Inflates name/value block stored in *in* with length *inlen*.  This
function performs decompression.  For each successful emission of
header name/value pair,
:enum:`nghttp2_hd_inflate_flag.NGHTTP2_HD_INFLATE_EMIT` is set in
*\*inflate_flags* and name/value pair is assigned to the *nv_out*
and the function returns.  The caller must not free the members of
*nv_out*.

The *nv_out* may include pointers to the memory region in the *in*.
The caller must retain the *in* while the *nv_out* is used.

The application should call this function repeatedly until the
``(*inflate_flags) & NGHTTP2_HD_INFLATE_FINAL`` is nonzero and
return value is non-negative.  If that happens, all given input
data (*inlen* bytes) are processed successfully.  Then the
application must call `nghttp2_hd_inflate_end_headers()` to prepare
for the next header block input.

In other words, if *in_final* is nonzero, and this function returns
*inlen*, you can assert that
:enum:`nghttp2_hd_inflate_final.NGHTTP2_HD_INFLATE_FINAL` is set in
*\*inflate_flags*.

The caller can feed complete compressed header block.  It also can
feed it in several chunks.  The caller must set *in_final* to
nonzero if the given input is the last block of the compressed
header.

This function returns the number of bytes processed if it succeeds,
or one of the following negative error codes:

:enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
    Out of memory.
:enum:`nghttp2_error.NGHTTP2_ERR_HEADER_COMP`
    Inflation process has failed.
:enum:`nghttp2_error.NGHTTP2_ERR_BUFFER_ERROR`
    The header field name or value is too large.

Example follows::

    int inflate_header_block(nghttp2_hd_inflater *hd_inflater,
                             uint8_t *in, size_t inlen, int final)
    {
        nghttp2_ssize rv;

        for(;;) {
            nghttp2_nv nv;
            int inflate_flags = 0;

            rv = nghttp2_hd_inflate_hd3(hd_inflater, &nv, &inflate_flags,
                                        in, inlen, final);

            if(rv < 0) {
                fprintf(stderr, "inflate failed with error code %td", rv);
                return -1;
            }

            in += rv;
            inlen -= rv;

            if(inflate_flags & NGHTTP2_HD_INFLATE_EMIT) {
                fwrite(nv.name, nv.namelen, 1, stderr);
                fprintf(stderr, ": ");
                fwrite(nv.value, nv.valuelen, 1, stderr);
                fprintf(stderr, "\n");
            }
            if(inflate_flags & NGHTTP2_HD_INFLATE_FINAL) {
                nghttp2_hd_inflate_end_headers(hd_inflater);
                break;
            }
            if((inflate_flags & NGHTTP2_HD_INFLATE_EMIT) == 0 &&
               inlen == 0) {
               break;
            }
        }

        return 0;
    }