fix(provider): ensure postcard buffers are appropriately sized

src/protocol.rs

@@ -40,12 +40,12 @@ pub(crate) struct Request {
     pub name: Hash,
 }
 
-#[derive(Deserialize, Serialize, Debug, PartialEq, Eq, Clone)]
+#[derive(Deserialize, Serialize, Debug, PartialEq, Eq, Clone, MaxSize)]
 pub(crate) struct Response {
     pub data: Res,
 }
 
-#[derive(Deserialize, Serialize, Debug, PartialEq, Eq, Clone)]
+#[derive(Deserialize, Serialize, Debug, PartialEq, Eq, Clone, MaxSize)]
 pub(crate) enum Res {
     NotFound,
     // If found, a stream of bao data is sent as next message.

src/provider.rs

@@ -24,6 +24,7 @@ use anyhow::{ensure, Context, Result};
 use bytes::{Bytes, BytesMut};
 use futures::future;
 use futures::Stream;
+use postcard::experimental::max_size::MaxSize;
 use quic_rpc::server::RpcChannel;
 use quic_rpc::transport::flume::FlumeConnection;
 use quic_rpc::transport::misc::DummyServerEndpoint;
@@ -922,7 +923,6 @@ async fn create_collection_inner(
     let mut db = HashMap::with_capacity(data_sources.len() + 1);
     let mut blobs = Vec::with_capacity(data_sources.len());
     let mut total_blobs_size: u64 = 0;
-    let mut blobs_encoded_size_estimate = 0;
 
     // compute outboards in parallel, using tokio's blocking thread pool
     let outboards = data_sources.into_iter().map(|data| {
@@ -974,7 +974,6 @@ async fn create_collection_inner(
                 .unwrap_or_default()
                 .to_string()
         });
-        blobs_encoded_size_estimate += name.len() + 32;
         blobs.push(Blob { name, hash });
     }
 
@@ -983,14 +982,8 @@ async fn create_collection_inner(
         blobs,
         total_blobs_size,
     };
-    blobs_encoded_size_estimate += c.name.len();
-
-    // NOTE: we can't use the postcard::MaxSize to estimate the encoding buffer size
-    // because the Collection and Blobs have `String` fields.
-    // So instead, we are tracking the filename + hash sizes of each blob, plus an extra 1024
-    // to account for any postcard encoding data.
-    let mut buffer = BytesMut::zeroed(blobs_encoded_size_estimate + 1024);
-    let data = postcard::to_slice(&c, &mut buffer)?;
+
+    let data = postcard::to_stdvec(&c).context("blob encoding")?;
     let (outboard, hash) = abao::encode::outboard(&data);
     let hash = Hash::from(hash);
     db.insert(
@@ -1009,8 +1002,8 @@ async fn write_response<W: AsyncWrite + Unpin>(
     let response = Response { data: res };
 
     // TODO: do not transfer blob data as part of the responses
-    if buffer.len() < 1024 {
-        buffer.resize(1024, 0u8);
+    if buffer.len() < Response::POSTCARD_MAX_SIZE {
+        buffer.resize(Response::POSTCARD_MAX_SIZE, 0u8);
     }
     let used = postcard::to_slice(&response, buffer)?;