[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, 2 insertions, 2 deletions

diff --git a/src/mod_rewrite.c b/src/mod_rewrite.c
index 195e6589..60a62feb 100644
--- a/src/mod_rewrite.c
+++ b/src/mod_rewrite.c
@@ -291,12 +291,12 @@ static handler_t process_rewrite_rules(request_st * const r, plugin_data *p, con
 	burl.port      = sock_addr_get_port(&r->con->srv_socket->addr);
 	burl.path      = &r->target; /*(uri-encoded and includes query-part)*/
 	burl.query     = &r->uri.query;
-	if (buffer_string_is_empty(burl.authority))
+	if (buffer_is_blank(burl.authority))
 		burl.authority = r->server_name;
 
 	buffer * const tb = r->tmp_buf;
 	rc = pcre_keyvalue_buffer_process(kvb, &ctx, &r->target, tb);
-	if (HANDLER_FINISHED == rc && !buffer_is_empty(tb) && tb->ptr[0] == '/') {
+	if (HANDLER_FINISHED == rc && !buffer_is_blank(tb) && tb->ptr[0] == '/') {
 		buffer_copy_buffer(&r->target, tb);
 		uintptr_t * const hctx = (uintptr_t *)(r->plugin_ctx + p->id);
 		*hctx |= REWRITE_STATE_REWRITTEN;