Run the oversized-$HOME case only where HOME survives the shell

MSYS rewrites HOME into a path of its own, so the engine never saw the long
value: it expanded ~/foo against the build directory instead of bailing. Gate
the case on the engine reporting the HOME we set; it still runs, and still
fails without the guard, on every platform that passes HOME through.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Xavier Roche <roche@httrack.com>

src/htsalias.c

@@ -567,24 +567,29 @@ int optinclude_file(const char *name, int *argc, char **argv, char *x_argvblk,
   return 0;
 }
 
-/* Get home directory, '.' if failed */
+/* Get home directory, '.' if unset or empty */
 /* example: /home/smith */
 const char *hts_gethome(void) {
   const char *home = getenv("HOME");
 
-  if (home)
-    return home;
-  else
-    return ".";
+  /* An empty $HOME would expand ~/foo into the absolute /foo */
+  return strnotempty(home) ? home : ".";
 }
 
-/* Convert ~/foo into /home/smith/foo */
+/* Convert ~/foo into /home/smith/foo (~user/ left alone: no getpwnam here) */
 void expand_home(String * str) {
-  if (StringSub(*str, 1) == '~') {
+  if (StringNotEmpty(*str) && StringSub(*str, 0) == '~' &&
+      (StringLength(*str) == 1 || StringSub(*str, 1) == '/')) {
     char BIGSTK tempo[HTS_URLMAXSIZE * 2];
+    const char *const home = hts_gethome();
+    const size_t homelen = strlen(home);
+    const size_t taillen = StringLength(*str) - 1;
 
-    strcpybuff(tempo, hts_gethome());
-    strcatbuff(tempo, StringBuff(*str) + 1);
-    StringCopy(*str, tempo);
+    /* Leave untouched rather than abort() in strcatbuff on a huge $HOME */
+    if (taillen < sizeof(tempo) && homelen < sizeof(tempo) - taillen) {
+      strcpybuff(tempo, home);
+      strcatbuff(tempo, StringBuff(*str) + 1);
+      StringCopy(*str, tempo);
+    }
   }
 }

src/htsselftest.c

@@ -45,6 +45,7 @@ Please visit our Website: http://www.httrack.com
 #include "htscore.h"
 #include "htsdefines.h"
 #include "htslib.h"
+#include "htsalias.h"
 #include "htsparse.h"
 #include "htscache.h"
 #include "htscache_selftest.h"
@@ -825,6 +826,21 @@ static int st_simplify(httrackp *opt, int argc, char **argv) {
   return 0;
 }
 
+static int st_expandhome(httrackp *opt, int argc, char **argv) {
+  String path = STRING_EMPTY;
+
+  (void) opt;
+  if (argc < 1) {
+    fprintf(stderr, "expandhome: needs a path\n");
+    return 1;
+  }
+  StringCopy(path, argv[0]);
+  expand_home(&path);
+  printf("expanded=%s\n", StringBuff(path));
+  StringFree(path);
+  return 0;
+}
+
 static int st_mime(httrackp *opt, int argc, char **argv) {
   char mime[256];
 
@@ -3079,6 +3095,7 @@ static const struct selftest_entry {
     {"filterbounds", "", "matcher length/work caps reject hostile patterns",
      st_filterbounds},
     {"simplify", "<path>", "collapse ./ and ../ in a path", st_simplify},
+    {"expandhome", "<path>", "expand a leading ~/ into $HOME", st_expandhome},
     {"stripquery", "", "--strip-query pattern/key stripping self-test",
      st_stripquery},
     {"urlhack", "", "-%u url-hack sub-flag (www/slash/query) self-test",

tests/01_engine-expandhome.test

@@ -0,0 +1,53 @@
+#!/bin/bash
+#
+
+# SC2088: the literal, unexpanded '~' is the input under test.
+# shellcheck disable=SC2088
+
+set -euo pipefail
+
+# ~ expansion for the -O base path (expand_home). $HOME is pinned so the cases
+# cannot depend on the caller's, but MSYS rewrites it into a Windows path
+# before the native httrack.exe reads it: ask the engine what it saw rather
+# than hardcoding the value.
+ask() {
+    HOME=HTSHOME httrack -O /dev/null -#test=expandhome "$1"
+}
+exp() {
+    test "$(ask "$1")" == "expanded=$2" || exit 1
+}
+
+home=$(ask '~')
+home=${home#expanded=}
+
+# or every case below is vacuous: '~' means expansion never fired, '.' means it
+# fell back to the default without ever reading $HOME
+test "$home" != '~' || exit 1
+test "$home" != '.' || exit 1
+
+exp '~' "$home"
+exp '~/foo' "$home/foo"
+exp '~/foo/bar/#' "$home/foo/bar/#"
+exp '~/' "$home/"
+exp '~/../x' "$home/../x"
+
+# ~user/ needs getpwnam: left alone rather than mangled into $HOME + "user/"
+exp '~smith/foo' '~smith/foo'
+exp '~root' '~root'
+
+# only a leading '~' expands; anything else is a literal path component
+exp 'a~/x' 'a~/x'
+exp './~/x' './~/x'
+exp 'foo~bar' 'foo~bar'
+
+# an unset or empty $HOME must not turn ~/foo into the absolute /foo
+test "$(env -u HOME httrack -O /dev/null -#test=expandhome '~/foo')" == "expanded=./foo" || exit 1
+test "$(HOME='' httrack -O /dev/null -#test=expandhome '~/foo')" == "expanded=./foo" || exit 1
+
+# A $HOME past the 2 * HTS_URLMAXSIZE buffer is left alone: strcatbuff aborts
+# rather than truncates. Only meaningful where the engine sees the value we set:
+# MSYS rewrites HOME into a path of its own choosing, long or not.
+if test "$home" = HTSHOME; then
+    long=$(printf '%04096d' 0 | tr '0' 'A')
+    test "$(HOME="$long" httrack -O /dev/null -#test=expandhome '~/foo')" == "expanded=~/foo" || exit 1
+fi

tests/Makefile.am

@@ -59,6 +59,7 @@ TESTS = \
 	01_engine-pause.test \
 	01_engine-rcfile.test \
 	01_engine-reconcile.test \
+	01_engine-expandhome.test \
 	01_engine-fsize.test \
 	01_engine-redirect.test \
 	01_engine-relative.test \