hsts: handle unlimited expiry

When setting a blank expire string, meaning unlimited, curl would pass
TIME_T_MAX to getime_r() when creating the output, while on 64 bit
systems such a large value cannot be convetered to a tm struct making
curl to exit the loop with an error instead. It can't be converted
because the year it would represent doesn't fit in the 'int tm_year'
field!

Starting now, unlimited expiry is instead handled differently by using a
human readable expiry date spelled out as "unlimited" instead of trying
to use a distant actual date.

Test 1660 and 1915 have been updated to help verify this change.

Reported-by: Jonathan Cardoso
Fixes #7720
Closes #7721

3 files changed, 22 insertions, 13 deletions

diff --git a/tests/data/test1660 b/tests/data/test1660
index 3ddd8d427..cbbcf7587 100644
--- a/tests/data/test1660
+++ b/tests/data/test1660
@@ -20,6 +20,7 @@ HSTS
 # This file was generated by libcurl! Edit at your own risk.
 .readfrom.example "20211001 04:47:41"
 .old.example "20161001 04:47:41"
+.new.example "unlimited"
 </file>
 
 # This date is exactly "20190124 22:34:21" UTC
@@ -59,7 +60,7 @@ foo.example.com [example.com]: 1569905261 includeSubDomains
 'forexample.net' is not HSTS
 'example.net' is not HSTS
 expire.example [expire.example]: 1548369268
-Number of entries: 3
+Number of entries: 4
 expire.example [expire.example]: 1548369268
 expire.example [expire.example]: 1548369268
 expire.example [expire.example]: 1548369268
@@ -74,6 +75,7 @@ expire.example [expire.example]: 1548369268
 <file name="log/hsts%TESTNUMBER" mode="text">
 # Your HSTS cache. https://curl.se/docs/hsts.html
 # This file was generated by libcurl! Edit at your own risk.
+.new.example "unlimited"
 .example.com "20191001 04:47:41"
 example.org "20200124 22:34:21"
 </file>
diff --git a/tests/data/test1915 b/tests/data/test1915
index 047a16e2e..d0b2862f9 100644
--- a/tests/data/test1915
+++ b/tests/data/test1915
@@ -42,9 +42,9 @@ http://%HOSTIP:%NOLISTENPORT/not-there/%TESTNUMBER
 </errorcode>
 <stdout>
 [0/4] 1.example.com 20370320 01:02:03
-[1/4] 2.example.com 20370320 01:02:03
-[2/4] 3.example.com 20370320 01:02:03
-[3/4] 4.example.com 20370320 01:02:03
+[1/4] 2.example.com 20370320 03:02:01
+[2/4] 3.example.com 20370319 01:02:03
+[3/4] 4.example.com unlimited
 </stdout>
 </verify>
 </testcase>
diff --git a/tests/libtest/lib1915.c b/tests/libtest/lib1915.c
index 7b4d91d3c..2bd6ffce8 100644
--- a/tests/libtest/lib1915.c
+++ b/tests/libtest/lib1915.c
@@ -25,12 +25,18 @@
 #include "warnless.h"
 #include "memdebug.h"
 
-static const char *preload_hosts[] = {
-  "1.example.com",
-  "2.example.com",
-  "3.example.com",
-  "4.example.com",
-  NULL /* end of list marker */
+struct entry {
+  const char *name;
+  const char *exp;
+};
+
+static struct entry preload_hosts[] = {
+  /* curl turns 39 that day just before 31-bit time_t overflow */
+  { "1.example.com", "20370320 01:02:03" },
+  { "2.example.com", "20370320 03:02:01" },
+  { "3.example.com", "20370319 01:02:03" },
+  { "4.example.com", "" },
+  { NULL, NULL } /* end of list marker */
 };
 
 struct state {
@@ -42,15 +48,16 @@ static CURLSTScode hstsread(CURL *easy, struct curl_hstsentry *e,
                             void *userp)
 {
   const char *host;
+  const char *expire;
   struct state *s = (struct state *)userp;
   (void)easy;
-  host = preload_hosts[s->index++];
+  host = preload_hosts[s->index].name;
+  expire = preload_hosts[s->index++].exp;
 
   if(host && (strlen(host) < e->namelen)) {
     strcpy(e->name, host);
     e->includeSubDomains = FALSE;
-    strcpy(e->expire, "20370320 01:02:03"); /* curl turns 39 that day
-                                   just before 31-bit time_t overflow */
+    strcpy(e->expire, expire);
     fprintf(stderr, "add '%s'\n", host);
   }
   else