Open a WebDAV server as a folder under the signature plugin (#1)

Co-authored-by: Danny Kim <temeddix@gmail.com>
Co-committed-by: Danny Kim <temeddix@gmail.com>

src/lib.rs

@@ -0,0 +1,414 @@
+//! A WebDAV folder for Memona that signs Markdown with an ENS name, speaking
+//! only the host's HTTP.
+
+mod dav;
+mod sdk;
+
+use sdk::host;
+use sdk::{
+  Capabilities, ChangePage, Entry, EntryKind, ErrorCode, FileInfo, Guest,
+  GuestReader, GuestWriter, ListPage, Locator, Reader, Setting, WriteCondition,
+  Writer,
+};
+use std::cell::{Cell, RefCell};
+
+/// The PROPFIND body. Asking for named properties rather than allprop keeps
+/// replies small on servers that store a great many of them.
+const PROPS: &str = concat!(
+  r#"<?xml version="1.0" encoding="utf-8"?>"#,
+  r#"<d:propfind xmlns:d="DAV:"><d:prop>"#,
+  "<d:resourcetype/><d:getcontentlength/><d:getetag/>",
+  "</d:prop></d:propfind>",
+);
+const MAX_CHUNK: u32 = 1024 * 1024;
+
+struct Session {
+  root: String,
+  authorization: Option<String>,
+}
+
+thread_local! {
+  static SESSION: RefCell<Option<Session>> = const { RefCell::new(None) };
+}
+
+struct Webdav;
+
+fn text(setting: Option<Setting>) -> Option<String> {
+  match setting {
+    Some(Setting::Text(value)) | Some(Setting::Secret(value)) => {
+      let value = value.trim().to_owned();
+      (!value.is_empty()).then_some(value)
+    }
+    Some(Setting::Toggle(_)) | None => None,
+  }
+}
+
+fn transport(error: host::HostError) -> ErrorCode {
+  match error {
+    host::HostError::Denied => ErrorCode::Denied,
+    host::HostError::Cancelled => ErrorCode::Cancelled,
+    host::HostError::InvalidInput => ErrorCode::InvalidInput,
+    host::HostError::Internal => ErrorCode::Internal,
+    host::HostError::Unavailable => ErrorCode::Unavailable,
+  }
+}
+
+/// The path a locator names, the only way the contract addresses a resource.
+fn route(target: &Locator) -> String {
+  let Locator::Path(path) = target;
+  path.clone()
+}
+
+fn session<T>(
+  read: impl FnOnce(&Session) -> Result<T, ErrorCode>,
+) -> Result<T, ErrorCode> {
+  SESSION.with_borrow(|session| match session {
+    Some(session) => read(session),
+    None => Err(ErrorCode::Internal),
+  })
+}
+
+/// Starts one request with this connection's credentials attached.
+fn begin(
+  method: host::Method,
+  path: &str,
+  extra: Vec<host::Header>,
+) -> Result<host::Exchange, ErrorCode> {
+  let (url, authorization) = session(|session| {
+    Ok((dav::url(&session.root, path), session.authorization.clone()))
+  })?;
+  let mut headers = extra;
+  if let Some(value) = authorization {
+    headers.push(host::Header {
+      name: "authorization".to_owned(),
+      value,
+    });
+  }
+  host::http(&host::Request {
+    method,
+    url,
+    headers,
+  })
+  .map_err(transport)
+}
+
+/// Runs one request that carries a small body and answers a small body.
+fn exchange(
+  method: host::Method,
+  path: &str,
+  extra: Vec<host::Header>,
+  body: &[u8],
+) -> Result<Vec<u8>, ErrorCode> {
+  let call = begin(method, path, extra)?;
+  if !body.is_empty() {
+    call.push(body).map_err(transport)?;
+  }
+  let head = call.respond().map_err(transport)?;
+  dav::outcome(head.status)?;
+  let mut data = Vec::new();
+  loop {
+    let chunk = call.pull(MAX_CHUNK).map_err(transport)?;
+    if chunk.is_empty() {
+      return Ok(data);
+    }
+    data.extend_from_slice(&chunk);
+    if data.len() > 8 * 1024 * 1024 {
+      return Err(ErrorCode::Unavailable);
+    }
+  }
+}
+
+fn depth(value: &str) -> host::Header {
+  host::Header {
+    name: "depth".to_owned(),
+    value: value.to_owned(),
+  }
+}
+
+fn content_type() -> host::Header {
+  host::Header {
+    name: "content-type".to_owned(),
+    value: "application/xml; charset=utf-8".to_owned(),
+  }
+}
+
+/// Asks the server about one path, and its children when `depth` is 1.
+fn describe(
+  path: &str,
+  depth_value: &str,
+) -> Result<Vec<dav::Found>, ErrorCode> {
+  let body = exchange(
+    host::Method::Propfind,
+    path,
+    vec![depth(depth_value), content_type()],
+    PROPS.as_bytes(),
+  )?;
+  dav::multistatus(&body)
+}
+
+fn info_of(found: &dav::Found) -> FileInfo {
+  FileInfo {
+    kind: if found.collection {
+      EntryKind::Directory
+    } else {
+      EntryKind::File
+    },
+    size: found.length,
+    revision: found.etag.clone(),
+  }
+}
+
+/// Reads one file through a GET that started at an offset.
+struct DavReader {
+  call: host::Exchange,
+  revision: Option<String>,
+  body: RefCell<dav::Body>,
+}
+
+impl GuestReader for DavReader {
+  fn pull(&self, limit: u32) -> Result<Vec<u8>, ErrorCode> {
+    self
+      .body
+      .borrow_mut()
+      .pull(limit.min(MAX_CHUNK) as usize, |wanted| {
+        self.call.pull(wanted).map_err(transport)
+      })
+  }
+  fn revision(&self) -> Option<String> {
+    self.revision.clone()
+  }
+}
+
+/// Writes one file through a PUT whose body is pushed in pieces.
+struct DavWriter {
+  call: host::Exchange,
+  done: RefCell<bool>,
+  written: Cell<u64>,
+}
+
+impl GuestWriter for DavWriter {
+  fn push(&self, data: Vec<u8>) -> Result<(), ErrorCode> {
+    if *self.done.borrow() {
+      return Err(ErrorCode::InvalidInput);
+    }
+    self.call.push(&data).map_err(transport)?;
+    self.written.set(self.written.get() + data.len() as u64);
+    Ok(())
+  }
+  /// One call is enough: the request body is already complete, so the response
+  /// head settles the write. The etag it returns, when the server sends one,
+  /// is the revision a later conditional write compares against.
+  fn finish(&self) -> Result<Option<FileInfo>, ErrorCode> {
+    if *self.done.borrow() {
+      return Err(ErrorCode::InvalidInput);
+    }
+    *self.done.borrow_mut() = true;
+    let head = self.call.respond().map_err(transport)?;
+    dav::outcome(head.status)?;
+    let revision = head
+      .headers
+      .iter()
+      .find(|header| header.name.eq_ignore_ascii_case("etag"))
+      .map(|header| header.value.clone());
+    Ok(Some(FileInfo {
+      kind: EntryKind::File,
+      size: self.written.get(),
+      revision,
+    }))
+  }
+}
+
+impl Guest for Webdav {
+  type Reader = DavReader;
+  type Writer = DavWriter;
+
+  fn open(
+    _provider_id: String,
+    config: Vec<(String, Setting)>,
+  ) -> Result<Capabilities, ErrorCode> {
+    let lookup = |wanted: &str| {
+      config
+        .iter()
+        .find(|(key, _)| key == wanted)
+        .and_then(|(_, value)| text(Some(value.clone())))
+    };
+    let root = lookup("url").ok_or(ErrorCode::InvalidInput)?;
+    if !root.starts_with("https://") && !root.starts_with("http://") {
+      return Err(ErrorCode::InvalidInput);
+    }
+    let authorization = match (lookup("username"), lookup("password")) {
+      (Some(username), Some(password)) => {
+        Some(dav::basic(&username, &password))
+      }
+      _ => None,
+    };
+    SESSION.set(Some(Session {
+      root,
+      authorization,
+    }));
+    Ok(Capabilities {
+      write: true,
+      mkdir: true,
+      rename: true,
+      remove: true,
+      // A server that returns etags supports If-Match, and one that does not
+      // will refuse the header rather than silently overwrite.
+      conditional_write: true,
+      watch: false,
+      virtual_directories: false,
+    })
+  }
+
+  fn close() {
+    SESSION.set(None);
+  }
+
+  fn stat(target: Locator) -> Result<FileInfo, ErrorCode> {
+    let found = describe(&route(&target), "0")?;
+    let entry = found.first().ok_or(ErrorCode::NotFound)?;
+    Ok(info_of(entry))
+  }
+
+  /// WebDAV has no cursor of its own, so one PROPFIND returns the whole
+  /// directory and the page is taken from the front of it.
+  fn list(
+    target: Locator,
+    cursor: Option<String>,
+    limit: u32,
+  ) -> Result<ListPage, ErrorCode> {
+    let path = route(&target);
+    let start: usize = match cursor {
+      Some(value) => value.parse().map_err(|_| ErrorCode::InvalidInput)?,
+      None => 0,
+    };
+    let found = describe(&path, "1")?;
+    let children: Vec<_> = dav::children(&found)?
+      .iter()
+      .map(|entry| Entry {
+        name: dav::name_of(&entry.href),
+        info: info_of(entry),
+      })
+      .collect();
+    let end = start.saturating_add(limit as usize).min(children.len());
+    let entries = children.get(start..end).unwrap_or_default().to_vec();
+    Ok(ListPage {
+      entries,
+      cursor: (end < children.len()).then(|| end.to_string()),
+    })
+  }
+
+  /// A GET on a collection answers with whatever page the server likes to
+  /// show, so the path is checked to be a file before any byte is read.
+  fn open_read(target: Locator, offset: u64) -> Result<Reader, ErrorCode> {
+    let path = route(&target);
+    let found = describe(&path, "0")?;
+    let entry = found.first().ok_or(ErrorCode::NotFound)?;
+    if entry.collection {
+      return Err(ErrorCode::InvalidInput);
+    }
+    let call = begin(
+      host::Method::Get,
+      &path,
+      vec![host::Header {
+        name: "range".to_owned(),
+        value: format!("bytes={offset}-"),
+      }],
+    )?;
+    let head = call.respond().map_err(transport)?;
+    let body = if dav::range_outcome(head.status)? {
+      dav::Body::default()
+    } else {
+      dav::Body::empty()
+    };
+    // The listing's etag is the one stat and list report, and the strong form
+    // a later conditional write must send; the GET's may be a weak variant.
+    let revision = entry.etag.clone().or_else(|| {
+      head
+        .headers
+        .iter()
+        .find(|header| header.name.eq_ignore_ascii_case("etag"))
+        .map(|header| header.value.clone())
+    });
+    Ok(Reader::new(DavReader {
+      call,
+      revision,
+      body: RefCell::new(body),
+    }))
+  }
+
+  fn open_write(
+    target: Locator,
+    condition: WriteCondition,
+    _size_hint: Option<u64>,
+  ) -> Result<Writer, ErrorCode> {
+    let path = route(&target);
+    let guard = match condition {
+      WriteCondition::CreateOnly => Some(host::Header {
+        name: "if-none-match".to_owned(),
+        value: "*".to_owned(),
+      }),
+      WriteCondition::IfMatch(revision) => Some(host::Header {
+        name: "if-match".to_owned(),
+        value: revision,
+      }),
+      WriteCondition::Overwrite => None,
+    };
+    let call = begin(host::Method::Put, &path, guard.into_iter().collect())?;
+    Ok(Writer::new(DavWriter {
+      call,
+      done: RefCell::new(false),
+      written: Cell::new(0),
+    }))
+  }
+
+  fn mkdir(target: Locator) -> Result<FileInfo, ErrorCode> {
+    let path = route(&target);
+    exchange(host::Method::Mkcol, &path, Vec::new(), &[])?;
+    Ok(FileInfo {
+      kind: EntryKind::Directory,
+      size: 0,
+      revision: None,
+    })
+  }
+
+  fn rename(
+    target: Locator,
+    destination: String,
+  ) -> Result<FileInfo, ErrorCode> {
+    let path = route(&target);
+    let to = session(|session| Ok(dav::url(&session.root, &destination)))?;
+    exchange(
+      host::Method::Move,
+      &path,
+      vec![
+        host::Header {
+          name: "destination".to_owned(),
+          value: to,
+        },
+        // Never clobber an existing target: a rename that would replace one is
+        // a conflict for the caller to resolve.
+        host::Header {
+          name: "overwrite".to_owned(),
+          value: "F".to_owned(),
+        },
+      ],
+      &[],
+    )?;
+    Self::stat(Locator::Path(destination))
+  }
+
+  /// DELETE takes a whole collection at once, so a directory is looked at
+  /// first and refused unless it is empty.
+  fn remove(target: Locator) -> Result<(), ErrorCode> {
+    let path = route(&target);
+    dav::removable(&describe(&path, "1")?)?;
+    exchange(host::Method::Delete, &path, Vec::new(), &[])?;
+    Ok(())
+  }
+
+  fn poll(_cursor: Option<String>) -> Result<ChangePage, ErrorCode> {
+    Err(ErrorCode::Unsupported)
+  }
+}
+
+sdk::export!(Webdav with_types_in sdk);