fill in the todo!()s

libs/pageserver_api/src/models.rs

@@ -1,5 +1,6 @@
 use std::{
     collections::HashMap,
+    io::Read,
     num::{NonZeroU64, NonZeroUsize},
     time::SystemTime,
 };
@@ -770,31 +771,44 @@ impl PagestreamBeMessage {
     pub fn deserialize(buf: Bytes) -> anyhow::Result<Self> {
         let mut buf = buf.reader();
         let msg_tag = buf.read_u8()?;
-        match msg_tag {
-            100 => todo!(),
-            101 => todo!(),
+        let ok = match msg_tag {
+            100 => {
+                let exists = buf.read_u8()?;
+                Self::Exists(PagestreamExistsResponse {
+                    exists: exists != 0,
+                })
+            }
+            101 => {
+                let n_blocks = buf.read_u32::<BigEndian>()?;
+                Self::Nblocks(PagestreamNblocksResponse { n_blocks })
+            }
             102 => {
-                let buf = buf.get_ref();
-                /* TODO use constant */
-                if buf.len() == 8192 {
-                    Ok(PagestreamBeMessage::GetPage(PagestreamGetPageResponse {
-                        page: buf.clone(),
-                    }))
-                } else {
-                    anyhow::bail!("invalid page size: {}", buf.len());
-                }
+                let mut page = vec![0; 8192]; // TODO: use MaybeUninit
+                buf.read_exact(&mut page)?;
+                PagestreamBeMessage::GetPage(PagestreamGetPageResponse { page: page.into() })
             }
             103 => {
                 let buf = buf.get_ref();
                 let cstr = std::ffi::CStr::from_bytes_until_nul(buf)?;
                 let rust_str = cstr.to_str()?;
-                Ok(PagestreamBeMessage::Error(PagestreamErrorResponse {
+                PagestreamBeMessage::Error(PagestreamErrorResponse {
                     message: rust_str.to_owned(),
-                }))
+                })
+            }
+            104 => {
+                let db_size = buf.read_i64::<BigEndian>()?;
+                Self::DbSize(PagestreamDbSizeResponse { db_size })
             }
-            104 => todo!(),
             _ => bail!("unknown tag: {:?}", msg_tag),
+        };
+        let remaining = buf.into_inner();
+        if !remaining.is_empty() {
+            anyhow::bail!(
+                "remaining bytes in msg with tag={msg_tag}: {}",
+                remaining.len()
+            );
         }
+        Ok(ok)
     }
 }