access: screening received changes

access::screen: a batch of received changes judged change by change,
those that change what rules read applied before the next is judged;
a refused change stays out with whatever builds on it, kept aside for
operators; changes missing dependencies wait.

Auth plan M6.

1 files changed, 27 insertions, 0 deletions

diff --git a/src/document/changes.rs b/src/document/changes.rs
index 57e2bf7..eef7dbc 100644
--- a/src/document/changes.rs
+++ b/src/document/changes.rs
@@ -240,6 +240,33 @@ pub(crate) fn misplaced_author(mut data: &[u8]) -> Option<MisplacedAuthor> {
     None
 }
 
+/// The changes in `data`, chunks as sync messages and downloads carry them: changes,
+/// compressed or not, bundles, documents. None if a chunk doesn't load.
+pub(crate) fn changes_in(mut data: &[u8]) -> Option<Vec<Change>> {
+    const MAGIC: [u8; 4] = [0x85, 0x6f, 0x4a, 0x83];
+    const HEADER: usize = 9;
+    let mut changes = Vec::new();
+    while !data.is_empty() {
+        if data.len() <= HEADER || data[..4] != MAGIC {
+            return None;
+        }
+        let kind = data[8];
+        let (length, read) = uleb128(&data[HEADER..])?;
+        let end = HEADER
+            .checked_add(read)?
+            .checked_add(usize::try_from(length).ok()?)?;
+        let chunk = data.get(..end)?;
+        data = &data[end..];
+        match kind {
+            1 | 2 => changes.push(Change::try_from(chunk).ok()?),
+            3 => changes.extend(automerge::Bundle::try_from(chunk).ok()?.to_changes().ok()?),
+            0 => changes.extend(Document::load(chunk).ok()?.get_changes(&[])),
+            _ => return None,
+        }
+    }
+    Some(changes)
+}
+
 /// `change`, if it names an author but isn't its actor's first (`misplaced_author`).
 fn misplaced_in(change: &Change) -> Option<MisplacedAuthor> {
     let author = change.author()?;