http: added options for allowing HTTP/0.9 responses

Added CURLOPT_HTTP09_ALLOWED and --http0.9 for this purpose.

For now, both the tool and library allow HTTP/0.9 by default.
docs/DEPRECATE.md lays out the plan for when to reverse that default: 6
months after the 7.64.0 release. The options are added already now so
that applications/scripts can start using them already now.

Fixes #2873
Closes #3383

5 files changed, 65 insertions, 2 deletions

diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index 1bec4c14d..6d63912d7 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -319,6 +319,8 @@ Do an HTTP GET request. See \fICURLOPT_HTTPGET(3)\fP
 Set the request target. \fICURLOPT_REQUEST_TARGET(3)\fP
 .IP CURLOPT_HTTP_VERSION
 HTTP version to use. \fICURLOPT_HTTP_VERSION(3)\fP
+.IP CURLOPT_HTTP09_ALLOWED
+Allow HTTP/0.9 responses. \fICURLOPT_HTTP09_ALLOWED(3)\fP
 .IP CURLOPT_IGNORE_CONTENT_LENGTH
 Ignore Content-Length. See \fICURLOPT_IGNORE_CONTENT_LENGTH(3)\fP
 .IP CURLOPT_HTTP_CONTENT_DECODING
diff --git a/docs/libcurl/opts/CURLOPT_HTTP09_ALLOWED.3 b/docs/libcurl/opts/CURLOPT_HTTP09_ALLOWED.3
new file mode 100644
index 000000000..3fa44993a
--- /dev/null
+++ b/docs/libcurl/opts/CURLOPT_HTTP09_ALLOWED.3
@@ -0,0 +1,58 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_HTTP09_ALLOWED 3 "17 Dec 2018" "libcurl 7.64.0" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_HTTP09 \- allow HTTP/0.9 response
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP09_ALLOWED, long allowed);
+.SH DESCRIPTION
+Pass the long argument \fIallowed\fP set to 1L to allow HTTP/0.9 responses.
+
+A HTTP/0.9 response is a server response entirely without headers and only a
+body, while you can connect to lots of random TCP services and still get a
+response that curl might consider to be HTTP/0.9.
+.SH DEFAULT
+curl allows HTTP/0.9 responses by default.
+
+A future curl version will require this option to be set to allow HTTP/0.9
+responses.
+.SH PROTOCOLS
+HTTP
+.SH EXAMPLE
+.nf
+CURL *curl = curl_easy_init();
+if(curl) {
+  CURLcode ret;
+  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
+  curl_easy_setopt(curl, CURLOPT_HTTP09_ALLOWED, 1L);
+  ret = curl_easy_perform(curl);
+}
+.fi
+.SH AVAILABILITY
+Option added in 7.64.0, present along with HTTP.
+.SH RETURN VALUE
+Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
+.SH "SEE ALSO"
+.BR CURLOPT_SSLVERSION "(3), " CURLOPT_HTTP_VERSION "(3), "
diff --git a/docs/libcurl/opts/CURLOPT_HTTP_VERSION.3 b/docs/libcurl/opts/CURLOPT_HTTP_VERSION.3
index 060db7578..7b7a08144 100644
--- a/docs/libcurl/opts/CURLOPT_HTTP_VERSION.3
+++ b/docs/libcurl/opts/CURLOPT_HTTP_VERSION.3
@@ -84,3 +84,4 @@ Along with HTTP
 Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
 .SH "SEE ALSO"
 .BR CURLOPT_SSLVERSION "(3), " CURLOPT_HTTP200ALIASES "(3), "
+.BR CURLOPT_HTTP09_ALLOWED "(3), "
diff --git a/docs/libcurl/opts/Makefile.inc b/docs/libcurl/opts/Makefile.inc
index 9bfd555f1..b21f32356 100644
--- a/docs/libcurl/opts/Makefile.inc
+++ b/docs/libcurl/opts/Makefile.inc
@@ -154,6 +154,7 @@ man_MANS =                                      \
   CURLOPT_HEADERDATA.3                          \
   CURLOPT_HEADERFUNCTION.3                      \
   CURLOPT_HEADEROPT.3                           \
+  CURLOPT_HTTP09_ALLOWED.3                      \
   CURLOPT_HTTP200ALIASES.3                      \
   CURLOPT_HTTPAUTH.3                            \
   CURLOPT_HTTPGET.3                             \
@@ -163,9 +164,9 @@ man_MANS =                                      \
   CURLOPT_HTTP_CONTENT_DECODING.3               \
   CURLOPT_HTTP_TRANSFER_DECODING.3              \
   CURLOPT_HTTP_VERSION.3                        \
-  CURLOPT_TRAILERFUNCTION.3                     \
-  CURLOPT_TRAILERDATA.3                         \
   CURLOPT_IGNORE_CONTENT_LENGTH.3               \
+  CURLOPT_TRAILERDATA.3                         \
+  CURLOPT_TRAILERFUNCTION.3                     \
   CURLOPT_INFILESIZE.3                          \
   CURLOPT_INFILESIZE_LARGE.3                    \
   CURLOPT_INTERFACE.3                           \
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index 8659346ce..f25009c2c 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -421,6 +421,7 @@ CURLOPT_HEADER                  7.1
 CURLOPT_HEADERDATA              7.10
 CURLOPT_HEADERFUNCTION          7.7.2
 CURLOPT_HEADEROPT               7.37.0
+CURLOPT_HTTP09_ALLOWED          7.64.0
 CURLOPT_HTTP200ALIASES          7.10.3
 CURLOPT_HTTPAUTH                7.10.6
 CURLOPT_HTTPGET                 7.8.1