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Refactor preview_images to use thread instead of subprocess #2167

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Refactor preview_images to use thread instead of subprocess #2167

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99 changes: 57 additions & 42 deletions pretext/pretext.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2090,7 +2090,7 @@ async def generate_previews(interactives, baseurl, dest_dir):
# First index contains original baseurl of hosted site (not used)
for preview_fragment in interactives:
# loaded page url containing interactive
input_page = os.path.join(baseurl, preview_fragment + ".html")
input_page = baseurl + "/" + preview_fragment + ".html"
# filename of saved preview image
filename = preview_fragment + "-preview.png"

Expand All @@ -2106,13 +2106,59 @@ async def generate_previews(interactives, baseurl, dest_dir):
# wait again, 5 seconds, for more than just splash screens, etc
await page.wait_for_timeout(5000)
# list of locations, need first (and only) one
elt = page.locator(xpath);
elt = page.locator(xpath)
await elt.screenshot(path=filename, scale="css")

# copy
shutil.copy2(filename, dest_dir)
await browser.close()

# Start http server in a thread
def start_server():
'''
Starts a simple http.server on port 8888 if available, or finds a random port. Returns the port and the server object.
'''
try:
import http.server
import socketserver
import threading
import random
except ImportError:
raise ImportError("http.server, socketserver, threading, random")

# Subclass SimpleHTTPRequestHandler to send messages to log.debug:
class MyHandler(http.server.SimpleHTTPRequestHandler):
def log_message(self, format, *args):
log.debug("http.server: " + format % args)
return
# Find a port to use
port = 8888
attempts = 0
max_attempts = 10
while attempts < max_attempts:
try:
log.debug("Trying http.server on port {}".format(port))
server = socketserver.TCPServer(("localhost", port), MyHandler)
thread = threading.Thread(target=server.serve_forever)
thread.start()
log.debug(f"Started http.server on port {port}")
return port, server
except Exception as e:
log.debug("http.server error: port {} in use; (error {})".format(port, e))
port = random.randint(49152, 65535)
attempts += 1
else:
raise OSError("Unable to open http.server for interactive previews")

def stop_server(server):
try:
log.debug("Stopping http.server")
server.shutdown()
log.debug("http.server shutdown successful")
except Exception as e:
log.warning("http.server shutdown failed; perhaps it wasn't running? error: {}".format(e))

# Main content of preview_images function:
log.info(
"using playwright package to create previews for interactives from {} for placement in {}".format(
xml_source, dest_dir
Expand Down Expand Up @@ -2145,54 +2191,23 @@ async def generate_previews(interactives, baseurl, dest_dir):
# place CSS and JS in scratch directory
copy_html_css_js(tmp_dir)

# Spawn a new process running a local html.server
import subprocess
import random
# Try a standard port and if it fails, try a random port
port = 8888
looking_for_port = True
numAttempt = 0
maxAttempts = 10 # In case failure is not due to blocked ports.
while looking_for_port and numAttempt < maxAttempts:
try:
numAttempt = numAttempt + 1
log.info(f"Opening subprocess http.server with port={port}")
# -u so that stdout and stderr are not cached
server = subprocess.Popen([sys.executable, "-u", "-m", "http.server", f"{port}", "-d", tmp_dir], stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
# Check if terminated. Allow 1 second to start-up.
try:
result = server.wait(1)
log.debug(f"Server startup failed")
port = random.randint(49152, 65535)
log.debug(f"Trying port {port} instead")
# The exception is success because process did not terminate.
except subprocess.TimeoutExpired:
looking_for_port = False
except OSError:
# Not sure if this will ever trigger b/c Python itself should start
log.debug(f"Subprocess to open http.server failed")
port = random.randint(49152, 65535)
log.debug(f"Trying port {port} instead.\n")
if numAttempt >= maxAttempts:
log.error("Unable to open http.server for interactive previews")

# filenames lead to placement in current working directory
# so change to temporary directory, and copy out
# TODO: just write to "dest_dir"?
with working_directory(tmp_dir):
# event loop and copy, terminating server process even if interrupted
try:
log.debug("Using http.server subprocess {}".format(server.pid))
log.debug("Starting event loop for playwright, after starting server")
port, server = start_server()
baseurl = "http://localhost:{}".format(port)
asyncio.get_event_loop().run_until_complete(generate_previews(interactives, baseurl, dest_dir))
asyncio.get_event_loop().run_until_complete(
generate_previews(interactives, baseurl, dest_dir)
)
finally:
# close the server and report (debug) results
log.info("Closing http.server subprocess")
server.kill()
log.debug("Log data from http.server:")
server_output = server.stderr.read()
for line in server_output.split("\n"):
log.debug(line)
# close the server
log.info("Closing http.server thread")
if server:
stop_server(server)


############
Expand Down