comment #1:

> When the required data spans more than one pbuf, null is passed in and the data cannot be copied out

That's the point I address below. If data spans more than one pbuf, NULL would be returned in which case further action (allocating a buffer on the stack, for example) would become necessary. But in cases where the payloads almost never (or actually never) span multiple pbufs, why force the user to always allocate a separate buffer that'll never get used?

The pbuf_get_contiguous currently requires a non-NULL buffer and a non-zero buffer size:

https://git.savannah.nongnu.org/cgit/lwip.git/tree/src/core/pbuf.c#n1111

It could be quite useful if an application could call it with NULL / 0, thus avoiding pbuf_copy_partial if possible, as well as memory allocation.

For instance:

struct foo *foo = pbuf_get_contiguous(pbuf, NULL, 0, sizeof(*foo), offset);
if (!foo)
{
  // error condition / malloc / stack call / etc
}

As it currently stands, additional stack would be required. For instance:

struct foo foo;
struct foo *pfoo = pbuf_get_contiguous(pbuf, &foo, sizeof(foo), sizeof(foo), offset);