Raise an exception when attempting to decompressing empty data

CHANGELOG.md

@@ -5,6 +5,7 @@ All notable changes to this project will be documented in this file.
 ## Unreleased
 
 - Upgrade zstd source code from v1.5.6 to [v1.5.7](https://github.com/facebook/zstd/releases/tag/v1.5.7)
+- Raise an exception when attempting to decompress empty data
 - Build wheels for Windows ARM64
 - Support for PyPy 3.11
 

src/bin_ext/decompressor.c

@@ -825,7 +825,7 @@ decompress(PyObject *module, PyObject *args, PyObject *kwargs)
 
     /* Check data integrity. at_frame_edge flag is 1 when both the input and
        output streams are at a frame edge. */
-    if (self.at_frame_edge == 0) {
+    if (self.at_frame_edge == 0 || in.pos == 0) {
         char *extra_msg = (Py_SIZE(ret) == 0) ? "." :
                           ", if want to output these decompressed data, use "
                           "decompress_stream function or "

src/bin_ext/file.c

@@ -19,6 +19,7 @@ typedef struct {
     /* File states. On Linux/macOS/Windows, Py_off_t is signed, so
        ZstdFile/SeekableZstdFile use int64_t as file position/size. */
     PyObject *fp;   /* File object */
+    int sof;        /* At SOF, 0 or 1. */
     int eof;        /* At EOF, 0 or 1. */
     int64_t pos;    /* Decompressed position, >= 0. */
     int64_t size;   /* File size, -1 means unknown. */
@@ -109,6 +110,7 @@ ZstdFileReader_init(ZstdFileReader *self, PyObject *args, PyObject *kwargs)
     assert(self->dict == NULL);
     assert(self->read_size == NULL);
     assert(self->fp == NULL);
+    assert(self->sof == 0);
     assert(self->eof == 0);
     assert(self->pos == 0);
     assert(self->size == 0);
@@ -139,6 +141,7 @@ ZstdFileReader_init(ZstdFileReader *self, PyObject *args, PyObject *kwargs)
     /* File states */
     Py_INCREF(fp);
     self->fp = fp;
+    self->sof = 1;
     self->size = -1;
 
     /* Decompression states */
@@ -239,7 +242,7 @@ decompress_into(ZstdFileReader *self,
 
             /* EOF */
             if (read_len == 0) {
-                if (self->at_frame_edge) {
+                if (self->at_frame_edge && !self->sof) {
                     self->eof = 1;
                     self->pos += out->pos - orig_pos;
                     self->size = self->pos;
@@ -254,6 +257,7 @@ decompress_into(ZstdFileReader *self,
             self->in.src = read_buf;
             self->in.size = read_len;
             self->in.pos = 0;
+            self->sof = 0;
         }
 
         /* Decompress */
@@ -423,6 +427,7 @@ ZstdFileReader_reset_session(ZstdFileReader *self)
 {
     /* Reset decompression states */
     self->needs_input = 1;
+    self->sof = 1;
     self->at_frame_edge = 1;
     self->in.size = 0;
     self->in.pos = 0;

src/cffi/decompressor.py

@@ -401,7 +401,7 @@ def decompress(data, zstd_dict=None, option=None):
 
     # Check data integrity. at_frame_edge flag is True when the both the input
     # and output streams are at a frame edge.
-    if not decomp._at_frame_edge:
+    if not decomp._at_frame_edge or not in_buf.pos:
         extra_msg = "." if (len(ret) == 0) \
                         else (", if want to output these decompressed data, use "
                               "decompress_stream function or "

src/cffi/file.py

@@ -15,6 +15,7 @@ def __init__(self, fp, zstd_dict, option, read_size):
 
         # File states, the last three are public attributes.
         self._fp = fp
+        self._sof = True  # start of file
         self.eof = False
         self.pos = 0     # Decompressed position
         self.size = -1   # File size, -1 means unknown.
@@ -68,7 +69,7 @@ def _decompress_into(self, out_b, fill_full):
                 self._in_dat = self._fp.read(self._read_size)
                 # EOF
                 if not self._in_dat:
-                    if self._at_frame_edge:
+                    if self._at_frame_edge and not self._sof:
                         self.eof = True
                         self.pos += out_b.pos - orig_pos
                         self.size = self.pos
@@ -79,6 +80,7 @@ def _decompress_into(self, out_b, fill_full):
                 in_b.src = ffi.from_buffer(self._in_dat)
                 in_b.size = _nbytes(self._in_dat)
                 in_b.pos = 0
+                self._sof = False
 
             # Decompress
             zstd_ret = m.ZSTD_decompressStream(self._dctx, out_b, in_b)
@@ -171,6 +173,7 @@ def forward(self, offset):
     def reset_session(self):
         # Reset decompression states
         self._needs_input = True
+        self._sof = True
         self._at_frame_edge = True
         self._in_buf.size = 0
         self._in_buf.pos = 0

tests/test_seekable.py

@@ -845,7 +845,8 @@ def test_load(self):
         # empty
         b = BytesIO()
         with SeekableZstdFile(b, 'r') as f:
-            self.assertEqual(f.read(10), b'')
+            with self.assertRaises(EOFError):
+                f.read(10)
 
         # not a seekable format
         b = BytesIO(COMPRESSED*10)
@@ -882,15 +883,8 @@ def test_read(self):
 
     def test_read_empty(self):
         with SeekableZstdFile(BytesIO(b''), 'r') as f:
-            self.assertEqual(f.read(), b'')
-            self.assertEqual(f.tell(), 0)
-
-            self.assertEqual(f.seek(2), 0)
-            self.assertEqual(f.read(), b'')
-            self.assertEqual(f.tell(), 0)
-
-            self.assertEqual(f.seek(-2), 0)
-            self.assertEqual(f.read(), b'')
+            with self.assertRaises(EOFError):
+                f.read()
             self.assertEqual(f.tell(), 0)
 
     def test_seek(self):

tests/test_zstd.py

@@ -1229,7 +1229,8 @@ def test_compress_empty(self):
         bo.close()
 
     def test_decompress_empty(self):
-        self.assertEqual(decompress(b''), b'')
+        with self.assertRaises(ZstdError):
+            decompress(b'')
 
         d = ZstdDecompressor()
         self.assertEqual(d.decompress(b''), b'')
@@ -1325,7 +1326,8 @@ def setUpClass(cls):
         cls.TRAIL = b'12345678abcdefg!@#$%^&*()_+|'
 
     def test_function_decompress(self):
-        self.assertEqual(decompress(b''), b'')
+        with self.assertRaises(ZstdError):
+            decompress(b'')
 
         self.assertEqual(len(decompress(COMPRESSED_100_PLUS_32KB)), 100+32*1024)
 
@@ -2234,8 +2236,8 @@ def test_empty_input(self):
         dat1 = b''
 
         # decompress() function
-        dat2 = decompress(dat1)
-        self.assertEqual(len(dat2), 0)
+        with self.assertRaises(ZstdError):
+            decompress(dat1)
 
         # ZstdDecompressor class
         d = ZstdDecompressor()
@@ -2880,10 +2882,12 @@ def test_read_0(self):
         # empty file
         with ZstdFile(BytesIO(b'')) as f:
             self.assertEqual(f.read(0), b"")
-            self.assertEqual(f.read(10), b"")
+            with self.assertRaises(EOFError):
+                f.read(10)
 
         with ZstdFile(BytesIO(b'')) as f:
-            self.assertEqual(f.read(10), b"")
+            with self.assertRaises(EOFError):
+                f.read(10)
 
     def test_read_10(self):
         with ZstdFile(BytesIO(COMPRESSED_100_PLUS_32KB)) as f:
@@ -3517,8 +3521,9 @@ def test_binary_modes(self):
     def test_text_modes(self):
         # empty input
         with open(BytesIO(b''), "rt", encoding="utf-8", newline='\n') as reader:
-            for _ in reader:
-                pass
+            with self.assertRaises(EOFError):
+                for _ in reader:
+                    pass
 
         # read
         uncompressed = THIS_FILE_STR.replace(os.linesep, "\n")