request.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use crate::response::HttpsState;
use crate::ReferrerPolicy;
use crate::ResourceTimingType;
use content_security_policy::{self as csp, CspList};
use http::header::{HeaderName, AUTHORIZATION};
use http::HeaderMap;
use http::Method;
use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
use mime::Mime;
use msg::constellation_msg::PipelineId;
use servo_url::{ImmutableOrigin, ServoUrl};
use std::sync::{Arc, Mutex};

/// An [initiator](https://fetch.spec.whatwg.org/#concept-request-initiator)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum Initiator {
    None,
    Download,
    ImageSet,
    Manifest,
    XSLT,
}

/// A request [destination](https://fetch.spec.whatwg.org/#concept-request-destination)
pub use csp::Destination;

/// A request [origin](https://fetch.spec.whatwg.org/#concept-request-origin)
#[derive(Clone, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum Origin {
    Client,
    Origin(ImmutableOrigin),
}

/// A [referer](https://fetch.spec.whatwg.org/#concept-request-referrer)
#[derive(Clone, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum Referrer {
    NoReferrer,
    /// Contains the url that "client" would be resolved to. See
    /// [https://w3c.github.io/webappsec-referrer-policy/#determine-requests-referrer](https://w3c.github.io/webappsec-referrer-policy/#determine-requests-referrer)
    ///
    /// If you are unsure you should probably use
    /// [`GlobalScope::get_referrer`](https://doc.servo.org/script/dom/globalscope/struct.GlobalScope.html#method.get_referrer)
    Client(ServoUrl),
    ReferrerUrl(ServoUrl),
}

/// A [request mode](https://fetch.spec.whatwg.org/#concept-request-mode)
#[derive(Clone, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum RequestMode {
    Navigate,
    SameOrigin,
    NoCors,
    CorsMode,
    WebSocket { protocols: Vec<String> },
}

/// Request [credentials mode](https://fetch.spec.whatwg.org/#concept-request-credentials-mode)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum CredentialsMode {
    Omit,
    CredentialsSameOrigin,
    Include,
}

/// [Cache mode](https://fetch.spec.whatwg.org/#concept-request-cache-mode)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum CacheMode {
    Default,
    NoStore,
    Reload,
    NoCache,
    ForceCache,
    OnlyIfCached,
}

/// [Service-workers mode](https://fetch.spec.whatwg.org/#request-service-workers-mode)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum ServiceWorkersMode {
    All,
    None,
}

/// [Redirect mode](https://fetch.spec.whatwg.org/#concept-request-redirect-mode)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum RedirectMode {
    Follow,
    Error,
    Manual,
}

/// [Response tainting](https://fetch.spec.whatwg.org/#concept-request-response-tainting)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum ResponseTainting {
    Basic,
    CorsTainting,
    Opaque,
}

/// [Window](https://fetch.spec.whatwg.org/#concept-request-window)
#[derive(Clone, Copy, MallocSizeOf, PartialEq)]
pub enum Window {
    NoWindow,
    Client, // TODO: Environmental settings object
}

/// [CORS settings attribute](https://html.spec.whatwg.org/multipage/#attr-crossorigin-anonymous)
#[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, PartialEq, Serialize)]
pub enum CorsSettings {
    Anonymous,
    UseCredentials,
}

/// [Parser Metadata](https://fetch.spec.whatwg.org/#concept-request-parser-metadata)
#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum ParserMetadata {
    Default,
    ParserInserted,
    NotParserInserted,
}

/// <https://fetch.spec.whatwg.org/#concept-body-source>
#[derive(Clone, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
pub enum BodySource {
    Null,
    Object,
}

/// Messages used to implement <https://fetch.spec.whatwg.org/#concept-request-transmit-body>
/// which are sent from script to net.
#[derive(Debug, Deserialize, Serialize)]
pub enum BodyChunkResponse {
    /// A chunk of bytes.
    Chunk(Vec<u8>),
    /// The body is done.
    Done,
    /// There was an error streaming the body,
    /// terminate fetch.
    Error,
}

/// Messages used to implement <https://fetch.spec.whatwg.org/#concept-request-transmit-body>
/// which are sent from net to script
/// (with the exception of Done, which is sent from script to script).
#[derive(Debug, Deserialize, Serialize)]
pub enum BodyChunkRequest {
    /// Connect a fetch in `net`, with a stream of bytes from `script`.
    Connect(IpcSender<BodyChunkResponse>),
    /// Re-extract a new stream from the source, following a redirect.
    Extract(IpcReceiver<BodyChunkRequest>),
    /// Ask for another chunk.
    Chunk,
    /// Signal the stream is done(sent from script to script).
    Done,
    /// Signal the stream has errored(sent from script to script).
    Error,
}

/// The net component's view into <https://fetch.spec.whatwg.org/#bodies>
#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
pub struct RequestBody {
    /// Net's channel to communicate with script re this body.
    #[ignore_malloc_size_of = "Channels are hard"]
    chan: Arc<Mutex<IpcSender<BodyChunkRequest>>>,
    /// <https://fetch.spec.whatwg.org/#concept-body-source>
    source: BodySource,
    /// <https://fetch.spec.whatwg.org/#concept-body-total-bytes>
    total_bytes: Option<usize>,
}

impl RequestBody {
    pub fn new(
        chan: IpcSender<BodyChunkRequest>,
        source: BodySource,
        total_bytes: Option<usize>,
    ) -> Self {
        RequestBody {
            chan: Arc::new(Mutex::new(chan)),
            source,
            total_bytes,
        }
    }

    /// Step 12 of https://fetch.spec.whatwg.org/#concept-http-redirect-fetch
    pub fn extract_source(&mut self) {
        match self.source {
            BodySource::Null => panic!("Null sources should never be re-directed."),
            BodySource::Object => {
                let (chan, port) = ipc::channel().unwrap();
                let mut selfchan = self.chan.lock().unwrap();
                let _ = selfchan.send(BodyChunkRequest::Extract(port));
                *selfchan = chan;
            },
        }
    }

    pub fn take_stream(&self) -> Arc<Mutex<IpcSender<BodyChunkRequest>>> {
        self.chan.clone()
    }

    pub fn source_is_null(&self) -> bool {
        self.source == BodySource::Null
    }

    pub fn len(&self) -> Option<usize> {
        self.total_bytes.clone()
    }
}

#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
pub struct RequestBuilder {
    #[serde(
        deserialize_with = "::hyper_serde::deserialize",
        serialize_with = "::hyper_serde::serialize"
    )]
    #[ignore_malloc_size_of = "Defined in hyper"]
    pub method: Method,
    pub url: ServoUrl,
    #[serde(
        deserialize_with = "::hyper_serde::deserialize",
        serialize_with = "::hyper_serde::serialize"
    )]
    #[ignore_malloc_size_of = "Defined in hyper"]
    pub headers: HeaderMap,
    pub unsafe_request: bool,
    pub body: Option<RequestBody>,
    pub service_workers_mode: ServiceWorkersMode,
    // TODO: client object
    pub destination: Destination,
    pub synchronous: bool,
    pub mode: RequestMode,
    pub cache_mode: CacheMode,
    pub use_cors_preflight: bool,
    pub credentials_mode: CredentialsMode,
    pub use_url_credentials: bool,
    pub origin: ImmutableOrigin,
    // XXXManishearth these should be part of the client object
    pub referrer: Referrer,
    pub referrer_policy: Option<ReferrerPolicy>,
    pub pipeline_id: Option<PipelineId>,
    pub redirect_mode: RedirectMode,
    pub integrity_metadata: String,
    // This is nominally a part of the client's global object.
    // It is copied here to avoid having to reach across the thread
    // boundary every time a redirect occurs.
    #[ignore_malloc_size_of = "Defined in rust-content-security-policy"]
    pub csp_list: Option<CspList>,
    // to keep track of redirects
    pub url_list: Vec<ServoUrl>,
    pub parser_metadata: ParserMetadata,
    pub initiator: Initiator,
    pub https_state: HttpsState,
    pub response_tainting: ResponseTainting,
    /// Servo internal: if crash details are present, trigger a crash error page with these details.
    pub crash: Option<String>,
}

impl RequestBuilder {
    pub fn new(url: ServoUrl, referrer: Referrer) -> RequestBuilder {
        RequestBuilder {
            method: Method::GET,
            url: url,
            headers: HeaderMap::new(),
            unsafe_request: false,
            body: None,
            service_workers_mode: ServiceWorkersMode::All,
            destination: Destination::None,
            synchronous: false,
            mode: RequestMode::NoCors,
            cache_mode: CacheMode::Default,
            use_cors_preflight: false,
            credentials_mode: CredentialsMode::CredentialsSameOrigin,
            use_url_credentials: false,
            origin: ImmutableOrigin::new_opaque(),
            referrer: referrer,
            referrer_policy: None,
            pipeline_id: None,
            redirect_mode: RedirectMode::Follow,
            integrity_metadata: "".to_owned(),
            url_list: vec![],
            parser_metadata: ParserMetadata::Default,
            initiator: Initiator::None,
            csp_list: None,
            https_state: HttpsState::None,
            response_tainting: ResponseTainting::Basic,
            crash: None,
        }
    }

    pub fn initiator(mut self, initiator: Initiator) -> RequestBuilder {
        self.initiator = initiator;
        self
    }

    pub fn method(mut self, method: Method) -> RequestBuilder {
        self.method = method;
        self
    }

    pub fn headers(mut self, headers: HeaderMap) -> RequestBuilder {
        self.headers = headers;
        self
    }

    pub fn unsafe_request(mut self, unsafe_request: bool) -> RequestBuilder {
        self.unsafe_request = unsafe_request;
        self
    }

    pub fn body(mut self, body: Option<RequestBody>) -> RequestBuilder {
        self.body = body;
        self
    }

    pub fn destination(mut self, destination: Destination) -> RequestBuilder {
        self.destination = destination;
        self
    }

    pub fn synchronous(mut self, synchronous: bool) -> RequestBuilder {
        self.synchronous = synchronous;
        self
    }

    pub fn mode(mut self, mode: RequestMode) -> RequestBuilder {
        self.mode = mode;
        self
    }

    pub fn use_cors_preflight(mut self, use_cors_preflight: bool) -> RequestBuilder {
        self.use_cors_preflight = use_cors_preflight;
        self
    }

    pub fn credentials_mode(mut self, credentials_mode: CredentialsMode) -> RequestBuilder {
        self.credentials_mode = credentials_mode;
        self
    }

    pub fn use_url_credentials(mut self, use_url_credentials: bool) -> RequestBuilder {
        self.use_url_credentials = use_url_credentials;
        self
    }

    pub fn origin(mut self, origin: ImmutableOrigin) -> RequestBuilder {
        self.origin = origin;
        self
    }

    pub fn referrer_policy(mut self, referrer_policy: Option<ReferrerPolicy>) -> RequestBuilder {
        self.referrer_policy = referrer_policy;
        self
    }

    pub fn pipeline_id(mut self, pipeline_id: Option<PipelineId>) -> RequestBuilder {
        self.pipeline_id = pipeline_id;
        self
    }

    pub fn redirect_mode(mut self, redirect_mode: RedirectMode) -> RequestBuilder {
        self.redirect_mode = redirect_mode;
        self
    }

    pub fn integrity_metadata(mut self, integrity_metadata: String) -> RequestBuilder {
        self.integrity_metadata = integrity_metadata;
        self
    }

    pub fn parser_metadata(mut self, parser_metadata: ParserMetadata) -> RequestBuilder {
        self.parser_metadata = parser_metadata;
        self
    }

    pub fn https_state(mut self, https_state: HttpsState) -> RequestBuilder {
        self.https_state = https_state;
        self
    }

    pub fn response_tainting(mut self, response_tainting: ResponseTainting) -> RequestBuilder {
        self.response_tainting = response_tainting;
        self
    }

    pub fn crash(mut self, crash: Option<String>) -> Self {
        self.crash = crash;
        self
    }

    pub fn build(self) -> Request {
        let mut request = Request::new(
            self.url.clone(),
            Some(Origin::Origin(self.origin)),
            self.referrer,
            self.pipeline_id,
            self.https_state,
        );
        request.initiator = self.initiator;
        request.method = self.method;
        request.headers = self.headers;
        request.unsafe_request = self.unsafe_request;
        request.body = self.body;
        request.service_workers_mode = self.service_workers_mode;
        request.destination = self.destination;
        request.synchronous = self.synchronous;
        request.mode = self.mode;
        request.use_cors_preflight = self.use_cors_preflight;
        request.credentials_mode = self.credentials_mode;
        request.use_url_credentials = self.use_url_credentials;
        request.cache_mode = self.cache_mode;
        request.referrer_policy = self.referrer_policy;
        request.redirect_mode = self.redirect_mode;
        let mut url_list = self.url_list;
        if url_list.is_empty() {
            url_list.push(self.url);
        }
        request.redirect_count = url_list.len() as u32 - 1;
        request.url_list = url_list;
        request.integrity_metadata = self.integrity_metadata;
        request.parser_metadata = self.parser_metadata;
        request.csp_list = self.csp_list;
        request.response_tainting = self.response_tainting;
        request.crash = self.crash;
        request
    }
}

/// A [Request](https://fetch.spec.whatwg.org/#concept-request) as defined by
/// the Fetch spec.
#[derive(Clone, MallocSizeOf)]
pub struct Request {
    /// <https://fetch.spec.whatwg.org/#concept-request-method>
    #[ignore_malloc_size_of = "Defined in hyper"]
    pub method: Method,
    /// <https://fetch.spec.whatwg.org/#local-urls-only-flag>
    pub local_urls_only: bool,
    /// <https://fetch.spec.whatwg.org/#sandboxed-storage-area-urls-flag>
    pub sandboxed_storage_area_urls: bool,
    /// <https://fetch.spec.whatwg.org/#concept-request-header-list>
    #[ignore_malloc_size_of = "Defined in hyper"]
    pub headers: HeaderMap,
    /// <https://fetch.spec.whatwg.org/#unsafe-request-flag>
    pub unsafe_request: bool,
    /// <https://fetch.spec.whatwg.org/#concept-request-body>
    pub body: Option<RequestBody>,
    // TODO: client object
    pub window: Window,
    // TODO: target browsing context
    /// <https://fetch.spec.whatwg.org/#request-keepalive-flag>
    pub keep_alive: bool,
    /// <https://fetch.spec.whatwg.org/#request-service-workers-mode>
    pub service_workers_mode: ServiceWorkersMode,
    /// <https://fetch.spec.whatwg.org/#concept-request-initiator>
    pub initiator: Initiator,
    /// <https://fetch.spec.whatwg.org/#concept-request-destination>
    pub destination: Destination,
    // TODO: priority object
    /// <https://fetch.spec.whatwg.org/#concept-request-origin>
    pub origin: Origin,
    /// <https://fetch.spec.whatwg.org/#concept-request-referrer>
    pub referrer: Referrer,
    /// <https://fetch.spec.whatwg.org/#concept-request-referrer-policy>
    pub referrer_policy: Option<ReferrerPolicy>,
    pub pipeline_id: Option<PipelineId>,
    /// <https://fetch.spec.whatwg.org/#synchronous-flag>
    pub synchronous: bool,
    /// <https://fetch.spec.whatwg.org/#concept-request-mode>
    pub mode: RequestMode,
    /// <https://fetch.spec.whatwg.org/#use-cors-preflight-flag>
    pub use_cors_preflight: bool,
    /// <https://fetch.spec.whatwg.org/#concept-request-credentials-mode>
    pub credentials_mode: CredentialsMode,
    /// <https://fetch.spec.whatwg.org/#concept-request-use-url-credentials-flag>
    pub use_url_credentials: bool,
    /// <https://fetch.spec.whatwg.org/#concept-request-cache-mode>
    pub cache_mode: CacheMode,
    /// <https://fetch.spec.whatwg.org/#concept-request-redirect-mode>
    pub redirect_mode: RedirectMode,
    /// <https://fetch.spec.whatwg.org/#concept-request-integrity-metadata>
    pub integrity_metadata: String,
    // Use the last method on url_list to act as spec current url field, and
    // first method to act as spec url field
    /// <https://fetch.spec.whatwg.org/#concept-request-url-list>
    pub url_list: Vec<ServoUrl>,
    /// <https://fetch.spec.whatwg.org/#concept-request-redirect-count>
    pub redirect_count: u32,
    /// <https://fetch.spec.whatwg.org/#concept-request-response-tainting>
    pub response_tainting: ResponseTainting,
    /// <https://fetch.spec.whatwg.org/#concept-request-parser-metadata>
    pub parser_metadata: ParserMetadata,
    // This is nominally a part of the client's global object.
    // It is copied here to avoid having to reach across the thread
    // boundary every time a redirect occurs.
    #[ignore_malloc_size_of = "Defined in rust-content-security-policy"]
    pub csp_list: Option<CspList>,
    pub https_state: HttpsState,
    /// Servo internal: if crash details are present, trigger a crash error page with these details.
    pub crash: Option<String>,
}

impl Request {
    pub fn new(
        url: ServoUrl,
        origin: Option<Origin>,
        referrer: Referrer,
        pipeline_id: Option<PipelineId>,
        https_state: HttpsState,
    ) -> Request {
        Request {
            method: Method::GET,
            local_urls_only: false,
            sandboxed_storage_area_urls: false,
            headers: HeaderMap::new(),
            unsafe_request: false,
            body: None,
            window: Window::Client,
            keep_alive: false,
            service_workers_mode: ServiceWorkersMode::All,
            initiator: Initiator::None,
            destination: Destination::None,
            origin: origin.unwrap_or(Origin::Client),
            referrer: referrer,
            referrer_policy: None,
            pipeline_id: pipeline_id,
            synchronous: false,
            mode: RequestMode::NoCors,
            use_cors_preflight: false,
            credentials_mode: CredentialsMode::CredentialsSameOrigin,
            use_url_credentials: false,
            cache_mode: CacheMode::Default,
            redirect_mode: RedirectMode::Follow,
            integrity_metadata: String::new(),
            url_list: vec![url],
            parser_metadata: ParserMetadata::Default,
            redirect_count: 0,
            response_tainting: ResponseTainting::Basic,
            csp_list: None,
            https_state: https_state,
            crash: None,
        }
    }

    /// <https://fetch.spec.whatwg.org/#concept-request-url>
    pub fn url(&self) -> ServoUrl {
        self.url_list.first().unwrap().clone()
    }

    /// <https://fetch.spec.whatwg.org/#concept-request-current-url>
    pub fn current_url(&self) -> ServoUrl {
        self.url_list.last().unwrap().clone()
    }

    /// <https://fetch.spec.whatwg.org/#concept-request-current-url>
    pub fn current_url_mut(&mut self) -> &mut ServoUrl {
        self.url_list.last_mut().unwrap()
    }

    /// <https://fetch.spec.whatwg.org/#navigation-request>
    pub fn is_navigation_request(&self) -> bool {
        self.destination == Destination::Document
    }

    /// <https://fetch.spec.whatwg.org/#subresource-request>
    pub fn is_subresource_request(&self) -> bool {
        match self.destination {
            Destination::Audio |
            Destination::Font |
            Destination::Image |
            Destination::Manifest |
            Destination::Script |
            Destination::Style |
            Destination::Track |
            Destination::Video |
            Destination::Xslt |
            Destination::None => true,
            _ => false,
        }
    }

    pub fn timing_type(&self) -> ResourceTimingType {
        if self.is_navigation_request() {
            ResourceTimingType::Navigation
        } else {
            ResourceTimingType::Resource
        }
    }
}

impl Referrer {
    pub fn to_url(&self) -> Option<&ServoUrl> {
        match *self {
            Referrer::NoReferrer => None,
            Referrer::Client(ref url) => Some(url),
            Referrer::ReferrerUrl(ref url) => Some(url),
        }
    }
}

// https://fetch.spec.whatwg.org/#cors-unsafe-request-header-byte
// TODO: values in the control-code range are being quietly stripped out by
// HeaderMap and never reach this function to be loudly rejected!
fn is_cors_unsafe_request_header_byte(value: &u8) -> bool {
    match value {
        0x00..=0x08 |
        0x10..=0x19 |
        0x22 |
        0x28 |
        0x29 |
        0x3A |
        0x3C |
        0x3E |
        0x3F |
        0x40 |
        0x5B |
        0x5C |
        0x5D |
        0x7B |
        0x7D |
        0x7F => true,
        _ => false,
    }
}

// https://fetch.spec.whatwg.org/#cors-safelisted-request-header
// subclause `accept`
fn is_cors_safelisted_request_accept(value: &[u8]) -> bool {
    !(value.iter().any(is_cors_unsafe_request_header_byte))
}

// https://fetch.spec.whatwg.org/#cors-safelisted-request-header
// subclauses `accept-language`, `content-language`
fn is_cors_safelisted_language(value: &[u8]) -> bool {
    value.iter().all(|&x| match x {
        0x30..=0x39 |
        0x41..=0x5A |
        0x61..=0x7A |
        0x20 |
        0x2A |
        0x2C |
        0x2D |
        0x2E |
        0x3B |
        0x3D => true,
        _ => false,
    })
}

// https://fetch.spec.whatwg.org/#cors-safelisted-request-header
// subclause `content-type`
fn is_cors_safelisted_request_content_type(value: &[u8]) -> bool {
    // step 1
    if value.iter().any(is_cors_unsafe_request_header_byte) {
        return false;
    }
    // step 2
    let value_string = if let Ok(s) = std::str::from_utf8(value) {
        s
    } else {
        return false;
    };
    let value_mime_result: Result<Mime, _> = value_string.parse();
    match value_mime_result {
        Err(_) => false, // step 3
        Ok(value_mime) => match (value_mime.type_(), value_mime.subtype()) {
            (mime::APPLICATION, mime::WWW_FORM_URLENCODED) |
            (mime::MULTIPART, mime::FORM_DATA) |
            (mime::TEXT, mime::PLAIN) => true,
            _ => false, // step 4
        },
    }
}

// TODO: "DPR", "Downlink", "Save-Data", "Viewport-Width", "Width":
// ... once parsed, the value should not be failure.
// https://fetch.spec.whatwg.org/#cors-safelisted-request-header
pub fn is_cors_safelisted_request_header<N: AsRef<str>, V: AsRef<[u8]>>(
    name: &N,
    value: &V,
) -> bool {
    let name: &str = name.as_ref();
    let value: &[u8] = value.as_ref();
    if value.len() > 128 {
        return false;
    }
    match name {
        "accept" => is_cors_safelisted_request_accept(value),
        "accept-language" | "content-language" => is_cors_safelisted_language(value),
        "content-type" => is_cors_safelisted_request_content_type(value),
        _ => false,
    }
}

/// <https://fetch.spec.whatwg.org/#cors-safelisted-method>
pub fn is_cors_safelisted_method(m: &Method) -> bool {
    match *m {
        Method::GET | Method::HEAD | Method::POST => true,
        _ => false,
    }
}

/// <https://fetch.spec.whatwg.org/#cors-non-wildcard-request-header-name>
pub fn is_cors_non_wildcard_request_header_name(name: &HeaderName) -> bool {
    name == AUTHORIZATION
}

/// <https://fetch.spec.whatwg.org/#cors-unsafe-request-header-names>
pub fn get_cors_unsafe_header_names(headers: &HeaderMap) -> Vec<HeaderName> {
    // Step 1
    let mut unsafe_names: Vec<&HeaderName> = vec![];
    // Step 2
    let mut potentillay_unsafe_names: Vec<&HeaderName> = vec![];
    // Step 3
    let mut safelist_value_size = 0;

    // Step 4
    for (name, value) in headers.iter() {
        if !is_cors_safelisted_request_header(&name, &value) {
            unsafe_names.push(name);
        } else {
            potentillay_unsafe_names.push(name);
            safelist_value_size += value.as_ref().len();
        }
    }

    // Step 5
    if safelist_value_size > 1024 {
        unsafe_names.extend_from_slice(&potentillay_unsafe_names);
    }

    // Step 6
    return convert_header_names_to_sorted_lowercase_set(unsafe_names);
}

/// <https://fetch.spec.whatwg.org/#ref-for-convert-header-names-to-a-sorted-lowercase-set>
pub fn convert_header_names_to_sorted_lowercase_set(
    header_names: Vec<&HeaderName>,
) -> Vec<HeaderName> {
    // HeaderName does not implement the needed traits to use a BTreeSet
    // So create a new Vec, sort, then dedup
    let mut ordered_set = header_names.to_vec();
    ordered_set.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
    ordered_set.dedup();
    return ordered_set.into_iter().cloned().collect();
}