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09b801a968
this reworks memory allocation throughout the support library.
the old DO_ALLOC macro had several problems:
1) only by reading the macro implementation is it possible to tell
what actually occurs. consider:
DO_ALLOC(x, ...);
vs.:
x = do_alloc(...);
only in the latter is it clear that x is being assigned to.
2) it looks like a typical macro/function call, except it alters the
control flow, usually by return'ing or executing a goto in the
enclosing function. this type of anti-pattern is explicitly called out
in the linux kernel coding style.
3) in one instance, setting the destination pointer to NULL is
actually a *success* return. in parse_required_member(), when parsing
a PROTOBUF_C_TYPE_BYTES wire field, it is possible that the field is
present but of zero length, in which case memory shouldn't be
allocated and nothing should actually be copied. this is not apparent
from reading:
DO_ALLOC(bd->data, allocator, len - pref_len, return 0);
memcpy(bd->data, data + pref_len, len - pref_len);
instead, make this behavior explicit:
if (len - pref_len > 0) {
bd->data = do_alloc(allocator, len - pref_len);
if (bd->data == NULL)
return 0;
memcpy(bd->data, data + pref_len, len - pref_len);
}
this is much more readable and makes it possible to write a
replacement for DO_ALLOC which returns NULL on failures.
this changes the protobuf_c_default_allocator to contain only NULL
values; if a replacement function pointer is not present (non-NULL) in
this struct, the default malloc/free implementations are used. this
makes it impossible to call the default allocator functions directly and
represents an API/ABI break, which required a fix to the
PROTOBUF_C_BUFFER_SIMPLE_CLEAR macro.
despite turning one-line allocations in the simple case:
DO_ALLOC(rv, allocator, desc->sizeof_message, return NULL);
into three-line statements like:
rv = do_alloc(allocator, desc->sizeof_message);
if (!rv)
return (NULL);
this changeset actually *reduces* the total number of lines in the
support library.