Fix write of partial blocks

Backport of #189 to fix #188

Bumps to 0.8.2

Author: thejpster

CHANGELOG.md

@@ -18,6 +18,12 @@ The format is based on [Keep a Changelog] and this project adheres to [Semantic
 
 - None
 
+## [Version 0.8.2] - 2025-06-07
+
+### Changed
+
+* Fixed writing at block start mid-file (previously overwrote subsequent file data with zeros up to the end of the block)
+
 ## [Version 0.8.1] - 2024-11-03
 
 ### Changed
@@ -174,7 +180,8 @@ The format is based on [Keep a Changelog] and this project adheres to [Semantic
 
 [Keep a Changelog]: http://keepachangelog.com/en/1.0.0/
 [Semantic Versioning]: http://semver.org/spec/v2.0.0.html
-[Unreleased]: https://github.com/rust-embedded-community/embedded-sdmmc-rs/compare/v0.8.1...develop
+[Unreleased]: https://github.com/rust-embedded-community/embedded-sdmmc-rs/compare/v0.8.2...develop
+[Version 0.8.2]: https://github.com/rust-embedded-community/embedded-sdmmc-rs/compare/v0.8.1...v0.8.2
 [Version 0.8.1]: https://github.com/rust-embedded-community/embedded-sdmmc-rs/compare/v0.8.0...v0.8.1
 [Version 0.8.0]: https://github.com/rust-embedded-community/embedded-sdmmc-rs/compare/v0.7.0...v0.8.0
 [Version 0.7.0]: https://github.com/rust-embedded-community/embedded-sdmmc-rs/compare/v0.6.0...v0.7.0

Cargo.toml

@@ -8,7 +8,7 @@ license = "MIT OR Apache-2.0"
 name = "embedded-sdmmc"
 readme = "README.md"
 repository = "https://github.com/rust-embedded-community/embedded-sdmmc-rs"
-version = "0.8.1"
+version = "0.8.2"
 
 [dependencies]
 byteorder = {version = "1", default-features = false}

src/volume_mgr.rs

@@ -753,8 +753,8 @@ where
             };
             let mut blocks = [Block::new()];
             let to_copy = core::cmp::min(block_avail, bytes_to_write - written);
-            if block_offset != 0 {
-                debug!("Partial block write");
+            if block_offset != 0  || to_copy != block_avail {
+                debug!("Partial block read/modify/write");
                 self.block_device
                     .read(&mut blocks, block_idx, "read")
                     .map_err(Error::DeviceError)?;

tests/write_file.rs

@@ -102,6 +102,65 @@ fn flush_file() {
     assert_eq!(entry.size, 64 * 3);
 }
 
+#[test]
+fn random_access_write_file() {
+    let time_source = utils::make_time_source();
+    let disk = utils::make_block_device(utils::DISK_SOURCE).unwrap();
+    let mut volume_mgr: VolumeManager<utils::RamDisk<Vec<u8>>, utils::TestTimeSource, 4, 2, 1> =
+        VolumeManager::new_with_limits(disk, time_source, 0xAA00_0000);
+    let volume = volume_mgr
+        .open_raw_volume(VolumeIdx(0))
+        .expect("open volume");
+    let root_dir = volume_mgr.open_root_dir(volume).expect("open root dir");
+
+    // Open with string
+    let f = volume_mgr
+        .open_file_in_dir(root_dir, "README.TXT", Mode::ReadWriteTruncate)
+        .expect("open file");
+
+    let test_data = vec![0xCC; 1024];
+    volume_mgr.write(f, &test_data).expect("file write");
+
+    let length = volume_mgr.file_length(f).expect("get length");
+    assert_eq!(length, 1024);
+
+    for seek_offset in [100, 0] {
+        let mut expected_buffer = [0u8; 4];
+
+        // fetch some data at offset seek_offset
+        volume_mgr
+            .file_seek_from_start(f, seek_offset)
+            .expect("Seeking");
+        volume_mgr.read(f, &mut expected_buffer).expect("read file");
+
+        // modify first byte
+        expected_buffer[0] ^= 0xff;
+
+        // write only first byte, expecting the rest to not change
+        volume_mgr
+            .file_seek_from_start(f, seek_offset)
+            .expect("Seeking");
+        volume_mgr
+            .write(f, &expected_buffer[0..1])
+            .expect("file write");
+        volume_mgr.flush_file(f).expect("file flush");
+
+        // read and verify
+        volume_mgr
+            .file_seek_from_start(f, seek_offset)
+            .expect("file seek");
+        let mut read_buffer = [0xffu8, 0xff, 0xff, 0xff];
+        volume_mgr.read(f, &mut read_buffer).expect("file read");
+        assert_eq!(
+            read_buffer, expected_buffer,
+            "mismatch seek+write at offset {seek_offset} from start"
+        );
+    }
+
+    volume_mgr.close_file(f).expect("close file");
+    volume_mgr.close_dir(root_dir).expect("close dir");
+    volume_mgr.close_volume(volume).expect("close volume");
+}
 // ****************************************************************************
 //
 // End Of File