Struct reqwest::header::HeaderMap

source · [−]
pub struct HeaderMap<T = HeaderValue> { /* private fields */ }
Expand description

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

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());

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());

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());

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());

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());

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);

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());

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);

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");

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");

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());

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"));

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);
}

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");
}

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);
}

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);
}

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");
}

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());

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);

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);

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());

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

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

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

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

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

Extends a collection with exactly one element.

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

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

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

Extends a collection with exactly one element.

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

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

Creates a value from an iterator. Read more

Try to convert a HashMap into a HeaderMap.

Examples

use std::collections::HashMap;
use http::{HttpTryFrom, header::HeaderMap};

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

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

Associated error with the conversion this implementation represents.

Associated error with the conversion this implementation represents.

Panics

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

The returned type after indexing.

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

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());

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

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

This method tests for !=.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Compare self to key and return true if they are equal.

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.

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

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

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

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.