http: allow overriding timecond with custom header

With CURLOPT_TIMECONDITION set, a header is automatically added (e.g.
If-Modified-Since).  Allow this to be replaced or suppressed with
CURLOPT_HTTPHEADER.

Fixes #4103
Closes #4109

lib/http.c

@@ -1881,9 +1881,10 @@ CURLcode Curl_add_custom_headers(struct connectdata *conn,
 }
 
 #ifndef CURL_DISABLE_PARSEDATE
-CURLcode Curl_add_timecondition(struct Curl_easy *data,
+CURLcode Curl_add_timecondition(const struct connectdata *conn,
                                 Curl_send_buffer *req_buffer)
 {
+  struct Curl_easy *data = conn->data;
   const struct tm *tm;
   struct tm keeptime;
   CURLcode result;
@@ -1916,6 +1917,11 @@ CURLcode Curl_add_timecondition(struct Curl_easy *data,
     break;
   }
 
+  if(Curl_checkheaders(conn, condp)) {
+    /* A custom header was specified; it will be sent instead. */
+    return CURLE_OK;
+  }
+
   /* The If-Modified-Since header family should have their times set in
    * GMT as RFC2616 defines: "All HTTP date/time stamps MUST be
    * represented in Greenwich Mean Time (GMT), without exception. For the
@@ -1941,10 +1947,10 @@ CURLcode Curl_add_timecondition(struct Curl_easy *data,
 }
 #else
 /* disabled */
-CURLcode Curl_add_timecondition(struct Curl_easy *data,
+CURLcode Curl_add_timecondition(const struct connectdata *conn,
                                 Curl_send_buffer *req_buffer)
 {
-  (void)data;
+  (void)conn;
   (void)req_buffer;
   return CURLE_OK;
 }
@@ -2683,7 +2689,7 @@ CURLcode Curl_http(struct connectdata *conn, bool *done)
   }
 #endif
 
-  result = Curl_add_timecondition(data, req_buffer);
+  result = Curl_add_timecondition(conn, req_buffer);
   if(result)
     return result;
 

lib/http.h

@@ -69,7 +69,7 @@ CURLcode Curl_add_buffer_send(Curl_send_buffer **inp,
                               size_t included_body_bytes,
                               int socketindex);
 
-CURLcode Curl_add_timecondition(struct Curl_easy *data,
+CURLcode Curl_add_timecondition(const struct connectdata *conn,
                                 Curl_send_buffer *buf);
 CURLcode Curl_add_custom_headers(struct connectdata *conn,
                                  bool is_connect,

lib/rtsp.c

@@ -491,7 +491,7 @@ static CURLcode rtsp_do(struct connectdata *conn, bool *done)
     return result;
 
   if((rtspreq == RTSPREQ_SETUP) || (rtspreq == RTSPREQ_DESCRIBE)) {
-    result = Curl_add_timecondition(data, req_buffer);
+    result = Curl_add_timecondition(conn, req_buffer);
     if(result)
       return result;
   }

tests/data/Makefile.inc

@@ -177,7 +177,7 @@ test1540 test1541 \
 test1550 test1551 test1552 test1553 test1554 test1555 test1556 test1557 \
 test1558 test1559 test1560 test1561 test1562 \
 \
-test1590 test1591 test1592 \
+test1590 test1591 test1592 test1593 \
 \
 test1600 test1601 test1602 test1603 test1604 test1605 test1606 test1607 \
 test1608 test1609 test1620 test1621 \

tests/data/test1593

@@ -0,0 +1,49 @@
+<testcase>
+<info>
+<keywords>
+HTTP
+HTTP GET
+HTTP replaced headers
+CURLOPT_TIMECONDITION
+If-Modified-Since
+</keywords>
+</info>
+
+# Server-side
+<reply>
+<data nocheck="yes">
+HTTP/1.1 304 Not Modified
+Date: Thu, 11 Jul 2019 02:26:59 GMT
+Server: test-server/swsclose
+
+</data>
+</reply>
+# Client-side
+<client>
+<server>
+http
+</server>
+<name>
+HTTP custom header overrides CURLOPT_TIMECONDITION
+</name>
+<tool>
+lib1593
+</tool>
+<command>
+http://%HOSTIP:%HTTPPORT/1593
+</command>
+</client>
+
+<verify>
+<strip>
+^User-Agent:.*
+</strip>
+# Note here the lack of If-Modified-Since
+<protocol>
+GET /1593 HTTP/1.1
+Host: %HOSTIP:%HTTPPORT
+Accept: */*
+
+</protocol>
+</verify>
+</testcase>

tests/libtest/Makefile.inc

@@ -32,7 +32,7 @@ noinst_PROGRAMS = chkhostname libauthretry libntlmconnect                \
  lib1540 lib1541 \
  lib1550 lib1551 lib1552 lib1553 lib1554 lib1555 lib1556 lib1557 \
  lib1558 lib1559 lib1560 \
- lib1591 lib1592 \
+ lib1591 lib1592 lib1593 \
  lib1900 lib1905 lib1906 \
  lib2033
 
@@ -541,6 +541,9 @@ lib1592_SOURCES = lib1592.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
 lib1592_LDADD = $(TESTUTIL_LIBS)
 lib1592_CPPFLAGS = $(AM_CPPFLAGS) -DLIB1592
 
+lib1593_SOURCES = lib1593.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
+lib1593_LDADD = $(TESTUTIL_LIBS)
+
 lib1900_SOURCES = lib1900.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
 lib1900_LDADD = $(TESTUTIL_LIBS)
 lib1900_CPPFLAGS = $(AM_CPPFLAGS)

tests/libtest/lib1593.c

@@ -0,0 +1,79 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2019, 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.
+ *
+ ***************************************************************************/
+
+/* Test suppressing the If-Modified-Since header */
+
+#include "test.h"
+
+#include "memdebug.h"
+
+int test(char *URL)
+{
+  struct curl_slist *header = NULL;
+  long unmet;
+  CURL *curl = NULL;
+  int res = 0;
+
+  global_init(CURL_GLOBAL_ALL);
+
+  easy_init(curl);
+
+  easy_setopt(curl, CURLOPT_URL, URL);
+  easy_setopt(curl, CURLOPT_TIMECONDITION, (long)CURL_TIMECOND_IFMODSINCE);
+  /* Some TIMEVALUE; it doesn't matter. */
+  easy_setopt(curl, CURLOPT_TIMEVALUE, 1566210680L);
+
+  header = curl_slist_append(NULL, "If-Modified-Since:");
+  if(!header) {
+    res = TEST_ERR_MAJOR_BAD;
+    goto test_cleanup;
+  }
+
+  easy_setopt(curl, CURLOPT_HTTPHEADER, header);
+
+  res = curl_easy_perform(curl);
+  if(res)
+    goto test_cleanup;
+
+  /* Confirm that the condition checking still worked, even though we
+   * suppressed the actual header.
+   * The server returns 304, which means the condition is "unmet".
+   */
+
+  res = curl_easy_getinfo(curl, CURLINFO_CONDITION_UNMET, &unmet);
+  if(res)
+    goto test_cleanup;
+
+  if(unmet != 1L) {
+    res = TEST_ERR_FAILURE;
+    goto test_cleanup;
+  }
+
+test_cleanup:
+
+  /* always cleanup */
+  curl_easy_cleanup(curl);
+  curl_slist_free_all(header);
+  curl_global_cleanup();
+
+  return res;
+}