[multiple] reduce redundant NULL buffer checks

This commit is a large set of code changes and results in removal of
hundreds, perhaps thousands, of CPU instructions, a portion of which
are on hot code paths.

Most (buffer *) used by lighttpd are not NULL, especially since buffers
were inlined into numerous larger structs such as request_st and chunk.

In the small number of instances where that is not the case, a NULL
check is often performed earlier in a function where that buffer is
later used with a buffer_* func.  In the handful of cases that remained,
a NULL check was added, e.g. with r->http_host and r->conf.server_tag.

- check for empty strings at config time and set value to NULL if blank
  string will be ignored at runtime; at runtime, simple pointer check
  for NULL can be used to check for a value that has been set and is not
  blank ("")
- use buffer_is_blank() instead of buffer_string_is_empty(),
  and use buffer_is_unset() instead of buffer_is_empty(),
  where buffer is known not to be NULL so that NULL check can be skipped
- use buffer_clen() instead of buffer_string_length() when buffer is
  known not to be NULL (to avoid NULL check at runtime)
- use buffer_truncate() instead of buffer_string_set_length() to
  truncate string, and use buffer_extend() to extend

Examples where buffer known not to be NULL:
  - cpv->v.b from config_plugin_values_init is not NULL if T_CONFIG_BOOL
    (though we might set it to NULL if buffer_is_blank(cpv->v.b))
  - address of buffer is arg (&foo)
    (compiler optimizer detects this in most, but not all, cases)
  - buffer is checked for NULL earlier in func
  - buffer is accessed in same scope without a NULL check (e.g. b->ptr)

internal behavior change:
  callers must not pass a NULL buffer to some funcs.
  - buffer_init_buffer() requires non-null args
  - buffer_copy_buffer() requires non-null args
  - buffer_append_string_buffer() requires non-null args
  - buffer_string_space() requires non-null arg

1 files changed, 5 insertions, 6 deletions

diff --git a/src/mod_authn_dbi.c b/src/mod_authn_dbi.c
index 37de01f0..f375d7ea 100644
--- a/src/mod_authn_dbi.c
+++ b/src/mod_authn_dbi.c
@@ -128,8 +128,7 @@ mod_authn_dbi_dbconf_setup (server *srv, const array *opts, void **vdata)
      * - encoding, default: database default
      */
 
-    if (!buffer_string_is_empty(sqlquery)
-        && !buffer_is_empty(dbname) && !buffer_is_empty(dbtype)) {
+    if (sqlquery && !buffer_is_blank(sqlquery) && dbname && dbtype) {
         /* create/initialise database */
         dbi_config *dbconf;
         dbi_inst dbinst = NULL;
@@ -153,7 +152,7 @@ mod_authn_dbi_dbconf_setup (server *srv, const array *opts, void **vdata)
         for (size_t j = 0; j < opts->used; ++j) {
             data_unset *du = opts->data[j];
             const buffer *opt = &du->key;
-            if (!buffer_string_is_empty(opt)) {
+            if (!buffer_is_blank(opt)) {
                 if (du->type == TYPE_INTEGER) {
                     data_integer *di = (data_integer *)du;
                     dbi_conn_set_option_numeric(dbconn, opt->ptr, di->value);
@@ -474,7 +473,7 @@ mod_authn_dbi_query_build (buffer * const sqlquery, dbi_config * const dbconf, h
             free(esc);
         }
         else {
-            d = dbconf->sqlquery->ptr + buffer_string_length(dbconf->sqlquery);
+            d = dbconf->sqlquery->ptr + buffer_clen(dbconf->sqlquery);
             buffer_append_string_len(sqlquery, b, (size_t)(d - b));
             break;
         }
@@ -546,9 +545,9 @@ mod_authn_dbi_basic (request_st * const r, void *p_d, const http_auth_require_t
     ai.dalgo    = HTTP_AUTH_DIGEST_NONE;
     ai.dlen     = 0;
     ai.username = username->ptr;
-    ai.ulen     = buffer_string_length(username);
+    ai.ulen     = buffer_clen(username);
     ai.realm    = require->realm->ptr;
-    ai.rlen     = buffer_string_length(require->realm);
+    ai.rlen     = buffer_clen(require->realm);
     rc = mod_authn_dbi_query(r, p_d, &ai, pw);
     if (HANDLER_GO_ON != rc) return rc;
     return http_auth_match_rules(require, username->ptr, NULL, NULL)