fix: MediaIoBaseDownload range header off-by-one (#1595)

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

Fixes #1593

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Fixes #1593 🦕

2 files changed, 18 insertions, 1 deletions

diff --git a/googleapiclient/http.py b/googleapiclient/http.py
index 1b661e1b2..927464e9f 100644
--- a/googleapiclient/http.py
+++ b/googleapiclient/http.py
@@ -733,7 +733,7 @@ class MediaIoBaseDownload(object):
         headers = self._headers.copy()
         headers["range"] = "bytes=%d-%d" % (
             self._progress,
-            self._progress + self._chunksize,
+            self._progress + self._chunksize - 1,
         )
         http = self._request.http
 
diff --git a/tests/test_http.py b/tests/test_http.py
index 852cd7e1a..e55e05662 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -488,6 +488,23 @@ class TestMediaIoBaseDownload(unittest.TestCase):
         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(
             [