Add resume for download function

It seems like it fails when it's a bit above 1Gb, try to add a resume so we can continue from the last failing point instead of download all again

Author: cccclai

backends/qualcomm/scripts/download_qnn_sdk.py

@@ -117,45 +117,66 @@ def _atomic_download(url: str, dest: pathlib.Path):
 
 
 def _download_archive(url: str, archive_path: pathlib.Path) -> bool:
-    """Robust streaming download with retries."""
+    """Reliable download with resume + retries."""
 
-    logger.debug("Archive will be saved to: %s", archive_path)
+    logger.info("Downloading with resume support: %s", url)
 
-    session = requests.Session()
-    retries = Retry(
-        total=5,
-        backoff_factor=1.0,
-        status_forcelist=[429, 500, 502, 503, 504],
-        allowed_methods=["GET"],
-    )
-    session.mount("https://", HTTPAdapter(max_retries=retries))
+    CHUNK_SIZE = 1024 * 1024   # 1MB
+    MAX_RETRIES = 5
 
-    try:
-        with session.get(url, stream=True) as r:
-            r.raise_for_status()
+    # Determine existing partial file size
+    downloaded = archive_path.stat().st_size if archive_path.exists() else 0
 
-            downloaded = 0
-            chunk_size = 1024 * 1024  # 1MB
+    # Get total size
+    head = requests.head(url)
+    if "content-length" not in head.headers:
+        logger.error("Server did not return content-length header!")
+        return False
+    total = int(head.headers["content-length"])
 
-            with open(archive_path, "wb") as f:
-                for chunk in r.iter_content(chunk_size):
-                    if chunk:
-                        f.write(chunk)
-                        downloaded += len(chunk)
+    if downloaded == total:
+        logger.info("File already fully downloaded.")
+        return True
 
-        logger.info("Download completed!")
+    logger.info("Resuming from %d / %d bytes", downloaded, total)
 
-    except Exception as e:
-        logger.exception("Error during download: %s", e)
-        return False
+    # Open file in append mode
+    with open(archive_path, "ab") as f:
 
-    if archive_path.exists() and archive_path.stat().st_size == 0:
-        logger.warning("Downloaded file is empty!")
-        return False
-    elif not archive_path.exists():
-        logger.error("File was not downloaded!")
+        while downloaded < total:
+            headers = {"Range": f"bytes={downloaded}-"}
+
+            try:
+                with requests.get(url, headers=headers, stream=True) as r:
+                    r.raise_for_status()
+
+                    for chunk in r.iter_content(CHUNK_SIZE):
+                        if chunk:
+                            f.write(chunk)
+                            downloaded += len(chunk)
+
+            except (requests.exceptions.ChunkedEncodingError,
+                    requests.exceptions.ConnectionError,
+                    requests.exceptions.ReadTimeout,
+                    urllib3.exceptions.IncompleteRead) as e:
+
+                logger.warning(
+                    "Connection drop during download at %d / %d bytes. Retrying... (%s)",
+                    downloaded, total, e,
+                )
+                time.sleep(1)
+                continue  # retry with updated downloaded value
+
+            # End of successful pass
+            break
+
+    # Validate final size
+    actual = archive_path.stat().st_size
+    if actual != total:
+        logger.error("Download incomplete: expected %d, got %d", total, actual)
         return False
 
+    logger.info("Download completed successfully.")
     return True