser covers openai-whisper convention only.
This commit is contained in:
Parfii-bot 2026-05-12 13:47:35 +08:00
parent 4dfe63b4e2
commit cb59b77ed2
28 changed files with 1926 additions and 0 deletions
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30
_primitives/_rust/Cargo.lock generated
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@ -4393,6 +4393,21 @@ dependencies = [
"toml",
]
[[package]]
name = "kei-stt"
version = "0.1.0"
dependencies = [
"async-trait",
"reqwest 0.12.28",
"serde",
"serde_json",
"tempfile",
"thiserror 1.0.69",
"tokio",
"tracing",
"wiremock",
]
[[package]]
name = "kei-svc-systemd"
version = "0.1.0"
@ -4455,6 +4470,21 @@ dependencies = [
"thiserror 1.0.69",
]
[[package]]
name = "kei-tts"
version = "0.1.0"
dependencies = [
"async-trait",
"base64 0.22.1",
"reqwest 0.12.28",
"serde",
"serde_json",
"thiserror 1.0.69",
"tokio",
"tracing",
"wiremock",
]
[[package]]
name = "kei-tty"
version = "0.1.0"

4
_primitives/_rust/Cargo.toml
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@ -183,6 +183,10 @@ members = [
"kei-buddy",
# Inbound Telegram webhook handler — parses Update payloads into typed WebhookEvent
"kei-telegram-webhook",
# TTS abstraction — 4 backends (ElevenLabs/OpenAI/Google/Piper) behind feature flags
"kei-tts",
# STT abstraction — 3 backends (whisper-local/Deepgram/OpenAI-Whisper) behind feature flags
"kei-stt",
]
[workspace.package]

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_primitives/_rust/kei-stt/Cargo.toml Normal file
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@ -0,0 +1,39 @@
[package]
name = "kei-stt"
version = "0.1.0"
edition.workspace = true
rust-version.workspace = true
description = "Speech-to-text abstraction trait with 3 backends (whisper-local/Deepgram/OpenAI). Default = whisper-local (free, local)."
authors.workspace = true
license.workspace = true
[lib]
name = "kei_stt"
path = "src/lib.rs"
[dependencies]
async-trait = { workspace = true }
serde = { workspace = true, features = ["derive"] }
serde_json = { workspace = true }
thiserror = { workspace = true }
tokio = { workspace = true, features = ["macros", "rt-multi-thread", "process", "io-util", "fs"] }
reqwest = { workspace = true, features = ["multipart"] }
tracing = "0.1"
tempfile = { workspace = true }
[features]
default = ["whisper-local"]
whisper-local = []
deepgram = []
openai-whisper = []
all-backends = ["whisper-local", "deepgram", "openai-whisper"]
[dev-dependencies]
wiremock = { workspace = true }
tokio = { workspace = true }
[package.metadata.keisei]
maturity = "alpha"
trait = "SttBackend"
description = "STT abstraction with 3 backends (whisper-local/Deepgram/OpenAI). Default = whisper-local."
authors = ["Denis Parfionovich <parfionovich@keilab.io>"]

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# kei-stt
Speech-to-text abstraction crate with 3 backends selected at runtime via
`KEI_STT_BACKEND`. Default backend is **whisper-local** (free, local, no API key).
## Backend matrix
| Backend | Feature flag | Cost | Latency | Quality |
|------------------|------------------|----------------|-------------|-----------|
| `whisper-local` | `whisper-local` | Free | 1–10× RT | Very good |
| `deepgram` | `deepgram` | ~$0.0043/min | 200–500 ms | Excellent |
| `openai-whisper` | `openai-whisper` | ~$0.006/min | 300–800 ms | Excellent |
RT = real-time factor (depends on hardware / model size for whisper-local).
## Environment variables
| Variable | Backend | Required | Description |
|----------------------------|-----------------|----------|------------------------------------------|
| `KEI_STT_BACKEND` | all | No | `whisper-local` (default) / `deepgram` / `openai-whisper` |
| `KEI_STT_WHISPER_BINARY` | whisper-local | No | Path to `whisper` CLI (default: PATH) |
| `KEI_STT_WHISPER_MODEL` | whisper-local | No | Model name (default: `base.en`) |
| `DEEPGRAM_API_KEY` | deepgram | Yes | Deepgram API key |
| `OPENAI_API_KEY` | openai-whisper | Yes | OpenAI API key |
## Usage
```toml
[dependencies]
kei-stt = { path = "../kei-stt", features = ["whisper-local"] }
```
```rust
#[tokio::main]
async fn main() -> Result<(), kei_stt::SttError> {
let backend = kei_stt::from_env()?;
let audio = std::fs::read("speech.wav").unwrap();
let req = kei_stt::SttRequest::new_wav(audio);
let resp = backend.transcribe(&req).await?;
println!("[{}] {}", backend.name(), resp.text);
for seg in &resp.segments {
println!(" {:>6}ms–{:>6}ms {}", seg.start_ms, seg.end_ms, seg.text);
}
Ok(())
}
```
## Compile-time features
```toml
# All backends:
kei-stt = { features = ["all-backends"] }
# Cloud only, no local whisper:
kei-stt = { features = ["deepgram", "openai-whisper"], default-features = false }
```
## whisper-local prerequisites
Install the `openai-whisper` Python package:
```sh
pip install openai-whisper
```
This makes the `whisper` CLI available. Alternatively point `KEI_STT_WHISPER_BINARY`
at a compatible binary (`faster-whisper`, etc. with identical CLI interface).

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Deepgram STT backend — calls `api.deepgram.com/v1/listen`.
//!
//! Endpoint: `POST /v1/listen?language={lang}&punctuate=true`
//! Auth: `Authorization: Token {DEEPGRAM_API_KEY}` header.
//! Body: raw audio bytes with the request MIME type.
//!
//! Response shape:
//! ```json
//! {"results":{"channels":[{"alternatives":[{
//! "transcript":"...",
//! "words":[{"word":"...","start":0.1,"end":0.4}]
//! }]}]}}
//! ```
//!
//! Constructor surface:
//! * [`DeepgramBackend::from_env`] — reads `DEEPGRAM_API_KEY`.
//! * [`DeepgramBackend::with_base_url`] — explicit URL + key (tests).
#![cfg(feature = "deepgram")]
use crate::error::SttError;
use crate::request::SttRequest;
use crate::response::{Segment, SttResponse};
use crate::trait_def::SttBackend;
const DEFAULT_BASE_URL: &str = "https://api.deepgram.com";
pub struct DeepgramBackend {
api_key: String,
client: reqwest::Client,
base_url: String,
}
impl DeepgramBackend {
/// Build from explicit base URL and API key (used in wiremock tests).
pub fn with_base_url(
base_url: impl Into<String>,
api_key: impl Into<String>,
) -> Self {
Self {
api_key: api_key.into(),
client: reqwest::Client::new(),
base_url: base_url.into().trim_end_matches('/').to_string(),
}
}
/// Build from `DEEPGRAM_API_KEY` env var.
pub fn from_env() -> Result<Self, SttError> {
let key = std::env::var("DEEPGRAM_API_KEY")
.map_err(|_| SttError::MissingEnv("DEEPGRAM_API_KEY".into()))?;
Ok(Self::with_base_url(DEFAULT_BASE_URL, key))
}
}
#[async_trait::async_trait]
impl SttBackend for DeepgramBackend {
fn name(&self) -> &'static str { "deepgram" }
async fn transcribe(&self, req: &SttRequest) -> Result<SttResponse, SttError> {
let mut url = format!("{}/v1/listen?punctuate=true", self.base_url);
if let Some(lang) = &req.language {
url.push_str(&format!("&language={lang}"));
}
let resp = self.client
.post(&url)
.header("Authorization", format!("Token {}", self.api_key))
.header("Content-Type", &req.mime_type)
.body(req.audio_bytes.clone())
.send()
.await?;
if !resp.status().is_success() {
let status = resp.status().as_u16();
let text = resp.text().await.unwrap_or_default();
return Err(SttError::Http(format!("http {status}: {text}")));
}
let body: serde_json::Value = resp.json().await
.map_err(|e| SttError::InvalidResponse(e.to_string()))?;
parse_deepgram_response(&body)
}
}
fn parse_deepgram_response(body: &serde_json::Value) -> Result<SttResponse, SttError> {
let alt = body
.pointer("/results/channels/0/alternatives/0")
.ok_or_else(|| SttError::InvalidResponse("missing alternatives".into()))?;
let text = alt["transcript"]
.as_str()
.unwrap_or_default()
.to_string();
let segments = alt["words"]
.as_array()
.unwrap_or(&vec![])
.iter()
.filter_map(|w| {
let start_ms = (w["start"].as_f64()? * 1000.0) as u64;
let end_ms = (w["end"].as_f64()? * 1000.0) as u64;
let word = w["word"].as_str()?.to_string();
Some(Segment { start_ms, end_ms, text: word })
})
.collect();
Ok(SttResponse { text, segments, language_detected: None })
}
#[cfg(test)]
#[path = "deepgram_test.rs"]
mod tests;

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Wiremock tests for `DeepgramBackend`.
//!
//! Verifies request headers, URL parameters, and response parsing.
#![cfg(all(test, feature = "deepgram"))]
use wiremock::matchers::{header, header_regex, method, path};
use wiremock::{Mock, MockServer, ResponseTemplate};
use crate::deepgram::DeepgramBackend;
use crate::request::SttRequest;
use crate::trait_def::SttBackend;
fn deepgram_response_body() -> serde_json::Value {
serde_json::json!({
"results": {
"channels": [{
"alternatives": [{
"transcript": "hello deepgram",
"words": [
{"word": "hello", "start": 0.1, "end": 0.5},
{"word": "deepgram", "start": 0.6, "end": 1.1}
]
}]
}]
}
})
}
#[tokio::test]
async fn deepgram_parses_transcript() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path("/v1/listen"))
.and(header_regex("authorization", "Token .+"))
.respond_with(
ResponseTemplate::new(200)
.set_body_json(deepgram_response_body()),
)
.mount(&server)
.await;
let backend = DeepgramBackend::with_base_url(server.uri(), "test-key");
let req = SttRequest {
audio_bytes: b"fake_audio".to_vec(),
mime_type: "audio/wav".to_string(),
language: None,
};
let resp = backend.transcribe(&req).await.expect("transcribe should succeed");
assert_eq!(resp.text, "hello deepgram");
assert_eq!(resp.segments.len(), 2);
assert_eq!(resp.segments[0].start_ms, 100);
assert_eq!(resp.segments[1].end_ms, 1100);
assert!(resp.language_detected.is_none());
}
#[tokio::test]
async fn deepgram_sends_auth_header() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path("/v1/listen"))
.and(header("authorization", "Token secret-key"))
.respond_with(
ResponseTemplate::new(200)
.set_body_json(deepgram_response_body()),
)
.mount(&server)
.await;
let backend = DeepgramBackend::with_base_url(server.uri(), "secret-key");
let req = SttRequest::new_wav(b"audio".to_vec());
backend.transcribe(&req).await.expect("auth header test should pass");
}
#[tokio::test]
async fn deepgram_http_error() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path("/v1/listen"))
.respond_with(ResponseTemplate::new(401).set_body_string("Unauthorized"))
.mount(&server)
.await;
let backend = DeepgramBackend::with_base_url(server.uri(), "bad-key");
let req = SttRequest::new_wav(b"audio".to_vec());
let err = backend.transcribe(&req).await.expect_err("should fail on 401");
assert!(matches!(err, crate::SttError::Http(_)));
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `SttError` — crate-level error enum for all STT backends.
//!
//! Each variant carries a human-readable string so call-sites can log
//! without leaking transport internals. `thiserror` provides `Display`
//! and the `Error` trait automatically.
use thiserror::Error;
/// Errors that can occur across any STT backend.
#[derive(Debug, Error)]
pub enum SttError {
/// HTTP transport or API error from a cloud backend.
#[error("http: {0}")]
Http(String),
/// Subprocess (whisper CLI) spawn or IO error.
#[error("subprocess: {0}")]
Subprocess(String),
/// Required environment variable is absent.
#[error("missing env var: {0}")]
MissingEnv(String),
/// Backend name was requested but its Cargo feature is not compiled in.
#[error("backend not enabled: {0}")]
BackendNotEnabled(String),
/// Unexpected or malformed response from a backend.
#[error("invalid response: {0}")]
InvalidResponse(String),
/// Input audio bytes are invalid or in an unsupported format.
#[error("invalid audio: {0}")]
InvalidAudio(String),
}
impl From<reqwest::Error> for SttError {
fn from(e: reqwest::Error) -> Self {
SttError::Http(e.to_string())
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `kei-stt` — speech-to-text abstraction with 3 backend impls.
//!
//! Backend is chosen at runtime via `KEI_STT_BACKEND` env var.
//! Compile-time feature flags gate which backends are available.
//!
//! | Feature | Backend | Default |
//! |------------------|---------------|---------|
//! | `whisper-local` | local subprocess | ✓ |
//! | `deepgram` | cloud API | – |
//! | `openai-whisper` | cloud API | – |
//!
//! # Quick start
//! ```no_run
//! # async fn example() -> Result<(), kei_stt::SttError> {
//! let backend = kei_stt::from_env()?;
//! let audio = std::fs::read("speech.wav").unwrap();
//! let req = kei_stt::SttRequest::new_wav(audio);
//! let resp = backend.transcribe(&req).await?;
//! println!("transcript: {}", resp.text);
//! # Ok(()) }
//! ```
pub mod error;
pub mod request;
pub mod response;
pub mod trait_def;
#[cfg(feature = "whisper-local")]
pub mod whisper_local;
#[cfg(feature = "deepgram")]
pub mod deepgram;
#[cfg(feature = "openai-whisper")]
pub mod openai_whisper;
pub use error::SttError;
pub use request::SttRequest;
pub use response::{Segment, SttResponse};
pub use trait_def::SttBackend;
/// Construct the backend selected by `KEI_STT_BACKEND`.
///
/// Defaults to `whisper-local` when the env var is absent or empty.
/// Returns `SttError::BackendNotEnabled` if the chosen backend's
/// feature flag was not compiled in.
pub fn from_env() -> Result<Box<dyn SttBackend>, SttError> {
let name = std::env::var("KEI_STT_BACKEND")
.unwrap_or_else(|_| "whisper-local".to_string());
build_backend(&name)
}
fn build_backend(name: &str) -> Result<Box<dyn SttBackend>, SttError> {
match name {
#[cfg(feature = "whisper-local")]
"whisper-local" => Ok(Box::new(whisper_local::WhisperLocalBackend::from_env())),
#[cfg(feature = "deepgram")]
"deepgram" => Ok(Box::new(deepgram::DeepgramBackend::from_env()?)),
#[cfg(feature = "openai-whisper")]
"openai-whisper" => Ok(Box::new(openai_whisper::OpenAiWhisperBackend::from_env()?)),
other => Err(SttError::BackendNotEnabled(other.to_string())),
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn from_env_defaults_to_whisper_local() {
std::env::remove_var("KEI_STT_BACKEND");
let backend = from_env().expect("whisper-local backend should construct");
assert_eq!(backend.name(), "whisper-local");
}
#[test]
fn from_env_unknown_backend_errors() {
std::env::remove_var("KEI_STT_BACKEND");
let result = build_backend("unknown_provider");
match result {
Err(SttError::BackendNotEnabled(name)) => {
assert_eq!(name, "unknown_provider");
}
Ok(_) => panic!("expected BackendNotEnabled, got Ok"),
Err(e) => panic!("expected BackendNotEnabled, got: {e}"),
}
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! OpenAI Whisper STT backend — calls `api.openai.com/v1/audio/transcriptions`.
//!
//! Sends a multipart/form-data POST with:
//! - `file`: audio bytes (filename derived from MIME type)
//! - `model`: `whisper-1`
//! - `response_format`: `verbose_json`
//! - `language`: BCP-47 code if provided
//!
//! Response `verbose_json` shape:
//! ```json
//! {"text":"...", "segments":[{"start":0.0,"end":1.0,"text":"..."}]}
//! ```
//!
//! Constructor surface:
//! * [`OpenAiWhisperBackend::from_env`] — reads `OPENAI_API_KEY`.
//! * [`OpenAiWhisperBackend::with_base_url`] — explicit URL + key (tests).
#![cfg(feature = "openai-whisper")]
use reqwest::multipart;
use crate::error::SttError;
use crate::request::SttRequest;
use crate::response::{Segment, SttResponse};
use crate::trait_def::SttBackend;
const DEFAULT_BASE_URL: &str = "https://api.openai.com";
const WHISPER_MODEL: &str = "whisper-1";
pub struct OpenAiWhisperBackend {
api_key: String,
client: reqwest::Client,
base_url: String,
}
impl OpenAiWhisperBackend {
/// Build from explicit base URL and API key (used in wiremock tests).
pub fn with_base_url(
base_url: impl Into<String>,
api_key: impl Into<String>,
) -> Self {
Self {
api_key: api_key.into(),
client: reqwest::Client::new(),
base_url: base_url.into().trim_end_matches('/').to_string(),
}
}
/// Build from `OPENAI_API_KEY` env var.
pub fn from_env() -> Result<Self, SttError> {
let key = std::env::var("OPENAI_API_KEY")
.map_err(|_| SttError::MissingEnv("OPENAI_API_KEY".into()))?;
Ok(Self::with_base_url(DEFAULT_BASE_URL, key))
}
fn filename_from_mime(mime: &str) -> &'static str {
match mime {
"audio/mpeg" => "audio.mp3",
"audio/ogg" => "audio.ogg",
"audio/flac" => "audio.flac",
_ => "audio.wav",
}
}
}
#[async_trait::async_trait]
impl SttBackend for OpenAiWhisperBackend {
fn name(&self) -> &'static str { "openai-whisper" }
async fn transcribe(&self, req: &SttRequest) -> Result<SttResponse, SttError> {
let url = format!("{}/v1/audio/transcriptions", self.base_url);
let filename = Self::filename_from_mime(&req.mime_type);
let file_part = multipart::Part::bytes(req.audio_bytes.clone())
.file_name(filename)
.mime_str(&req.mime_type)
.map_err(|e| SttError::InvalidAudio(e.to_string()))?;
let mut form = multipart::Form::new()
.part("file", file_part)
.text("model", WHISPER_MODEL)
.text("response_format", "verbose_json");
if let Some(lang) = &req.language {
form = form.text("language", lang.clone());
}
let resp = self.client
.post(&url)
.bearer_auth(&self.api_key)
.multipart(form)
.send()
.await?;
if !resp.status().is_success() {
let status = resp.status().as_u16();
let text = resp.text().await.unwrap_or_default();
return Err(SttError::Http(format!("http {status}: {text}")));
}
let body: serde_json::Value = resp.json().await
.map_err(|e| SttError::InvalidResponse(e.to_string()))?;
parse_openai_whisper_response(&body)
}
}
fn parse_openai_whisper_response(body: &serde_json::Value) -> Result<SttResponse, SttError> {
let text = body["text"]
.as_str()
.unwrap_or_default()
.trim()
.to_string();
let language_detected = body["language"]
.as_str()
.map(|s| s.to_string());
let segments = body["segments"]
.as_array()
.unwrap_or(&vec![])
.iter()
.filter_map(|s| {
let start_ms = (s["start"].as_f64()? * 1000.0) as u64;
let end_ms = (s["end"].as_f64()? * 1000.0) as u64;
let seg_text = s["text"].as_str()?.trim().to_string();
Some(Segment { start_ms, end_ms, text: seg_text })
})
.collect();
Ok(SttResponse { text, segments, language_detected })
}
#[cfg(test)]
#[path = "openai_whisper_test.rs"]
mod tests;

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Wiremock tests for `OpenAiWhisperBackend`.
//!
//! Verifies Bearer auth, multipart body, and verbose_json segment parsing.
#![cfg(all(test, feature = "openai-whisper"))]
use wiremock::matchers::{header, method, path};
use wiremock::{Mock, MockServer, ResponseTemplate};
use crate::openai_whisper::OpenAiWhisperBackend;
use crate::request::SttRequest;
use crate::trait_def::SttBackend;
fn verbose_json_body() -> serde_json::Value {
serde_json::json!({
"text": "hello openai",
"language": "english",
"segments": [
{"start": 0.0, "end": 0.5, "text": "hello"},
{"start": 0.5, "end": 1.2, "text": "openai"}
]
})
}
#[tokio::test]
async fn openai_whisper_parses_segments() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path("/v1/audio/transcriptions"))
.and(header("authorization", "Bearer test-key"))
.respond_with(
ResponseTemplate::new(200)
.set_body_json(verbose_json_body()),
)
.mount(&server)
.await;
let backend = OpenAiWhisperBackend::with_base_url(server.uri(), "test-key");
let req = SttRequest {
audio_bytes: b"fake_audio".to_vec(),
mime_type: "audio/wav".to_string(),
language: None,
};
let resp = backend.transcribe(&req).await.expect("transcribe should succeed");
assert_eq!(resp.text, "hello openai");
assert_eq!(resp.segments.len(), 2);
assert_eq!(resp.segments[0].start_ms, 0);
assert_eq!(resp.segments[0].end_ms, 500);
assert_eq!(resp.segments[1].start_ms, 500);
assert_eq!(resp.segments[1].end_ms, 1200);
assert_eq!(resp.language_detected.as_deref(), Some("english"));
}
#[tokio::test]
async fn openai_whisper_http_error() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path("/v1/audio/transcriptions"))
.respond_with(ResponseTemplate::new(429).set_body_string("Rate limited"))
.mount(&server)
.await;
let backend = OpenAiWhisperBackend::with_base_url(server.uri(), "test-key");
let req = SttRequest::new_wav(b"audio".to_vec());
let err = backend.transcribe(&req).await.expect_err("should fail on 429");
assert!(matches!(err, crate::SttError::Http(_)));
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `SttRequest` — input type for all STT backends.
//!
//! Deliberately backend-agnostic: each backend maps its fields to
//! provider-specific parameters in its own module.
use serde::{Deserialize, Serialize};
/// Parameters for a single STT transcription request.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SttRequest {
/// Raw audio bytes to transcribe.
pub audio_bytes: Vec<u8>,
/// MIME type of the audio data (e.g. `"audio/wav"`, `"audio/mpeg"`, `"audio/ogg"`).
pub mime_type: String,
/// BCP-47 language hint (e.g. `"en"`, `"ru"`). `None` → auto-detect.
pub language: Option<String>,
}
impl SttRequest {
/// Convenience constructor for WAV audio with no language hint.
pub fn new_wav(audio_bytes: Vec<u8>) -> Self {
Self {
audio_bytes,
mime_type: "audio/wav".to_string(),
language: None,
}
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `SttResponse` and `Segment` — output types for all STT backends.
//!
//! `segments` is empty when the backend does not provide word-level timing.
use serde::{Deserialize, Serialize};
/// A timed text segment from the transcription.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Segment {
/// Start of the segment in milliseconds from the audio start.
pub start_ms: u64,
/// End of the segment in milliseconds from the audio start.
pub end_ms: u64,
/// Transcribed text for this segment.
pub text: String,
}
/// Result of a successful STT transcription call.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SttResponse {
/// Full transcribed text (concatenation of all segments).
pub text: String,
/// Word/sentence-level timing segments.
/// Empty when the backend does not provide timing data.
pub segments: Vec<Segment>,
/// BCP-47 language code detected by the backend. `None` if not reported.
pub language_detected: Option<String>,
}
impl SttResponse {
/// Construct a minimal response with text only.
pub fn text_only(text: impl Into<String>) -> Self {
Self {
text: text.into(),
segments: Vec::new(),
language_detected: None,
}
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `SttBackend` — the core async trait all backend impls satisfy.
//!
//! Implementing this trait is sufficient to plug a new STT provider into
//! the `from_env()` dispatch without modifying `lib.rs`. Each backend
//! module is self-contained and feature-gated.
use crate::error::SttError;
use crate::request::SttRequest;
use crate::response::SttResponse;
/// Async STT transcription backend.
///
/// Implementations must be `Send + Sync` so they can be stored in a
/// `Box<dyn SttBackend>` and shared across Tokio tasks.
#[async_trait::async_trait]
pub trait SttBackend: Send + Sync {
/// Transcribe the audio in `req` and return the text plus optional segments.
async fn transcribe(&self, req: &SttRequest) -> Result<SttResponse, SttError>;
/// Short, stable identifier for this backend (e.g. `"whisper-local"`).
fn name(&self) -> &'static str;
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Whisper-local STT backend — spawns the `whisper` CLI subprocess.
//!
//! Invocation:
//! `<binary> <audio_file> --model <model> --output_format json --output_dir <dir>`
//!
//! The openai-whisper Python package writes `<stem>.json` into `--output_dir`.
//! We parse `text` + `segments[].{start,end,text}` from that JSON.
//!
//! Constructor surface:
//! * [`WhisperLocalBackend::from_env`] — reads `KEI_STT_WHISPER_BINARY` +
//! `KEI_STT_WHISPER_MODEL` (default `base.en`).
//! * [`WhisperLocalBackend::with_binary`] + [`WhisperLocalBackend::with_model`]
//! — explicit overrides for testability.
#![cfg(feature = "whisper-local")]
use std::path::PathBuf;
use tokio::process::Command;
use crate::error::SttError;
use crate::request::SttRequest;
use crate::response::{Segment, SttResponse};
use crate::trait_def::SttBackend;
const DEFAULT_BINARY: &str = "whisper";
const DEFAULT_MODEL: &str = "base.en";
pub struct WhisperLocalBackend {
binary: PathBuf,
model: String,
}
impl WhisperLocalBackend {
/// Build from explicit binary and model (used in tests).
pub fn new(binary: impl Into<PathBuf>, model: impl Into<String>) -> Self {
Self { binary: binary.into(), model: model.into() }
}
/// Build from env vars.
/// Optional: `KEI_STT_WHISPER_BINARY` (default `whisper`).
/// Optional: `KEI_STT_WHISPER_MODEL` (default `base.en`).
pub fn from_env() -> Self {
let binary = std::env::var("KEI_STT_WHISPER_BINARY")
.unwrap_or_else(|_| DEFAULT_BINARY.to_string());
let model = std::env::var("KEI_STT_WHISPER_MODEL")
.unwrap_or_else(|_| DEFAULT_MODEL.to_string());
Self::new(binary, model)
}
fn ext_from_mime(mime: &str) -> &'static str {
match mime {
"audio/mpeg" => "mp3",
"audio/ogg" => "ogg",
"audio/flac" => "flac",
_ => "wav",
}
}
}
#[async_trait::async_trait]
impl SttBackend for WhisperLocalBackend {
fn name(&self) -> &'static str { "whisper-local" }
async fn transcribe(&self, req: &SttRequest) -> Result<SttResponse, SttError> {
let ext = Self::ext_from_mime(&req.mime_type);
// Write audio bytes to a named temp file.
let audio_file = tempfile::Builder::new()
.suffix(&format!(".{ext}"))
.tempfile()
.map_err(|e| SttError::Subprocess(e.to_string()))?;
let out_dir = tempfile::tempdir()
.map_err(|e| SttError::Subprocess(e.to_string()))?;
tokio::fs::write(audio_file.path(), &req.audio_bytes)
.await
.map_err(|e| SttError::Subprocess(e.to_string()))?;
// Build and run whisper CLI command.
let mut cmd = Command::new(&self.binary);
cmd.arg(audio_file.path())
.arg("--model").arg(&self.model)
.arg("--output_format").arg("json")
.arg("--output_dir").arg(out_dir.path());
if let Some(lang) = &req.language {
cmd.arg("--language").arg(lang);
}
let output = cmd.output().await
.map_err(|e| SttError::Subprocess(e.to_string()))?;
if !output.status.success() {
let stderr = String::from_utf8_lossy(&output.stderr).into_owned();
return Err(SttError::Subprocess(format!(
"whisper exited {}: {stderr}", output.status
)));
}
// Find the produced JSON file (stem of input + ".json").
let stem = audio_file.path()
.file_stem()
.and_then(|s| s.to_str())
.unwrap_or("audio");
let json_path = out_dir.path().join(format!("{stem}.json"));
let json_bytes = tokio::fs::read(&json_path).await
.map_err(|e| SttError::InvalidResponse(format!("json file: {e}")))?;
parse_whisper_json(&json_bytes)
}
}
fn parse_whisper_json(bytes: &[u8]) -> Result<SttResponse, SttError> {
let v: serde_json::Value = serde_json::from_slice(bytes)
.map_err(|e| SttError::InvalidResponse(e.to_string()))?;
let text = v["text"].as_str()
.unwrap_or_default()
.trim()
.to_string();
let segments = v["segments"]
.as_array()
.unwrap_or(&vec![])
.iter()
.filter_map(|s| {
let start_ms = (s["start"].as_f64()? * 1000.0) as u64;
let end_ms = (s["end"].as_f64()? * 1000.0) as u64;
let seg_text = s["text"].as_str()?.trim().to_string();
Some(Segment { start_ms, end_ms, text: seg_text })
})
.collect();
Ok(SttResponse { text, segments, language_detected: None })
}
#[cfg(test)]
mod tests {
use super::*;
#[tokio::test]
async fn whisper_local_subprocess_error_on_bad_binary() {
let backend = WhisperLocalBackend::new("/nonexistent/whisper", "base.en");
let req = SttRequest::new_wav(b"RIFF....".to_vec());
let err = backend.transcribe(&req).await
.expect_err("should fail with non-existent binary");
assert!(
matches!(err, SttError::Subprocess(_)),
"expected Subprocess error, got: {err:?}"
);
}
#[test]
fn parse_whisper_json_full() {
let json = br#"{
"text": " Hello world",
"segments": [
{"start": 0.0, "end": 1.5, "text": " Hello"},
{"start": 1.5, "end": 2.0, "text": " world"}
]
}"#;
let resp = parse_whisper_json(json).expect("parse should succeed");
assert_eq!(resp.text, "Hello world");
assert_eq!(resp.segments.len(), 2);
assert_eq!(resp.segments[0].end_ms, 1500);
assert_eq!(resp.segments[1].start_ms, 1500);
}
#[test]
fn parse_whisper_json_no_segments() {
let json = br#"{"text": " Hi"}"#;
let resp = parse_whisper_json(json).expect("parse should succeed");
assert_eq!(resp.text, "Hi");
assert!(resp.segments.is_empty());
}
}

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[package]
name = "kei-tts"
version = "0.1.0"
edition.workspace = true
rust-version.workspace = true
description = "Text-to-speech abstraction trait with 4 backends (ElevenLabs/OpenAI/Google/Piper). Default = piper (local, free, zero latency)."
authors.workspace = true
license.workspace = true
[lib]
name = "kei_tts"
path = "src/lib.rs"
[dependencies]
async-trait = { workspace = true }
serde = { workspace = true, features = ["derive"] }
serde_json = { workspace = true }
thiserror = { workspace = true }
tokio = { workspace = true, features = ["macros", "rt-multi-thread", "process", "io-util"] }
reqwest = { workspace = true }
tracing = "0.1"
base64 = { version = "0.22", optional = true }
[features]
default = ["piper"]
elevenlabs = []
openai = []
google = ["dep:base64"]
piper = []
all-backends = ["elevenlabs", "openai", "google", "piper"]
[dev-dependencies]
wiremock = { workspace = true }
tokio = { workspace = true }
[package.metadata.keisei]
maturity = "alpha"
trait = "TtsBackend"
description = "TTS abstraction with 4 backends (ElevenLabs/OpenAI/Google/Piper). Default = piper."
authors = ["Denis Parfionovich <parfionovich@keilab.io>"]

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# kei-tts
Text-to-speech abstraction crate with 4 backends selected at runtime via
`KEI_TTS_BACKEND`. Default backend is **piper** (local, free, zero latency).
## Backend matrix
| Backend | Feature flag | Cost | Latency | Quality | Language coverage |
|-------------|---------------|-------------|------------|-----------|-------------------|
| `piper` | `piper` | Free | ~50–200 ms | Good | 20+ language packs |
| `elevenlabs`| `elevenlabs` | ~$0.30/1k ch| 300–600 ms | Excellent | 30+ languages |
| `openai` | `openai` | ~$0.015/1k ch| 200–500 ms| Very good | 50+ languages |
| `google` | `google` | ~$4/1M ch | 200–400 ms | Very good | 40+ languages |
## Environment variables
| Variable | Backend | Required | Description |
|-------------------------|-------------|----------|------------------------------------|
| `KEI_TTS_BACKEND` | all | No | `piper` (default) / `elevenlabs` / `openai` / `google` |
| `ELEVENLABS_API_KEY` | elevenlabs | Yes | ElevenLabs API key |
| `OPENAI_API_KEY` | openai | Yes | OpenAI API key |
| `KEI_TTS_OPENAI_MODEL` | openai | No | `tts-1` (default) or `tts-1-hd` |
| `GOOGLE_TTS_API_KEY` | google | Yes | Google Cloud API key |
| `KEI_TTS_PIPER_MODEL` | piper | Yes | Path to `.onnx` piper model file |
| `KEI_TTS_PIPER_BINARY` | piper | No | Path to `piper-tts` (default: PATH)|
## Usage
```toml
[dependencies]
kei-tts = { path = "../kei-tts", features = ["piper"] }
```
```rust
#[tokio::main]
async fn main() -> Result<(), kei_tts::TtsError> {
let backend = kei_tts::from_env()?;
let req = kei_tts::TtsRequest::new("Hello, world!");
let resp = backend.synth(&req).await?;
std::fs::write("out.mp3", &resp.audio_bytes).ok();
println!("synthesised {} bytes via {}", resp.audio_bytes.len(), backend.name());
Ok(())
}
```
## Compile-time features
```toml
# All backends:
kei-tts = { features = ["all-backends"] }
# Cloud only, no piper:
kei-tts = { features = ["elevenlabs", "openai", "google"], default-features = false }
```

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! ElevenLabs TTS backend — streams audio from `api.elevenlabs.io`.
//!
//! Endpoint: `POST /v1/text-to-speech/{voice_id}/stream`
//! Auth: `xi-api-key: {ELEVENLABS_API_KEY}` header.
//! Response: raw audio bytes (format-specific Content-Type).
//!
//! Constructor surface:
//! * [`ElevenLabsBackend::from_env`] — reads `ELEVENLABS_API_KEY`.
//! * [`ElevenLabsBackend::with_base_url`] — explicit URL + key (tests).
#![cfg(feature = "elevenlabs")]
use crate::error::TtsError;
use crate::request::{AudioFormat, TtsRequest};
use crate::response::TtsResponse;
use crate::trait_def::TtsBackend;
const DEFAULT_BASE_URL: &str = "https://api.elevenlabs.io";
const DEFAULT_VOICE_ID: &str = "21m00Tcm4TlvDq8ikWAM"; // Rachel
pub struct ElevenLabsBackend {
api_key: String,
client: reqwest::Client,
base_url: String,
}
impl ElevenLabsBackend {
/// Build from explicit base URL and API key (used in wiremock tests).
pub fn with_base_url(
base_url: impl Into<String>,
api_key: impl Into<String>,
) -> Self {
Self {
api_key: api_key.into(),
client: reqwest::Client::new(),
base_url: base_url.into().trim_end_matches('/').to_string(),
}
}
/// Build from `ELEVENLABS_API_KEY` env var.
pub fn from_env() -> Result<Self, TtsError> {
let key = std::env::var("ELEVENLABS_API_KEY")
.map_err(|_| TtsError::MissingEnv("ELEVENLABS_API_KEY".into()))?;
Ok(Self::with_base_url(DEFAULT_BASE_URL, key))
}
fn format_param(fmt: AudioFormat) -> &'static str {
match fmt {
AudioFormat::Mp3 => "mp3_44100_128",
AudioFormat::Ogg => "ogg_48000",
AudioFormat::Wav | AudioFormat::Raw => "pcm_44100",
}
}
}
#[async_trait::async_trait]
impl TtsBackend for ElevenLabsBackend {
fn name(&self) -> &'static str { "elevenlabs" }
async fn synth(&self, req: &TtsRequest) -> Result<TtsResponse, TtsError> {
let voice = req.voice_id.as_deref().unwrap_or(DEFAULT_VOICE_ID);
let url = format!(
"{}/v1/text-to-speech/{}/stream",
self.base_url, voice
);
let body = serde_json::json!({
"text": req.text,
"output_format": Self::format_param(req.format),
});
let resp = self.client
.post(&url)
.header("xi-api-key", &self.api_key)
.header("Content-Type", "application/json")
.json(&body)
.send()
.await?;
if !resp.status().is_success() {
let status = resp.status().as_u16();
let text = resp.text().await.unwrap_or_default();
return Err(TtsError::Http(format!("http {status}: {text}")));
}
let mime = req.format.mime_type().to_string();
let bytes = resp.bytes().await
.map_err(|e| TtsError::Http(e.to_string()))?
.to_vec();
Ok(TtsResponse::new(bytes, mime))
}
}
#[cfg(test)]
#[path = "elevenlabs_test.rs"]
mod tests;

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Wiremock tests for `ElevenLabsBackend`.
//!
//! Verifies request shape (path, header) and response byte parsing.
#![cfg(all(test, feature = "elevenlabs"))]
use wiremock::matchers::{header, method, path_regex};
use wiremock::{Mock, MockServer, ResponseTemplate};
use crate::elevenlabs::ElevenLabsBackend;
use crate::request::{AudioFormat, TtsRequest};
use crate::trait_def::TtsBackend;
#[tokio::test]
async fn elevenlabs_synth_ok() {
let server = MockServer::start().await;
let fake_audio = b"FAKE_AUDIO_BYTES".to_vec();
Mock::given(method("POST"))
.and(path_regex(r"/v1/text-to-speech/.+/stream"))
.and(header("xi-api-key", "test-key"))
.respond_with(
ResponseTemplate::new(200)
.set_body_bytes(fake_audio.clone())
.append_header("Content-Type", "audio/mpeg"),
)
.mount(&server)
.await;
let backend = ElevenLabsBackend::with_base_url(server.uri(), "test-key");
let req = TtsRequest {
text: "hello".into(),
voice_id: Some("voice123".into()),
language: None,
format: AudioFormat::Mp3,
};
let resp = backend.synth(&req).await.expect("synth should succeed");
assert_eq!(resp.audio_bytes, fake_audio);
assert_eq!(resp.mime_type, "audio/mpeg");
}
#[tokio::test]
async fn elevenlabs_synth_http_error() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path_regex(r"/v1/text-to-speech/.+/stream"))
.respond_with(ResponseTemplate::new(401).set_body_string("Unauthorized"))
.mount(&server)
.await;
let backend = ElevenLabsBackend::with_base_url(server.uri(), "bad-key");
let req = TtsRequest::new("hello");
let err = backend.synth(&req).await.expect_err("should fail on 401");
assert!(matches!(err, crate::TtsError::Http(_)));
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `TtsError` — crate-level error enum for all TTS backends.
//!
//! Each variant carries a human-readable string so call-sites can log
//! without leaking transport internals. `thiserror` provides `Display`
//! and the `Error` trait automatically.
use thiserror::Error;
/// Errors that can occur across any TTS backend.
#[derive(Debug, Error)]
pub enum TtsError {
/// HTTP transport or API error from a cloud backend.
#[error("http: {0}")]
Http(String),
/// Subprocess (piper-tts) spawn or IO error.
#[error("subprocess: {0}")]
Subprocess(String),
/// Required environment variable is absent.
#[error("missing env var: {0}")]
MissingEnv(String),
/// Backend name was requested but its Cargo feature is not compiled in.
#[error("backend not enabled: {0}")]
BackendNotEnabled(String),
/// Unexpected or malformed response from a backend.
#[error("invalid response: {0}")]
InvalidResponse(String),
}
impl From<reqwest::Error> for TtsError {
fn from(e: reqwest::Error) -> Self {
TtsError::Http(e.to_string())
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Google Cloud TTS backend — calls `texttospeech.googleapis.com`.
//!
//! Endpoint: `POST /v1/text:synthesize?key={api_key}`
//! Response: JSON `{"audioContent": "<base64>"}`. Base64-decoded bytes
//! are returned as `TtsResponse.audio_bytes`.
//!
//! Constructor surface:
//! * [`GoogleBackend::from_env`] — reads `GOOGLE_TTS_API_KEY`.
//! * [`GoogleBackend::with_base_url`] — explicit URL + key (tests).
#![cfg(feature = "google")]
use base64::{engine::general_purpose::STANDARD as B64, Engine as _};
use crate::error::TtsError;
use crate::request::{AudioFormat, TtsRequest};
use crate::response::TtsResponse;
use crate::trait_def::TtsBackend;
const DEFAULT_BASE_URL: &str = "https://texttospeech.googleapis.com";
const DEFAULT_VOICE: &str = "en-US-Wavenet-D";
const DEFAULT_LANG: &str = "en-US";
pub struct GoogleBackend {
api_key: String,
client: reqwest::Client,
base_url: String,
}
impl GoogleBackend {
/// Build from explicit parameters (used in wiremock tests).
pub fn with_base_url(
base_url: impl Into<String>,
api_key: impl Into<String>,
) -> Self {
Self {
api_key: api_key.into(),
client: reqwest::Client::new(),
base_url: base_url.into().trim_end_matches('/').to_string(),
}
}
/// Build from `GOOGLE_TTS_API_KEY` env var.
pub fn from_env() -> Result<Self, TtsError> {
let key = std::env::var("GOOGLE_TTS_API_KEY")
.map_err(|_| TtsError::MissingEnv("GOOGLE_TTS_API_KEY".into()))?;
Ok(Self::with_base_url(DEFAULT_BASE_URL, key))
}
fn encoding_str(fmt: AudioFormat) -> &'static str {
match fmt {
AudioFormat::Mp3 => "MP3",
AudioFormat::Ogg => "OGG_OPUS",
AudioFormat::Wav | AudioFormat::Raw => "LINEAR16",
}
}
}
#[derive(serde::Deserialize)]
struct GoogleResponse {
#[serde(rename = "audioContent")]
audio_content: String,
}
#[async_trait::async_trait]
impl TtsBackend for GoogleBackend {
fn name(&self) -> &'static str { "google" }
async fn synth(&self, req: &TtsRequest) -> Result<TtsResponse, TtsError> {
let url = format!(
"{}/v1/text:synthesize?key={}",
self.base_url, self.api_key
);
let voice_name = req.voice_id.as_deref().unwrap_or(DEFAULT_VOICE);
let lang = req.language.as_deref().unwrap_or(DEFAULT_LANG);
let body = serde_json::json!({
"input": { "text": req.text },
"voice": { "languageCode": lang, "name": voice_name },
"audioConfig": { "audioEncoding": Self::encoding_str(req.format) },
});
let resp = self.client
.post(&url)
.json(&body)
.send()
.await?;
if !resp.status().is_success() {
let status = resp.status().as_u16();
let text = resp.text().await.unwrap_or_default();
return Err(TtsError::Http(format!("http {status}: {text}")));
}
let parsed: GoogleResponse = resp.json().await
.map_err(|e| TtsError::InvalidResponse(e.to_string()))?;
let bytes = B64.decode(&parsed.audio_content)
.map_err(|e| TtsError::InvalidResponse(format!("base64: {e}")))?;
Ok(TtsResponse::new(bytes, req.format.mime_type().to_string()))
}
}
#[cfg(test)]
#[path = "google_test.rs"]
mod tests;

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Wiremock tests for `GoogleBackend`.
//!
//! Verifies JSON request shape and base64 `audioContent` decoding.
#![cfg(all(test, feature = "google"))]
use base64::{engine::general_purpose::STANDARD as B64, Engine as _};
use wiremock::matchers::{method, path};
use wiremock::{Mock, MockServer, ResponseTemplate};
use crate::google::GoogleBackend;
use crate::request::{AudioFormat, TtsRequest};
use crate::trait_def::TtsBackend;
#[tokio::test]
async fn google_synth_ok() {
let server = MockServer::start().await;
let fake_audio = b"GOOGLE_AUDIO".to_vec();
let encoded = B64.encode(&fake_audio);
let body = serde_json::json!({ "audioContent": encoded }).to_string();
Mock::given(method("POST"))
.and(path("/v1/text:synthesize"))
.respond_with(
ResponseTemplate::new(200)
.set_body_string(body)
.append_header("Content-Type", "application/json"),
)
.mount(&server)
.await;
let backend = GoogleBackend::with_base_url(server.uri(), "test-key");
let req = TtsRequest {
text: "hello google".into(),
voice_id: None,
language: Some("en-US".into()),
format: AudioFormat::Mp3,
};
let resp = backend.synth(&req).await.expect("synth should succeed");
assert_eq!(resp.audio_bytes, fake_audio);
assert_eq!(resp.mime_type, "audio/mpeg");
}
#[tokio::test]
async fn google_synth_invalid_base64() {
let server = MockServer::start().await;
let body = serde_json::json!({ "audioContent": "!!!not_b64!!!" }).to_string();
Mock::given(method("POST"))
.and(path("/v1/text:synthesize"))
.respond_with(
ResponseTemplate::new(200)
.set_body_string(body)
.append_header("Content-Type", "application/json"),
)
.mount(&server)
.await;
let backend = GoogleBackend::with_base_url(server.uri(), "test-key");
let req = TtsRequest::new("hello");
let err = backend.synth(&req).await.expect_err("should fail on bad b64");
assert!(matches!(err, crate::TtsError::InvalidResponse(_)));
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `kei-tts` — text-to-speech abstraction with 4 backend impls.
//!
//! Backend is chosen at runtime via `KEI_TTS_BACKEND` env var.
//! Compile-time feature flags gate which backends are available.
//!
//! | Feature | Backend | Default |
//! |---------------|------------|---------|
//! | `piper` | local | ✓ |
//! | `elevenlabs` | cloud | – |
//! | `openai` | cloud | – |
//! | `google` | cloud | – |
//!
//! # Quick start
//! ```no_run
//! # async fn example() -> Result<(), kei_tts::TtsError> {
//! let backend = kei_tts::from_env()?;
//! let req = kei_tts::TtsRequest::new("Hello, world!");
//! let resp = backend.synth(&req).await?;
//! std::fs::write("out.mp3", &resp.audio_bytes).ok();
//! # Ok(()) }
//! ```
pub mod error;
pub mod request;
pub mod response;
pub mod trait_def;
#[cfg(feature = "elevenlabs")]
pub mod elevenlabs;
#[cfg(feature = "google")]
pub mod google;
#[cfg(feature = "openai")]
pub mod openai;
#[cfg(feature = "piper")]
pub mod piper;
pub use error::TtsError;
pub use request::{AudioFormat, TtsRequest};
pub use response::TtsResponse;
pub use trait_def::TtsBackend;
/// Construct the backend selected by `KEI_TTS_BACKEND`.
///
/// Defaults to `piper` when the env var is absent or empty.
/// Returns `TtsError::BackendNotEnabled` if the chosen backend's
/// feature flag was not compiled in.
pub fn from_env() -> Result<Box<dyn TtsBackend>, TtsError> {
let name = std::env::var("KEI_TTS_BACKEND")
.unwrap_or_else(|_| "piper".to_string());
build_backend(&name)
}
fn build_backend(name: &str) -> Result<Box<dyn TtsBackend>, TtsError> {
match name {
#[cfg(feature = "piper")]
"piper" => Ok(Box::new(piper::PiperBackend::from_env()?)),
#[cfg(feature = "elevenlabs")]
"elevenlabs" => Ok(Box::new(elevenlabs::ElevenLabsBackend::from_env()?)),
#[cfg(feature = "openai")]
"openai" => Ok(Box::new(openai::OpenAiBackend::from_env()?)),
#[cfg(feature = "google")]
"google" => Ok(Box::new(google::GoogleBackend::from_env()?)),
other => Err(TtsError::BackendNotEnabled(other.to_string())),
}
}
#[cfg(test)]
mod tests {
use super::*;
/// NOTE: env-var tests are run with `-- --test-threads=1` to avoid
/// races between tests that mutate process-global env.
#[test]
fn from_env_defaults_to_piper() {
// Ensure a previous test has not leaked KEI_TTS_BACKEND.
std::env::remove_var("KEI_TTS_BACKEND");
// piper backend requires KEI_TTS_PIPER_MODEL — set a dummy path.
std::env::set_var("KEI_TTS_PIPER_MODEL", "/tmp/dummy.onnx");
let backend = from_env().expect("piper backend should construct from env");
assert_eq!(backend.name(), "piper");
std::env::remove_var("KEI_TTS_PIPER_MODEL");
}
#[test]
fn from_env_unknown_backend_errors() {
std::env::remove_var("KEI_TTS_BACKEND");
let result = build_backend("invalid_provider");
match result {
Err(TtsError::BackendNotEnabled(name)) => {
assert_eq!(name, "invalid_provider");
}
Ok(_) => panic!("expected BackendNotEnabled, got Ok"),
Err(e) => panic!("expected BackendNotEnabled, got different error: {e}"),
}
}
/// Verify piper backend propagates subprocess error on bad model path.
/// Skipped entirely when `piper-tts` binary is not on PATH.
#[cfg(feature = "piper")]
#[tokio::test]
async fn piper_subprocess_error_on_bad_model() {
let available = std::process::Command::new("piper-tts")
.arg("--help")
.output()
.is_ok();
if !available {
eprintln!("piper-tts not on PATH — skipping binary test");
return;
}
use crate::piper::PiperBackend;
use crate::trait_def::TtsBackend;
let backend = PiperBackend::new("piper-tts", "/nonexistent/model.onnx");
let req = TtsRequest::new("hello");
let err = backend.synth(&req).await
.expect_err("bad model path should fail");
assert!(matches!(err, TtsError::Subprocess(_)));
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! OpenAI TTS backend — calls `api.openai.com/v1/audio/speech`.
//!
//! Supported models: `tts-1` (fast) and `tts-1-hd` (higher quality).
//! Default voice: `alloy`. Format negotiated via `response_format` field.
//!
//! Constructor surface:
//! * [`OpenAiBackend::from_env`] — reads `OPENAI_API_KEY`.
//! * [`OpenAiBackend::with_base_url`] — explicit URL + key + model (tests).
#![cfg(feature = "openai")]
use crate::error::TtsError;
use crate::request::{AudioFormat, TtsRequest};
use crate::response::TtsResponse;
use crate::trait_def::TtsBackend;
const DEFAULT_BASE_URL: &str = "https://api.openai.com";
const DEFAULT_MODEL: &str = "tts-1";
const DEFAULT_VOICE: &str = "alloy";
pub struct OpenAiBackend {
api_key: String,
model: String,
client: reqwest::Client,
base_url: String,
}
impl OpenAiBackend {
/// Build from explicit parameters (used in wiremock tests).
pub fn with_base_url(
base_url: impl Into<String>,
api_key: impl Into<String>,
model: impl Into<String>,
) -> Self {
Self {
api_key: api_key.into(),
model: model.into(),
client: reqwest::Client::new(),
base_url: base_url.into().trim_end_matches('/').to_string(),
}
}
/// Build from `OPENAI_API_KEY` env var. Reads optional
/// `KEI_TTS_OPENAI_MODEL` (default `tts-1`).
pub fn from_env() -> Result<Self, TtsError> {
let key = std::env::var("OPENAI_API_KEY")
.map_err(|_| TtsError::MissingEnv("OPENAI_API_KEY".into()))?;
let model = std::env::var("KEI_TTS_OPENAI_MODEL")
.unwrap_or_else(|_| DEFAULT_MODEL.to_string());
Ok(Self::with_base_url(DEFAULT_BASE_URL, key, model))
}
fn format_str(fmt: AudioFormat) -> &'static str {
match fmt {
AudioFormat::Mp3 => "mp3",
AudioFormat::Ogg => "opus",
AudioFormat::Wav => "wav",
AudioFormat::Raw => "pcm",
}
}
}
#[async_trait::async_trait]
impl TtsBackend for OpenAiBackend {
fn name(&self) -> &'static str { "openai" }
async fn synth(&self, req: &TtsRequest) -> Result<TtsResponse, TtsError> {
let url = format!("{}/v1/audio/speech", self.base_url);
let voice = req.voice_id.as_deref().unwrap_or(DEFAULT_VOICE);
let body = serde_json::json!({
"model": self.model,
"input": req.text,
"voice": voice,
"response_format": Self::format_str(req.format),
});
let resp = self.client
.post(&url)
.bearer_auth(&self.api_key)
.json(&body)
.send()
.await?;
if !resp.status().is_success() {
let status = resp.status().as_u16();
let text = resp.text().await.unwrap_or_default();
return Err(TtsError::Http(format!("http {status}: {text}")));
}
let mime = req.format.mime_type().to_string();
let bytes = resp.bytes().await
.map_err(|e| TtsError::Http(e.to_string()))?
.to_vec();
Ok(TtsResponse::new(bytes, mime))
}
}
#[cfg(test)]
#[path = "openai_test.rs"]
mod tests;

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Wiremock tests for `OpenAiBackend`.
//!
//! Verifies request JSON shape, Bearer auth, and response byte parsing.
#![cfg(all(test, feature = "openai"))]
use wiremock::matchers::{header, method, path};
use wiremock::{Mock, MockServer, ResponseTemplate};
use crate::openai::OpenAiBackend;
use crate::request::{AudioFormat, TtsRequest};
use crate::trait_def::TtsBackend;
#[tokio::test]
async fn openai_synth_ok() {
let server = MockServer::start().await;
let fake_audio = b"OPENAI_AUDIO".to_vec();
Mock::given(method("POST"))
.and(path("/v1/audio/speech"))
.and(header("authorization", "Bearer test-key"))
.respond_with(
ResponseTemplate::new(200)
.set_body_bytes(fake_audio.clone())
.append_header("Content-Type", "audio/mpeg"),
)
.mount(&server)
.await;
let backend = OpenAiBackend::with_base_url(server.uri(), "test-key", "tts-1");
let req = TtsRequest {
text: "hello openai".into(),
voice_id: Some("nova".into()),
language: None,
format: AudioFormat::Mp3,
};
let resp = backend.synth(&req).await.expect("synth should succeed");
assert_eq!(resp.audio_bytes, fake_audio);
assert_eq!(resp.mime_type, "audio/mpeg");
}
#[tokio::test]
async fn openai_synth_http_error() {
let server = MockServer::start().await;
Mock::given(method("POST"))
.and(path("/v1/audio/speech"))
.respond_with(ResponseTemplate::new(429).set_body_string("Rate limited"))
.mount(&server)
.await;
let backend = OpenAiBackend::with_base_url(server.uri(), "test-key", "tts-1");
let req = TtsRequest::new("hello");
let err = backend.synth(&req).await.expect_err("should fail on 429");
assert!(matches!(err, crate::TtsError::Http(_)));
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! Piper TTS backend — spawns the `piper-tts` subprocess.
//!
//! Invocation: `piper-tts --model <model> --output_raw`
//! Text is written to stdin; raw PCM bytes are read from stdout.
//! A minimal RIFF WAV header is prepended when `format = Wav`.
//!
//! Constructor surface:
//! * [`PiperBackend::from_env`] — reads `KEI_TTS_PIPER_MODEL` +
//! optional `KEI_TTS_PIPER_BINARY` (default `piper-tts`).
//! * [`PiperBackend::new`] — explicit binary + model paths (tests).
#![cfg(feature = "piper")]
use std::path::PathBuf;
use tokio::io::AsyncWriteExt as _;
use tokio::process::Command;
use crate::error::TtsError;
use crate::request::{AudioFormat, TtsRequest};
use crate::response::TtsResponse;
use crate::trait_def::TtsBackend;
const DEFAULT_BINARY: &str = "piper-tts";
// PCM parameters piper-tts emits by default.
const SAMPLE_RATE: u32 = 22050;
const CHANNELS: u16 = 1;
const BITS_PER_SAMPLE: u16 = 16;
pub struct PiperBackend {
binary: PathBuf,
model: PathBuf,
}
impl PiperBackend {
/// Build from explicit binary path and model path.
pub fn new(binary: impl Into<PathBuf>, model: impl Into<PathBuf>) -> Self {
Self { binary: binary.into(), model: model.into() }
}
/// Build from env vars.
/// Required: `KEI_TTS_PIPER_MODEL` (path to `.onnx` model file).
/// Optional: `KEI_TTS_PIPER_BINARY` (default `piper-tts`).
pub fn from_env() -> Result<Self, TtsError> {
let model = std::env::var("KEI_TTS_PIPER_MODEL")
.map_err(|_| TtsError::MissingEnv("KEI_TTS_PIPER_MODEL".into()))?;
let binary = std::env::var("KEI_TTS_PIPER_BINARY")
.unwrap_or_else(|_| DEFAULT_BINARY.to_string());
Ok(Self::new(binary, model))
}
}
/// Build a minimal 44-byte RIFF WAV header for PCM data.
fn wav_header(data_len: u32) -> Vec<u8> {
let byte_rate = SAMPLE_RATE * u32::from(CHANNELS) * u32::from(BITS_PER_SAMPLE) / 8;
let block_align: u16 = CHANNELS * BITS_PER_SAMPLE / 8;
let mut h = Vec::with_capacity(44);
h.extend_from_slice(b"RIFF");
h.extend_from_slice(&(36u32 + data_len).to_le_bytes());
h.extend_from_slice(b"WAVE");
h.extend_from_slice(b"fmt ");
h.extend_from_slice(&16u32.to_le_bytes()); // subchunk1 size
h.extend_from_slice(&1u16.to_le_bytes()); // PCM
h.extend_from_slice(&CHANNELS.to_le_bytes());
h.extend_from_slice(&SAMPLE_RATE.to_le_bytes());
h.extend_from_slice(&byte_rate.to_le_bytes());
h.extend_from_slice(&block_align.to_le_bytes());
h.extend_from_slice(&BITS_PER_SAMPLE.to_le_bytes());
h.extend_from_slice(b"data");
h.extend_from_slice(&data_len.to_le_bytes());
h
}
#[async_trait::async_trait]
impl TtsBackend for PiperBackend {
fn name(&self) -> &'static str { "piper" }
async fn synth(&self, req: &TtsRequest) -> Result<TtsResponse, TtsError> {
let mut child = Command::new(&self.binary)
.arg("--model")
.arg(&self.model)
.arg("--output_raw")
.stdin(std::process::Stdio::piped())
.stdout(std::process::Stdio::piped())
.stderr(std::process::Stdio::null())
.spawn()
.map_err(|e| TtsError::Subprocess(e.to_string()))?;
if let Some(mut stdin) = child.stdin.take() {
stdin.write_all(req.text.as_bytes()).await
.map_err(|e| TtsError::Subprocess(e.to_string()))?;
}
let output = child.wait_with_output().await
.map_err(|e| TtsError::Subprocess(e.to_string()))?;
if !output.status.success() {
return Err(TtsError::Subprocess(format!(
"piper-tts exited with {}", output.status
)));
}
let pcm = output.stdout;
match req.format {
AudioFormat::Wav => {
let mut wav = wav_header(pcm.len() as u32);
wav.extend_from_slice(&pcm);
Ok(TtsResponse::new(wav, "audio/wav"))
}
_ => Ok(TtsResponse::new(pcm, "audio/pcm")),
}
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `TtsRequest` and `AudioFormat` — input types for all TTS backends.
//!
//! `TtsRequest` is deliberately backend-agnostic: each backend maps its
//! fields to provider-specific parameters in its own module.
use serde::{Deserialize, Serialize};
/// Output audio encoding requested from the backend.
///
/// Not every backend supports every format; unsupported formats result
/// in `TtsError::InvalidResponse`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum AudioFormat {
/// MPEG Layer 3 — the most widely supported lossy format.
Mp3,
/// Ogg Vorbis — open, patent-free lossy format.
Ogg,
/// RIFF WAVE — uncompressed PCM container.
Wav,
/// Raw PCM bytes with no container header (piper default).
Raw,
}
impl AudioFormat {
/// Returns the MIME type string for the format.
pub fn mime_type(self) -> &'static str {
match self {
AudioFormat::Mp3 => "audio/mpeg",
AudioFormat::Ogg => "audio/ogg",
AudioFormat::Wav => "audio/wav",
AudioFormat::Raw => "audio/pcm",
}
}
}
/// Parameters for a single TTS synthesis request.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TtsRequest {
/// The text to synthesise.
pub text: String,
/// Backend-specific voice identifier. `None` lets the backend use
/// its own default voice.
pub voice_id: Option<String>,
/// BCP-47 language tag (e.g. `"ru"`, `"en-US"`). `None` → auto.
pub language: Option<String>,
/// Desired output audio encoding.
pub format: AudioFormat,
}
impl TtsRequest {
/// Convenience constructor for plain text with backend defaults.
pub fn new(text: impl Into<String>) -> Self {
Self {
text: text.into(),
voice_id: None,
language: None,
format: AudioFormat::Mp3,
}
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `TtsResponse` — output of a successful TTS synthesis call.
use serde::{Deserialize, Serialize};
/// Audio data returned by a TTS backend.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TtsResponse {
/// Raw bytes of the synthesised audio file.
pub audio_bytes: Vec<u8>,
/// MIME type of the audio data (e.g. `"audio/mpeg"`, `"audio/wav"`).
pub mime_type: String,
}
impl TtsResponse {
/// Construct a response with explicit audio data and MIME type.
pub fn new(audio_bytes: Vec<u8>, mime_type: impl Into<String>) -> Self {
Self { audio_bytes, mime_type: mime_type.into() }
}
}

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 <author org>
//! `TtsBackend` — the core async trait all backend impls satisfy.
//!
//! Implementing this trait is sufficient to plug a new TTS provider into
//! the `from_env()` dispatch without modifying `lib.rs`. Each backend
//! module is self-contained and feature-gated.
use crate::error::TtsError;
use crate::request::TtsRequest;
use crate::response::TtsResponse;
/// Async TTS synthesis backend.
///
/// Implementations must be `Send + Sync` so they can be stored in a
/// `Box<dyn TtsBackend>` and shared across Tokio tasks.
#[async_trait::async_trait]
pub trait TtsBackend: Send + Sync {
/// Synthesise `req.text` and return the audio bytes.
async fn synth(&self, req: &TtsRequest) -> Result<TtsResponse, TtsError>;
/// Short, stable identifier for this backend (e.g. `"piper"`).
fn name(&self) -> &'static str;
}