ipx-feed's lib.rs splits into leaf modules (#356)

lib.rs held 2,000 lines: fetching, parsing, OPML, Patreon, discovery,
artwork, categories, Jev and redaction, and their tests. It is now the
module list and the re-exports, so ipx and the directory call
feed::fetch, feed::parse and the rest as before:

  fetch.rs      fetch and its limits    parse.rs     RSS and Atom
  outlines.rs   OPML (not opml.rs, which would shadow the opml crate)
  patreon.rs    a creator's shows       discover.rs  finding a feed
  wordpress.rs  WordPress.com's API     failure.rs   failures in words
  privacy.rs    redact, looks_private   artwork.rs   https art, icons
  category.rs   Apple's categories      jev.rs       Jev's category

Moved verbatim, private items pub(crate) where a sibling calls them,
calls across modules module::function. Every definition and doc comment
line of the old lib.rs is in exactly one of the new files; each test
went with what it tests, and all 40 run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/feed/src/artwork.rs

@@ -0,0 +1,117 @@
+//! Artwork: on https when its host serves it there, and a site icon where a feed has none.
+
+use crate::{discover, fetch};
+use std::collections::HashMap;
+use std::time::Duration;
+
+/// Artwork for a feed that has none: the icon its site's page names, or else the site's
+/// `/favicon.ico`. None if neither is there.
+#[tracing::instrument(skip_all, fields(site = site))]
+pub async fn site_icon(client: &reqwest::Client, site: &str) -> Option<String> {
+    let timeout = Duration::from_secs(20);
+    let resp = client.get(site).timeout(timeout).send().await.ok()?;
+    // Relative to where the page ended up, not where it was asked for: a site that redirects
+    // to /en/ would otherwise have its icon looked for in the wrong place.
+    let base = resp.url().clone();
+    // The icon a page names can be gone: antirez.com names /images/favicon.png, a 404, while its
+    // /favicon.ico is there. Stored unchecked, it was a broken image that was never looked up again.
+    if resp.status().is_success()
+        && let Ok(page) = fetch::read_capped(resp).await
+        && let Some(href) = page_icon(&page)
+        && let Ok(url) = base.join(&href)
+        && is_image(client, url.as_str()).await
+    {
+        return Some(url.into());
+    }
+    let ico = base.join("/favicon.ico").ok()?;
+    is_image(client, ico.as_str()).await.then(|| ico.into())
+}
+
+/// How many hosts one scan of a feed asks whether its artwork is on https.
+pub(crate) const MAX_ART_HOSTS: usize = 8;
+
+/// Artwork's address on https when its host serves it there, else as it was. The page is https
+/// and must not load http; the host is asked once per `known` (one feed's read), and an http
+/// address it does not serve on https stays, for /api/art to fetch (#90). Four of the five
+/// hosts the catalogue had on http served the same image on https; The Secret Cabal's CDN
+/// presents another name's certificate (#110).
+pub async fn prefer_https(client: &reqwest::Client, url: &str, known: &mut HashMap<String, bool>) -> String {
+    let Some(rest) = url.strip_prefix("http://") else { return url.to_owned() };
+    let host = rest.split('/').next().unwrap_or("").to_owned();
+    let secure = format!("https://{rest}");
+    let ok = match known.get(&host) {
+        Some(ok) => *ok,
+        // Each new host is a probe of up to 20 s, one after another on the scan, and the feed's
+        // author decides how many hosts there are: ports and user names make as many as they like
+        // of one server (#339). Real feeds put their artwork on a few.
+        None if known.len() >= MAX_ART_HOSTS => false,
+        None => {
+            let ok = is_image(client, &secure).await;
+            known.insert(host, ok);
+            ok
+        }
+    };
+    if ok { secure } else { url.to_owned() }
+}
+
+/// Whether `url` answers with an image. A site with no favicon often answers 200 with its home
+/// page, which is not an icon.
+pub async fn is_image(client: &reqwest::Client, url: &str) -> bool {
+    let timeout = Duration::from_secs(20);
+    let Ok(resp) = client.get(url).timeout(timeout).send().await else { return false };
+    resp.status().is_success()
+        && resp
+            .headers()
+            .get(reqwest::header::CONTENT_TYPE)
+            .and_then(|v| v.to_str().ok())
+            .is_some_and(|t| t.starts_with("image/"))
+}
+
+/// The icon a web page names in its `<link>` tags, the larger apple-touch-icon first: a plain
+/// `icon` is often 16 pixels, which blurs at the size the list draws artwork.
+pub(crate) fn page_icon(bytes: &[u8]) -> Option<String> {
+    let text = String::from_utf8_lossy(bytes);
+    // ASCII only, so byte offsets in the lowered copy stay valid in the original.
+    let lower = text.to_ascii_lowercase();
+    let (mut touch, mut icon) = (None, None);
+    let mut pos = 0;
+    while let Some(at) = lower[pos..].find("<link") {
+        let start = pos + at;
+        let Some(end) = lower[start..].find('>').map(|e| start + e) else { break };
+        pos = end + 1;
+        let tag = &text[start..end];
+        let Some(rel) = discover::tag_attr(tag, "rel").map(|r| r.to_ascii_lowercase()) else { continue };
+        let rels: Vec<&str> = rel.split_whitespace().collect();
+        if touch.is_none() && rels.iter().any(|r| r.starts_with("apple-touch-icon")) {
+            touch = discover::tag_attr(tag, "href");
+        } else if icon.is_none() && rels.contains(&"icon") {
+            icon = discover::tag_attr(tag, "href");
+        }
+    }
+    touch.or(icon).filter(|h| !h.is_empty())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn artwork_on_more_hosts_than_the_limit_is_not_asked_about() {
+        let mut known: std::collections::HashMap<String, bool> =
+            (0..MAX_ART_HOSTS).map(|n| (format!("h{n}:80"), false)).collect();
+        // No server answers here: were it asked, this would wait on a connection, not return.
+        let url = "http://192.0.2.1:9/a.png";
+        assert_eq!(prefer_https(&reqwest::Client::new(), url, &mut known).await, url);
+        assert_eq!(known.len(), MAX_ART_HOSTS);
+    }
+
+    #[test]
+    fn page_icon_prefers_the_touch_icon() {
+        let page = br#"<head><link rel="stylesheet" href="/a.css">
+            <link rel="shortcut icon" href="/fav.ico">
+            <LINK REL="apple-touch-icon-precomposed" sizes="180x180" href='/touch.png'></head>"#;
+        assert_eq!(page_icon(page).as_deref(), Some("/touch.png"));
+        assert_eq!(page_icon(br#"<link rel="icon" href="i.svg">"#).as_deref(), Some("i.svg"));
+        assert_eq!(page_icon(br#"<link rel="stylesheet" href="/a.css">"#), None);
+    }
+}