Added bpkg_manager package that can download packages in a subprocess

Also contains a SubprocMixin mix-in class that can help to write
operators that run & monitor subprocesses.

Messages sent back & forth between Blender and the subprocess MUST subclass
either BlenderMessage or SubprocMessage.

bpkg_manager/subproc.py

@@ -0,0 +1,134 @@
+"""
+All the stuff that needs to run in a subprocess.
+"""
+
+import logging
+import pathlib
+
+
+class Message:
+    """Superclass for all message sent over pipes."""
+
+
+class BlenderMessage(Message):
+    """Superclass for all messages sent from Blender to the subprocess."""
+
+
+class SubprocMessage(Message):
+    """Superclass for all messages sent from the subprocess to Blender."""
+
+
+class Abort(BlenderMessage):
+    """Sent when the user requests abortion of a task."""
+
+
+class Progress(SubprocMessage):
+    """Send from subprocess to Blender to report progress.
+
+    :ivar progress: the progress percentage, from 0-1.
+    """
+
+    def __init__(self, progress: float):
+        self.progress = progress
+
+
+class DownloadError(SubprocMessage):
+    """Sent when there was an error downloading something."""
+
+    def __init__(self, status_code: int, description: str):
+        self.status_code = status_code
+        self.description = description
+
+
+class Success(SubprocMessage):
+    """Sent when an operation finished sucessfully."""
+
+
+class Aborted(SubprocMessage):
+    """Sent as response to Abort message."""
+
+
+def _download(pipe_to_blender, package_url: str, download_dir: pathlib.Path) -> pathlib.Path:
+    """Downloads the given package
+
+    :returns: path to the downloaded file, or None in case of error.
+    """
+
+    import requests
+
+    log = logging.getLogger('%s.download' % __name__)
+    log.info('Going to download %s to %s', package_url, download_dir)
+    pipe_to_blender.send(Progress(0.0))
+
+    log.info('Downloading %s', package_url)
+    resp = requests.get(package_url, stream=True, verify=True)
+
+    try:
+        resp.raise_for_status()
+    except requests.HTTPError as ex:
+        log.error('Error downloading %s: %s', package_url, ex)
+        pipe_to_blender.send(DownloadError(resp.status_code, str(ex)))
+        return None
+
+    try:
+        # Use float so that we can also use infinity
+        content_length = float(resp.headers['content-length'])
+    except KeyError:
+        log.warning('Server did not send content length, cannot report progress.')
+        content_length = float('inf')
+
+    # TODO: get filename from Content-Disposition header, if available.
+    # TODO: use urllib.parse to parse the URL.
+    local_filename = package_url.split('/')[-1] or 'download.tmp'
+    local_fpath = download_dir / local_filename
+
+    downloaded_length = 0
+    with local_fpath.open('wb') as outfile:
+        for chunk in resp.iter_content(chunk_size=1024 ** 2):
+            # Handle abort messages from Blender
+            while pipe_to_blender.poll():
+                recvd = pipe_to_blender.recv()
+                if isinstance(recvd, Abort):
+                    log.warning('Aborting download of %s by request', package_url)
+                    pipe_to_blender.send(Aborted())
+                    return None
+                log.warning('Unknown message %s received, ignoring', recvd)
+
+            if not chunk:  # filter out keep-alive new chunks
+                continue
+
+            outfile.write(chunk)
+
+            downloaded_length += len(chunk)
+
+            # TODO: use multiplier for progress, so that we can count up to 70% and
+            # leave 30% "progress" for installation of the package.
+            pipe_to_blender.send(Progress(downloaded_length / content_length))
+
+    pipe_to_blender.send(Success())
+    return local_fpath
+
+
+def download_and_install(pipe_to_blender, package_url: str):
+    """Downloads and installs the given package."""
+
+    from . import cache
+
+    log = logging.getLogger('%s.download_and_install' % __name__)
+
+    cache_dir = cache.cache_directory('downloads')
+    downloaded = _download(pipe_to_blender, package_url, cache_dir)
+
+    if not downloaded:
+        log.debug('Download failed/aborted, not going to install anything.')
+        return
+
+    # TODO: actually install the package
+    log.warning('Installing is not actually implemented, install %s yourself.', downloaded)
+
+
+def debug_hang():
+    """Hangs for an hour. For testing purposes only."""
+
+    import time
+    time.sleep(3600)