# Struct 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));

## Implementations

### `impl HeaderMap` [src]

#### `pub fn new() -> Self` [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"));

#### `pub fn iter(&self) -> Iter<'_, T>ⓘ

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

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

### Notable traits for IterMut<'a, T>

`impl<'a, T> Iterator for IterMut<'a, T> type Item = (&'a HeaderName, &'a mut 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");
    }

#### `pub fn keys(&self) -> Keys<'_, T>ⓘ

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

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

#### `pub fn values(&self) -> Values<'_, T>ⓘ

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

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

### Notable traits for ValuesMut<'a, T>

`impl<'a, T> Iterator for ValuesMut<'a, T> type Item = &'a mut 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");
    }

#### `pub fn drain(&mut self) -> Drain<'_, T>ⓘ

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

`impl<'a, T> Iterator for Drain<'a, T> type Item = (Option<HeaderName>, T);`
` [src]

Clears the map, returning all entries as an iterator.

The internal memory is kept for reuse.

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

    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();

    assert_eq!(drain.next(), Some((Some(HOST), "hello".parse().unwrap())));
    assert_eq!(drain.next(), Some((None, "goodbye".parse().unwrap())));

    assert_eq!(drain.next(), Some((Some(CONTENT_LENGTH), "123".parse().unwrap())));

    assert_eq!(drain.next(), None);

#### `pub fn entry<K>(&mut self, key: K) -> Entry<'_, T> where
K: IntoHeaderName,` [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).or_insert(0);
        *counter += 1;
    }

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

#### `pub fn try_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.

# Errors

This method differs from `entry` by allowing types that may not be valid `HeaderName`s to passed as the key (such as `String`). If they do not parse as a valid `HeaderName`, this returns an `InvalidHeaderName` error.

#### `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: Clone> Clone for HeaderMap<T>` [src]

#### `fn clone(&self) -> HeaderMap<T>` [src]

Returns a copy of the value. Read more

#### `pub fn clone_from(&mut self, source: &Self)`1.0.0 [src]

Performs copy-assignment from `source`. Read more

### `impl<T: Debug> Debug for HeaderMap<T>` [src]

#### `fn fmt(&self, f: &mut Formatter<'_>) -> Result` [src]

Formats the value using the given formatter. Read more

### `impl<T> Default for HeaderMap<T>` [src]

#### `fn default() -> Self` [src]

Returns the “default value” for a type. Read more

### `impl<T: Eq> Eq for HeaderMap<T>` [src]

### `impl<T> Extend<(HeaderName, T)> for HeaderMap<T>` [src]

#### `fn extend<I: IntoIterator<Item = (HeaderName, T)>>(&mut self, iter: I)` [src]

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

#### `pub fn extend_one(&mut self, item: A)` [src]

🔬 This is a nightly-only experimental API. (`extend_one`)

Extends a collection with exactly one element.

#### `pub fn extend_reserve(&mut self, additional: usize)` [src]

🔬 This is a nightly-only experimental API. (`extend_one`)

Reserves capacity in a collection for the given number of additional elements. Read more

### `impl<T> Extend<(Option<HeaderName>, T)> for HeaderMap<T>` [src]

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

#### `pub fn extend_one(&mut self, item: A)` [src]

🔬 This is a nightly-only experimental API. (`extend_one`)

Extends a collection with exactly one element.

#### `pub fn extend_reserve(&mut self, additional: usize)` [src]

🔬 This is a nightly-only experimental API. (`extend_one`)

Reserves capacity in a collection for the given number of additional elements. Read more

### `impl<T> FromIterator<(HeaderName, T)> for HeaderMap<T>` [src]

#### `fn from_iter<I>(iter: I) -> Self where
I: IntoIterator<Item = (HeaderName, T)>,` [src]

Creates a value from 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.

#### `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?

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

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

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

Creates an iterator from a value. Read more

### `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>ⓘ

### Notable traits for IterMut<'a, T>

`impl<'a, T> Iterator for IterMut<'a, T> type Item = (&'a HeaderName, &'a mut 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?

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

### Notable traits for IntoIter<T>

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

Creates a consuming iterator, that is, one that moves keys and values out of the map in arbitrary 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<T: PartialEq> PartialEq<HeaderMap<T>> for HeaderMap<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]pub fn ne(&self, other: &Rhs) -> bool` 1.0.0 [src]

This method tests for `!=`.

### `impl<'a, K, V, T> TryFrom<&'a HashMap<K, V, RandomState>> for HeaderMap<T> where
K: Eq + Hash,
HeaderName: TryFrom<&'a K>,
<HeaderName as TryFrom<&'a K>>::Error: Into<Error>,
T: TryFrom<&'a V>,
T::Error: Into<Error>,` [src]

Try to convert a `HashMap` into a `HeaderMap`.

# Examples

    use std::collections::HashMap;
    use std::convert::TryInto;
    use http::HeaderMap;

    let mut map = HashMap::new();
    map.insert("X-Custom-Header".to_string(), "my value".to_string());

    let headers: HeaderMap = (&map).try_into().expect("valid headers");
    assert_eq!(headers["X-Custom-Header"], "my value");

#### `type Error = Error`

The type returned in the event of a conversion error.

#### `fn try_from(c: &'a HashMap<K, V>) -> Result<Self, Self::Error>` [src]

Performs the conversion.

## Auto Trait Implementations

### `impl<T> RefUnwindSafe for HeaderMap<T> where
T: RefUnwindSafe,`

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

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

### `impl<T> Unpin for HeaderMap<T> where
T: Unpin,`

### `impl<T> UnwindSafe for HeaderMap<T> where
T: UnwindSafe,`

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&self) -> TypeId` [src]

Gets the `TypeId` of `self`. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&self) -> &T` [src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut self) -> &mut T` [src]

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T` [src]

#### `pub fn from(t: T) -> T` [src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `pub fn into(self) -> U` [src]

Performs the conversion.

### `impl<T> ToOwned for T where
T: Clone,` [src]

#### `type Owned = T`

The resulting type after obtaining ownership.

#### `pub fn to_owned(&self) -> T` [src]

Creates owned data from borrowed data, usually by cloning. Read more

#### `pub fn clone_into(&self, target: &mut T)` [src]

🔬 This is a nightly-only experimental API. (`toowned_clone_into`)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>` [src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>` [src]

Performs the conversion.