fix: resolve omitted search handles before saving channels

src/youtube.rs

@@ -196,6 +196,25 @@ pub fn full_description(output: &str, expected_id: &str) -> Result<String, Strin
     Ok(description)
 }
 
+pub fn channel_handle(output: &str, expected_id: &str) -> Result<String, String> {
+    #[derive(Deserialize)]
+    struct Channel {
+        channel_id: String,
+        uploader_id: Option<String>,
+    }
+    let channel: Channel = serde_json::from_str(output)
+        .map_err(|error| format!("Invalid channel metadata: {error}"))?;
+    if channel.channel_id != expected_id {
+        return Err("Channel metadata did not match the requested channel".into());
+    }
+    let handle = channel
+        .uploader_id
+        .filter(|handle| handle.starts_with('@'))
+        .ok_or_else(|| "This channel has no available handle; no channel was saved.".to_owned())?;
+    crate::config::normalize_channel(&handle).map_err(|error| error.to_string())?;
+    Ok(handle)
+}
+
 fn page_end(start: usize) -> io::Result<usize> {
     start
         .checked_add(PAGE_SIZE - 1)
@@ -251,6 +270,22 @@ impl Job {
         )
     }
 
+    pub fn channel(id: &str) -> io::Result<Self> {
+        if !valid_channel_id(id) {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "Invalid YouTube channel ID",
+            ));
+        }
+        Self::spawn(extractor().args([
+            "--flat-playlist",
+            "--playlist-end",
+            "1",
+            "--dump-single-json",
+            &format!("https://www.youtube.com/channel/{id}/videos"),
+        ]))
+    }
+
     pub fn description(id: &str) -> io::Result<Self> {
         Self::spawn(extractor().args([
             "--no-playlist",
@@ -839,6 +874,26 @@ mod tests {
         assert_eq!(exhausted.videos.len(), 2);
     }
 
+    #[test]
+    fn channel_handles_require_the_requested_identity_and_a_valid_handle() {
+        let id = "UChAQQ9at2MDlXjvQX3vL3Yw";
+        for handle in ["@ch.1676", "@敷嶋てとら"] {
+            let metadata = serde_json::json!({"channel_id": id, "uploader_id": handle}).to_string();
+            assert_eq!(channel_handle(&metadata, id).unwrap(), handle);
+            assert!(channel_handle(&metadata, "UCaYhcUwRBNscFNUKTjgPFiA").is_err());
+        }
+        for handle in [
+            None,
+            Some("ch.1676"),
+            Some("@bad/handle"),
+            Some("@bad\u{1b}"),
+        ] {
+            let metadata = serde_json::json!({"channel_id": id, "uploader_id": handle}).to_string();
+            assert!(channel_handle(&metadata, id).is_err());
+        }
+        assert!(channel_handle("not JSON", id).is_err());
+    }
+
     #[test]
     fn full_descriptions_preserve_paragraphs_and_reject_mismatched_videos() {
         let metadata = r#"{"id":"jNQXAC9IVRw","description":"First paragraph.\n\n日本語\tsecond paragraph.\u001b\nLast line."}"#;