Simplify sendfile logic

A safe and reliable check for whether a file descriptor supports mmap
is to directly check if it is seekable. However, some seekable file
descriptors may also report a zero size when calling fstat. If there
is no content length specified for the response and it cannot be
determined from the file descriptor then it is not possible to know
what chunk size to send to the client. In this case, is it necessary
to fall back to unwinding the body by iteration.

The above conditions together reveal a straightforward and reliable
way to check for sendfile support. This patch modifies the Response
class to assert these conditions using a try/catch block as part of
a new, simplified sendfile method. This method returns False if it
is not possible to serve the response using sendfile. Otherwise, it
serves the response and returns True. By returning False when SSL is
in use, the code is made even simpler by removing the special support
for SSL, which is served well enough by the iteration protocol.

Fix #1038

gunicorn/http/wsgi.py

@@ -12,7 +12,6 @@
 from gunicorn._compat import unquote_to_wsgi_str
 from gunicorn.six import string_types, binary_type, reraise
 from gunicorn import SERVER_SOFTWARE
-import gunicorn.six as six
 import gunicorn.util as util
 
 try:
@@ -24,6 +23,10 @@
     except ImportError:
         sendfile = None
 
+# Send files in at most 1GB blocks as some operating systems can have problems
+# with sending files in blocks over 2GB.
+BLKSIZE = 0x3FFFFFFF
+
 NORMALIZE_SPACE = re.compile(r'(?:\r\n)?[ \t]+')
 
 log = logging.getLogger(__name__)
@@ -344,77 +347,51 @@ def write(self, arg):
         util.write(self.sock, arg, self.chunked)
 
     def can_sendfile(self):
-        return (self.cfg.sendfile and (sendfile is not None))
-
-    def sendfile_all(self, fileno, sockno, offset, nbytes):
-        # Send file in at most 1GB blocks as some operating
-        # systems can have problems with sending files in blocks
-        # over 2GB.
-
-        BLKSIZE = 0x3FFFFFFF
-
-        if nbytes > BLKSIZE:
-            for m in range(0, nbytes, BLKSIZE):
-                self.sendfile_all(fileno, sockno, offset, min(nbytes, BLKSIZE))
-                offset += BLKSIZE
-                nbytes -= BLKSIZE
-        else:
-            sent = 0
-            sent += sendfile(sockno, fileno, offset + sent, nbytes - sent)
-            while sent != nbytes:
-                sent += sendfile(sockno, fileno, offset + sent, nbytes - sent)
+        return self.cfg.sendfile and sendfile is not None
 
-    def sendfile_use_send(self, fileno, fo_offset, nbytes):
-
-        # send file in blocks of 8182 bytes
-        BLKSIZE = 8192
-
-        sent = 0
-        while sent != nbytes:
-            data = os.read(fileno, BLKSIZE)
-            if not data:
-                break
+    def sendfile(self, respiter):
+        if self.cfg.is_ssl or not self.can_sendfile():
+            return False
 
-            sent += len(data)
-            if sent > nbytes:
-                data = data[:nbytes - sent]
+        try:
+            fileno = respiter.filelike.fileno()
+            offset = os.lseek(fileno, 0, os.SEEK_CUR)
+            if self.response_length is None:
+                filesize = os.fstat(fileno).st_size
 
-            util.write(self.sock, data, self.chunked)
+                # The file may be special and sendfile will fail.
+                # It may also be zero-length, but that is okay.
+                if filesize == 0:
+                    return False
 
-    def write_file(self, respiter):
-        if self.can_sendfile() and util.is_fileobject(respiter.filelike):
-            # sometimes the fileno isn't a callable
-            if six.callable(respiter.filelike.fileno):
-                fileno = respiter.filelike.fileno()
+                nbytes = filesize - offset
             else:
-                fileno = respiter.filelike.fileno
+                nbytes = self.response_length
+        except (OSError, io.UnsupportedOperation):
+            return False
 
-            fd_offset = os.lseek(fileno, 0, os.SEEK_CUR)
-            fo_offset = respiter.filelike.tell()
-            nbytes = max(os.fstat(fileno).st_size - fo_offset, 0)
+        self.send_headers()
 
-            if self.response_length:
-                nbytes = min(nbytes, self.response_length)
+        if self.is_chunked():
+            chunk_size = "%X\r\n" % nbytes
+            self.sock.sendall(chunk_size.encode('utf-8'))
 
-            if nbytes == 0:
-                return
+        sockno = self.sock.fileno()
+        sent = 0
 
-            self.send_headers()
+        for m in range(0, nbytes, BLKSIZE):
+            count = min(nbytes - sent, BLKSIZE)
+            sent += sendfile(sockno, fileno, offset + sent, count)
 
-            if self.cfg.is_ssl:
-                self.sendfile_use_send(fileno, fo_offset, nbytes)
-            else:
-                if self.is_chunked():
-                    chunk_size = "%X\r\n" % nbytes
-                    self.sock.sendall(chunk_size.encode('utf-8'))
+        if self.is_chunked():
+            self.sock.sendall(b"\r\n")
 
-                self.sendfile_all(fileno, self.sock.fileno(), fo_offset, nbytes)
+        os.lseek(fileno, offset, os.SEEK_SET)
 
-                if self.is_chunked():
-                    self.sock.sendall(b"\r\n")
+        return True
 
-            os.lseek(fileno, fd_offset, os.SEEK_SET)
-        else:
+    def write_file(self, respiter):
+        if not self.sendfile(respiter):
             for item in respiter:
                 self.write(item)
 

gunicorn/util.py

@@ -7,7 +7,6 @@
 
 import email.utils
 import fcntl
-import io
 import os
 import pkg_resources
 import random
@@ -517,19 +516,6 @@ def to_latin1(value):
     return value.encode("latin-1")
 
 
-def is_fileobject(obj):
-    if not hasattr(obj, "tell") or not hasattr(obj, "fileno"):
-        return False
-
-    # check BytesIO case and maybe others
-    try:
-        obj.fileno()
-    except (IOError, io.UnsupportedOperation):
-        return False
-
-    return True
-
-
 def warn(msg):
     print("!!!", file=sys.stderr)