test-run-dev: Use a pipe rather than polling a log file.

This avoids unnecessary polling delays, quadratic string operations,
and hardcoded paths in /tmp.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

tools/test-run-dev

@@ -1,10 +1,11 @@
 #!/usr/bin/env python3
 
+import itertools
 import os
 import signal
 import subprocess
 import sys
-import time
+import types
 from typing import Tuple
 
 from lib import sanity_check
@@ -12,36 +13,40 @@ sanity_check.check_venv(__file__)
 
 TOOLS_DIR = os.path.dirname(os.path.abspath(__file__))
 
-def start_server(logfile_name: str) -> Tuple[bool, str]:
-    failure = True
-    key = "Quit the server with CTRL-C."
-    datalog = []
-    with open(logfile_name, 'rb', buffering=0) as logfile:
-        for i in range(200):
-            time.sleep(0.5)
-            print("{}. Polling run-dev...".format(i))
-            new_data = logfile.read().decode()
-            if new_data:
-                datalog.append(new_data)
+def start_server(run_dev: subprocess.Popen) -> Tuple[bool, str]:
+    failure = False
+    i = 0
 
-            if key in ''.join(datalog):
-                failure = False
-                break
+    def on_timer(signum: int, frame: types.FrameType) -> None:
+        nonlocal failure, i
+        print("{}. Polling run-dev...".format(i))
+        i += 1
+        if i == 200:
+            failure = True
+            run_dev.send_signal(signal.SIGINT)
+            signal.setitimer(signal.ITIMER_REAL, 0, 0)
 
-    return failure, ''.join(datalog)
+    key = "Quit the server with CTRL-C.\n"
+    old_handler = signal.signal(signal.SIGALRM, on_timer)
+    signal.setitimer(signal.ITIMER_REAL, 0.5, 0.5)
+    log1, log2 = itertools.tee(run_dev.stdout)
+    if key not in log1:
+        failure = True
+    elif not failure:
+        run_dev.send_signal(signal.SIGINT)
+    signal.setitimer(signal.ITIMER_REAL, 0, 0)
+    signal.signal(signal.SIGALRM, old_handler)
+    return failure, ''.join(log2)
 
 if __name__ == '__main__':
     print("Testing development server start!")
 
-    logfile_name = '/tmp/run-dev-output'
-    with open(logfile_name, 'wb', buffering=0) as logfile:
-        run_dev = subprocess.Popen(
+    with subprocess.Popen(
             [os.path.join(TOOLS_DIR, "run-dev.py")],
-            stdout=logfile, stderr=subprocess.STDOUT)
-        failure, log = start_server(logfile_name)
-
-    run_dev.send_signal(signal.SIGINT)
-    run_dev.wait()
+            bufsize=1,  # line buffered
+            stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
+            universal_newlines=True) as run_dev:
+        failure, log = start_server(run_dev)
 
     if 'Traceback' in log:
         failure = True