On 13-Sep-21 07:01, Daniel Stenberg via curl-library wrote: > > # Feedback > > I'm all ears. Especially if you have alternative solutions to suggest > or if you have an opinion on which way to go. > > This is not a problem we must solve *right now*, but I would feel > better if we have an idea about how to address it when we get there. > Because I'm convinced we will reach this point eventually. > Here's an approach that has some short-term pain, but solves the problem permanently - including for protocol 65, 129, ...
Switch to an expandable array of bits, similar to select()'s FDSETS:
Deprecate the existing CURLOPT_PROTOCOLS and CURLOPT_REDIR_PROTOCOLS,
replace with CURLOPT_PROTOCOLS_EXT and CURLOPT_REDIR_PROTOCOLS_EXT.
Use indices rather than bitmasks for CURLPROTO_* (e.g. add
CURLPROTO_DICTn, CURLPROTO_FTPn, etc)
Switch from a long to a pointer to typedef struct { unsigned int size;
uint8 bits[(CURL_PROTO_MAXn + 7)/8]} CURLPROTO.
Provide some macros along the lines of FD_CLR/FD_ISSET/FD_SET/FD_ZERO,
but instead of the FD_SETSIZE hack, use the 'size' value of the
structure, which will increase every time you add 8 more protocols. But
clients compiled earlier will have a smaller "size", so will not
inadvertently enable new protocols.
e.g. the user-visible functions might be something like:
#define CURLPROTO_SET( str, bit ) do { ASSERT((bit) <= CURL_PROTO_MAXn
&& (bit) <= (str)->size); (str)->bits[(bit)>>3] |= 1u<<((bit)&7); }
while(0) /* Could also provide a vararg function to set multiple */
#define CURLPROTO_ISSET( str, bit ) ( ((bit) > CURL_PROTO_MAXn || (bit)
> (str)->size))? 0 : (str)->bits[(bit)>>3] & 1u<<((bit)&7) )
So specifying protocols looks something like:
CURLPROTO allow = { sizeof( CURLPROTO ) }; /* The initialization could
be a macro - e.g CURL_PROTO_DECL(allow); */
CURLPROTO_ZERO(&allow); /* If a stack or malloc()'d variable */
CURLPROTO_SET( &allow, CURL_PROTO_FTPn );
CURLPROTO_SET(&allow, CURL_PROTO_HTTPSn);
curl_easy_setopt( handle, CURLOPT_PROTOCOLS_EXT, &allow);
Internally, use the current (usually larger) size so you don't have to
bounds-check every reference; just memcpy min(libraryMAX, 'size'
provided) to an internal structure. Convert the deprecated functions to
set(or clear) the first few bits in the internal structure as specified;
they should zero all bits 32+. (Be careful about endianisms.)
There ought to be a function to return, in the same format, a structure
listing all the protocols implemented by the current library.
This scheme provides backward compatibility with infinite
expandability. There's some overhead for the client, but these aren't
critical path - they're probably setup once and tested never. In the
library, the assertions will optimize out, and a compiler will optimize
the bit references to be no more expensive than the current bit tests.
The compatibility layer is pretty thin - it probably ends up being a
cast & possible byteswap.
With bit more thought (pun intended), you might be able to avoid
introducing the new CURLPROTO_*n symbols - but at first blush, it seems
expensive to do that while also exposing the existing API.
Polishing is left as an exercise for the reader...
Timothe Litt
ACM Distinguished Engineer
--------------------------
This communication may not represent the ACM or my employer's views,
if any, on the matters discussed.
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