libcras_stub: Stub implementation

Stub the required parts of libcras so that upstream builds with
audio_cras feature

BUG=b:244618503
TEST=cargo build --features audio_cras

Change-Id: I21eb3bcb9a61990740b1419f124401878619481e
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3911099
Reviewed-by: Dennis Kempin <denniskempin@google.com>
Commit-Queue: Vineeth Pillai <vineethrp@google.com>

Cargo.lock

@@ -1046,6 +1046,10 @@ checksum = "349d5a591cd28b49e1d1037471617a32ddcda5731b99419008085f72d5a53836"
 [[package]]
 name = "libcras"
 version = "0.1.0"
+dependencies = [
+ "audio_streams",
+ "serde",
+]
 
 [[package]]
 name = "libdbus-sys"

Cargo.toml

@@ -110,6 +110,7 @@ exclude = [
 [features]
 all-linux = [
     # TODO(b/203105868): Enable remaining features on linux builds.
+    "audio_cras",
     "composite-disk",
     "default",
     "gdb",

libcras_stub/Cargo.toml

@@ -6,3 +6,7 @@ edition = "2021"
 
 [lib]
 path = "src/libcras.rs"
+
+[dependencies]
+audio_streams = "*"
+serde = "*"

libcras_stub/src/libcras.rs

@@ -2,4 +2,131 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// This space intentionally left blank.
+// Minimal implementation of interfaces in libcras for external builds.
+//
+// These just exist to allow us to build and clippy check the audio feature
+// when building outside of ChromeOS. When building for ChromeOS, this stub
+// will be replaced by the actual libcras implementation:
+// https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/third_party/adhd/cras/client/libcras/
+//
+// Any changes to the libcras API used in crosvm needs to be reflected in this
+// stub as well so as to have a successful crosvm build outside of ChromeOS.
+//
+// Instantiating a CrasClient using this will always panic!
+
+use audio_streams::{
+    shm_streams::{SharedMemory, ShmStream, ShmStreamSource},
+    BoxError, SampleFormat, StreamDirection, StreamEffect, StreamSource, StreamSourceGenerator,
+};
+use std::error;
+use std::fmt;
+use std::str::FromStr;
+
+use serde::Deserialize;
+use serde::Deserializer;
+use serde::Serialize;
+
+#[derive(Debug, Clone, Copy, PartialEq, Deserialize, Serialize)]
+#[allow(non_camel_case_types)]
+pub enum CRAS_CLIENT_TYPE {
+    CRAS_CLIENT_TYPE_ARCVM,
+    CRAS_CLIENT_TYPE_CROSVM,
+}
+
+pub type CrasClientType = CRAS_CLIENT_TYPE;
+
+#[derive(Debug, Clone, Copy, PartialEq, Deserialize, Serialize)]
+#[serde(rename_all = "lowercase")]
+pub enum CrasSocketType {
+    Legacy,
+    Unified,
+}
+
+#[derive(Debug)]
+pub enum Error {
+    InvalidClientType,
+    InvalidSocketType,
+}
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "")
+    }
+}
+
+impl error::Error for Error {}
+
+pub type CrasSysError = Error;
+
+impl FromStr for CrasClientType {
+    type Err = CrasSysError;
+    fn from_str(cras_type: &str) -> std::result::Result<Self, Self::Err> {
+        match cras_type {
+            "crosvm" => Ok(CrasClientType::CRAS_CLIENT_TYPE_CROSVM),
+            "arcvm" => Ok(CrasClientType::CRAS_CLIENT_TYPE_ARCVM),
+            _ => Err(Error::InvalidClientType),
+        }
+    }
+}
+
+impl FromStr for CrasSocketType {
+    type Err = Error;
+    fn from_str(sock_type: &str) -> std::result::Result<Self, Self::Err> {
+        match sock_type {
+            "legacy" => Ok(CrasSocketType::Legacy),
+            "unified" => Ok(CrasSocketType::Unified),
+            _ => Err(Error::InvalidSocketType),
+        }
+    }
+}
+
+pub struct CrasStreamSourceGenerator {}
+
+impl CrasStreamSourceGenerator {
+    pub fn new(_capture: bool, _client_type: CrasClientType, _socket_type: CrasSocketType) -> Self {
+        panic!("Cannot create cras audio device on non-chromeos crosvm builds.")
+    }
+}
+
+impl StreamSourceGenerator for CrasStreamSourceGenerator {
+    fn generate(&self) -> std::result::Result<Box<dyn StreamSource>, BoxError> {
+        panic!("Cannot create cras audio device on non-chromeos crosvm builds.")
+    }
+}
+
+pub fn deserialize_cras_client_type<'de, D: Deserializer<'de>>(
+    deserializer: D,
+) -> std::result::Result<CRAS_CLIENT_TYPE, D::Error> {
+    let s = String::deserialize(deserializer)?;
+
+    match s.parse() {
+        Ok(client_type) => Ok(client_type),
+        Err(e) => Err(serde::de::Error::custom(e.to_string())),
+    }
+}
+
+type Result<T> = std::result::Result<T, Error>;
+
+pub struct CrasClient {}
+impl CrasClient {
+    pub fn with_type(_: CrasSocketType) -> Result<Self> {
+        panic!("Cannot create cras audio device on non-chromeos crosvm builds.")
+    }
+    pub fn set_client_type(&mut self, _: CrasClientType) {}
+    pub fn enable_cras_capture(&mut self) {}
+}
+
+impl<E: std::error::Error> ShmStreamSource<E> for CrasClient {
+    fn new_stream(
+        &mut self,
+        _direction: StreamDirection,
+        _num_channels: usize,
+        _format: SampleFormat,
+        _frame_rate: u32,
+        _buffer_size: usize,
+        _effects: &[StreamEffect],
+        _client_shm: &dyn SharedMemory<Error = E>,
+        _buffer_offsets: [u64; 2],
+    ) -> std::result::Result<Box<dyn ShmStream>, BoxError> {
+        panic!("Cannot create cras audio device on non-chromeos crosvm builds.")
+    }
+}