build: gate htssafe pointer-dest regressions with -Werror=attribute-warning

The strcpybuff/strcatbuff/strncatbuff family in htssafe.h silently degrades
to an unchecked strcpy/strcat/strncat when the destination is a bare char*
(capacity unknown); the pointer-destination stubs carry a 'warning' function
attribute to flag every such call. The migration that converted those 241
sites is complete, so any new char* destination is a regression.

Promote that attribute to a hard error in our own build via
-Werror=attribute-warning (gcc) / -Werror=user-defined-warnings (clang),
probed with AX_CHECK_COMPILE_FLAG so each compiler picks up only the spelling
it accepts. htssafe.h is unchanged, so downstream consumers of the installed
header still see a plain warning rather than a build break.

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

configure

@@ -15541,6 +15541,91 @@ else case e in #(
 esac
 fi
 
+# Make htssafe.h's pointer-dest 'warning' attribute a hard error in our build
+# (migration is at zero; a new char* dest is a regression). gcc/clang each take
+# only their own spelling; downstream keeps the plain warning, not a build break.
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -Werror=attribute-warning" >&5
+printf %s "checking whether C compiler accepts -Werror=attribute-warning... " >&6; }
+if test ${ax_cv_check_cflags___Werror_attribute_warning+y}
+then :
+  printf %s "(cached) " >&6
+else case e in #(
+  e)
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS  -Werror=attribute-warning"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  ax_cv_check_cflags___Werror_attribute_warning=yes
+else case e in #(
+  e) ax_cv_check_cflags___Werror_attribute_warning=no ;;
+esac
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags___Werror_attribute_warning" >&5
+printf "%s\n" "$ax_cv_check_cflags___Werror_attribute_warning" >&6; }
+if test "x$ax_cv_check_cflags___Werror_attribute_warning" = xyes
+then :
+  DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Werror=attribute-warning"
+else case e in #(
+  e) : ;;
+esac
+fi
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -Werror=user-defined-warnings" >&5
+printf %s "checking whether C compiler accepts -Werror=user-defined-warnings... " >&6; }
+if test ${ax_cv_check_cflags___Werror_user_defined_warnings+y}
+then :
+  printf %s "(cached) " >&6
+else case e in #(
+  e)
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS  -Werror=user-defined-warnings"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  ax_cv_check_cflags___Werror_user_defined_warnings=yes
+else case e in #(
+  e) ax_cv_check_cflags___Werror_user_defined_warnings=no ;;
+esac
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags___Werror_user_defined_warnings" >&5
+printf "%s\n" "$ax_cv_check_cflags___Werror_user_defined_warnings" >&6; }
+if test "x$ax_cv_check_cflags___Werror_user_defined_warnings" = xyes
+then :
+  DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Werror=user-defined-warnings"
+else case e in #(
+  e) : ;;
+esac
+fi
+
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -fstrict-aliasing -Wstrict-aliasing" >&5
 printf %s "checking whether C compiler accepts -fstrict-aliasing -Wstrict-aliasing... " >&6; }
 if test ${ax_cv_check_cflags___fstrict_aliasing__Wstrict_aliasing+y}

configure.ac

@@ -84,6 +84,11 @@ AX_CHECK_COMPILE_FLAG([-Wformat-nonliteral], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -W
 AX_CHECK_COMPILE_FLAG([-Wmissing-parameter-type], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Wmissing-parameter-type"])
 AX_CHECK_COMPILE_FLAG([-Wold-style-definition], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Wold-style-definition"])
 AX_CHECK_COMPILE_FLAG([-Wignored-qualifiers], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Wignored-qualifiers"])
+# Make htssafe.h's pointer-dest 'warning' attribute a hard error in our build
+# (migration is at zero; a new char* dest is a regression). gcc/clang each take
+# only their own spelling; downstream keeps the plain warning, not a build break.
+AX_CHECK_COMPILE_FLAG([-Werror=attribute-warning], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Werror=attribute-warning"])
+AX_CHECK_COMPILE_FLAG([-Werror=user-defined-warnings], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -Werror=user-defined-warnings"])
 AX_CHECK_COMPILE_FLAG([-fstrict-aliasing -Wstrict-aliasing], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -fstrict-aliasing -Wstrict-aliasing"])
 AX_CHECK_COMPILE_FLAG([-fstack-protector], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -fstack-protector"])
 AX_CHECK_COMPILE_FLAG([-fstack-clash-protection], [DEFAULT_CFLAGS="$DEFAULT_CFLAGS -fstack-clash-protection"])

src/htsserver.c

@@ -129,7 +129,8 @@ HTS_UNUSED static int linputsoc_t(T_SOC soc, char *s, int max, int timeout);
 HTS_UNUSED static int linput(FILE * fp, char *s, int max);
 
 /* Language files */
-HTS_UNUSED static int htslang_load(char *limit_to, const char *apppath);
+HTS_UNUSED static int htslang_load(char *limit_to, size_t limit_size,
+                                   const char *apppath);
 HTS_UNUSED static void conv_printf(const char *from, char *to);
 HTS_UNUSED static void LANG_DELETE(void);
 HTS_UNUSED static void LANG_INIT(const char *path);
@@ -325,7 +326,7 @@ int smallserver(T_SOC soc, char *url, char *method, char *data, char *path) {
 
   /* Load strings */
   htslang_init();
-  if (!htslang_load(NULL, path)) {
+  if (!htslang_load(NULL, 0, path)) {
     fprintf(stderr, "unable to find lang.def and/or lang/ strings in %s\n",
             path);
     return 0;
@@ -511,7 +512,7 @@ int smallserver(T_SOC soc, char *url, char *method, char *data, char *path) {
         char *s = buffer;
         char *e, *f;
 
-        strcatbuff(buffer, "&");
+        strlcatbuff(buffer, "&", buffer_size);
         while(s && (e = strchr(s, '=')) && (f = strchr(s, '&'))) {
           const char *ua;
           String sua = STRING_EMPTY;
@@ -935,7 +936,7 @@ int smallserver(T_SOC soc, char *url, char *method, char *data, char *path) {
                     int listDefault = 0;
 
                     name[0] = '\0';
-                    strncatbuff(name, str, n);
+                    strlncatbuff(name, str, sizeof(name_), n);
 
                     if (strncmp(name, "/*", 2) == 0) {
                       /* comments */
@@ -1490,7 +1491,7 @@ int smallserver_setkeyarr(const char *key, int id, const char *key2, const char
   return coucal_write(NewLangList, tmp, (intptr_t) strdup(value));
 }
 
-static int htslang_load(char *limit_to, const char *path) {
+static int htslang_load(char *limit_to, size_t limit_size, const char *path) {
   const char *hashname;
   char catbuff[CATBUFF_SIZE];
 
@@ -1545,7 +1546,7 @@ static int htslang_load(char *limit_to, const char *path) {
             char *const buff = (char *) malloc(len + 1);
 
             if (buff) {
-              strcpybuff(buff, intkey);
+              strlcpybuff(buff, intkey, len + 1);
               coucal_add(NewLangStrKeys, key, (intptr_t) buff);
             }
           }
@@ -1568,9 +1569,9 @@ static int htslang_load(char *limit_to, const char *path) {
   /* Get only language name */
   if (limit_to) {
     if (hashname)
-      strcpybuff(limit_to, hashname);
+      strlcpybuff(limit_to, hashname, limit_size);
     else
-      strcpybuff(limit_to, "???");
+      strlcpybuff(limit_to, "???", limit_size);
     return 0;
   }
 
@@ -1750,7 +1751,7 @@ static void LANG_INIT(const char *path) {
 static int LANG_T(const char *path, int l) {
   if (l >= 0) {
     QLANG_T(l);
-    htslang_load(NULL, path);
+    htslang_load(NULL, 0, path);
   }
   return QLANG_T(-1);           // 0=default (english)
 }
@@ -1764,7 +1765,7 @@ static int LANG_SEARCH(const char *path, const char *iso) {
   do {
     QLANG_T(i);
     strcpybuff(lang_str, "LANGUAGE_ISO");
-    htslang_load(lang_str, path);
+    htslang_load(lang_str, sizeof(lang_str), path);
     if (strfield(iso, lang_str)) {
       found = i;
     }
@@ -1782,11 +1783,11 @@ static int LANG_LIST(const char *path, char *buffer, size_t buffer_size) {
   buffer[0] = '\0';
   do {
     QLANG_T(i);
-    strlcpybuff(lang_str, "LANGUAGE_NAME", buffer_size);
-    htslang_load(lang_str, path);
+    strlcpybuff(lang_str, "LANGUAGE_NAME", sizeof(lang_str));
+    htslang_load(lang_str, sizeof(lang_str), path);
     if (strlen(lang_str) > 0) {
       if (buffer[0])
-        strcatbuff(buffer, "\n");
+        strlcatbuff(buffer, "\n", buffer_size);
       strlcatbuff(buffer, lang_str, buffer_size);
     }
     i++;