Merge pull request #258 from mmaudet/fix/self-heal-missing-content

fix: self-heal a missing content blob in download-message

crates/core/src/envelope/extractor.rs

@@ -16,11 +16,13 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+use crate::cache::imap::mailbox::MailBox;
 use crate::common::AddrVec;
 use crate::envelope::meta::parse_bichon_metadata;
 use crate::envelope::utils::normalize_subject;
 use crate::error::code::ErrorCode;
 use crate::error::BichonResult;
+use crate::imap::executor::ImapExecutor;
 use crate::message::content::AttachmentInfo;
 use crate::store::blob::{DetachedEmail, BLOB_MANAGER};
 use crate::store::tantivy::attachment::ATTACHMENT_MANAGER;
@@ -515,6 +517,115 @@ pub fn reattach_eml_content(
     Ok((e.envelope, Bytes::from(restored_eml)))
 }
 
+/// Returns the raw EML for an indexed message, self-healing a missing content blob.
+///
+/// Behaves like [`reattach_eml_content`], but when the message's content blob is
+/// absent from the blob store it fetches that single message on demand from the
+/// IMAP server (`UID FETCH <uid> (BODY.PEEK[])`), persists it for future requests,
+/// and returns it. If the on-demand fetch itself fails, the original "content not
+/// found" error from [`reattach_eml_content`] is surfaced unchanged so the caller
+/// still produces its 404.
+pub async fn reattach_eml_content_self_healing(
+    account_id: u64,
+    envelope_id: String,
+) -> BichonResult<(Envelope, Bytes)> {
+    let envelope = ENVELOPE_MANAGER
+        .get_envelope_by_id(account_id, &envelope_id)?
+        .ok_or_else(|| {
+            raise_error!(
+                format!(
+                    "Envelope not found: account_id={} envelope_id={}",
+                    account_id, &envelope_id
+                ),
+                ErrorCode::ResourceNotFound
+            )
+        })?
+        .envelope;
+
+    // Fast path: the content blob is present, reuse the regular reattach logic.
+    if BLOB_MANAGER.get_email(&envelope.content_hash)?.is_some() {
+        return reattach_eml_content(account_id, envelope_id);
+    }
+
+    // The blob is missing. Try to recover it directly from the IMAP server.
+    match recover_message_blob(&envelope).await {
+        Ok(raw_body) => {
+            tracing::info!(
+                account_id,
+                envelope_id = %envelope_id,
+                uid = envelope.uid,
+                "Self-healed missing email content blob via on-demand IMAP fetch"
+            );
+            Ok((envelope, raw_body))
+        }
+        Err(e) => {
+            tracing::warn!(
+                account_id,
+                envelope_id = %envelope_id,
+                uid = envelope.uid,
+                error = %e,
+                "On-demand IMAP fetch for missing content blob failed; returning not-found"
+            );
+            // Surface the canonical "content not found" error to the caller.
+            reattach_eml_content(account_id, envelope_id)
+        }
+    }
+}
+
+/// Fetches one message from IMAP and re-stores its detached blob.
+///
+/// On success the freshly fetched raw RFC822 body is returned; it is also queued
+/// (in detached form) into the blob store so subsequent requests hit the cache.
+/// Fails if the message cannot be fetched, or if the fetched bytes do not match
+/// the archived `content_hash` (the server-side message no longer matches what
+/// Bichon archived, so it cannot be treated as a recovery of that blob).
+async fn recover_message_blob(envelope: &Envelope) -> BichonResult<Bytes> {
+    let mailbox = MailBox::find_mailbox(envelope.account_id, envelope.mailbox_id)?
+        .ok_or_else(|| {
+            raise_error!(
+                format!(
+                    "Mailbox not found: account_id={} mailbox_id={}",
+                    envelope.account_id, envelope.mailbox_id
+                ),
+                ErrorCode::ResourceNotFound
+            )
+        })?;
+
+    let mut session = ImapExecutor::create_connection(envelope.account_id).await?;
+    let result = ImapExecutor::fetch_single_message_body(
+        &mut session,
+        &mailbox.encoded_name(),
+        envelope.uid,
+    )
+    .await;
+    session.logout().await.ok();
+    let raw_body = result?;
+
+    let fetched_hash = compute_content_hash(&raw_body);
+    if fetched_hash != envelope.content_hash {
+        return Err(raise_error!(
+            format!(
+                "Fetched message does not match archived content: expected content_hash={} got={}",
+                envelope.content_hash, fetched_hash
+            ),
+            ErrorCode::ImapUnexpectedResult
+        ));
+    }
+
+    // Re-create the detached blob (stripped EML + attachments) so the missing
+    // blob is repopulated for future requests. The detached EML is queued under
+    // `fetched_hash`, which equals `envelope.content_hash`.
+    let message = MessageParser::new().parse(raw_body.as_slice()).ok_or_else(|| {
+        raise_error!(
+            "Failed to parse fetched email content".into(),
+            ErrorCode::InternalError
+        )
+    })?;
+    detach_and_store_attachments(&raw_body, &message, &fetched_hash).await;
+
+    Ok(Bytes::from(raw_body))
+}
+
 #[cfg(test)]
 mod test {
     use html2text::config;

crates/core/src/imap/executor.rs

@@ -289,6 +289,58 @@ impl ImapExecutor {
         Ok(())
     }
 
+    /// Fetches the raw RFC822 body of a single message by UID.
+    ///
+    /// Selects (read-only) the given mailbox and issues `UID FETCH <uid> (BODY.PEEK[])`.
+    /// Used for on-demand self-healing when an indexed message's content blob is missing.
+    /// Returns the raw bytes, or an error if the message cannot be retrieved.
+    pub async fn fetch_single_message_body(
+        session: &mut Session<Box<dyn SessionStream>>,
+        encoded_mailbox_name: &str,
+        uid: u32,
+    ) -> BichonResult<Vec<u8>> {
+        session
+            .examine(encoded_mailbox_name)
+            .await
+            .map_err(|e| raise_error!(format!("{:#?}", e), ErrorCode::ImapCommandFailed))?;
+
+        let mut stream = session
+            .uid_fetch(uid.to_string(), BODY_FETCH_COMMAND)
+            .await
+            .map_err(|e| raise_error!(format!("{:#?}", e), ErrorCode::ImapCommandFailed))?;
+
+        let fetch = stream
+            .try_next()
+            .await
+            .map_err(|e| raise_error!(format!("{:#?}", e), ErrorCode::ImapCommandFailed))?
+            .ok_or_else(|| {
+                raise_error!(
+                    format!("UID {uid} not found on IMAP server"),
+                    ErrorCode::ResourceNotFound
+                )
+            })?;
+
+        let body = fetch
+            .body()
+            .ok_or_else(|| {
+                raise_error!(
+                    format!("No body returned for UID {uid}"),
+                    ErrorCode::ImapUnexpectedResult
+                )
+            })?
+            .to_vec();
+
+        // Drain any remaining items so the stream is fully consumed before reuse.
+        while stream
+            .try_next()
+            .await
+            .map_err(|e| raise_error!(format!("{:#?}", e), ErrorCode::ImapCommandFailed))?
+            .is_some()
+        {}
+
+        Ok(body)
+    }
+
     pub async fn create_connection(
         account_id: u64,
     ) -> BichonResult<Session<Box<dyn SessionStream>>> {

crates/core/src/store/blob.rs

@@ -18,7 +18,7 @@
 
 use crate::{
     common::signal::SIGNAL_MANAGER,
-    envelope::extractor::reattach_eml_content,
+    envelope::extractor::reattach_eml_content_self_healing,
     error::{code::ErrorCode, BichonResult},
     settings::dir::DATA_DIR_MANAGER,
 };
@@ -232,7 +232,13 @@ impl BlobManager {
     }
 }
 
-pub fn get_reader(account_id: u64, eid: String) -> BichonResult<Cursor<Bytes>> {
+/// Returns a reader over the raw EML for an indexed message.
-    let (_, data) = reattach_eml_content(account_id, eid)?;
+///
+/// If the message's content blob is missing from the blob store, it is fetched
+/// on demand from the IMAP server, persisted, and returned (self-healing). The
+/// underlying "content not found" error is only surfaced if that on-demand
+/// fetch itself fails.
+pub async fn get_reader(account_id: u64, eid: String) -> BichonResult<Cursor<Bytes>> {
+    let (_, data) = reattach_eml_content_self_healing(account_id, eid).await?;
     Ok(Cursor::new(data))
 }

crates/server/src/rest/api/message.rs

@@ -225,7 +225,7 @@ impl MessageApi {
         AccountModel::check_account_exists(account_id)?;
         context.require_permission(Some(account_id), Permission::DATA_RAW_DOWNLOAD)?;
         let envelope_id = envelope_id.0;
-        let reader = get_reader(account_id, envelope_id.clone())?;
+        let reader = get_reader(account_id, envelope_id.clone()).await?;
         let body = Body::from_async_read(reader);
         let attachment = Attachment::new(body)
             .attachment_type(AttachmentType::Attachment)