add a Rust client for Pageserver's page_service

Part of getpage@lsn benchmark epic: https://github.com/neondatabase/neon/issues/5771

Cargo.lock

@@ -3139,6 +3139,7 @@ dependencies = [
  "tokio",
  "tokio-io-timeout",
  "tokio-postgres",
+ "tokio-stream",
  "tokio-tar",
  "tokio-util",
  "toml_edit",

libs/pageserver_api/src/models.rs

@@ -765,6 +765,36 @@ impl PagestreamBeMessage {
 
         bytes.into()
     }
+
+    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!(),
+            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());
+                }
+            }
+            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 {
+                    message: rust_str.to_owned(),
+                }))
+            }
+            104 => todo!(),
+            _ => bail!("unknown tag: {:?}", msg_tag),
+        }
+    }
 }
 
 #[cfg(test)]

pageserver/Cargo.toml

@@ -62,6 +62,7 @@ thiserror.workspace = true
 tokio = { workspace = true, features = ["process", "sync", "fs", "rt", "io-util", "time"] }
 tokio-io-timeout.workspace = true
 tokio-postgres.workspace = true
+tokio-stream.workspace = true
 tokio-util.workspace = true
 toml_edit = { workspace = true, features = [ "serde" ] }
 tracing.workspace = true

pageserver/src/client/page_service.rs

@@ -0,0 +1,145 @@
+use std::pin::Pin;
+
+use futures::SinkExt;
+use pageserver_api::{
+    models::{
+        PagestreamBeMessage, PagestreamFeMessage, PagestreamGetPageRequest,
+        PagestreamGetPageResponse,
+    },
+    reltag::RelTag,
+};
+use tokio::task::JoinHandle;
+use tokio_postgres::CopyOutStream;
+use tokio_stream::StreamExt;
+use tokio_util::sync::CancellationToken;
+use utils::{
+    id::{TenantId, TimelineId},
+    lsn::Lsn,
+};
+
+pub struct Client {
+    client: tokio_postgres::Client,
+    cancel_on_client_drop: Option<tokio_util::sync::DropGuard>,
+    conn_task: JoinHandle<()>,
+}
+
+pub struct BasebackupRequest {
+    pub tenant_id: TenantId,
+    pub timeline_id: TimelineId,
+    pub lsn: Option<Lsn>,
+    pub gzip: bool,
+}
+
+impl Client {
+    pub async fn new(connstring: String) -> anyhow::Result<Self> {
+        let (client, connection) = tokio_postgres::connect(&connstring, postgres::NoTls).await?;
+
+        let conn_task_cancel = CancellationToken::new();
+        let conn_task = tokio::spawn({
+            let conn_task_cancel = conn_task_cancel.clone();
+            async move {
+                tokio::select! {
+                    _ = conn_task_cancel.cancelled() => { }
+                    res = connection => {
+                        res.unwrap();
+                    }
+                }
+            }
+        });
+        Ok(Self {
+            cancel_on_client_drop: Some(conn_task_cancel.drop_guard()),
+            conn_task,
+            client,
+        })
+    }
+
+    pub async fn pagestream(
+        self,
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+    ) -> anyhow::Result<PagestreamClient> {
+        let copy_both: tokio_postgres::CopyBothDuplex<bytes::Bytes> = self
+            .client
+            .copy_both_simple(&format!("pagestream {tenant_id} {timeline_id}"))
+            .await?;
+        let Client {
+            cancel_on_client_drop,
+            conn_task,
+            client: _,
+        } = self;
+        Ok(PagestreamClient {
+            copy_both: Box::pin(copy_both),
+            conn_task,
+            cancel_on_client_drop,
+        })
+    }
+
+    pub async fn basebackup(&self, req: &BasebackupRequest) -> anyhow::Result<CopyOutStream> {
+        let BasebackupRequest {
+            tenant_id,
+            timeline_id,
+            lsn,
+            gzip,
+        } = req;
+        let mut args = Vec::with_capacity(5);
+        args.push("basebackup".to_string());
+        args.push(format!("{tenant_id}"));
+        args.push(format!("{timeline_id}"));
+        if let Some(lsn) = lsn {
+            args.push(format!("{lsn}"));
+        }
+        if *gzip {
+            args.push(format!("--gzip"))
+        }
+        Ok(self.client.copy_out(&args.join(" ")).await?)
+    }
+}
+
+/// Create using [`Client::pagestream`].
+pub struct PagestreamClient {
+    copy_both: Pin<Box<tokio_postgres::CopyBothDuplex<bytes::Bytes>>>,
+    cancel_on_client_drop: Option<tokio_util::sync::DropGuard>,
+    conn_task: JoinHandle<()>,
+}
+
+pub struct RelTagBlockNo {
+    pub rel_tag: RelTag,
+    pub block_no: u32,
+}
+
+impl PagestreamClient {
+    pub async fn shutdown(mut self) {
+        let _ = self.cancel_on_client_drop.take();
+        self.conn_task.await.unwrap();
+    }
+
+    pub async fn getpage(
+        &mut self,
+        key: RelTagBlockNo,
+        lsn: Lsn,
+    ) -> anyhow::Result<PagestreamGetPageResponse> {
+        let req = PagestreamGetPageRequest {
+            latest: false,
+            rel: key.rel_tag,
+            blkno: key.block_no,
+            lsn,
+        };
+        let req = PagestreamFeMessage::GetPage(req);
+        let req: bytes::Bytes = req.serialize();
+        // let mut req = tokio_util::io::ReaderStream::new(&req);
+        let mut req = tokio_stream::once(Ok(req));
+
+        self.copy_both.send_all(&mut req).await?;
+
+        let next: Option<Result<bytes::Bytes, _>> = self.copy_both.next().await;
+        let next = next.unwrap().unwrap();
+
+        match PagestreamBeMessage::deserialize(next)? {
+            PagestreamBeMessage::Exists(_) => todo!(),
+            PagestreamBeMessage::Nblocks(_) => todo!(),
+            PagestreamBeMessage::GetPage(p) => Ok(p),
+            PagestreamBeMessage::Error(e) => anyhow::bail!("Error: {:?}", e),
+            PagestreamBeMessage::DbSize(_) => todo!(),
+        }
+    }
+}