pub fn entry_bin<K>(&mut self, key: K) -> Result<Entry<'_, Binary>, InvalidMetadataKey>
    where
        K: AsMetadataKey<Binary>,
    {
        self.generic_entry::<Binary, K>(key)
    }
Gets the given Binary key's corresponding entry in the map for in-place
manipulation.

# Examples

```
# use tonic::metadata::*;
# use std::str;
let mut map = MetadataMap::default();

let headers = &[
"content-length-bin",
"x-hello-bin",
"Content-Length-bin",
"x-world-bin",
];

for &header in headers {
let counter = map.entry_bin(header).unwrap().or_insert(MetadataValue::from_bytes(b""));
*counter = MetadataValue::from_bytes(format!("{}{}", str::from_utf8(counter.to_bytes().unwrap().as_ref()).unwrap(), "1").as_bytes());
}

assert_eq!(map.get_bin("content-length-bin").unwrap(), "11");
assert_eq!(map.get_bin("x-hello-bin").unwrap(), "1");

// Attempting to read a key of the wrong type fails by not
// finding anything.
map.append("host", "world".parse().unwrap());
assert!(!map.entry_bin("host").is_ok());
assert!(!map.entry_bin("host".to_string()).is_ok());
assert!(!map.entry_bin(&("host".to_string())).is_ok());

// Attempting to read an invalid key string fails by not
// finding anything.
assert!(!map.entry_bin("host{}-bin").is_ok());
assert!(!map.entry_bin("host{}-bin".to_string()).is_ok());
assert!(!map.entry_bin(&("host{}-bin".to_string())).is_ok());
```
tonic/src/metadata/map.rs