fix: MediaIoBaseDownload range header off-by-one

Issue: It looks like Range header end value was constructed by adding chunk size to
current position. This leads into the request being one byte longer, and also
the received response body is one byte longer than anticipated.

Fix: adjust the end to be one byte earlier.

For example with `chunksize=1024` and current position being 0, the range header
should be set to `bytes=0-1023`.

See: https://httpwg.org/specs/rfc7233.html#rule.ranges-specifier

Resolves: #1593

googleapiclient/http.py

@@ -733,7 +733,7 @@ def next_chunk(self, num_retries=0):
         headers = self._headers.copy()
         headers["range"] = "bytes=%d-%d" % (
             self._progress,
-            self._progress + self._chunksize,
+            self._progress + self._chunksize - 1,
         )
         http = self._request.http
 

tests/test_http.py

@@ -488,6 +488,23 @@ def test_media_io_base_download(self):
         self.assertEqual(5, download._progress)
         self.assertEqual(5, download._total_size)
 
+    def test_media_io_base_download_range_request_header(self):
+        self.request.http = HttpMockSequence(
+            [
+                (
+                    {"status": "200", "content-range": "0-2/5"},
+                    "echo_request_headers_as_json",
+                ),
+            ]
+        )
+
+        download = MediaIoBaseDownload(fd=self.fd, request=self.request, chunksize=3)
+
+        status, done = download.next_chunk()
+        result = json.loads(self.fd.getvalue().decode("utf-8"))
+
+        self.assertEqual(result.get("range"), "bytes=0-2")
+
     def test_media_io_base_download_custom_request_headers(self):
         self.request.http = HttpMockSequence(
             [