Support sparse files

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add non-standard CompressionOptions support ([#584](https://github.com/wcampbell0x2a/backhand/pull/584))
   - Add `CompressionAction::compression_options` to override the default compression options emitted during writing.
   - Add `FilesystemWriter::set_emit_compression_options`
+- Support sparse file extraction ([#624](https://github.com/wcampbell0x2a/backhand/pull/624))
 
 ### `backhand-cli`
 - Add `--no-compression-options` to `add` and `replace` to remove compression options from image after modification.

backhand-test/tests/test.rs

@@ -507,7 +507,6 @@ fn test_socket_fifo() {
 #[test]
 #[cfg(any(feature = "zstd"))]
 fn no_qemu_test_crates_zstd() {
-    tracing::trace!("nice");
     const FILE_NAME: &str = "crates-io.squashfs";
     let asset_defs = [TestAssetDef {
         filename: FILE_NAME.to_string(),
@@ -519,3 +518,17 @@ fn no_qemu_test_crates_zstd() {
 
     full_test(&asset_defs, FILE_NAME, TEST_PATH, 0, Verify::Extract, false);
 }
+
+#[test]
+#[cfg(feature = "xz")]
+fn test_slow_sparse_data_issue_623() {
+    const FILE_NAME: &str = "aosc-os_buildkit_20240916_amd64.squashfs";
+    let asset_defs = [TestAssetDef {
+        filename: FILE_NAME.to_string(),
+        hash: "02b0069d480df7c351b64e640025cb6b84890d8f9e377f15cc24fc70d5617905".to_string(),
+        url: "https://releases.aosc.io/os-amd64/buildkit/aosc-os_buildkit_20240916_amd64.squashfs"
+            .to_string(),
+    }];
+    const TEST_PATH: &str = "test-assets/test_sparse_data_issue_623";
+    full_test(&asset_defs, FILE_NAME, TEST_PATH, 0, Verify::Extract, true);
+}

backhand/src/filesystem/reader.rs

@@ -265,6 +265,11 @@ impl<'a, 'b> SquashfsRawData<'a, 'b> {
         match block {
             BlockFragment::Block(block) => {
                 let block_size = block.size() as usize;
+                // sparse file, don't read from reader, just fill with superblock.block size of 0's
+                if block_size == 0 {
+                    *data = vec![0; self.file.system.block_size as usize];
+                    return Ok(RawDataBlock { fragment: false, uncompressed: true });
+                }
                 data.resize(block_size, 0);
                 //NOTE: storing/restoring the file-pos is not required at the
                 //moment of writing, but in the future, it may.
@@ -346,10 +351,10 @@ impl<'a, 'b> SquashfsRawData<'a, 'b> {
         input_buf: &mut Vec<u8>,
         output_buf: &mut Vec<u8>,
     ) -> Result<(), BackhandError> {
-        //append to the output_buf is not allowed, it need to be empty
+        // append to the output_buf is not allowed, it need to be empty
         assert!(output_buf.is_empty());
-        //input is already decompress, so just swap the input/output, so the
-        //output_buf contains the final data.
+        // input is already decompress, so just swap the input/output, so the
+        // output_buf contains the final data.
         if data.uncompressed {
             std::mem::swap(input_buf, output_buf);
         } else {