Function parse_payload_type 

pub fn parse_payload_type(value: &[u8]) -> Result<&str, CratestackError>

Parse a received PAYLOAD_TYPE_HEADER value, strictly.

Checks the grammar only; whether the type may be sealed or is allowed for an op is the caller’s decision (is_sealable_payload_type, the op’s declared types).

use cratestack_core::parse_payload_type;

assert_eq!(
    parse_payload_type(b"application/x-www-form-urlencoded").unwrap(),
    "application/x-www-form-urlencoded"
);
assert!(parse_payload_type(b"Application/JSON").is_err());
assert!(parse_payload_type(b"application/json; charset=utf-8").is_err());