Implement seek based on io.BytesIO

Author: allanlei

zipstream/__init__.py

@@ -19,7 +19,8 @@
     str, bytes,
     ZIP64_VERSION,
     ZIP_BZIP2, BZIP2_VERSION,
-    ZIP_LZMA, LZMA_VERSION)
+    ZIP_LZMA, LZMA_VERSION,
+    SEEK_SET, SEEK_CUR, SEEK_END)
 
 from zipfile import (
     ZIP_STORED, ZIP64_LIMIT, ZIP_FILECOUNT_LIMIT, ZIP_MAX_COMMENT,
@@ -71,7 +72,15 @@ def next(self):
         raise NotImplementedError()
 
     def seek(self, offset, whence=None):
-        raise NotImplementedError()
+        if whence == SEEK_SET:
+            if offset < 0:
+                raise ValueError('negative seek value -1')
+            self.data_pointer = offset
+        elif whence == SEEK_CUR:
+            self.data_pointer = max(0, self.data_pointer + offset)
+        elif whence == SEEK_END:
+            self.data_pointer = max(0, offset)
+        return self.data_pointer
 
     def tell(self):
         return self.data_pointer

zipstream/compat.py

@@ -65,4 +65,10 @@
 try:
     from zipfile import ZIP_MAX_COMMENT
 except ImportError:
-    ZIP_MAX_COMMENT = (1 << 16) - 1
+    ZIP_MAX_COMMENT = (1 << 16) - 1
+
+
+# Copy from io
+SEEK_SET = 0  # start of the stream (the default); offset should be zero or positive
+SEEK_CUR = 1  # current stream position; offset may be negative
+SEEK_END = 2  # end of the stream; offset is usually negative