Add the BookOrbit OPDS client module

Searches BookOrbit's OPDS catalog for an issue's Standard edition and
extracts the book/file ids the web reader route needs. Hand-rolled Atom
parsing, no new dependencies; unit-tested against the real feed shape.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Va5eMEmWEnjMXBsBob5FDW

src/bookorbit.rs

@@ -0,0 +1,508 @@
+//! BookOrbit OPDS catalog lookup support.
+//!
+//! BookOrbit is the companion library and browser-based EPUB reader used by
+//! this service. Its OPDS catalog is preferable to its JSON API here because
+//! OPDS uses static HTTP Basic credentials and therefore needs no JWT/refresh
+//! token lifecycle. Searches use `/api/v1/opds/catalog?q=<date>`, acquisition
+//! links expose `/api/v1/opds/<book_id>/download?fileId=<file_id>`, and browser
+//! links use `/read/<book_id>/<file_id>`. See
+//! `docs/plans/2026-09-05-bookorbit-read-link.md` for the integration design.
+
+use jiff::civil::Date;
+use reqwest::header::ACCEPT;
+
+const ACQUISITION_REL: &str = "http://opds-spec.org/acquisition";
+const DOWNLOAD_PREFIX: &str = "/api/v1/opds/";
+
+/// The BookOrbit book and file identifiers required by its reader route.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct BookorbitIds {
+    /// BookOrbit's identifier for the issue's book record.
+    pub book_id: i64,
+    /// BookOrbit's identifier for the EPUB file attached to the book.
+    pub file_id: i64,
+}
+
+/// A failure while querying or parsing BookOrbit's OPDS catalog.
+#[derive(Debug, thiserror::Error)]
+pub enum BookorbitError {
+    /// The OPDS endpoint could not be reached.
+    #[error("BookOrbit unreachable: {0}")]
+    Unreachable(#[source] reqwest::Error),
+    /// BookOrbit rejected the configured OPDS Basic credentials.
+    #[error("BookOrbit rejected the OPDS credentials")]
+    Unauthorized,
+    /// BookOrbit returned an unexpected non-success status.
+    #[error("BookOrbit returned HTTP {0}")]
+    Status(reqwest::StatusCode),
+    /// BookOrbit returned a body that could not be read as the expected feed.
+    #[error("BookOrbit returned an unreadable OPDS feed: {0}")]
+    Malformed(String),
+}
+
+/// Search BookOrbit's OPDS catalog for the Standard edition of the issue dated `date`.
+///
+/// `api_url` must have no trailing slash. `Ok(None)` means BookOrbit has not
+/// indexed the issue yet.
+pub async fn find_issue(
+    client: &reqwest::Client,
+    api_url: &str,
+    opds_user: &str,
+    opds_pass: &str,
+    issue_title: &str,
+    date: Date,
+) -> Result<Option<BookorbitIds>, BookorbitError> {
+    let response = client
+        .get(format!("{api_url}/api/v1/opds/catalog"))
+        .query(&[("q", date.to_string())])
+        .basic_auth(opds_user, Some(opds_pass))
+        .header(ACCEPT, "application/atom+xml")
+        .send()
+        .await
+        .map_err(BookorbitError::Unreachable)?;
+
+    let status = response.status();
+    if matches!(
+        status,
+        reqwest::StatusCode::UNAUTHORIZED | reqwest::StatusCode::FORBIDDEN
+    ) {
+        return Err(BookorbitError::Unauthorized);
+    }
+    if !status.is_success() {
+        return Err(BookorbitError::Status(status));
+    }
+
+    let feed_xml = response.text().await.map_err(|error| {
+        if error.is_timeout() || error.is_connect() {
+            BookorbitError::Unreachable(error)
+        } else {
+            BookorbitError::Malformed(error.to_string())
+        }
+    })?;
+    let ids = select_issue_entry(&feed_xml, issue_title, date)?;
+    if let Some(ids) = ids {
+        tracing::info!(
+            book_id = ids.book_id,
+            file_id = ids.file_id,
+            "resolved BookOrbit issue"
+        );
+    }
+    Ok(ids)
+}
+
+/// Select the Standard issue from an Atom feed without performing network I/O.
+pub fn select_issue_entry(
+    feed_xml: &str,
+    issue_title: &str,
+    date: Date,
+) -> Result<Option<BookorbitIds>, BookorbitError> {
+    if find_open_tag(feed_xml, "feed", 0).is_none() {
+        return Err(BookorbitError::Malformed(
+            "response does not contain an Atom <feed> element".to_string(),
+        ));
+    }
+
+    let fallback_title = format!("The Daily EPUB - {date}");
+    let mut fallback_entry = None;
+
+    for entry in entry_bodies(feed_xml) {
+        let Some(title) = element_text(entry, "title") else {
+            continue;
+        };
+        let title = xml_unescape(title);
+        let title = title.trim();
+        if title.ends_with("(X4)") {
+            continue;
+        }
+        if title == issue_title {
+            return acquisition_ids(entry);
+        }
+        if title == fallback_title && fallback_entry.is_none() {
+            fallback_entry = Some(entry);
+        }
+    }
+
+    fallback_entry.map_or(Ok(None), acquisition_ids)
+}
+
+/// Build the public BookOrbit reader URL for `ids`.
+///
+/// `public_url` must have no trailing slash.
+pub fn reader_url(public_url: &str, ids: BookorbitIds) -> String {
+    format!("{public_url}/read/{}/{}", ids.book_id, ids.file_id)
+}
+
+fn entry_bodies(feed_xml: &str) -> Vec<&str> {
+    let mut entries = Vec::new();
+    let mut cursor = 0;
+
+    while let Some(start) = find_open_tag(feed_xml, "entry", cursor) {
+        let Some(open_end_offset) = feed_xml[start..].find('>') else {
+            break;
+        };
+        let body_start = start + open_end_offset + 1;
+        let Some(close_offset) = feed_xml[body_start..].find("</entry>") else {
+            break;
+        };
+        let body_end = body_start + close_offset;
+        entries.push(&feed_xml[body_start..body_end]);
+        cursor = body_end + "</entry>".len();
+    }
+
+    entries
+}
+
+fn element_text<'a>(xml: &'a str, name: &str) -> Option<&'a str> {
+    let start = find_open_tag(xml, name, 0)?;
+    let open_end = start + xml[start..].find('>')?;
+    let text_start = open_end + 1;
+    let close = format!("</{name}>");
+    let text_end = text_start + xml[text_start..].find(&close)?;
+    Some(&xml[text_start..text_end])
+}
+
+fn find_open_tag(xml: &str, name: &str, mut cursor: usize) -> Option<usize> {
+    let needle = format!("<{name}");
+    while let Some(offset) = xml[cursor..].find(&needle) {
+        let start = cursor + offset;
+        let after_name = start + needle.len();
+        if xml
+            .as_bytes()
+            .get(after_name)
+            .is_some_and(|byte| byte.is_ascii_whitespace() || matches!(byte, b'>' | b'/'))
+        {
+            return Some(start);
+        }
+        cursor = after_name;
+    }
+    None
+}
+
+fn acquisition_ids(entry: &str) -> Result<Option<BookorbitIds>, BookorbitError> {
+    let mut cursor = 0;
+    let mut saw_acquisition = false;
+
+    while let Some(start) = find_open_tag(entry, "link", cursor) {
+        let Some(end_offset) = entry[start..].find('>') else {
+            break;
+        };
+        let end = start + end_offset;
+        let attributes = &entry[start + "<link".len()..end];
+        if attribute_value(attributes, "rel") == Some(ACQUISITION_REL) {
+            saw_acquisition = true;
+            if let Some(href) = attribute_value(attributes, "href") {
+                let href = xml_unescape(href);
+                if let Some(ids) = parse_download_href(&href) {
+                    return Ok(Some(ids));
+                }
+            }
+        }
+        cursor = end + 1;
+    }
+
+    if saw_acquisition {
+        Err(BookorbitError::Malformed(
+            "qualifying entry has an invalid acquisition href".to_string(),
+        ))
+    } else {
+        Ok(None)
+    }
+}
+
+fn attribute_value<'a>(attributes: &'a str, wanted: &str) -> Option<&'a str> {
+    let bytes = attributes.as_bytes();
+    let mut cursor = 0;
+
+    while cursor < bytes.len() {
+        while cursor < bytes.len() && (bytes[cursor].is_ascii_whitespace() || bytes[cursor] == b'/')
+        {
+            cursor += 1;
+        }
+        let name_start = cursor;
+        while cursor < bytes.len()
+            && !bytes[cursor].is_ascii_whitespace()
+            && !matches!(bytes[cursor], b'=' | b'/' | b'>')
+        {
+            cursor += 1;
+        }
+        if name_start == cursor {
+            cursor += 1;
+            continue;
+        }
+        let name = &attributes[name_start..cursor];
+
+        while cursor < bytes.len() && bytes[cursor].is_ascii_whitespace() {
+            cursor += 1;
+        }
+        if bytes.get(cursor) != Some(&b'=') {
+            continue;
+        }
+        cursor += 1;
+        while cursor < bytes.len() && bytes[cursor].is_ascii_whitespace() {
+            cursor += 1;
+        }
+
+        let quote = *bytes.get(cursor)?;
+        if !matches!(quote, b'\'' | b'"') {
+            return None;
+        }
+        cursor += 1;
+        let value_start = cursor;
+        while cursor < bytes.len() && bytes[cursor] != quote {
+            cursor += 1;
+        }
+        if cursor == bytes.len() {
+            return None;
+        }
+        let value = &attributes[value_start..cursor];
+        cursor += 1;
+        if name == wanted {
+            return Some(value);
+        }
+    }
+
+    None
+}
+
+fn parse_download_href(href: &str) -> Option<BookorbitIds> {
+    let path = href.strip_prefix(DOWNLOAD_PREFIX)?;
+    let (book_id, query) = path.split_once("/download?fileId=")?;
+    if book_id.is_empty() || !book_id.bytes().all(|byte| byte.is_ascii_digit()) {
+        return None;
+    }
+
+    let file_id = match query.split_once('&') {
+        Some((file_id, extra_params))
+            if !extra_params.is_empty() && !extra_params.split('&').any(str::is_empty) =>
+        {
+            file_id
+        }
+        Some(_) => return None,
+        None => query,
+    };
+    if file_id.is_empty() || !file_id.bytes().all(|byte| byte.is_ascii_digit()) {
+        return None;
+    }
+
+    Some(BookorbitIds {
+        book_id: book_id.parse().ok()?,
+        file_id: file_id.parse().ok()?,
+    })
+}
+
+fn xml_unescape(text: &str) -> String {
+    let mut output = String::with_capacity(text.len());
+    let mut cursor = 0;
+
+    while let Some(offset) = text[cursor..].find('&') {
+        let ampersand = cursor + offset;
+        output.push_str(&text[cursor..ampersand]);
+        let entity_start = ampersand + 1;
+        let Some(end_offset) = text[entity_start..].find(';') else {
+            output.push_str(&text[ampersand..]);
+            return output;
+        };
+        let entity_end = entity_start + end_offset;
+        let entity = &text[entity_start..entity_end];
+        if let Some(character) = decode_entity(entity) {
+            output.push(character);
+        } else {
+            output.push_str(&text[ampersand..=entity_end]);
+        }
+        cursor = entity_end + 1;
+    }
+
+    output.push_str(&text[cursor..]);
+    output
+}
+
+fn decode_entity(entity: &str) -> Option<char> {
+    match entity {
+        "amp" => Some('&'),
+        "lt" => Some('<'),
+        "gt" => Some('>'),
+        "quot" => Some('"'),
+        "apos" => Some('\''),
+        _ => entity
+            .strip_prefix("#x")
+            .or_else(|| entity.strip_prefix("#X"))
+            .and_then(|digits| u32::from_str_radix(digits, 16).ok())
+            .or_else(|| {
+                entity
+                    .strip_prefix('#')
+                    .and_then(|digits| digits.parse().ok())
+            })
+            .and_then(char::from_u32),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const REAL_SHAPE_FEED: &str = r#"<?xml version="1.0" encoding="UTF-8"?>
+<feed xmlns="http://www.w3.org/2005/Atom">
+  <id>urn:bookorbit:catalog</id>
+  <title>BookOrbit Catalog</title>
+  <entry data-source="watch-folder">
+    <title>The Daily EPUB — 2026-09-05 (X4)</title>
+    <id>urn:bookorbit:book:410</id>
+    <link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/410/download?fileId=901" type="application/epub+zip" title="EPUB"/>
+  </entry>
+  <entry data-source="watch-folder">
+    <title>The Daily EPUB — 2026-09-05</title>
+    <id>urn:bookorbit:book:411</id>
+    <link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/411/download?fileId=902" type="application/epub+zip" title="EPUB"/>
+  </entry>
+</feed>"#;
+
+    fn date() -> Date {
+        "2026-09-05".parse().expect("date")
+    }
+
+    fn feed(entries: &str) -> String {
+        format!(r#"<feed xmlns="http://www.w3.org/2005/Atom">{entries}</feed>"#)
+    }
+
+    #[test]
+    fn exact_title_match_returns_the_right_ids() {
+        let xml = feed(
+            r#"<entry><title>Another book</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/1/download?fileId=2"/></entry>
+               <entry><title>The Daily EPUB — 2026-09-05</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/31/download?fileId=47"/></entry>"#,
+        );
+
+        assert_eq!(
+            select_issue_entry(&xml, "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            Some(BookorbitIds {
+                book_id: 31,
+                file_id: 47
+            })
+        );
+    }
+
+    #[test]
+    fn x4_entry_listed_first_is_skipped_for_standard() {
+        assert_eq!(
+            select_issue_entry(REAL_SHAPE_FEED, "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            Some(BookorbitIds {
+                book_id: 411,
+                file_id: 902
+            })
+        );
+    }
+
+    #[test]
+    fn hyphen_form_fallback_works_without_em_dash_title() {
+        let xml = feed(
+            r#"<entry><title>The Daily EPUB - 2026-09-05</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/52/download?fileId=81"/></entry>"#,
+        );
+
+        assert_eq!(
+            select_issue_entry(&xml, "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            Some(BookorbitIds {
+                book_id: 52,
+                file_id: 81
+            })
+        );
+    }
+
+    #[test]
+    fn exact_title_outranks_an_earlier_fallback() {
+        let xml = feed(
+            r#"<entry><title>The Daily EPUB - 2026-09-05</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/1/download?fileId=2"/></entry>
+               <entry><title>The Daily EPUB — 2026-09-05</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/3/download?fileId=4"/></entry>"#,
+        );
+
+        assert_eq!(
+            select_issue_entry(&xml, "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            Some(BookorbitIds {
+                book_id: 3,
+                file_id: 4
+            })
+        );
+    }
+
+    #[test]
+    fn no_matching_entry_returns_none() {
+        let xml = feed(
+            r#"<entry><title>Unrelated</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/7/download?fileId=8"/></entry>"#,
+        );
+
+        assert_eq!(
+            select_issue_entry(&xml, "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            None
+        );
+        assert_eq!(
+            select_issue_entry(&feed(""), "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            None
+        );
+    }
+
+    #[test]
+    fn malformed_acquisition_href_is_an_error_for_a_match() {
+        let xml = feed(
+            r#"<entry><title>The Daily EPUB — 2026-09-05</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/nope/download?fileId=8"/></entry>"#,
+        );
+
+        assert!(matches!(
+            select_issue_entry(&xml, "The Daily EPUB — 2026-09-05", date()),
+            Err(BookorbitError::Malformed(_))
+        ));
+    }
+
+    #[test]
+    fn title_entities_are_unescaped_before_comparison() {
+        let xml = feed(
+            r#"<entry><title>Books &amp; News — 2026-09-05</title><link rel="http://opds-spec.org/acquisition" href="/api/v1/opds/12/download?fileId=13"/></entry>"#,
+        );
+
+        assert_eq!(
+            select_issue_entry(&xml, "Books & News — 2026-09-05", date()).unwrap(),
+            Some(BookorbitIds {
+                book_id: 12,
+                file_id: 13
+            })
+        );
+    }
+
+    #[test]
+    fn attributed_entry_and_reordered_link_attributes_parse() {
+        let xml = feed(
+            r#"<entry data-index="1"><title type="text">The Daily EPUB — 2026-09-05</title><link title="EPUB" href="/api/v1/opds/63/download?fileId=64&amp;download=true" type="application/epub+zip" rel="http://opds-spec.org/acquisition"/></entry>"#,
+        );
+
+        assert_eq!(
+            select_issue_entry(&xml, "The Daily EPUB — 2026-09-05", date()).unwrap(),
+            Some(BookorbitIds {
+                book_id: 63,
+                file_id: 64
+            })
+        );
+    }
+
+    #[test]
+    fn reader_url_formats_the_reader_route() {
+        assert_eq!(
+            reader_url(
+                "https://bookorbit.example",
+                BookorbitIds {
+                    book_id: 14,
+                    file_id: 29
+                }
+            ),
+            "https://bookorbit.example/read/14/29"
+        );
+    }
+
+    #[test]
+    fn body_without_feed_is_malformed() {
+        assert!(matches!(
+            select_issue_entry(
+                "<html><body>not an Atom feed</body></html>",
+                "The Daily EPUB — 2026-09-05",
+                date()
+            ),
+            Err(BookorbitError::Malformed(_))
+        ));
+    }
+}

src/lib.rs

@@ -13,6 +13,7 @@
 //! ```
 
 pub mod auth;
+pub mod bookorbit;
 pub mod comments;
 pub mod config;
 pub mod curate;