Support opening Vortex files without I/O (#1920)

Part of #1676

vortex-file/src/v2/open/mod.rs

@@ -32,8 +32,8 @@ pub struct VortexOpenOptions {
     layout_ctx: LayoutContextRef,
     /// An optional, externally provided, file layout.
     file_layout: Option<FileLayout>,
-    /// An optional, externally provided, dtype.
-    dtype: Option<DType>,
+    /// An optional, externally provided, file size.
+    file_size: Option<u64>,
     // TODO(ngates): also support a messages_middleware that can wrap a message cache to provide
     //  additional caching, metrics, or other intercepts, etc. It should support synchronous
     //  read + write of Map<MessageId, ByteBuffer> or similar.
@@ -51,7 +51,7 @@ impl VortexOpenOptions {
             ctx,
             layout_ctx: LayoutContextRef::default(),
             file_layout: None,
-            dtype: None,
+            file_size: None,
             initial_read_size: INITIAL_READ_SIZE,
             split_by: SplitBy::Layout,
             segment_cache: None,
@@ -60,6 +60,24 @@ impl VortexOpenOptions {
         }
     }
 
+    /// Configure a known file layout.
+    ///
+    /// If this is provided, then the Vortex file can be opened without performing any I/O.
+    /// Once open, the [`FileLayout`] can be accessed via [`VortexFile::file_layout`].
+    pub fn with_file_layout(mut self, file_layout: FileLayout) -> Self {
+        self.file_layout = Some(file_layout);
+        self
+    }
+
+    /// Configure a known file size.
+    ///
+    /// This helps to prevent an I/O request to discover the size of the file.
+    /// Of course, all bets are off if you pass an incorrect value.
+    pub fn with_file_size(mut self, file_size: u64) -> Self {
+        self.file_size = Some(file_size);
+        self
+    }
+
     /// Configure the initial read size for the Vortex file.
     pub fn with_initial_read_size(mut self, initial_read_size: u64) -> VortexResult<Self> {
         if self.initial_read_size < u16::MAX as u64 {
@@ -91,9 +109,60 @@ impl VortexOpenOptions {
 
 impl VortexOpenOptions {
     /// Open the Vortex file using asynchronous IO.
-    pub async fn open<R: VortexReadAt>(self, read: R) -> VortexResult<VortexFile<FileIoDriver<R>>> {
+    pub async fn open<R: VortexReadAt>(
+        mut self,
+        read: R,
+    ) -> VortexResult<VortexFile<FileIoDriver<R>>> {
+        // Set up our segment cache.
+        let segment_cache = self
+            .segment_cache
+            .as_ref()
+            .cloned()
+            .unwrap_or_else(|| Arc::new(InMemorySegmentCache::default()));
+
+        // If we need to read the file layout, then do so.
+        let file_layout = match self.file_layout.take() {
+            None => self.read_file_layout(&read, segment_cache.as_ref()).await?,
+            Some(file_layout) => file_layout,
+        };
+
+        // Set up the I/O driver.
+        let io_driver = FileIoDriver {
+            read,
+            file_layout: file_layout.clone(),
+            concurrency: self.io_concurrency,
+        };
+
+        // Set up the execution driver.
+        let exec_driver = self
+            .execution_mode
+            .unwrap_or(ExecutionMode::Inline)
+            .into_driver();
+
+        // Compute the splits of the file.
+        let splits = self.split_by.splits(&file_layout.root_layout)?.into();
+
+        // Finally, create the VortexFile.
+        Ok(VortexFile {
+            ctx: self.ctx.clone(),
+            file_layout,
+            io_driver,
+            exec_driver,
+            splits,
+        })
+    }
+
+    /// Read the [`FileLayout`] from the file.
+    async fn read_file_layout<R: VortexReadAt>(
+        &self,
+        read: &R,
+        segment_cache: &dyn SegmentCache,
+    ) -> VortexResult<FileLayout> {
         // Fetch the file size and perform the initial read.
-        let file_size = read.size().await?;
+        let file_size = match self.file_size {
+            None => read.size().await?,
+            Some(file_size) => file_size,
+        };
         let initial_read_size = self.initial_read_size.min(file_size);
         let initial_offset = file_size - initial_read_size;
         let initial_read: ByteBuffer = read
@@ -105,11 +174,10 @@ impl VortexOpenOptions {
         let postscript = self.parse_postscript(&initial_read)?;
 
         // Check if we need to read more bytes.
-        // NOTE(ngates): for now, we assume the dtype and layout segments are adjacent.
-        let (initial_offset, initial_read) = if (self.dtype.is_none()
-            && postscript.dtype.offset < initial_offset)
-            || (self.file_layout.is_none() && postscript.file_layout.offset < initial_offset)
+        let (initial_offset, initial_read) = if (postscript.dtype.offset < initial_offset)
+            || (postscript.file_layout.offset < initial_offset)
         {
+            // NOTE(ngates): for now, we assume the dtype and layout segments are adjacent.
             let offset = postscript.dtype.offset.min(postscript.file_layout.offset);
             let mut new_initial_read =
                 ByteBufferMut::with_capacity(usize::try_from(file_size - offset)?);
@@ -125,10 +193,9 @@ impl VortexOpenOptions {
         };
 
         // Now we try to read the DType and Layout segments.
-        let dtype = self.dtype.clone().unwrap_or_else(|| {
-            self.parse_dtype(initial_offset, &initial_read, postscript.dtype)
-                .vortex_expect("Failed to parse dtype")
-        });
+        let dtype = self
+            .parse_dtype(initial_offset, &initial_read, postscript.dtype)
+            .vortex_expect("Failed to parse dtype");
         let file_layout = self.file_layout.clone().unwrap_or_else(|| {
             self.parse_file_layout(
                 initial_offset,
@@ -139,44 +206,12 @@ impl VortexOpenOptions {
             .vortex_expect("Failed to parse file layout")
         });
 
-        // Set up our segment cache and for good measure, we populate any segments that were
-        // covered by the initial read.
-        let segment_cache = self
-            .segment_cache
-            .as_ref()
-            .cloned()
-            .unwrap_or_else(|| Arc::new(InMemorySegmentCache::default()));
-        self.populate_segments(
-            initial_offset,
-            &initial_read,
-            &file_layout,
-            segment_cache.as_ref(),
-        )?;
-
-        // Set up the I/O driver.
-        let io_driver = FileIoDriver {
-            read,
-            file_layout: file_layout.clone(),
-            concurrency: self.io_concurrency,
-        };
-
-        // Set up the execution driver.
-        let exec_driver = self
-            .execution_mode
-            .unwrap_or(ExecutionMode::Inline)
-            .into_driver();
+        // If the initial read happened to cover any segments, then we can populate the
+        // segment cache
+        self.populate_segments(initial_offset, &initial_read, &file_layout, segment_cache)
+            .await?;
 
-        // Compute the splits of the file.
-        let splits = self.split_by.splits(&file_layout.root_layout)?.into();
-
-        // Finally, create the VortexFile.
-        Ok(VortexFile {
-            ctx: self.ctx.clone(),
-            file_layout,
-            io_driver,
-            exec_driver,
-            splits,
-        })
+        Ok(file_layout)
     }
 
     /// Parse the postscript from the initial read.
@@ -268,8 +303,7 @@ impl VortexOpenOptions {
     }
 
     /// Populate segments in the cache that were covered by the initial read.
-    #[allow(unused_variables)]
-    fn populate_segments(
+    async fn populate_segments(
         &self,
         initial_offset: u64,
         initial_read: &ByteBuffer,
@@ -285,9 +319,7 @@ impl VortexOpenOptions {
             let offset = usize::try_from(segment.offset - initial_offset)?;
             let buffer = initial_read.slice(offset..offset + (segment.length as usize));
 
-            // FIXME(ngates): how should we write into the segment cache? Feels like it should be
-            //  non-blocking and on some other thread?
-            // segments.put(segment_id, buffer)?;
+            segments.put(segment_id, buffer).await?;
         }
         Ok(())
     }