Store the cache self-tests' X-Save verbatim, and feed the sniff BOM as hex

The cache self-tests built the X-Save path with fconcat(), which rewrites
every '/' to '\' on Windows -- including the path_html_utf8 prefix the
reader matches on. cache_readex then took the pre-3.40 compat branch and
re-rooted the name into a path that does not exist, so -#test=cache's
disk-fallback read and -#test=cache-corrupt's headers-only and in-memory
cases all failed on MSVC builds. The engine keeps save names in '/' form and
DOS-ifies only at the syscall boundary; the self-tests now do the same.

The sniff test passed a UTF-8 BOM as raw bytes through argv, where Windows
routes it via the ANSI codepage and U+FEFF has no mapping, so it arrived as
'?'. Use the hex: body form the self-test already accepts.

Both are self-test bugs: neither path is reachable from the crawler, which
never sniffs argv and never DOS-ifies a stored save name.

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

src/htscache_selftest.c

@@ -232,11 +232,10 @@ static int disk_fallback_selftest(httrackp *opt) {
   static const char body[] = "BINARY-on-disk-body-0123456789-no-trailing-nul";
   const size_t body_len = sizeof(body) - 1;
 
-  /* X-Save must start with path_html_utf8 so the reader resolves it verbatim
-     (otherwise it re-roots it as a pre-3.40 relative path); then the body we
-     create at fconv(save) is exactly where cache_readex looks for it. */
-  fconcat(save, sizeof(save), StringBuff(opt->path_html_utf8),
-          "example.com/blob.bin");
+  /* a DOS-ified X-Save loses the path_html_utf8 prefix the reader matches on,
+     and gets re-rooted as a pre-3.40 relative path; fconv() only on access */
+  concat(save, sizeof(save), StringBuff(opt->path_html_utf8),
+         "example.com/blob.bin");
 
   /* write only the header (X-In-Cache: 0); the body stays on disk */
   selftest_open_for_write(&cache, opt);
@@ -1253,8 +1252,9 @@ static void corrupt_build_disk(httrackp *opt) {
   memset(corrupt_body_a, 'a', sizeof(corrupt_body_a) - 1);
   remove(reconcile_st_path(opt, "hts-cache/new.zip"));
   remove(reconcile_st_path(opt, "hts-cache/old.zip"));
-  fconcat(save, sizeof(save), StringBuff(opt->path_html_utf8),
-          CORRUPT_ADR "/victim.bin");
+  /* X-Save stored verbatim: see disk_fallback_selftest */
+  concat(save, sizeof(save), StringBuff(opt->path_html_utf8),
+         CORRUPT_ADR "/victim.bin");
   selftest_open_for_write(&cache, opt);
   store_entry(opt, &cache, CORRUPT_ADR, "/canary.html", "canary.html", 200,
               "OK", "text/html", "utf-8", "", "", "", "", corrupt_body_a,

tests/01_engine-sniff.test

@@ -35,7 +35,8 @@ chk image/avif hex:0000001C6674797061766966 "$yes"
 chk image/avif hex:0000001C6674797068656963 "$no" # heic brand is not avif
 chk image/heic hex:0000001C6674797068656963 "$yes"
 chk image/svg+xml '<svg xmlns="x">' "$yes"
-chk image/svg+xml $'\xef\xbb\xbf  <?xml version="1.0"?>' "$yes" # BOM+ws skip
+# BOM+ws skip; hex, as Windows argv cannot carry the raw BOM through the ANSI codepage
+chk image/svg+xml hex:EFBBBF20203C3F786D6C2076657273696F6E3D22312E30223F3E "$yes"
 
 # audio / video
 chk audio/mpeg 'ID3xxx' "$yes"