Avoid copies in old gnu sparse map parsing
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 561163d..6c54d3b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,7 @@
## 0.4.0
- Support generating tar files with GNU-style long link names
- - Add `format` parameter to `tarWritingSink` and `tarTransformerWith`
+ - Add `format` parameter to `tarWritingSink` and `tarWriterWith`
## 0.3.3
diff --git a/lib/src/reader.dart b/lib/src/reader.dart
index 713235a..d46a28d 100644
--- a/lib/src/reader.dart
+++ b/lib/src/reader.dart
@@ -639,54 +639,47 @@
throw TarException.header('Tried to read sparse map of non-GNU header');
}
+ // Read the real size of the file when sparse holes are expanded.
header.size = rawHeader.readNumeric(483, 12);
- final sparseMaps = <Uint8List>[];
+ final sparseEntries = <SparseEntry>[];
- var sparse = rawHeader.sublistView(386, 483);
- sparseMaps.add(sparse);
+ bool readEntry(Uint8List source, int offset) {
+ // If a sparse header starts with a null byte, it marks the end of the
+ // sparse structures.
+ if (rawHeader[offset] == 0) return false;
- while (true) {
- final maxEntries = sparse.length ~/ 24;
- if (sparse[24 * maxEntries] > 0) {
- // If there are more entries, read an extension header and parse its
- // entries.
- sparse = await _chunkedStream.readBytes(blockSize);
- sparseMaps.add(sparse);
- continue;
+ final fileOffset = source.readNumeric(offset, 12);
+ final length = source.readNumeric(offset + 12, 12);
+
+ sparseEntries.add(SparseEntry(fileOffset, length));
+ return true;
+ }
+
+ // The first four sparse headers are stored in the tar header itself
+ for (var i = 0; i < 4; i++) {
+ final offset = 386 + 24 * i;
+ if (!readEntry(rawHeader, offset)) break;
+ }
+
+ var isExtended = rawHeader[482] != 0;
+
+ while (isExtended) {
+ // Ok, we have a new block of sparse headers to process
+ final block = await _chunkedStream.readBytes(blockSize);
+ if (block.length < blockSize) {
+ throw TarException.header('Unexpected EoF while reading sparse maps');
}
- break;
- }
-
- try {
- return _processOldGNUSparseMap(sparseMaps);
- } on FormatException {
- throw TarException('Invalid old GNU Sparse Map');
- }
- }
-
- /// Process [sparseMaps], which is known to be an OLD GNU v0.1 sparse map.
- ///
- /// For details, see https://www.gnu.org/software/tar/manual/html_section/tar_94.html#SEC191
- List<SparseEntry> _processOldGNUSparseMap(List<Uint8List> sparseMaps) {
- final sparseData = <SparseEntry>[];
-
- for (final sparseMap in sparseMaps) {
- final maxEntries = sparseMap.length ~/ 24;
- for (var i = 0; i < maxEntries; i++) {
- // This termination condition is identical to GNU and BSD tar.
- if (sparseMap[i * 24] == 0) {
- // Don't return, need to process extended headers (even if empty)
- break;
- }
-
- final offset = sparseMap.readNumeric(i * 24, 12);
- final length = sparseMap.readNumeric(i * 24 + 12, 12);
-
- sparseData.add(SparseEntry(offset, length));
+ // A full block of sparse data contains up to 21 entries
+ for (var i = 0; i < 21; i++) {
+ if (!readEntry(block, i * 24)) break;
}
+
+ // The last bytes indicates whether another sparse header block follows.
+ isExtended = block[504] != 0;
}
- return sparseData;
+
+ return sparseEntries;
}
}
