# actix_web::http::header::HeaderMap - Rust
API documentation for the Rust `HeaderMap` struct in crate `actix_web`.
Keywords: rust, rustlang, rust-lang, HeaderMap

# Struct actix_web::http::header::HeaderMap [−] [src]

    pub struct HeaderMap<T = HeaderValue> { /* fields omitted */ }

A set of HTTP headers

`HeaderMap` is an multimap of `HeaderName` to values.

# Examples

Basic usage

    let mut headers = HeaderMap::new();

    headers.insert(HOST, "example.com".parse().unwrap());
    headers.insert(CONTENT_LENGTH, "123".parse().unwrap());

    assert!(headers.contains_key(HOST));
    assert!(!headers.contains_key(LOCATION));

    assert_eq!(headers[HOST], "example.com");

    headers.remove(HOST);

    assert!(!headers.contains_key(HOST));

## Methods

###

`impl HeaderMap<HeaderValue>`

[src]

####

`pub fn new() -> HeaderMap<HeaderValue>`

[src]

Create an empty `HeaderMap`.

The map will be created without any capacity. This function will not allocate.

# Examples

    let map = HeaderMap::new();

    assert!(map.is_empty());
    assert_eq!(0, map.capacity());

###

`impl<T> HeaderMap<T>`

[src]

####

`pub fn with_capacity(capacity: usize) -> HeaderMap<T>`

[src]

Create an empty `HeaderMap` with the specified capacity.

The returned map will allocate internal storage in order to hold about `capacity` elements without reallocating. However, this is a "best effort" as there are usage patterns that could cause additional allocations before `capacity` headers are stored in the map.

More capacity than requested may be allocated.

# Examples

    let map: HeaderMap<u32> = HeaderMap::with_capacity(10);

    assert!(map.is_empty());
    assert_eq!(12, map.capacity());

####

`pub fn len(&self) -> usize`

[src]

Returns the number of headers stored in the map.

This number represents the total number of values stored in the map. This number can be greater than or equal to the number of keys stored given that a single key may have more than one associated value.

# Examples

    let mut map = HeaderMap::new();

    assert_eq!(0, map.len());

    map.insert(ACCEPT, "text/plain".parse().unwrap());
    map.insert(HOST, "localhost".parse().unwrap());

    assert_eq!(2, map.len());

    map.append(ACCEPT, "text/html".parse().unwrap());

    assert_eq!(3, map.len());

####

`pub fn keys_len(&self) -> usize`

[src]

Returns the number of keys stored in the map.

This number will be less than or equal to `len()` as each key may have more than one associated value.

# Examples

    let mut map = HeaderMap::new();

    assert_eq!(0, map.keys_len());

    map.insert(ACCEPT, "text/plain".parse().unwrap());
    map.insert(HOST, "localhost".parse().unwrap());

    assert_eq!(2, map.keys_len());

    map.insert(ACCEPT, "text/html".parse().unwrap());

    assert_eq!(2, map.keys_len());

####

`pub fn is_empty(&self) -> bool`

[src]

Returns true if the map contains no elements.

# Examples

    let mut map = HeaderMap::new();

    assert!(map.is_empty());

    map.insert(HOST, "hello.world".parse().unwrap());

    assert!(!map.is_empty());

####

`pub fn clear(&mut self)`

[src]

Clears the map, removing all key-value pairs. Keeps the allocated memory for reuse.

# Examples

    let mut map = HeaderMap::new();
    map.insert(HOST, "hello.world".parse().unwrap());

    map.clear();
    assert!(map.is_empty());
    assert!(map.capacity() > 0);

####

`pub fn capacity(&self) -> usize`

[src]

Returns the number of headers the map can hold without reallocating.

This number is an approximation as certain usage patterns could cause additional allocations before the returned capacity is filled.

# Examples

    let mut map = HeaderMap::new();

    assert_eq!(0, map.capacity());

    map.insert(HOST, "hello.world".parse().unwrap());
    assert_eq!(6, map.capacity());

####

`pub fn reserve(&mut self, additional: usize)`

[src]

Reserves capacity for at least `additional` more headers to be inserted into the `HeaderMap`.

The header map may reserve more space to avoid frequent reallocations. Like with `with_capacity`, this will be a "best effort" to avoid allocations until `additional` more headers are inserted. Certain usage patterns could cause additional allocations before the number is reached.

# Panics

Panics if the new allocation size overflows `usize`.

# Examples

    let mut map = HeaderMap::new();
    map.reserve(10);

####

`pub fn get<K>(&self, key: K) -> Option<&T> where K: AsHeaderName,`

[src]

Returns a reference to the value associated with the key.

If there are multiple values associated with the key, then the first one is returned. Use `get_all` to get all values associated with a given key. Returns `None` if there are no values associated with the key.

# Examples

    let mut map = HeaderMap::new();
    assert!(map.get("host").is_none());

    map.insert(HOST, "hello".parse().unwrap());
    assert_eq!(map.get(HOST).unwrap(), &"hello");
    assert_eq!(map.get("host").unwrap(), &"hello");

    map.append(HOST, "world".parse().unwrap());
    assert_eq!(map.get("host").unwrap(), &"hello");

####

`pub fn get_mut<K>(&mut self, key: K) -> Option<&mut T> where K: AsHeaderName,`

[src]

Returns a mutable reference to the value associated with the key.

If there are multiple values associated with the key, then the first one is returned. Use `entry` to get all values associated with a given key. Returns `None` if there are no values associated with the key.

# Examples

    let mut map = HeaderMap::default();
    map.insert(HOST, "hello".to_string());
    map.get_mut("host").unwrap().push_str("-world");

    assert_eq!(map.get(HOST).unwrap(), &"hello-world");

####

`pub fn get_all<K>(&self, key: K) -> GetAll<T> where K: AsHeaderName,`

[src]

Returns a view of all values associated with a key.

The returned view does not incur any allocations and allows iterating the values associated with the key. See `GetAll` for more details. Returns `None` if there are no values associated with the key.

# Examples

    let mut map = HeaderMap::new();

    map.insert(HOST, "hello".parse().unwrap());
    map.append(HOST, "goodbye".parse().unwrap());

    let view = map.get_all("host");

    let mut iter = view.iter();
    assert_eq!(&"hello", iter.next().unwrap());
    assert_eq!(&"goodbye", iter.next().unwrap());
    assert!(iter.next().is_none());

####

`pub fn contains_key<K>(&self, key: K) -> bool where K: AsHeaderName,`

[src]

Returns true if the map contains a value for the specified key.

# Examples

    let mut map = HeaderMap::new();
    assert!(!map.contains_key(HOST));

    map.insert(HOST, "world".parse().unwrap());
    assert!(map.contains_key("host"));

####
ⓘImportant traits for Iter<'a, T>

### Important traits for Iter<'a, T>

`impl<'a, T> Iterator for Iter<'a, T> type Item = (&'a HeaderName, &'a T);`

`pub fn iter(&self) -> Iter<T>`

[src]

An iterator visiting all key-value pairs.

The iteration order is arbitrary, but consistent across platforms for the same crate version. Each key will be yielded once per associated value. So, if a key has 3 associated values, it will be yielded 3 times.

# Examples

    let mut map = HeaderMap::new();

    map.insert(HOST, "hello".parse().unwrap());
    map.append(HOST, "goodbye".parse().unwrap());
    map.insert(CONTENT_LENGTH, "123".parse().unwrap());

    for (key, value) in map.iter() {
        println!("{:?}: {:?}", key, value);
    }

####

`pub fn iter_mut(&mut self) -> IterMut<T>`

[src]

An iterator visiting all key-value pairs, with mutable value references.

The iterator order is arbitrary, but consistent across platforms for the same crate version. Each key will be yielded once per associated value, so if a key has 3 associated values, it will be yielded 3 times.

# Examples

    let mut map = HeaderMap::default();

    map.insert(HOST, "hello".to_string());
    map.append(HOST, "goodbye".to_string());
    map.insert(CONTENT_LENGTH, "123".to_string());

    for (key, value) in map.iter_mut() {
        value.push_str("-boop");
    }

####
ⓘImportant traits for Keys<'a, T>

### Important traits for Keys<'a, T>

`impl<'a, T> Iterator for Keys<'a, T> type Item = &'a HeaderName;`

`pub fn keys(&self) -> Keys<T>`

[src]

An iterator visiting all keys.

The iteration order is arbitrary, but consistent across platforms for the same crate version. Each key will be yielded only once even if it has multiple associated values.

# Examples

    let mut map = HeaderMap::new();

    map.insert(HOST, "hello".parse().unwrap());
    map.append(HOST, "goodbye".parse().unwrap());
    map.insert(CONTENT_LENGTH, "123".parse().unwrap());

    for key in map.keys() {
        println!("{:?}", key);
    }

####
ⓘImportant traits for Values<'a, T>

### Important traits for Values<'a, T>

`impl<'a, T> Iterator for Values<'a, T> type Item = &'a T;`

`pub fn values(&self) -> Values<T>`

[src]

An iterator visiting all values.

The iteration order is arbitrary, but consistent across platforms for the same crate version.

# Examples

    let mut map = HeaderMap::new();

    map.insert(HOST, "hello".parse().unwrap());
    map.append(HOST, "goodbye".parse().unwrap());
    map.insert(CONTENT_LENGTH, "123".parse().unwrap());

    for value in map.values() {
        println!("{:?}", value);
    }

####

`pub fn values_mut(&mut self) -> ValuesMut<T>`

[src]

An iterator visiting all values mutably.

The iteration order is arbitrary, but consistent across platforms for the same crate version.

# Examples

    let mut map = HeaderMap::default();

    map.insert(HOST, "hello".to_string());
    map.append(HOST, "goodbye".to_string());
    map.insert(CONTENT_LENGTH, "123".to_string());

    for value in map.values_mut() {
        value.push_str("-boop");
    }

####
ⓘImportant traits for Drain<'a, T>

### Important traits for Drain<'a, T>

`impl<'a, T> Iterator for Drain<'a, T> type Item = (HeaderName, ValueDrain<'a, T>);`

`pub fn drain(&mut self) -> Drain<T>`

[src]

Clears the map, returning all entries as an iterator.

The internal memory is kept for reuse.

# Examples

    let mut map = HeaderMap::new();

    map.insert(HOST, "hello".parse().unwrap());
    map.append(HOST, "goodbye".parse().unwrap());
    map.insert(CONTENT_LENGTH, "123".parse().unwrap());

    let mut drain = map.drain();

    let (key, mut vals) = drain.next().unwrap();

    assert_eq!("host", key);
    assert_eq!("hello", vals.next().unwrap());
    assert_eq!("goodbye", vals.next().unwrap());
    assert!(vals.next().is_none());

    let (key, mut vals) = drain.next().unwrap();

    assert_eq!("content-length", key);
    assert_eq!("123", vals.next().unwrap());
    assert!(vals.next().is_none());

####

`pub fn entry<K>(&mut self, key: K) -> Result<Entry<T>, InvalidHeaderName> where K: AsHeaderName,`

[src]

Gets the given key's corresponding entry in the map for in-place manipulation.

# Examples

    let mut map: HeaderMap<u32> = HeaderMap::default();

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

    for &header in headers {
        let counter = map.entry(header).unwrap().or_insert(0);
        *counter += 1;
    }

    assert_eq!(map["content-length"], 2);
    assert_eq!(map["x-hello"], 1);

####

`pub fn insert<K>(&mut self, key: K, val: T) -> Option<T> where K: IntoHeaderName,`

[src]

Inserts a key-value pair into the map.

If the map did not previously have this key present, then `None` is returned.

If the map did have this key present, the new value is associated with the key and all previous values are removed. Note that only a single one of the previous values is returned. If there are multiple values that have been previously associated with the key, then the first one is returned. See `insert_mult` on `OccupiedEntry` for an API that returns all values.

The key is not updated, though; this matters for types that can be `==` without being identical.

# Examples

    let mut map = HeaderMap::new();
    assert!(map.insert(HOST, "world".parse().unwrap()).is_none());
    assert!(!map.is_empty());

    let mut prev = map.insert(HOST, "earth".parse().unwrap()).unwrap();
    assert_eq!("world", prev);

####

`pub fn append<K>(&mut self, key: K, value: T) -> bool where K: IntoHeaderName,`

[src]

Inserts a key-value pair into the map.

If the map did not previously have this key present, then `false` is returned.

If the map did have this key present, the new value is pushed to the end of the list of values currently associated with the key. The key is not updated, though; this matters for types that can be `==` without being identical.

# Examples

    let mut map = HeaderMap::new();
    assert!(map.insert(HOST, "world".parse().unwrap()).is_none());
    assert!(!map.is_empty());

    map.append(HOST, "earth".parse().unwrap());

    let values = map.get_all("host");
    let mut i = values.iter();
    assert_eq!("world", *i.next().unwrap());
    assert_eq!("earth", *i.next().unwrap());

####

`pub fn remove<K>(&mut self, key: K) -> Option<T> where K: AsHeaderName,`

[src]

Removes a key from the map, returning the value associated with the key.

Returns `None` if the map does not contain the key. If there are multiple values associated with the key, then the first one is returned. See `remove_entry_mult` on `OccupiedEntry` for an API that yields all values.

# Examples

    let mut map = HeaderMap::new();
    map.insert(HOST, "hello.world".parse().unwrap());

    let prev = map.remove(HOST).unwrap();
    assert_eq!("hello.world", prev);

    assert!(map.remove(HOST).is_none());

## Trait Implementations

###

`impl<T> Default for HeaderMap<T>`

[src]

####

`fn default() -> HeaderMap<T>`

[src]

Returns the "default value" for a type. Read more

###

`impl<T> Eq for HeaderMap<T> where T: Eq,`

[src]

###

`impl<T> PartialEq<HeaderMap<T>> for HeaderMap<T> where T: PartialEq<T>,`

[src]

####

`fn eq(&self, other: &HeaderMap<T>) -> bool`

[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

####

`#[must_use] fn ne(&self, other: &Rhs) -> bool`

1.0.0
[src]

This method tests for `!=`.

###

`impl<T> Extend<(Option<HeaderName>, T)> for HeaderMap<T>`

[src]

####

`fn extend<I>(&mut self, iter: I) where I: IntoIterator<Item = (Option<HeaderName>, T)>,`

[src]

Extend a `HeaderMap` with the contents of another `HeaderMap`.

This function expects the yielded items to follow the same structure as `IntoIter`.

# Panics

This panics if the first yielded item does not have a `HeaderName`.

# Examples

    let mut map = HeaderMap::new();

    map.insert(ACCEPT, "text/plain".parse().unwrap());
    map.insert(HOST, "hello.world".parse().unwrap());

    let mut extra = HeaderMap::new();

    extra.insert(HOST, "foo.bar".parse().unwrap());
    extra.insert(COOKIE, "hello".parse().unwrap());
    extra.append(COOKIE, "world".parse().unwrap());

    map.extend(extra);

    assert_eq!(map["host"], "foo.bar");
    assert_eq!(map["accept"], "text/plain");
    assert_eq!(map["cookie"], "hello");

    let v = map.get_all("host");
    assert_eq!(1, v.iter().count());

    let v = map.get_all("cookie");
    assert_eq!(2, v.iter().count());

###

`impl<T> Extend<(HeaderName, T)> for HeaderMap<T>`

[src]

####

`fn extend<I>(&mut self, iter: I) where I: IntoIterator<Item = (HeaderName, T)>,`

[src]

Extends a collection with the contents of an iterator. Read more

###

`impl<'a, K, T> Index<K> for HeaderMap<T> where K: AsHeaderName,`

[src]

#### `type Output = T`

The returned type after indexing.

####
ⓘImportant traits for &'a mut R

### Important traits for &'a mut R

`impl<'a, R> Read for &'a mut R where
R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;`

`fn index(&self, index: K) -> &T`

[src]

# Panics

Using the index operator will cause a panic if the header you're querying isn't set.

###

`impl<'a, T> IntoIterator for &'a HeaderMap<T>`

[src]

#### `type Item = (&'a HeaderName, &'a T)`

The type of the elements being iterated over.

#### `type IntoIter = Iter<'a, T>`

Which kind of iterator are we turning this into?

####
ⓘImportant traits for Iter<'a, T>

### Important traits for Iter<'a, T>

`impl<'a, T> Iterator for Iter<'a, T> type Item = (&'a HeaderName, &'a T);`

`fn into_iter(self) -> Iter<'a, T>`

[src]

Creates an iterator from a value. Read more

###

`impl<T> IntoIterator for HeaderMap<T>`

[src]

#### `type Item = (Option<HeaderName>, T)`

The type of the elements being iterated over.

#### `type IntoIter = IntoIter<T>`

Which kind of iterator are we turning this into?

####
ⓘImportant traits for IntoIter<T>

### Important traits for IntoIter<T>

`impl<T> Iterator for IntoIter<T> type Item = (Option<HeaderName>, T);`

`fn into_iter(self) -> IntoIter<T>`

[src]

Creates a consuming iterator, that is, one that moves keys and values out of the map in arbitary order. The map cannot be used after calling this.

For each yielded item that has `None` provided for the `HeaderName`, then the associated header name is the same as that of the previously yielded item. The first yielded item will have `HeaderName` set.

# Examples

Basic usage.

    let mut map = HeaderMap::new();
    map.insert(header::CONTENT_LENGTH, "123".parse().unwrap());
    map.insert(header::CONTENT_TYPE, "json".parse().unwrap());

    let mut iter = map.into_iter();
    assert_eq!(iter.next(), Some((Some(header::CONTENT_LENGTH), "123".parse().unwrap())));
    assert_eq!(iter.next(), Some((Some(header::CONTENT_TYPE), "json".parse().unwrap())));
    assert!(iter.next().is_none());

Multiple values per key.

    let mut map = HeaderMap::new();

    map.append(header::CONTENT_LENGTH, "123".parse().unwrap());
    map.append(header::CONTENT_LENGTH, "456".parse().unwrap());

    map.append(header::CONTENT_TYPE, "json".parse().unwrap());
    map.append(header::CONTENT_TYPE, "html".parse().unwrap());
    map.append(header::CONTENT_TYPE, "xml".parse().unwrap());

    let mut iter = map.into_iter();

    assert_eq!(iter.next(), Some((Some(header::CONTENT_LENGTH), "123".parse().unwrap())));
    assert_eq!(iter.next(), Some((None, "456".parse().unwrap())));

    assert_eq!(iter.next(), Some((Some(header::CONTENT_TYPE), "json".parse().unwrap())));
    assert_eq!(iter.next(), Some((None, "html".parse().unwrap())));
    assert_eq!(iter.next(), Some((None, "xml".parse().unwrap())));
    assert!(iter.next().is_none());

###

`impl<'a, T> IntoIterator for &'a mut HeaderMap<T>`

[src]

#### `type Item = (&'a HeaderName, &'a mut T)`

The type of the elements being iterated over.

#### `type IntoIter = IterMut<'a, T>`

Which kind of iterator are we turning this into?

####

`fn into_iter(self) -> IterMut<'a, T>`

[src]

Creates an iterator from a value. Read more

###

`impl<T> Clone for HeaderMap<T> where T: Clone,`

[src]

####

`fn clone(&self) -> HeaderMap<T>`

[src]

Returns a copy of the value. Read more

####

`fn clone_from(&mut self, source: &Self)`

1.0.0
[src]

Performs copy-assignment from `source`. Read more

###

`impl<T> Debug for HeaderMap<T> where T: Debug,`

[src]

####

`fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`

[src]

Formats the value using the given formatter. Read more

###

`impl<T> FromIterator<(HeaderName, T)> for HeaderMap<T>`

[src]

####

`fn from_iter<I>(iter: I) -> HeaderMap<T> where I: IntoIterator<Item = (HeaderName, T)>,`

[src]

Creates a value from an iterator. Read more

## Auto Trait Implementations

###

`impl<T> Send for HeaderMap<T> where T: Send,`

###

`impl<T> Sync for HeaderMap<T> where T: Sync,`

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