From 199b748b8efecb856d269312c73e00dfed49bcc9 Mon Sep 17 00:00:00 2001
From: George Stagg <george.stagg@posit.co>
Date: Sun, 22 Dec 2024 19:10:00 +0000
Subject: [PATCH] Set mmap size based on seek when running under Emscripten
---
crates/polars-io/src/utils/other.rs | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/crates/polars-io/src/utils/other.rs b/crates/polars-io/src/utils/other.rs
index f4ef629821a9..e6f51b5f3b6d 100644
--- a/crates/polars-io/src/utils/other.rs
+++ b/crates/polars-io/src/utils/other.rs
@@ -1,6 +1,8 @@
#[cfg(any(feature = "ipc_streaming", feature = "parquet"))]
use std::borrow::Cow;
use std::io::Read;
+#[cfg(target_os = "emscripten")]
+use std::io::{Seek, SeekFrom};
use once_cell::sync::Lazy;
use polars_core::prelude::*;
@@ -23,6 +25,15 @@ pub fn get_reader_bytes<R: Read + MmapBytesReader + ?Sized>(
{
let mut options = memmap::MmapOptions::new();
options.offset(offset);
+
+ // Set mmap size based on seek to end when running under Emscripten
+ #[cfg(target_os = "emscripten")]
+ {
+ let mut file = file;
+ let size = file.seek(SeekFrom::End(0)).unwrap();
+ options.len((size - offset) as usize);
+ }
+
let mmap = MMapSemaphore::new_from_file_with_options(file, options)?;
Ok(ReaderBytes::Owned(MemSlice::from_mmap(Arc::new(mmap))))
} else {