Rust/rusty: Make use of uwr_get_http_total_content_sent()

When the uwr_get_http_content_str() function, which returns the request
body content as a string, was added it used uwr_get_http_content_len()
to determine the length of the returned string (the request body content
is not null-terminated).

This could potentially in some circumstances return too much data if the
request was split over multiple calls into the Wasm module and
uwr_get_http_content_str() was called before all the data had actually
been received.

Instead use the newly introduced uwr_get_http_total_content_sent()
function to determine the amount of data to return in the string as it
currently stands.

Fixes: bf968c9 ("Rust/rusty: Add uwr_get_http_content_str()")
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Author: ac000

src/rust/unit-wasm-sys/rusty.rs

@@ -115,7 +115,7 @@ pub fn uwr_get_http_content_str(ctx: *const luw_ctx_t) -> &'static str {
     unsafe {
         let slice = slice::from_raw_parts(
             uwr_get_http_content(ctx),
-            uwr_get_http_content_len(ctx),
+            uwr_get_http_total_content_sent(ctx),
         );
         str::from_utf8(slice).unwrap()
     }