Issue #20331: Fixed possible FD leaks in various modules:

http.server, imghdr, mailcap, mimetypes, xml.etree.

Lib/http/server.py

@@ -670,7 +670,9 @@ class SimpleHTTPRequestHandler(BaseHTTPRequestHandler):
         """Serve a GET request."""
         f = self.send_head()
         if f:
+            try:
                 self.copyfile(f, self.wfile)
+            finally:
                 f.close()
 
     def do_HEAD(self):
@@ -712,6 +714,7 @@ class SimpleHTTPRequestHandler(BaseHTTPRequestHandler):
         except IOError:
             self.send_error(404, "File not found")
             return None
+        try:
             self.send_response(200)
             self.send_header("Content-type", ctype)
             fs = os.fstat(f.fileno())
@@ -719,6 +722,9 @@ class SimpleHTTPRequestHandler(BaseHTTPRequestHandler):
             self.send_header("Last-Modified", self.date_time_string(fs.st_mtime))
             self.end_headers()
             return f
+        except:
+            f.close()
+            raise
 
     def list_directory(self, path):
         """Helper to produce a directory listing (absent index.html).

Lib/imghdr.py

@@ -7,6 +7,8 @@ __all__ = ["what"]
 #-------------------------#
 
 def what(file, h=None):
+    f = None
+    try:
         if h is None:
             if isinstance(file, str):
                 f = open(file, 'rb')
@@ -15,10 +17,6 @@ def what(file, h=None):
                 location = file.tell()
                 h = file.read(32)
                 file.seek(location)
-            f = None
-    else:
-        f = None
-    try:
         for tf in tests:
             res = tf(h, f)
             if res:

Lib/mailcap.py

@@ -22,8 +22,8 @@ def getcaps():
             fp = open(mailcap, 'r')
         except IOError:
             continue
+        with fp:
             morecaps = readmailcapfile(fp)
-        fp.close()
         for key, value in morecaps.items():
             if not key in caps:
                 caps[key] = value

Lib/mimetypes.py

@@ -363,6 +363,7 @@ def read_mime_types(file):
         f = open(file)
     except IOError:
         return None
+    with f:
         db = MimeTypes()
         db.readfp(f, True)
         return db.types_map[True]

Lib/xml/etree/ElementInclude.py

@@ -76,14 +76,13 @@ class FatalIncludeError(SyntaxError):
 
 def default_loader(href, parse, encoding=None):
     if parse == "xml":
-        file = open(href, 'rb')
+        with open(href, 'rb') as file:
             data = ElementTree.parse(file).getroot()
     else:
         if not encoding:
             encoding = 'UTF-8'
-        file = open(href, 'r', encoding=encoding)
+        with open(href, 'r', encoding=encoding) as file:
             data = file.read()
-    file.close()
     return data
 
 ##