PHP: Implement better error handling.

Previously the PHP module would produce one of four status codes

  200 OK
  301 Moved Permanently
  500 Internal Server Error
  503 Service Unavailable

200 for successful requests, 301 for cases where the url was a directory
without a trailing '/', 500 for bad PHP or non-existing PHP file and 503
for all other errors.

With this commit we now handle missing files and directories, returning
404 Not Found and files and directories that don't allow access,
returning 403 Forbidden.

We do these checks in two places, when we check if we should do a
directory redirect (bar -> bar/) and in the nxt_php_execute() function.

One snag with the latter is that the php_execute_script() function only
returns success/failure (no reason). However while it took a
zend_file_handle structure with the filename of the script to run, we
can instead pass through an already opened file-pointer (FILE *) via
that structure. So we can try opening the script ourselves and do the
required checks before calling php_execute_script().

We also make use of the zend_stream_init_fp() function that initialises
the zend_file_handle structure if it's available otherwise we use our
own version. This is good because the zend_file_handle structure has
changed over time and the zend_stream_init_fp() function should change
with it.

Closes: <https://github.com/nginx/unit/issues/767>
Reviewed-by: Alejandro Colomar <alx@nginx.com>
Cc: Andrei Zeliankou <zelenkov@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

src/nxt_php_sapi.c

@@ -102,12 +102,13 @@ static void nxt_php_str_trim_lead(nxt_str_t *str, u_char t);
 nxt_inline u_char *nxt_realpath(const void *c);
 
 static nxt_int_t nxt_php_do_301(nxt_unit_request_info_t *req);
+static nxt_int_t nxt_php_handle_fs_err(nxt_unit_request_info_t *req);
 
 static void nxt_php_request_handler(nxt_unit_request_info_t *req);
 static void nxt_php_dynamic_request(nxt_php_run_ctx_t *ctx,
     nxt_unit_request_t *r);
 #if (PHP_VERSION_ID < 70400)
-static void nxt_zend_stream_init_filename(zend_file_handle *handle,
+static void nxt_zend_stream_init_fp(zend_file_handle *handle, FILE *fp,
     const char *filename);
 #endif
 static void nxt_php_execute(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r);
@@ -984,6 +985,24 @@ nxt_php_do_301(nxt_unit_request_info_t *req)
 }
 
 
+static nxt_int_t
+nxt_php_handle_fs_err(nxt_unit_request_info_t *req)
+{
+    switch (nxt_errno) {
+    case ELOOP:
+    case EACCES:
+    case ENFILE:
+        return nxt_unit_response_init(req, NXT_HTTP_FORBIDDEN, 0, 0);
+    case ENOENT:
+    case ENOTDIR:
+    case ENAMETOOLONG:
+        return nxt_unit_response_init(req, NXT_HTTP_NOT_FOUND, 0, 0);
+    }
+
+    return NXT_UNIT_ERROR;
+}
+
+
 static void
 nxt_php_request_handler(nxt_unit_request_info_t *req)
 {
@@ -1062,6 +1081,8 @@ nxt_php_dynamic_request(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r)
         ret = stat(tpath, &sb);
         if (ret == 0 && S_ISDIR(sb.st_mode)) {
             ec = nxt_php_do_301(ctx->req);
+        } else if (ret == -1) {
+            ec = nxt_php_handle_fs_err(ctx->req);
         }
 
         nxt_unit_request_done(ctx->req, ec);
@@ -1115,20 +1136,23 @@ nxt_php_dynamic_request(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r)
 
 #if (PHP_VERSION_ID < 70400)
 static void
-nxt_zend_stream_init_filename(zend_file_handle *handle, const char *filename)
+nxt_zend_stream_init_fp(zend_file_handle *handle, FILE *fp,
+                        const char *filename)
 {
     nxt_memzero(handle, sizeof(zend_file_handle));
-    handle->type = ZEND_HANDLE_FILENAME;
+    handle->type = ZEND_HANDLE_FP;
+    handle->handle.fp = fp;
     handle->filename = filename;
 }
 #else
-#define nxt_zend_stream_init_filename  zend_stream_init_filename
+#define nxt_zend_stream_init_fp  zend_stream_init_fp
 #endif
 
 
 static void
 nxt_php_execute(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r)
 {
+    FILE              *fp;
 #if (PHP_VERSION_ID < 50600)
     void              *read_post;
 #endif
@@ -1140,6 +1164,17 @@ nxt_php_execute(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r)
 
     nxt_unit_req_debug(ctx->req, "PHP execute script %s", filename);
 
+    fp = fopen(filename, "re");
+    if (fp == NULL) {
+        nxt_int_t  ec;
+
+        nxt_unit_req_debug(ctx->req, "PHP fopen(\"%s\") failed", filename);
+
+        ec = nxt_php_handle_fs_err(ctx->req);
+        nxt_unit_request_done(ctx->req, ec);
+        return;
+    }
+
     SG(server_context) = ctx;
     SG(options) |= SAPI_OPTION_NO_CHDIR;
     SG(request_info).request_uri = nxt_unit_sptr_get(&r->target);
@@ -1198,7 +1233,7 @@ nxt_php_execute(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r)
         nxt_php_vcwd_chdir(ctx->req, ctx->script_dirname.start);
     }
 
-    nxt_zend_stream_init_filename(&file_handle, filename);
+    nxt_zend_stream_init_fp(&file_handle, fp, filename);
 
     php_execute_script(&file_handle TSRMLS_CC);