[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, 7 insertions, 7 deletions

diff --git a/src/mod_alias.c b/src/mod_alias.c
index d2c67f30..119c3dcc 100644
--- a/src/mod_alias.c
+++ b/src/mod_alias.c
@@ -52,10 +52,10 @@ static void mod_alias_patch_config(request_st * const r, plugin_data * const p)
 static int mod_alias_check_order(server * const srv, const array * const a) {
     for (uint32_t j = 0; j < a->used; ++j) {
         const buffer * const prefix = &a->data[j]->key;
-        const size_t plen = buffer_string_length(prefix);
+        const size_t plen = buffer_clen(prefix);
         for (uint32_t k = j + 1; k < a->used; ++k) {
             const buffer * const key = &a->data[k]->key;
-            if (buffer_string_length(key) < plen) {
+            if (buffer_clen(key) < plen) {
                 break;
             }
             if (memcmp(key->ptr, prefix->ptr, plen) != 0) {
@@ -121,10 +121,10 @@ static handler_t
 mod_alias_remap (request_st * const r, const array * const aliases)
 {
     /* do not include trailing slash on basedir */
-    uint32_t basedir_len = buffer_string_length(&r->physical.basedir);
+    uint32_t basedir_len = buffer_clen(&r->physical.basedir);
     if (buffer_has_pathsep_suffix(&r->physical.basedir)) --basedir_len;
 
-    const uint32_t path_len = buffer_string_length(&r->physical.path);
+    const uint32_t path_len = buffer_clen(&r->physical.path);
     if (0 == path_len || path_len < basedir_len) return HANDLER_GO_ON;
 
     const uint32_t uri_len = path_len - basedir_len;
@@ -137,8 +137,8 @@ mod_alias_remap (request_st * const r, const array * const aliases)
 
     /* matched */
 
-    const uint32_t alias_len = buffer_string_length(&ds->key);
-    const uint32_t vlen = buffer_string_length(&ds->value);
+    const uint32_t alias_len = buffer_clen(&ds->key);
+    const uint32_t vlen = buffer_clen(&ds->value);
 
     /* check for path traversal in url-path following alias if key
      * does not end in slash, but replacement value ends in slash */
@@ -163,7 +163,7 @@ mod_alias_remap (request_st * const r, const array * const aliases)
             buffer_string_prepare_append(&r->physical.path, nlen - path_len);
         memmove(r->physical.path.ptr + vlen,
                 uri_ptr + alias_len, uri_len - alias_len);
-        buffer_string_set_length(&r->physical.path, nlen);
+        buffer_truncate(&r->physical.path, nlen);
     }
     memcpy(r->physical.path.ptr, ds->value.ptr, vlen);