An NGINX HTTP handler receives a request pointer and returns an integer request-processing status. A calculator handler can turn POST requests to `/calculate` into an HTTP interface for an existing Reverse Polish Notation calculator. NGINX supplies the C module; Rust supplies the handler through a foreign function interface (FFI). section 4.0 section 4.2
The request body takes a separate step to read:
- Expose the Rust handler to C as `#[no_mangle] pub unsafe extern "C" fn ngx_http_calculator_handler(r: *mut ngx_http_request_t) -> ngx_int_t`. The C module declares the same handler by name. section 4.2 section 4.4
- Call `ngx_http_read_client_request_body(r, Some(read_body_handler))`. Return a nonzero result immediately; otherwise return `0`. The callback runs when the body has been read. section 4.4
- In the callback, reject a null request pointer before accessing it. The example helper checks body-buffer pointers, forms a byte slice, and converts it to UTF-8; this stage logs the body rather than returning a calculation. section 4.4
Calculator request
`curl -X POST -d '3 4 +' http://localhost:8080/calculate` illustrates the intended interface, with `7` as its result. Loading the dynamic module and enabling `calculate on` at that location connects the endpoint to the handler; the shown body-reading implementation is only one step toward that result. section 4.0 section 4.2 section 4.4
unsafe fn request_body_as_str<'a>(
request: &'a ngx_http_request_t,
) -> Result<&'a str, &'static str> {
if request.request_body.is_null()
|| (*request.request_body).bufs.is_null()
|| (*(*request.request_body).bufs).buf.is_null()
{
return Err("Request body buffers
were not initialized as expected");
}
let buf = (*(*request.request_body).bufs).buf;
let start = (*buf).pos;
let len = (*buf).last.offset_from(start) as usize;
let body_bytes = std::slice::from_raw_parts(start, len);
let body_str = std::str::from_utf8(body_bytes)
.map_err(|_| "Body contains invalid UTF-8")?;
Ok(body_str)
}
Follow the pointer checks, buffer positions, byte-slice creation, and UTF-8 conversion that turn a loaded request body into a Rust string. section 4.4
