HTTP/1.0 - ignore Expect: 100-continue

* ignore on HTTP/1.0 (would possibly confuse a client or proxy)
* refuse requests with unknown expectations

https://datatracker.ietf.org/doc/html/rfc9110#section-10.1.1

gunicorn/http/errors.py

@@ -47,6 +47,14 @@ class InvalidRequestMethod(ParseException):
         return "Invalid HTTP method: %r" % self.method
 
 
+class ExpectationFailed(ParseException):
+    def __init__(self, expect):
+        self.expect = expect
+
+    def __str__(self):
+        return "Unable to comply with expectation: %r" % (self.expect, )
+
+
 class InvalidHTTPVersion(ParseException):
     def __init__(self, version):
         self.version = version

gunicorn/http/message.py

@@ -14,6 +14,7 @@ from gunicorn.http.errors import (
     InvalidRequestLine, InvalidRequestMethod, InvalidHTTPVersion,
     LimitRequestLine, LimitRequestHeaders,
     UnsupportedTransferCoding, ObsoleteFolding,
+    ExpectationFailed,
 )
 from gunicorn.http.errors import InvalidProxyLine, InvalidProxyHeader, ForbiddenProxyRequest
 from gunicorn.http.errors import InvalidSchemeHeaders
@@ -90,6 +91,7 @@ class Message:
         self.body = None
         self.scheme = "https" if cfg.is_ssl else "http"
         self.must_close = False
+        self._expected_100_continue = False
 
         # set headers limits
         self.limit_request_fields = cfg.limit_request_fields
@@ -180,6 +182,21 @@ class Message:
             if header_length > self.limit_request_field_size > 0:
                 raise LimitRequestHeaders("limit request headers fields size")
 
+            if not from_trailer and name == "EXPECT":
+                # https://datatracker.ietf.org/doc/html/rfc9110#section-10.1.1
+                # "The Expect field value is case-insensitive."
+                if value.lower() == "100-continue":
+                    if self.version < (1, 1):
+                        # https://datatracker.ietf.org/doc/html/rfc9110#section-10.1.1-12
+                        # "A server that receives a 100-continue expectation
+                        #  in an HTTP/1.0 request MUST ignore that expectation."
+                        pass
+                    else:
+                        self._expected_100_continue = True
+                    # N.B. understood but ignored expect header does not return 417
+                else:
+                    raise ExpectationFailed(value)
+
             if name in secure_scheme_headers:
                 secure = value == secure_scheme_headers[name]
                 scheme = "https" if secure else "http"

gunicorn/http/wsgi.py

@@ -117,13 +117,14 @@ def create(req, sock, client, server, cfg):
     host = None
     script_name = os.environ.get("SCRIPT_NAME", "")
 
+    if req._expected_100_continue:
+        sock.send(b"HTTP/1.1 100 Continue\r\n\r\n")
+        # rfc9112: Expect MUST be forwarded if the request is forwarded
+        # N.B. gunicorn just sends at most one - application might send another
+
     # add the headers to the environ
     for hdr_name, hdr_value in req.headers:
-        if hdr_name == "EXPECT":
+        if hdr_name == 'HOST':
-            # handle expect
-            if hdr_value.lower() == "100-continue":
-                sock.send(b"HTTP/1.1 100 Continue\r\n\r\n")
-        elif hdr_name == 'HOST':
             host = hdr_value
         elif hdr_name == "SCRIPT_NAME":
             script_name = hdr_value

gunicorn/workers/base.py

@@ -19,7 +19,7 @@ from gunicorn.http.errors import (
     InvalidProxyLine, InvalidRequestLine,
     InvalidRequestMethod, InvalidSchemeHeaders,
     LimitRequestHeaders, LimitRequestLine,
-    UnsupportedTransferCoding,
+    UnsupportedTransferCoding, ExpectationFailed,
     ConfigurationProblem, ObsoleteFolding,
 )
 from gunicorn.http.wsgi import Response, default_environ
@@ -212,7 +212,7 @@ class Worker:
             LimitRequestLine, LimitRequestHeaders,
             InvalidProxyLine, ForbiddenProxyRequest,
             InvalidSchemeHeaders, UnsupportedTransferCoding,
-            ConfigurationProblem, ObsoleteFolding,
+            ConfigurationProblem, ObsoleteFolding, ExpectationFailed,
             SSLError,
         )):
 
@@ -239,6 +239,10 @@ class Worker:
                     req = exc.req  # for access log
             elif isinstance(exc, LimitRequestLine):
                 mesg = "%s" % str(exc)
+            elif isinstance(exc, ExpectationFailed):
+                reason = "Expectation Failed"
+                mesg = str(exc)
+                status_int = 417
             elif isinstance(exc, LimitRequestHeaders):
                 reason = "Request Header Fields Too Large"
                 mesg = "Error parsing headers: '%s'" % str(exc)