fix(core): rewrite asset protocol streaming, closes #6375 (#6390)

Co-authored-by: Lucas Nogueira <lucas@tauri.studio>

Author: amrbashir

.changes/core-asset-protocol-streaming-crash.md

@@ -0,0 +1,5 @@
+---
+'tauri': 'patch:enhance'
+---
+
+Enhance the `asset` protocol to support streaming of large files.

core/tauri/src/asset_protocol.rs

@@ -0,0 +1,217 @@
+// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+#![cfg(protocol_asset)]
+
+use crate::api::file::SafePathBuf;
+use crate::scope::FsScope;
+use rand::RngCore;
+use std::io::SeekFrom;
+use tauri_runtime::http::HttpRange;
+use tauri_runtime::http::{
+  header::*, status::StatusCode, MimeType, Request, Response, ResponseBuilder,
+};
+use tauri_utils::debug_eprintln;
+use tokio::fs::File;
+use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt};
+use url::Position;
+use url::Url;
+
+pub fn asset_protocol_handler(
+  request: &Request,
+  scope: FsScope,
+  window_origin: String,
+) -> Result<Response, Box<dyn std::error::Error>> {
+  let parsed_path = Url::parse(request.uri())?;
+  let filtered_path = &parsed_path[..Position::AfterPath];
+  let path = filtered_path
+    .strip_prefix("asset://localhost/")
+    // the `strip_prefix` only returns None when a request is made to `https://tauri.$P` on Windows
+    // where `$P` is not `localhost/*`
+    .unwrap_or("");
+  let path = percent_encoding::percent_decode(path.as_bytes())
+    .decode_utf8_lossy()
+    .to_string();
+
+  if let Err(e) = SafePathBuf::new(path.clone().into()) {
+    debug_eprintln!("asset protocol path \"{}\" is not valid: {}", path, e);
+    return ResponseBuilder::new().status(403).body(Vec::new());
+  }
+
+  if !scope.is_allowed(&path) {
+    debug_eprintln!("asset protocol not configured to allow the path: {}", path);
+    return ResponseBuilder::new().status(403).body(Vec::new());
+  }
+
+  let mut resp = ResponseBuilder::new().header("Access-Control-Allow-Origin", &window_origin);
+
+  crate::async_runtime::block_on(async move {
+    let mut file = File::open(&path).await?;
+
+    // get file length
+    let len = {
+      let old_pos = file.stream_position().await?;
+      let len = file.seek(SeekFrom::End(0)).await?;
+      file.seek(SeekFrom::Start(old_pos)).await?;
+      len
+    };
+
+    // get file mime type
+    let (mime_type, read_bytes) = {
+      let nbytes = len.min(8192);
+      let mut magic_buf = Vec::with_capacity(nbytes as usize);
+      let old_pos = file.stream_position().await?;
+      (&mut file).take(nbytes).read_to_end(&mut magic_buf).await?;
+      file.seek(SeekFrom::Start(old_pos)).await?;
+      (
+        MimeType::parse(&magic_buf, &path),
+        // return the `magic_bytes` if we read the whole file
+        // to avoid reading it again later if this is not a range request
+        if len < 8192 { Some(magic_buf) } else { None },
+      )
+    };
+
+    resp = resp.header(CONTENT_TYPE, &mime_type);
+
+    // handle 206 (partial range) http requests
+    let response = if let Some(range_header) = request
+      .headers()
+      .get("range")
+      .and_then(|r| r.to_str().map(|r| r.to_string()).ok())
+    {
+      resp = resp.header(ACCEPT_RANGES, "bytes");
+
+      let not_satisfiable = || {
+        ResponseBuilder::new()
+          .status(StatusCode::RANGE_NOT_SATISFIABLE)
+          .header(CONTENT_RANGE, format!("bytes */{len}"))
+          .body(vec![])
+      };
+
+      // parse range header
+      let ranges = if let Ok(ranges) = HttpRange::parse(&range_header, len) {
+        ranges
+          .iter()
+          // map the output to spec range <start-end>, example: 0-499
+          .map(|r| (r.start, r.start + r.length - 1))
+          .collect::<Vec<_>>()
+      } else {
+        return not_satisfiable();
+      };
+
+      /// The Maximum bytes we send in one range
+      const MAX_LEN: u64 = 1000 * 1024;
+
+      // single-part range header
+      if ranges.len() == 1 {
+        let &(start, mut end) = ranges.first().unwrap();
+
+        // check if a range is not satisfiable
+        //
+        // this should be already taken care of by the range parsing library
+        // but checking here again for extra assurance
+        if start >= len || end >= len || end < start {
+          return not_satisfiable();
+        }
+
+        // adjust end byte for MAX_LEN
+        end = start + (end - start).min(len - start).min(MAX_LEN - 1);
+
+        // calculate number of bytes needed to be read
+        let nbytes = end + 1 - start;
+
+        let mut buf = Vec::with_capacity(nbytes as usize);
+        file.seek(SeekFrom::Start(start)).await?;
+        file.take(nbytes).read_to_end(&mut buf).await?;
+
+        resp = resp.header(CONTENT_RANGE, format!("bytes {start}-{end}/{len}"));
+        resp = resp.header(CONTENT_LENGTH, end + 1 - start);
+        resp = resp.status(StatusCode::PARTIAL_CONTENT);
+        resp.body(buf)
+      } else {
+        // multi-part range header
+        let mut buf = Vec::new();
+        let ranges = ranges
+          .iter()
+          .filter_map(|&(start, mut end)| {
+            // filter out unsatisfiable ranges
+            //
+            // this should be already taken care of by the range parsing library
+            // but checking here again for extra assurance
+            if start >= len || end >= len || end < start {
+              None
+            } else {
+              // adjust end byte for MAX_LEN
+              end = start + (end - start).min(len - start).min(MAX_LEN - 1);
+              Some((start, end))
+            }
+          })
+          .collect::<Vec<_>>();
+
+        let boundary = random_boundary();
+        let boundary_sep = format!("\r\n--{boundary}\r\n");
+        let boundary_closer = format!("\r\n--{boundary}\r\n");
+
+        resp = resp.header(
+          CONTENT_TYPE,
+          format!("multipart/byteranges; boundary={boundary}"),
+        );
+
+        for (end, start) in ranges {
+          // a new range is being written, write the range boundary
+          buf.write_all(boundary_sep.as_bytes()).await?;
+
+          // write the needed headers `Content-Type` and `Content-Range`
+          buf
+            .write_all(format!("{CONTENT_TYPE}: {mime_type}\r\n").as_bytes())
+            .await?;
+          buf
+            .write_all(format!("{CONTENT_RANGE}: bytes {start}-{end}/{len}\r\n").as_bytes())
+            .await?;
+
+          // write the separator to indicate the start of the range body
+          buf.write_all("\r\n".as_bytes()).await?;
+
+          // calculate number of bytes needed to be read
+          let nbytes = end + 1 - start;
+
+          let mut local_buf = Vec::with_capacity(nbytes as usize);
+          file.seek(SeekFrom::Start(start)).await?;
+          (&mut file).take(nbytes).read_to_end(&mut local_buf).await?;
+          buf.extend_from_slice(&local_buf);
+        }
+        // all ranges have been written, write the closing boundary
+        buf.write_all(boundary_closer.as_bytes()).await?;
+
+        resp.body(buf)
+      }
+    } else {
+      // avoid reading the file if we already read it
+      // as part of mime type detection
+      let buf = if let Some(b) = read_bytes {
+        b
+      } else {
+        let mut local_buf = Vec::with_capacity(len as usize);
+        file.read_to_end(&mut local_buf).await?;
+        local_buf
+      };
+      resp = resp.header(CONTENT_LENGTH, len);
+      resp.body(buf)
+    };
+
+    response
+  })
+}
+
+fn random_boundary() -> String {
+  let mut x = [0_u8; 30];
+  rand::thread_rng().fill_bytes(&mut x);
+  (x[..])
+    .iter()
+    .map(|&x| format!("{x:x}"))
+    .fold(String::new(), |mut a, x| {
+      a.push_str(x.as_str());
+      a
+    })
+}

core/tauri/src/lib.rs

@@ -184,13 +184,14 @@ mod pattern;
 pub mod plugin;
 pub mod window;
 use tauri_runtime as runtime;
+#[cfg(protocol_asset)]
+mod asset_protocol;
 /// The allowlist scopes.
 pub mod scope;
 mod state;
 #[cfg(updater)]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "updater")))]
 pub mod updater;
-
 pub use tauri_utils as utils;
 
 /// A Tauri [`Runtime`] wrapper around wry.