[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, 3 insertions, 3 deletions

diff --git a/src/sock_addr.c b/src/sock_addr.c
index c67a06fa..19e72c6e 100644
--- a/src/sock_addr.c
+++ b/src/sock_addr.c
@@ -319,10 +319,10 @@ int sock_addr_stringify_append_buffer(buffer * const restrict b, const sock_addr
         buffer_append_string_len(b, CONST_STR_LEN("["));
         if (0 != sock_addr_inet_ntop_append_buffer(b, saddr)) {
           #ifdef __COVERITY__
-            force_assert(buffer_string_length(b) > 0); /*(appended "[")*/
+            force_assert(buffer_clen(b) > 0); /*(appended "[")*/
           #endif
             /* coverity[overflow_sink : FALSE] */
-            buffer_string_set_length(b, buffer_string_length(b)-1);
+            buffer_truncate(b, buffer_clen(b)-1);
             return -1;
         }
         buffer_append_string_len(b, CONST_STR_LEN("]:"));
@@ -656,7 +656,7 @@ int sock_addr_from_str_numeric(sock_addr * const restrict saddr, const char * co
 int sock_addr_from_buffer_hints_numeric(sock_addr * const restrict saddr, socklen_t * const restrict len, const buffer * const restrict b, int family, unsigned short port, log_error_st * const restrict errh)
 {
     /*(this routine originates from mod_fastcgi.c and mod_scgi.c)*/
-    if (buffer_string_is_empty(b)) {
+    if (!b || buffer_is_blank(b)) {
         /*(preserve existing behavior (for now))*/
         /*(would be better if initialized default when reading config)*/
         memset(&saddr->ipv4, 0, sizeof(struct sockaddr_in));