Improved error messages for module loading failures.

There are several reasons why a file cannot be opened. Without
extra information, especially in containerized environments, these
problems are difficult to debug. Adding errno status to the
error output helps identify the root cause.

Additionally, error messages are now aligned between njs and QuickJS.

nginx/ngx_js.c

@@ -1979,10 +1979,15 @@ ngx_qjs_module_loader(JSContext *cx, const char *module_name, void *opaque)
     info.name.start = (u_char *) module_name;
     info.name.length = njs_strlen(module_name);
 
+    errno = 0;
     ret = ngx_js_module_lookup(conf, &info);
     if (ret != NJS_OK) {
-        JS_ThrowReferenceError(cx, "could not load module filename '%s'",
-                               module_name);
+        if (errno != 0) {
+            JS_ThrowReferenceError(cx, "Cannot load module \"%s\" "
+                                   "(%s:%s)", module_name,
+                                   ngx_js_errno_string(errno), strerror(errno));
+        }
+
         return NULL;
     }
 
@@ -3764,8 +3769,14 @@ ngx_js_module_loader(njs_vm_t *vm, njs_external_ptr_t external, njs_str_t *name)
 
     info.name = *name;
 
+    errno = 0;
     ret = ngx_js_module_lookup(conf, &info);
     if (njs_slow_path(ret != NJS_OK)) {
+        if (errno != 0) {
+            njs_vm_ref_error(vm, "Cannot load module \"%V\" (%s:%s)", name,
+                             ngx_js_errno_string(errno), strerror(errno));
+        }
+
         return NULL;
     }
 
@@ -4076,6 +4087,341 @@ ngx_js_monotonic_time(void)
 }
 
 
+#define ngx_js_errno_case(e)                                                \
+    case e:                                                                 \
+        return #e;
+
+
+const char*
+ngx_js_errno_string(int errnum)
+{
+    switch (errnum) {
+#ifdef EACCES
+    ngx_js_errno_case(EACCES);
+#endif
+
+#ifdef EADDRINUSE
+    ngx_js_errno_case(EADDRINUSE);
+#endif
+
+#ifdef EADDRNOTAVAIL
+    ngx_js_errno_case(EADDRNOTAVAIL);
+#endif
+
+#ifdef EAFNOSUPPORT
+    ngx_js_errno_case(EAFNOSUPPORT);
+#endif
+
+#ifdef EAGAIN
+    ngx_js_errno_case(EAGAIN);
+#endif
+
+#ifdef EWOULDBLOCK
+#if EAGAIN != EWOULDBLOCK
+    ngx_js_errno_case(EWOULDBLOCK);
+#endif
+#endif
+
+#ifdef EALREADY
+    ngx_js_errno_case(EALREADY);
+#endif
+
+#ifdef EBADF
+    ngx_js_errno_case(EBADF);
+#endif
+
+#ifdef EBADMSG
+    ngx_js_errno_case(EBADMSG);
+#endif
+
+#ifdef EBUSY
+    ngx_js_errno_case(EBUSY);
+#endif
+
+#ifdef ECANCELED
+    ngx_js_errno_case(ECANCELED);
+#endif
+
+#ifdef ECHILD
+    ngx_js_errno_case(ECHILD);
+#endif
+
+#ifdef ECONNABORTED
+    ngx_js_errno_case(ECONNABORTED);
+#endif
+
+#ifdef ECONNREFUSED
+    ngx_js_errno_case(ECONNREFUSED);
+#endif
+
+#ifdef ECONNRESET
+    ngx_js_errno_case(ECONNRESET);
+#endif
+
+#ifdef EDEADLK
+    ngx_js_errno_case(EDEADLK);
+#endif
+
+#ifdef EDESTADDRREQ
+    ngx_js_errno_case(EDESTADDRREQ);
+#endif
+
+#ifdef EDOM
+    ngx_js_errno_case(EDOM);
+#endif
+
+#ifdef EDQUOT
+    ngx_js_errno_case(EDQUOT);
+#endif
+
+#ifdef EEXIST
+    ngx_js_errno_case(EEXIST);
+#endif
+
+#ifdef EFAULT
+    ngx_js_errno_case(EFAULT);
+#endif
+
+#ifdef EFBIG
+    ngx_js_errno_case(EFBIG);
+#endif
+
+#ifdef EHOSTUNREACH
+    ngx_js_errno_case(EHOSTUNREACH);
+#endif
+
+#ifdef EIDRM
+    ngx_js_errno_case(EIDRM);
+#endif
+
+#ifdef EILSEQ
+    ngx_js_errno_case(EILSEQ);
+#endif
+
+#ifdef EINPROGRESS
+    ngx_js_errno_case(EINPROGRESS);
+#endif
+
+#ifdef EINTR
+    ngx_js_errno_case(EINTR);
+#endif
+
+#ifdef EINVAL
+    ngx_js_errno_case(EINVAL);
+#endif
+
+#ifdef EIO
+    ngx_js_errno_case(EIO);
+#endif
+
+#ifdef EISCONN
+    ngx_js_errno_case(EISCONN);
+#endif
+
+#ifdef EISDIR
+    ngx_js_errno_case(EISDIR);
+#endif
+
+#ifdef ELOOP
+    ngx_js_errno_case(ELOOP);
+#endif
+
+#ifdef EMFILE
+    ngx_js_errno_case(EMFILE);
+#endif
+
+#ifdef EMLINK
+    ngx_js_errno_case(EMLINK);
+#endif
+
+#ifdef EMSGSIZE
+    ngx_js_errno_case(EMSGSIZE);
+#endif
+
+#ifdef EMULTIHOP
+    ngx_js_errno_case(EMULTIHOP);
+#endif
+
+#ifdef ENAMETOOLONG
+    ngx_js_errno_case(ENAMETOOLONG);
+#endif
+
+#ifdef ENETDOWN
+    ngx_js_errno_case(ENETDOWN);
+#endif
+
+#ifdef ENETRESET
+    ngx_js_errno_case(ENETRESET);
+#endif
+
+#ifdef ENETUNREACH
+    ngx_js_errno_case(ENETUNREACH);
+#endif
+
+#ifdef ENFILE
+    ngx_js_errno_case(ENFILE);
+#endif
+
+#ifdef ENOBUFS
+    ngx_js_errno_case(ENOBUFS);
+#endif
+
+#ifdef ENODATA
+    ngx_js_errno_case(ENODATA);
+#endif
+
+#ifdef ENODEV
+    ngx_js_errno_case(ENODEV);
+#endif
+
+#ifdef ENOENT
+    ngx_js_errno_case(ENOENT);
+#endif
+
+#ifdef ENOEXEC
+    ngx_js_errno_case(ENOEXEC);
+#endif
+
+#ifdef ENOLINK
+    ngx_js_errno_case(ENOLINK);
+#endif
+
+#ifdef ENOLCK
+#if ENOLINK != ENOLCK
+    ngx_js_errno_case(ENOLCK);
+#endif
+#endif
+
+#ifdef ENOMEM
+    ngx_js_errno_case(ENOMEM);
+#endif
+
+#ifdef ENOMSG
+    ngx_js_errno_case(ENOMSG);
+#endif
+
+#ifdef ENOPROTOOPT
+    ngx_js_errno_case(ENOPROTOOPT);
+#endif
+
+#ifdef ENOSPC
+    ngx_js_errno_case(ENOSPC);
+#endif
+
+#ifdef ENOSR
+    ngx_js_errno_case(ENOSR);
+#endif
+
+#ifdef ENOSTR
+    ngx_js_errno_case(ENOSTR);
+#endif
+
+#ifdef ENOSYS
+    ngx_js_errno_case(ENOSYS);
+#endif
+
+#ifdef ENOTCONN
+    ngx_js_errno_case(ENOTCONN);
+#endif
+
+#ifdef ENOTDIR
+    ngx_js_errno_case(ENOTDIR);
+#endif
+
+#ifdef ENOTEMPTY
+#if ENOTEMPTY != EEXIST
+    ngx_js_errno_case(ENOTEMPTY);
+#endif
+#endif
+
+#ifdef ENOTSOCK
+    ngx_js_errno_case(ENOTSOCK);
+#endif
+
+#ifdef ENOTSUP
+    ngx_js_errno_case(ENOTSUP);
+#else
+#ifdef EOPNOTSUPP
+    ngx_js_errno_case(EOPNOTSUPP);
+#endif
+#endif
+
+#ifdef ENOTTY
+    ngx_js_errno_case(ENOTTY);
+#endif
+
+#ifdef ENXIO
+    ngx_js_errno_case(ENXIO);
+#endif
+
+#ifdef EOVERFLOW
+    ngx_js_errno_case(EOVERFLOW);
+#endif
+
+#ifdef EPERM
+    ngx_js_errno_case(EPERM);
+#endif
+
+#ifdef EPIPE
+    ngx_js_errno_case(EPIPE);
+#endif
+
+#ifdef EPROTO
+    ngx_js_errno_case(EPROTO);
+#endif
+
+#ifdef EPROTONOSUPPORT
+    ngx_js_errno_case(EPROTONOSUPPORT);
+#endif
+
+#ifdef EPROTOTYPE
+    ngx_js_errno_case(EPROTOTYPE);
+#endif
+
+#ifdef ERANGE
+    ngx_js_errno_case(ERANGE);
+#endif
+
+#ifdef EROFS
+    ngx_js_errno_case(EROFS);
+#endif
+
+#ifdef ESPIPE
+    ngx_js_errno_case(ESPIPE);
+#endif
+
+#ifdef ESRCH
+    ngx_js_errno_case(ESRCH);
+#endif
+
+#ifdef ESTALE
+    ngx_js_errno_case(ESTALE);
+#endif
+
+#ifdef ETIME
+    ngx_js_errno_case(ETIME);
+#endif
+
+#ifdef ETIMEDOUT
+    ngx_js_errno_case(ETIMEDOUT);
+#endif
+
+#ifdef ETXTBSY
+    ngx_js_errno_case(ETXTBSY);
+#endif
+
+#ifdef EXDEV
+    ngx_js_errno_case(EXDEV);
+#endif
+
+    default:
+        break;
+    }
+
+    return "UNKNOWN CODE";
+}
+
+
 ngx_js_queue_t *
 ngx_js_queue_create(ngx_pool_t *pool, ngx_uint_t capacity)
 {

nginx/ngx_js.h

@@ -412,6 +412,7 @@ njs_int_t ngx_js_ext_flags(njs_vm_t *vm, njs_object_prop_t *prop,
 
 ngx_int_t ngx_js_string(njs_vm_t *vm, njs_value_t *value, njs_str_t *str);
 ngx_int_t ngx_js_integer(njs_vm_t *vm, njs_value_t *value, ngx_int_t *n);
+const char *ngx_js_errno_string(int errnum);
 
 ngx_js_queue_t *ngx_js_queue_create(ngx_pool_t *pool, ngx_uint_t capacity);
 ngx_int_t ngx_js_queue_push(ngx_js_queue_t *queue, void *item);

src/njs.h

@@ -72,6 +72,8 @@ extern const njs_value_t            njs_value_undefined;
     njs_vm_error2(vm, 2, fmt, ##__VA_ARGS__)
 #define njs_vm_range_error(vm, fmt, ...)                                      \
     njs_vm_error2(vm, 3, fmt, ##__VA_ARGS__)
+#define njs_vm_ref_error(vm, fmt, ...)                                        \
+    njs_vm_error2(vm, 4, fmt, ##__VA_ARGS__)
 #define njs_vm_syntax_error(vm, fmt, ...)                                     \
     njs_vm_error2(vm, 5, fmt, ##__VA_ARGS__)
 #define njs_vm_type_error(vm, fmt, ...)                                       \