feat(resolver/engine): add yt-dlp support

unm_resolver/Cargo.toml

@@ -9,6 +9,7 @@ edition = "2021"
 anyhow = "1.0.52"
 async-trait = "0.1.52"
 http = "0.2.6"
+log = "0.4.14"
 once_cell = "1.9.0"
 rayon = "1.5.1"
 reqwest = { version = "0.11.8", features = ["json", "brotli", "deflate", "gzip"] }

unm_resolver/src/engine.rs

@@ -5,6 +5,7 @@
 
 pub mod bilibili;
 pub mod pyncm;
+pub mod ytdlp;
 
 pub use async_trait::async_trait;
 use reqwest::Proxy;

unm_resolver/src/engine/ytdlp.rs

@@ -0,0 +1,60 @@
+//! UNM Resolver [Engine]: yt-dlp
+//!
+//! It can fetch audio from YouTube.
+
+use serde::Deserialize;
+
+use super::{Provider, Song, Proxy};
+
+/// The response that `yt-dlp` will return.
+#[derive(Deserialize)]
+struct YtDlpResponse {
+    /// The audio URL.
+    url: String,
+}
+
+/// The search and track engine powered by `yt-dlp`.
+pub struct YtDlpEngine;
+
+#[async_trait::async_trait]
+impl Provider for YtDlpEngine {
+    // TODO: allow specifying proxy
+    async fn check(&self, info: &Song, _: Option<Proxy>) -> anyhow::Result<Option<String>> {
+        Ok(fetch_from_youtube(&info.keyword()).await?.map(|r| r.url))
+    }
+}
+
+/// Get the response from `yt-dlp`.
+///
+/// ```plain
+/// yt-dlp -f bestaudio --dump-json ytsearch1:{keyword}
+///     -f bestaudio    choose the best quality of the audio
+///     --dump-json     dump the information as JSON without downloading it
+/// ```
+async fn fetch_from_youtube(keyword: &str) -> anyhow::Result<Option<YtDlpResponse>> {
+    let mut cmd = tokio::process::Command::new("yt-dlp");
+
+    let child = cmd
+        .args(&["-f", "bestaudio", "--dump-json"])
+        .arg(format!("ytsearch1:{keyword}"))
+        .kill_on_drop(true)
+        .output()
+        .await?;
+
+    if child.status.success() {
+        let response = String::from_utf8_lossy(&child.stdout);
+
+        Ok(if response.is_empty() {
+            None
+        } else {
+            let json = serde_json::from_str::<'_, YtDlpResponse>(&response)?;
+            Some(json)
+        })
+    } else {
+        log::error!("Failed to run `youtube-dl`.");
+        log::error!("Code: {code:?}", code = child.status.code());
+        log::error!("Stderr: {}", String::from_utf8_lossy(&child.stderr));
+
+        Err(anyhow::anyhow!("Failed to run `youtube-dl`."))
+    }
+}