Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This function returns the total amount of content that the Wasm module
has received so far.

This will be used in the rusty API's uwr_get_http_content_str() function
which returns the body content as a string. Due to the body content not
being null-terminated we need to know how much data to use for the
string, for which we are currently using uwr_get_http_content_len(),
which could in some cases return too much if a request is being split
over multiple calls the module.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Technically the context pointer can be passed in const even though we
then un-const it passing it to the luw_foreach_http_hdr() macro.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This was used to specify the index of the response header being added,
starting at 0 and incrementing by one for each header.

Instead of having the programmer specify this, track it internally.

We add an extra check in luw_http_add_header() to make sure we aren't
trying to add more headers than we said with luw_http_init_headers(), if
we are, simply return.

This updates the API-C.md and the various examples and 'rusty' API
wrapper.

Suggested-by: Liam Crilly <liam@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

The rust build failed when trying to publish new crates, although for
some reason it didn't fail before that, due to the luw_srb_flags_t enums
generated by bindgen being 32 bit unsigned integers and the flags
argument to luw_set_req_buf() being an unsigned long (which is 64 bits
on my system) and thus producing a type mismatch error.

Rather than fight with rust just make the flags argument an unsigned
int, 32 bits is more than enough for this anyway.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

When I added the luw_http_hdr_get_value() function I needed to include
strings.h, unfortunately I added it to unit-wasm.h instead of
libunit-wasm.c

This had the undesirable effect of requiring the wasi-sysroot when
building the rust stuff for generating the libunit-wasm rust bindings.

By including strings.h in the right file we get rid of that requirement
which a subsequent commit will take care of.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

There was a luw_destroy_ctx() function at one point and its prototype
was still in the header file...

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

No reason why this needed to be a separate #define.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

libunit-wasm and example C and Rust WebAssembly modules for NGINX Unit.

Co-developed-by: Timo Stark <t.stark@nginx.com>
Co-developed-by: Liam Crilly <liam@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>