fáith - Rust-powered fetch API for Node.js

/ˈɸaːθj/ — pronounced FATH, like FATHER without the ER. This is an old irish word that is a folk etymology of "fetch", and means poet, soothsayer, seer, and later, prophet.

Fáith is of course a pun with faith, and is meant to be a faithful implementation of the fetch API for Node.js, but using a Rust-based network stack instead of undici + libuv.

Most fetch implementations for Node.js are based on the Node.js TCP stack (via libuv) and cannot easily work around its limitations. The native fetch implementation, undici, explicitly targets HTTP/1.1, and doesn't support HTTP/2+, among many other complaints (of course, for HTTP/1, undici is a very good effort! it just feels like a bit of an outdated choice today).

Fáith tries to bring a Node.js fetch that is closer to the browser's fetch, notably by having transparent support for HTTP/2 and HTTP/3, IPv6 and IPv4 using the "Happy Eyeballs" algorithm, a DNS cache, an optional cookie jar, and your choice of two HTTP caches.

Installation

npm install @passcod/faith

Usage

Basic fetch

import { fetch } from '@passcod/faith';

async function example() {
  const response = await fetch('https://httpbin.org/get');
  console.log(response.status); // 200
  console.log(response.ok); // true

  const data = response.json();
  console.log(data.url); // https://httpbin.org/get
}

Fetch with options

import { fetch } from '@passcod/faith';

const response = await fetch('https://httpbin.org/post', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Custom-Header': 'value'
  },
  body: JSON.stringify({ message: 'Hello' }),
});

Fetch with HTTP cache

import { fetch, Agent } from '@passcod/faith';

const agent = new Agent({
  cache: {
    store: 'memory',
  },
});
const response = await fetch('https://httpbin.org/post', {
  agent,
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Custom-Header': 'value'
  },
  body: JSON.stringify({ message: 'Hello' }),
});

API Reference

Conforms to the fetch API.

In the following documentation, italics are parts that are identical to how native fetch works (as per MDN), and non-italics document where behaviour varies and is specific to fáith (unless otherwise specified).

fetch()

Syntax

import { fetch } from '@passcod/faith';
fetch(resource);
fetch(resource, options);

Parameters

resource

This defines the resource that you wish to fetch. This can either be:

• A string or any other object with a stringifier — including a URL object — that provides the URL of the resource you want to fetch. The URL must be absolute and include a scheme.

• A Request object.

options (Optional)

A RequestInit object containing any custom settings that you want to apply to the request. In practice the RequestInit class does not exist in browsers or Node.js, and so this is always a "plain object" or "dictionary". The fields supported by Fáith are documented below.

Return value

A Promise that resolves to a Response object.

Request

Fáith does not implement its own Request object. Instead, you can pass a Web API Request object to fetch(), and it will internally be converted to the right options.

RequestInit object

The RequestInit dictionary of the Fetch API represents the set of options that can be used to configure a fetch request.

You can pass a RequestInit object into the Request() constructor, or directly into the fetch() function call. Note that Fáith has additional options available, and those will not survive a trip through Request. Prefer to supply RequestInit directly to fetch().

You can also construct a Request with a RequestInit, and pass the Request to a fetch() call along with another RequestInit. If you do this, and the same option is set in both places, then the value passed directly into fetch() is used.

Note that you can include options that Fáith does not support; they will simply be ignored.

FetchOptions.agent: Agent

This is custom to Fáith.

You can create an Agent, and pass it here to have the request executed by the Agent. See the documentation for the Agent options you can set with this, and the agent data you can access. Notably an agent has a DNS cache, and may be configured to handle cookies and/or an HTTP cache.

When not provided, a global default Agent is created on first use.

FetchOptions.attributionReporting

Fáith deliberately does not implement this.

FetchOptions.body

The request body contains content to send to the server, for example in a POST or PUT request. It is specified as an instance of any of the following types:

• a string
• ArrayBuffer
• Blob
• DataView
• File
• FormData
• TypedArray
• URLSearchParams
• ReadableStream

If body is a ReadableStream, the duplex option must also be set.

FetchOptions.browsingTopics

Fáith deliberately does not implement this.

FetchOptions.cache

The cache mode you want to use for the request. This may be any one of the following values:

• default: The client looks in its HTTP cache for a response matching the request.

  • If there is a match and it is fresh, it will be returned from the cache.
  • If there is a match but it is stale, the client will make a conditional request to the remote server. If the server indicates that the resource has not changed, it will be returned from the cache. Otherwise the resource will be downloaded from the server and the cache will be updated.
  • If there is no match, the client will make a normal request, and will update the cache with the downloaded resource.

• no-store: The client fetches the resource from the remote server without first looking in the cache, and will not update the cache with the downloaded resource.

• reload: The client fetches the resource from the remote server without first looking in the cache, but then will update the cache with the downloaded resource.

• no-cache: The client looks in its HTTP cache for a response matching the request.

  • If there is a match, fresh or stale, the client will make a conditional request to the remote server. If the server indicates that the resource has not changed, it will be returned from the cache. Otherwise the resource will be downloaded from the server and the cache will be updated.
  • If there is no match, the client will make a normal request, and will update the cache with the downloaded resource.

• force-cache: The client looks in its HTTP cache for a response matching the request.

  • If there is a match, fresh or stale, it will be returned from the cache.
  • If there is no match, the client will make a normal request, and will update the cache with the downloaded resource.

• only-if-cached: The client looks in its HTTP cache for a response matching the request.

  • If there is a match, fresh or stale, it will be returned from the cache.
  • If there is no match, a network error is returned.

• ignore-rules: Custom to Fáith. Overrides the check that determines if a response can be cached to always return true on 200. Uses any response in the HTTP cache matching the request, not paying attention to staleness. If there was no response, it creates a normal request and updates the HTTP cache with the response.

FetchOptions.credentials: string

Controls whether or not the client sends credentials with the request, as well as whether any Set-Cookie response headers are respected. Credentials are cookies, ~~TLS client certificates,~~ or authentication headers containing a username and password. This option may be any one of the following values:

• omit: Never send credentials in the request or include credentials in the response.
• ~~same-origin~~: Fáith does not implement this, as there is no concept of "origin" on the server.
• include: Always include credentials, ~~even for cross-origin requests.~~

Fáith ignores the Access-Control-Allow-Credentials and Access-Control-Allow-Origin headers.

Fáith currently does not omit the TLS client certificate when the request's Agent has one configured. This is an upstream limitation.

If the request's Agent has cookies enabled, new cookies from the response will be added to the cookie jar, even as Fáith strips them from the request and response headers returned to the user. This is an upstream limitation.

Defaults to include (browsers default to same-origin).

FetchOptions.duplex: string

Controls duplex behavior of the request. If this is present it must have the value half, meaning that Fáith will send the entire request before processing the response.

This option must be present when body is a ReadableStream.

FetchOptions.headers: Headers | object

Any headers you want to add to your request, contained within a Headers object or an object literal whose keys are the names of headers and whose values are the header values.

Fáith allows all request headers to be set (unlike browsers, which forbid a number of them).

FetchOptions.integrity: string

Contains the subresource integrity value of the request.

The format of this option is <hash-algo>-<hash-source> where:

• <hash-algo> is one of the following values: sha256, sha384, or sha512
• <hash-source> is the Base64-encoding of the result of hashing the resource with the specified hash algorithm.

Multiple space-separated values are supported; if any matches, verification passes. Unknown algorithms are silently ignored (but if all algorithms are unknown, an error is thrown).

Fáith only checks the integrity when using bytes(), json(), text(), arrayBuffer(), and blob(). Verification when reading through the body stream is not currently supported.

Note that browsers will throw at the fetch() call when integrity fails, but Fáith will only throw when the above methods are called, as until then the body contents are not available.

FetchOptions.keepalive

Not supported.

Note that this is different from Connection: keep-alive; Fáith connections are pooled within each single Agent, so subsequent requests to the same endpoint are faster until the pooled connection times out. The keepalive option in browsers is instead a way to send a fetch() right before the page is unloaded, for tracking or analytics purposes. This concept does not exist in Node.js.

FetchOptions.method: string

The request method. Defaults to GET.

FetchOptions.mode

Fáith deliberately does not implement this, as there is no CORS/origin.

FetchOptions.priority

Not supported.

FetchOptions.redirect

Fáith does not respect this option on the RequestInit dictionary. Instead, the option is present on Agent and applies to all requests made with that Agent.

FetchOptions.referrer

Fáith deliberately does not implement this, as there is no origin.

However, Fáith does set the Referer header when redirecting automatically.

FetchOptions.referrerPolicy

Fáith deliberately does not implement this, as there is no origin.

However, Fáith does set the Referer header when redirecting automatically.

FetchOptions.signal: AbortSignal

An AbortSignal. If this option is set, the request can be canceled by calling abort() on the corresponding AbortController.

FetchOptions.timeout: number

Custom to Fáith. Cancels the request after this many milliseconds.

This will give a different error to using signal with a timeout, which might be preferable in some cases. It also has a slightly different internal behaviour: signal may abort the request only until the response headers have been received, while timeout will apply through the entire response receipt.

Response

The Response interface of the Fetch API represents the response to a request.

Fáith does not allow its Response object to be constructed. If you need to, you may use the webResponse() method to convert one into a Web API Response object; note the caveats.

Response.body: ReadableStream | null

The body read-only property of the Response interface is a ReadableStream of the body contents, or null for any actual HTTP response that has no body, such as HEAD requests and 204 No Content responses.

Note that browsers currently do not return null for those responses, but the spec requires it. Fáith chooses to respect the spec rather than the browsers in this case.

Response.bodyUsed: boolean

The bodyUsed read-only property of the Response interface is a boolean value that indicates whether the body has been read yet.

In Fáith, this indicates whether the body stream has ever been read from or canceled, as defined in the spec. Note that accessing the .body property counts as a read, even if you don't actually consume any bytes of content.

Response.headers: Headers

The headers read-only property of the Response interface contains the Headers object associated with the response.

Note that Fáith does not provide a custom Headers class; instead the Web API Headers structure is used directly and constructed by Fáith when needed.

Response.ok: boolean

The ok read-only property of the Response interface contains a boolean stating whether the response was successful (status in the range 200-299) or not.

Response.peer: object

Custom to Fáith.

The peer read-only property of the Response interface contains an object with information about the remote peer that sent this response:

Response.peer.address: string | null

The IP address and port of the peer, if available.

Response.peer.certificate: Buffer | null

When connected over HTTPS, this is the DER-encoded leaf certificate of the peer.

Response.redirected: boolean

The redirected read-only property of the Response interface indicates whether or not the response is the result of a request you made which was redirected.

Note that by the time you read this property, the redirect will already have happened, and you cannot prevent it by aborting the fetch at this point.

Response.status: number

The status read-only property of the Response interface contains the HTTP status codes of the response. For example, 200 for success, 404 if the resource could not be found.

Response.statusText: string

The statusText read-only property of the Response interface contains the status message corresponding to the HTTP status code in Response.status. For example, this would be OK for a status code 200, Continue for 100, Not Found for 404.

In HTTP/1, servers can send custom status text. This is returned here. In HTTP/2 and HTTP/3, custom status text is not supported at all, and the statusText property is either empty or simulated from well-known status codes.

Response.trailers: Promise<Headers | null>

The trailers() read-only property of the Response interface returns a promise that resolves to either null or a Headers structure that contains the HTTP/2 or /3 trailing headers.

Note that this will never resolve if you don't also consume the body in some way.

Custom to Fáith. This was once in the spec but was removed as it wasn't implemented by any browser.

Response.type: string

The type read-only property of the Response interface contains the type of the response. The type determines whether scripts are able to access the response body and headers.

In Fáith, this is always set to basic.

Response.url: string

The url read-only property of the Response interface contains the URL of the response. The value of the url property will be the final URL obtained after any redirects.

Response.version: string

The version read-only property of the Response interface contains the HTTP version of the response. The value will be the final HTTP version after any redirects and protocol upgrades.

This is custom to Fáith.

Response.arrayBuffer(): Promise<ArrayBuffer>

The arrayBuffer() method of the Response interface takes a Response stream and reads it to completion. It returns a promise that resolves with an ArrayBuffer.

Response.blob(): Promise<Blob>

The blob() method of the Response interface takes a Response stream and reads it to completion. It returns a promise that resolves with a Blob.

The type of the Blob is set to the value of the Content-Type response header.

Response.bytes(): Promise<Buffer>

The bytes() method of the Response interface takes a Response stream and reads it to completion. It returns a promise that resolves with a Uint8Array.

In Fáith, this returns a Node.js Buffer, which can be used as (and is a subclass of) a Uint8Array.

Response.clone(): Response

The clone() method of the Response interface creates a clone of a response object, identical in every way, but stored in a different variable.

clone() throws an error if the response body has already been used.

Response.discard(): Promise<void>

Discard the response body, releasing the connection back to the pool.

This is useful when you don't need the body but want to ensure the connection can be reused for subsequent requests. If you don't call this and don't consume the body, the connection may be held open until the response is garbage collected. When the connection is HTTP/2 or /3, calling this is not necessary as the connection can be reused regardless, but it's still good practice to make it explicit and won't do unnecessary work in those cases.

The returned promise resolves when the body has been fully discarded.

This is custom to Fáith.

Response.formData(): !

Fáith deliberately does not implement this. The method exists so the types work out, but it will always throw.

Response.json(): Promise<unknown>

The json() method of the Response interface takes a Response stream and reads it to completion. It returns a promise which resolves with the result of parsing the body text as JSON.

Note that despite the method being named json(), the result is not JSON but is instead the result of taking JSON as input and parsing it to produce a JavaScript object.

Further note that, at least in Fáith, this method first reads the entire response body as bytes, and then parses that as JSON. This can use up to double the amount of memory. If you need more efficient access, consider handling the response body as a stream.

Response.text(): Promise<string>

The text() method of the Response interface takes a Response stream and reads it to completion. It returns a promise that resolves with a String. The response is always decoded using UTF-8.

Response.webResponse(): globalThis.Response

This is entirely custom to Fáith. It returns a Web API Response instead of Fáith's custom Response class. However, it's not possible to construct a Web API Response that has all the properties of a Fáith Response (or of another Web Response, for that matter). So this method only returns a Response from:

• the body stream
• the status, statusCode, and headers properties

Note that if json(), bytes(), etc has been called on the original response, the body stream of the new Web Response will be empty or inaccessible. If the body stream of the original response has been partially read, only the remaining bytes will be available in the new Response.

Agent

The Agent interface of the Fáith API represents an instance of an HTTP client. Each Agent has its own options, connection pool, caches, etc. There are also conveniences such as headers for setting default headers on all requests done with the agent, and statistics collected by the agent.

Re-using connections between requests is a significant performance improvement: not only because the TCP and TLS handshake is only performed once across many different requests, but also because the DNS lookup doesn't need to occur for subsequent requests on the same connection. Depending on DNS technology (DoH and DoT add a whole separate handshake to the process) and overall latency, this can not only speed up requests on average, but also reduce system load.

For this reason, and also because in browsers this behaviour is standard, all requests with Fáith use an Agent. For fetch() calls that don't specify one explicitly, a global agent with default options is created on first use.

There are a lot more options that could be exposed here; if you want one, open an issue.

Syntax

new Agent()
new Agent(options)

AgentOptions.cache: object

Settings related to the HTTP cache. This is a nested object.

AgentOptions.cache.store: string

Which cache store to use: either disk or memory.

Default: none (cache disabled).

AgentOptions.cache.capacity: number

If cache.store: "memory", the maximum amount of items stored.

Default: 10_000.

AgentOptions.cache.mode: string

Default cache mode. This is the same as FetchOptions.cache, and is used if no cache mode is set on a request.

Default: "default".

AgentOptions.cache.path: string

If cache.store: "disk", then this is the path at which the cache data is. Must be writeable.

Required if cache.store: "disk".

AgentOptions.cache.shared: boolean

If true, then the response is evaluated from a perspective of a shared cache (i.e. private is not cacheable and s-maxage is respected). If false, then the response is evaluated from a perspective of a single-user cache (i.e. private is cacheable and s-maxage is ignored). shared: true is required for proxies and multi-user caches.

Default: true.

AgentOptions.cookies: bool

Enable a persistent cookie store for the agent. Cookies received in responses will be preserved and included in additional requests.

Default: false.

You may use agent.getCookie(url: string) and agent.addCookie(url: string, value: string) to add and retrieve cookies from the store.

AgentOptions.dns: object

Settings related to DNS. This is a nested object.

AgentOptions.dns.system: boolean

Use the system's DNS (via getaddrinfo or equivalent) rather than Fáith's own DNS client (based on Hickory). If you experience issues with DNS where Fáith does not work but e.g. curl or native fetch does, this should be your first port of call.

Enabling this also disables Happy Eyeballs (for IPv6 / IPv4 best-effort resolution), the in-memory DNS cache, and may lead to worse performance even discounting the cache.

Default: false.

AgentOptions.dns.overrides: Array<{ domain: string; addresses: string[] }>

Override DNS resolution for specific domains. This takes effect even with dns.system: true.

Will throw if addresses are in invalid formats. You may provide a port number as part of the address, it will default to port 0 otherwise, which will select the conventional port for the protocol in use (e.g. 80 for plaintext HTTP). If the URL passed to fetch() has an explicit port number, that one will be used instead. Resolving a domain to an empty addresses array effectively blocks that domain from this agent.

Default: no overrides.

AgentOptions.headers: Array<{ name: string, value: string, sensitive?: bool }>

Sets the default headers for every request.

If header names or values are invalid, they are silently omitted. Sensitive headers (e.g. Authorization) should be marked.

Default: none.

AgentOptions.http3: object

Settings related to HTTP/3. This is a nested object.

AgentOptions.http3.congestion: string

The congestion control algorithm. The default is cubic, which is the same used in TCP in the Linux stack. It's fair for all traffic, but not the most optimal, especially for networks with a lot of available bandwidth, high latency, or a lot of packet loss. Cubic reacts to packet loss by dropping the speed by 30%, and takes a long time to recover. BBR instead tries to maximise bandwidth use and optimises for round-trip time, while ignoring packet loss.

In some networks, BBR can lead to pathological degradation of overall network conditions, by flooding the network by up to 100 times more retransmissions. This is fixed in BBRv2 and BBRv3, but Fáith (or rather its underlying QUIC library quinn, does not implement those yet).

Note that this only controls the "upload" congestion window (the server controls the "download" side), so this setting only makes a difference for upload-heavy (large bodies) applications.

Default: cubic. Accepted values: cubic, bbr1.

AgentOptions.http3.maxIdleTimeout: number

Maximum duration of inactivity to accept before timing out the connection, in seconds. Note that this only sets the timeout on this side of the connection: the true idle timeout is the minimum of this and the peer’s own max idle timeout. While the underlying library has no limits, Fáith defines bounds for safety: minimum 1 second, maximum 2 minutes (120 seconds).

Default: 30.

AgentOptions.http3.upgradeEnabled: bool

Fáith keeps track of "Alt-Svc" advertisements from the servers, which indicate if and how HTTP/3 is available. It then uses those advertisements to attempt connection over HTTP/3, and also keeps track of failures, so it doesn't waste time retrying HTTP/3 for hosts that don't actually support it even if they did advertise it.

Setting this setting to false disables this mechanism, which effectively disables HTTP/3 usage.

Default: true.

AgentOptions.http3.hints: Array<{ host: string; port: number }>

If you know upfront that a host has HTTP/3 support, and at what port it's listening, you can skip a first HTTP/1 or /2 connection by providing a hint here. If the connection fails, the hint will be ignored for the upgradeFailedTtl duration, just like for the normal pathway with Alt-Svc advertisements (essentially, hints pre-populate the Alt-Svc advertisements cache).

AgentOptions.http3.upgradeAdvertisedTtl: number

AgentOptions.http3.upgradeConfirmedTtl: number

AgentOptions.http3.upgradeFailedTtl: number

AgentOptions.http3.upgradeCacheCapacity: number

These four settings allow tweaking the HTTP/3 advertisement/knowledge cache behaviour.

AgentOptions.pool: object

Settings related to the connection pool. This is a nested object.

AgentOptions.pool.idleTimeout: number

How many seconds of inactivity before a connection is closed.

Default: 90 seconds.

AgentOptions.pool.maxIdlePerHost: number | null

The maximum amount of idle connections per host to allow in the pool. Connections will be closed to keep the idle connections (per host) under that number.

Default: null (no limit).

AgentOptions.redirect: string

Determines the behavior in case the server replies with a redirect status. One of the following values:

• follow: automatically follow redirects. Fáith limits this to 10 redirects.
• error: reject the promise with a network error when a redirect status is returned.
• ~~manual:~~ not supported.
• stop: (Fáith custom) don't follow any redirects, return the responses.

Defaults to follow.

AgentOptions.timeout: object

Timeouts for requests made with this agent. This is a nested object.

AgentOptions.timeout.connect: number | null

Set a timeout for only the connect phase, in milliseconds.

Default: none.

AgentOptions.timeout.read: number | null

Set a timeout for read operations, in milliseconds.

The timeout applies to each read operation, and resets after a successful read. This is more appropriate for detecting stalled connections when the size isn’t known beforehand.

Default: none.

AgentOptions.timeout.total: number | null

Set a timeout for the entire request-response cycle, in milliseconds.

The timeout applies from when the request starts connecting until the response body has finished. Also considered a total deadline.

Default: none.

AgentOptions.tls: object

Settings related to the connection pool. This is a nested object.

AgentOptions.tls.earlyData: boolean

Enable TLS 1.3 Early Data. Early data is an optimisation where the client sends the first packet of application data alongside the opening packet of the TLS handshake. That can enable the server to answer faster, improving latency by up to one round-trip. However, Early Data has significant security implications: it's vulnerable to replay attacks and has weaker forward secrecy. It should really only be used for static assets or to squeeze out the last drop of performance for endpoints that are replay-safe.

This is only really useful with HTTP/3.

Default: false.

AgentOptions.tls.identity: string | Buffer

Provide a PEM-formatted certificate and private key to present as a TLS client certificate (also called mutual TLS or mTLS) authentication.

The input should contain a PEM encoded private key and at least one PEM encoded certificate. The private key must be in RSA, SEC1 Elliptic Curve or PKCS#8 format. This is one of the few options that will cause the Agent constructor to throw if the input is in the wrong format.

AgentOptions.tls.required

Disables plain-text HTTP.

Default: false.

AgentOptions.userAgent

Custom user agent string.

Default: Faith/{version} reqwest/{version}.

You may use the USER_AGENT constant if you wish to prepend your own agent to the default, e.g.

import { Agent, USER_AGENT } from '@passcod/faith';
const agent = new Agent({
  userAgent: `YourApp/1.2.3 ${USER_AGENT}`,
});

Agent.addCookie(url: string, cookie: string)

Add a cookie into the agent.

Does nothing if:

• the cookie store is disabled
• the url is malformed

Agent.getCookie(url: string): string | null

Retrieve a cookie from the store.

Returns null if:

• there's no cookie at this url
• the cookie store is disabled
• the url is malformed
• the cookie cannot be represented as a string

Agent.connections(): Array<object>

Returns information on current (TCP) connections open by this agent.

Only tracks TCP connections currently (upstream limitation). Stats are updated once a second: this makes it possible to track indicators over time to find the retransmission rate, for example. The lostPackets and deliveryRateBps stats are only available on Linux. Some other fields might also be missing depending on platform support; and no forward guarantees are made on field availability. If the platform isn't supported at all, this will always return empty.

{
    // always set to `tcp` currently.
    // if QUIC connections are able to be tracked in future, this will be `quic`.
    connectionType: 'tcp',

    // local and remote addresses and ports for this connection.
    // this uniquely identifies the connection for its duration.
    localAddress: '10.0.100.10',
    localPort: 58336,
    remoteAddress: '142.250.195.132',
    remotePort: 443,

    // how many responses were handled by this connection.
    // this may undercount when redirects are handled internally.
    responseCount: 1,

    // when the first request done on the connection returned as a response.
    firstSeen: new Date('2026-01-05T08:42:48.695Z'),

    // when the latest request done on the connection returned as a response.
    lastSeen: new Date('2026-01-05T08:42:48.695Z'),

    // an estimate of when the connection is due to expire out of the pool.
    // this will be pushed back on connection reuse.
    expiry: new Date('2026-01-05T08:44:18.695Z'),

    // round-trip time estimate in microseconds.
    rttUs: 27317,
    // round-trip time variance in microseconds.
    rttVarUs: 882,

    // (Linux-only) count of segments considered lost (requiring retransmission).
    lostPackets: 0,

    // how many retransmitted segments are in-flight right now.
    retransmits: 0,

    // how many segments were retransmitted in total.
    totalRetransmits: 0,

    // the maximum number of segments allowed in flight at any one time.
    // this is what is varied by the congestion control algorithm (CUBIC, BBR).
    congestionWindow: 10,

    // (Linux-only) the goodput (application-level throughput).
    // the rate at which data was actually delivered, in bytes per second.
    deliveryRateBps: 210887,
}

Agent.stats(): object

Returns statistics gathered by this agent:

• requestsSent
• responsesReceived
• bodiesStarted
• bodiesFinished

Error mapping

Fáith produces fine-grained errors, but maps them to a few javascript error types for fetch compatibility. The .code property on errors thrown from Fáith is set to a stable name for each error kind, documented in this comprehensive mapping:

• JS AbortError:
  • Aborted — request was aborted using signal
  • Timeout — request timed out
• JS NetworkError:
  • Network — network error
  • Redirect — when the agent is configured to error on redirects
• JS SyntaxError:
  • AddressParse — IP parse error for AgentOptions.dns.overrides
  • InvalidIntegrity — SRI parse error for RequestInit.integrity
  • JsonParse — JSON parse error for response.json()
  • PemParse — PEM parse error for AgentOptions.tls.identity
  • Utf8Parse — UTF8 decoding error for response.text()
• JS TypeError:
  • InvalidHeader — invalid header name or value
  • InvalidMethod — invalid HTTP method
  • InvalidUrl — invalid URL string
  • ResponseAlreadyDisturbed — body already read (mutually exclusive operations)
  • ResponseBodyNotAvailable — body is null or not available
• JS generic Error:
  • BodyStream — internal stream handling error
  • Config — invalid agent configuration
  • IntegrityMismatch — SRI checksum mismatch (with RequestInit.integrity)
  • RuntimeThread — failed to start or schedule threads on the internal tokio runtime

The library exports an ERROR_CODES object which has every error code the library throws, and every error thrown also has a code property that is set to one of those codes. So you can accurately respond to the exact error kind by checking its code and matching against the right constant from ERROR_CODES, instead of doing string matching on the error message, or coarse instance of matching.

Due to technical limitations, when reading a body stream, reads might fail, but that error will not have a code property.

Versions

Two version constants are exposed:

• FAITH_VERSION is the version of the Fáith library itself
• REQWEST_VERSION is the version of the underlying reqwest library

These can be used to construct your own user agent strings, in logging, or for seeking help.