htsparse: bound the URL-end scan against a missing closing delimiter

Reviewing the @import change, ASan flagged a pre-existing heap overflow:
when a quoted/parenthesized link token has no closing delimiter before the
buffer ends (truncated input such as `@import "x`, `@import "`, `url("x`),
the scan stops at the terminating NUL, then `c += ndelim` steps past it and
`while (*c == ' ')` / the terminator test read out of bounds. Such input
aborts under ASan on master.

Skip the URL-end scan and capture when no closing delimiter was found
(`*c == '\0'` right after the scan); c never advances past the NUL.
Well-formed tokens are unaffected.

01_engine-parse.test gains a truncated-@import fixture (the valid sibling
import is still captured, the unterminated one is not) that trips the
overflow under the CI ASan job, plus a check that an @import's trailing
media/supports/layer condition survives the rewrite verbatim.

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

src/htsparse.c

@@ -1341,6 +1341,9 @@ int htsparse(htsmoduleStruct * str, htsmoduleStructExtended * stre) {
                     int can_avoid_quotes = 0;
                     char quotes_replacement = '\0';
                     int ensure_not_mime = 0;
+                    // @import: the quoted token is the URL; a trailing
+                    // media/supports/layer condition is not part of it
+                    int is_import = 0;
 
                     if (inscript_tag)
                       expected_end = ";\"\'";   // voir a href="javascript:doc.location='foo'"
@@ -1390,6 +1393,7 @@ int htsparse(htsmoduleStruct * str, htsmoduleStructExtended * stre) {
                         if ((nc = strfield(html, "import"))) {   // import "url"
                           if (is_space(*(html + nc))) {
                             expected = 0;       // no char expected
+                            is_import = 1;
                           } else
                             nc = 0;
                         }
@@ -1407,6 +1411,7 @@ int htsparse(htsmoduleStruct * str, htsmoduleStructExtended * stre) {
                           if ((*a == 34) || (*a == '\'') || (can_avoid_quotes)) {
                             const char *b, *c;
                             int ndelim = 1;
+                            int valid_url = 0;
 
                             if ((*a == 34) || (*a == '\''))
                               a++;
@@ -1421,12 +1426,20 @@ int htsparse(htsmoduleStruct * str, htsmoduleStructExtended * stre) {
                                 b++;
                             }
                             c = b--;
-                            c += ndelim;
-                            while(*c == ' ')
-                              c++;
-                            if ((strchr(expected_end, *c)) || (*c == '\n')
-                                || (*c == '\r')) {
-                              c -= (ndelim + 1);
+                            // no closing delimiter here (truncated input):
+                            // Don't scan past the buffer NUL or capture it.
+                            if (*c != '\0') {
+                              c += ndelim;
+                              while (*c == ' ')
+                                c++;
+                              valid_url =
+                                  (strchr(expected_end, *c)) || (*c == '\n') ||
+                                  (*c == '\r') ||
+                                  (is_import && *(b + 1 + ndelim) == ' ');
+                            }
+                            if (valid_url) {
+                              // URL end = last char (b), not the delimiter
+                              c = b;
                               if ((int) (c - a + 1)) {
                                 if (ensure_not_mime) {
                                   int i = 0;
@@ -1485,7 +1498,6 @@ int htsparse(htsmoduleStruct * str, htsmoduleStructExtended * stre) {
                                 }
                               }
                             }
-
                           }
                         }
                       }

tests/01_engine-parse.test

@@ -176,4 +176,48 @@ notfound "ns.gif" "$out3"
 notfound "og.gif" "$out3"
 notfound "rdfs.gif" "$out3"
 
+# CSS @import (#94): every form's target is captured, crawling the .css directly.
+# The "cond"/"sup"/"spc" cases carry a trailing media/supports/layer condition (or
+# a space before ';'); they are the negative controls: without the parser fix the
+# URL is dropped, so a regression fails these found() checks.
+site4="$tmp/cssimport"
+mkdir -p "$site4"
+for f in nq dqu squ dqs sqs med cond sup lay spc; do printf 'body{}\n' >"$site4/$f.css"; done
+cat >"$site4/main.css" <<'EOF'
+@import url(nq.css);
+@import url("dqu.css");
+@import url('squ.css');
+@import "dqs.css";
+@import 'sqs.css';
+@import url(med.css) screen and (min-width: 400px);
+@import "cond.css" screen;
+@import "sup.css" supports(display: flex);
+@import url(lay.css) layer(base);
+@import "spc.css" ;
+EOF
+out4="$tmp/cssimport-out"
+crawl "$site4/main.css" "$out4"
+for f in nq dqu squ dqs sqs med cond sup lay spc; do found "$f.css" "$out4"; done
+
+# Over-capture guard: the trailing condition is not part of the URL, so it must
+# survive the rewrite verbatim. A regression that grabs it would mangle these.
+m4=$(find "$out4" -type f -path '*/file/*' -name main.css -print -quit)
+test -n "$m4" || ! echo "FAIL: saved main.css not found" || exit 1
+for cond in '@import "cond.css" screen;' 'supports(display: flex)' 'layer(base)'; do
+    grep -Fq "$cond" "$m4" ||
+        ! echo "FAIL #94: '$cond' altered on rewrite (condition captured as URL?)" || exit 1
+done
+
+# Malformed input: an unterminated @import quote (truncated CSS) must not crash or
+# capture a bogus link; a valid sibling import is still captured. Guards a heap
+# overflow on the URL-end scan that aborts under ASan (CI sanitizer job).
+site5="$tmp/cssimport-trunc"
+mkdir -p "$site5"
+printf 'body{}\n' >"$site5/good.css"
+printf '@import "good.css";\n@import "trunc' >"$site5/main.css"
+out5="$tmp/cssimport-trunc-out"
+crawl "$site5/main.css" "$out5"
+found "good.css" "$out5"
+notfound "trunc" "$out5"
+
 exit 0