auth.validate-registration
Validate a sign-up form (email, password, name) in one call, with a message per field, in the browser and the API alike.
1.0.0 · published 2026-10-03 by charlie · Anterra
Pinned by 14 tests, run in TypeScript, Python and Rust.
What it does
One call checks a whole sign-up form and answers in the shape an API's `validation_failed` error and a form both want:
validateRegistration(" Ada@Example.com ", "short", "Ada Lovelace", passwordPolicy("nist-800-63b-4-single-factor"))
# {valid: false, email: "Ada@example.com", name: "Ada Lovelace",
# fields: {"password": "Use at least 15 characters."}}
For example
validate_registration( Ada@Example.COM , correct horse battery staple, Ada Lovelace , name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, blo…)→ valid true, email Ada@example.com, name Ada Lovelace, fields … a good form: the email normalised and the name trimmed for storagevalidate_registration(ada@example.com, short, Ada Lovelace, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true)→ valid false, email ada@example.com, name Ada Lovelace, fields … a short passwordvalidate_registration(ada@example.com, password, Ada Lovelace, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true)→ valid false, email ada@example.com, name Ada Lovelace, fields … several password failures are joined into one message
The function
The same function in TypeScript, Python and Rust, pinned by the same tests. Pick your language; the choice follows you around the registry.
pub fn validate_registration(email: &str, password: &str, name: &str, policy: &PasswordPolicy) -> RegistrationCheck
| string | as typed; normalised with auth.normalise-email | |
| password | string | as typed; checked with auth.password-policy against the email and name |
| name | string | as typed; trimmed, 1 to 100 characters, no control characters |
| policy | PasswordPolicy | usually passwordPolicy("nist-800-63b-4-single-factor") |
| returns | RegistrationCheck | valid with the values to store, or a message for each field that needs fixing |
The type it declares, generated into your project
/// A sign-up form's verdict, shaped for an API's validation error and a form's field messages.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct RegistrationCheck {
pub valid: bool,
/// normalised, when the email is valid
pub email: Option<String>,
/// trimmed, when the name is valid
pub name: Option<String>,
/// field name to message, only for fields that need fixing; empty when valid
pub fields: Vec<(String, String)>,
}
Your code names it in one line, in the file that uses it
fune!(auth.validate-registration@^1); // then call validate_registration(…)
Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.
use super::funejson::Value; ← the fune runtime: the JSON value the test vectors use; fune build keeps it only where a signature takes one
use super::auth_normalise_email::normalise_email; ← from auth.normalise-email ^1.0.0 · built alongside by fune
use super::auth_password_policy_check_password::{check_password, password_policy_from_value};
use super::auth_password_policy_types::PasswordPolicy;
const MAX_NAME: usize = 100;
fn is_ascii_space(ch: char) -> bool {
matches!(ch, ' ' | '\t' | '\n' | '\r' | '\u{0C}' | '\u{0B}')
}
/// A sign-up form's email, password and name checked together: the values
/// to store when valid, and a message for each field that needs fixing.
///
/// # Panics
/// Panics on a policy whose numbers make no sense.
pub fn validate_registration(email: &str, password: &str, name: &str, policy: &PasswordPolicy) -> RegistrationCheck {
let mut fields: Vec<(String, String)> = Vec::new();
let normalised = normalise_email(email);
if normalised.is_none() {
let message = if email.trim_matches(is_ascii_space).is_empty() {
"Enter your email address."
} else {
"Enter a valid email address, like name@example.com."
};
fields.push(("email".to_string(), message.to_string()));
}
let trimmed_name = name.trim_matches(is_ascii_space);
let count = trimmed_name.chars().count();
let name_error: Option<String> = if count == 0 {
Some("Enter your name.".to_string())
} else if count > MAX_NAME {
Some(format!("Use no more than {} characters for your name.", MAX_NAME))
} else if trimmed_name.chars().any(|ch| (ch as u32) < 0x20 || ch as u32 == 0x7F) {
Some("Your name cannot contain control characters.".to_string())
} else {
None
};
let check = check_password(
password,
normalised.as_deref(),
if name_error.is_none() { Some(trimmed_name) } else { None },
policy,
);
if password.is_empty() {
fields.push(("password".to_string(), "Enter a password.".to_string()));
} else if !check.valid {
let joined: Vec<&str> = check.failures.iter().map(|f| f.message.as_str()).collect();
fields.push(("password".to_string(), joined.join(" ")));
}
let valid_name = name_error.is_none();
if let Some(message) = name_error {
fields.push(("name".to_string(), message));
}
RegistrationCheck {
valid: fields.is_empty(),
email: normalised,
name: if valid_name { Some(trimmed_name.to_string()) } else { None },
fields,
}
}
pub fn registration_check_to_value(check: &RegistrationCheck) -> Value {
let text = |v: &Option<String>| v.as_deref().map(Value::str).unwrap_or(Value::Null);
Value::obj(vec![
("valid", Value::Bool(check.valid)),
("email", text(&check.email)),
("name", text(&check.name)),
(
"fields",
Value::Obj(check.fields.iter().map(|(k, v)| (k.clone(), Value::str(v))).collect()),
),
])
}
pub fn fune_vector(args: &[Value]) -> Value {
// A non-string is an empty field, as in TypeScript and Python.
let policy = password_policy_from_value(&args[3]);
registration_check_to_value(&validate_registration(
args[0].as_str(),
args[1].as_str(),
args[2].as_str(),
&policy,
))
}Install
fune build
With that line in your source, in a Rust project (language rust in fune.project), fune build resolves it and its 2 dependencies, pins them in fune.lock, downloads only the Rust package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. A crate’s build.rs runs it before every compile. Or pin a range in fune.project and build in one step:
fune add auth.validate-registration
The manifest, vectors and README with only the Rust implementation. Install it without the registry with fune add ./auth.validate-registration-1.0.0-rust.fune, or fetch it from a terminal with fune pull auth.validate-registration@1.0.0:rust.
The whole function, every language, is one file too: auth.validate-registration-1.0.0.fune, 20,018 bytes, sha256 61f73a1f82c59d4baea20cec7e33b7e61e88780f6af7fc6438ddca4bad4208e4. It installs into a project of any language.
Customise it in your app
The seams this capability offers. Put a marker directly above a function of your own and fune build wires it into the built code; the package on the registry is not changed, the built file’s header lists it under CUSTOMISED, and fune hooks lists every hook in the project. How hooks work.
before — your function gets the arguments and returns them, changed or not, or throws to refuse the call.
// fune: before auth.validate-registration
after — your function gets the result and the arguments, and returns the final result.
// fune: after auth.validate-registration
replace — inside this capability’s code only, calls to a dependency go to your function, with the same signature. Other capabilities that use it are unaffected; write in * to replace it everywhere.
// fune: replace auth.normalise-email in auth.validate-registration
// fune: replace auth.password-policy in auth.validate-registration
step — your function runs at a numbered point inside the function’s body, receives the in-scope values it names as parameters, and may return replacements. List the points with fune show auth.validate-registration --steps.
// fune: step auth.validate-registration after <n|label>
Tests
A version published now needs at least 8 tests for every function, and one that expects the error for each function that throws; the registry refuses it otherwise. fune verify --all runs each case in TypeScript, Python and Rust, and a project runs them again with fune verify. This page lists the cases; it does not run them. The exact JSON is vectors.json.
| Case | Arguments | Expected | |
|---|---|---|---|
| a good form: the email normalised and the name trimmed for storage | Ada@Example.COM , correct horse battery staple, Ada Lovelace , name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, blo… | → | valid true, email Ada@example.com, name Ada Lovelace, fields … |
| a short password | ada@example.com, short, Ada Lovelace, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid false, email ada@example.com, name Ada Lovelace, fields … |
| several password failures are joined into one message | ada@example.com, password, Ada Lovelace, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid false, email ada@example.com, name Ada Lovelace, fields … |
| the password contains the (normalised) email's local part and the trimmed name | Ada@example.com, ada-lovelace-rules-ok, Ada Lovelace, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal … | → | valid false, email Ada@example.com, name Ada Lovelace, fields … |
| every field empty | , , , name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid false, email —, name —, fields … |
| an email that is only spaces counts as empty | , correct horse battery staple, Ada, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid false, email —, name Ada, fields … |
| an email that is not an address | ada@localhost, correct horse battery staple, Ada, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid false, email —, name Ada, fields … |
| a name of 101 characters | ada@example.com, correct horse battery staple, xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx, name nist-800-63b-4-single-fa… | → | valid false, email ada@example.com, name —, fields … |
| a name of exactly 100 characters, counted in code points (emoji are one each) | ada@example.com, correct horse battery staple, 😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀… | → | valid true, email ada@example.com, name 😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀�… |
| a control character inside the name | ada@example.com, correct horse battery staple, Ada Lovelace, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block pe… | → | valid false, email ada@example.com, name —, fields … |
Show the other 4 tests
| Case | Arguments | Expected | |
|---|---|---|---|
| names in any script are fine | li@example.cn, correct horse battery staple, 李小龍, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid true, email li@example.cn, name 李小龍, fields … |
| the multi-factor policy accepts 8 characters | ada@example.com, tr0ub4dor, Ada Lovelace, name nist-800-63b-4-multi-factor, min length 8, max length 128, min character classes 0, block common true, block personal true | → | valid true, email ada@example.com, name Ada Lovelace, fields … |
| a password that is not a string (a malformed JSON body) is treated as empty | ada@example.com, 12,345, Ada, name nist-800-63b-4-single-factor, min length 15, max length 128, min character classes 0, block common true, block personal true | → | valid false, email ada@example.com, name Ada, fields … |
| a nonsensical policy is the caller's error | ada@example.com, x, Ada, name nist-800-63b-4-single-factor, min length 0, max length 128, min character classes 0, block common true, block personal true | → | error: policy minLength must be a whole number of at least 1 |
More from the author
The browser runs it on submit to show messages beside the fields; the API runs the very same function and returns `fields` in its 400 response, so the two can never disagree about what is acceptable. When `valid` is true, store `email` and `name` from the result (normalised and trimmed), never the raw input.
**email** goes through `auth.normalise-email` (trimmed, domain lower-cased). Empty after trimming: "Enter your email address."; otherwise not an address `validation.email` accepts: "Enter a valid email address, like name@example.com."
**password** goes through `auth.password-policy`'s `checkPassword`, with the normalised email and trimmed name as the personal words to refuse. Empty: "Enter a password."; otherwise every failure's message, joined with a space in the policy's fixed order, so the field shows the whole story ("Use at least 15 characters. This password is too common. Choose something harder to guess.").
**name** is trimmed of ASCII whitespace and must then be 1 to 100 characters (code points), with no control characters (U+0000 to U+001F and U+007F): "Enter your name.", "Use no more than 100 characters for your name." or "Your name cannot contain control characters.". Any script is welcome; names are not otherwise judged (see "Falsehoods Programmers Believe About Names").
`fields` lists only the fields that need fixing, keyed `email`, `password`, `name`, in that order. A value that is not a string (a JSON body with a number where the password goes) is treated as empty, so a malformed request gets field messages rather than an exception. A nonsensical policy throws, as in `checkPassword`.
Whether the email is already taken is not a rule a pure function can know; the API checks its database after this passes (409 `email_taken`).
Files
| Path | Bytes |
|---|---|
| README.md | 2,172 |
| impl/python.py | 2,060 |
| impl/rust.rs | 3,208 |
| impl/typescript.ts | 2,435 |
| vectors.json | 6,412 |