rfc3987-syntax2

Helper functions to parse and validate the syntax of terms defined in RFC 3987 — the IETF standard for Internationalized Resource Identifiers (IRIs).

[!NOTE]
This is a maintained fork of https://github.com/willynilly/rfc3987-syntax.

🎯 Purpose

The goal of rfc3987-syntax2 is to provide a lightweight, permissively licensed Python module for validating that strings conform to the ABNF grammar defined in RFC 3987. These helpers are:

✅ Strictly aligned with the syntax rules of RFC 3987
✅ Built using a permissive MIT license
✅ Designed for both open source and proprietary use
✅ Powered by Lark, a fast, EBNF-based parser

🧠 Note: This project focuses on syntax validation only. RFC 3987 specifies additional semantic rules (e.g., Unicode normalization, BiDi constraints, percent-encoding requirements) that are intentionally out of scope.

📄 License, Attribution, and Citation

rfc3987-syntax2 is licensed under the MIT License, which allows reuse in both open source and commercial software.

This project:

❌ Does not depend on the rfc3987 Python package (GPL-licensed)
✅ Uses lark, licensed under MIT
✅ Implements grammar from RFC 3987, using RFC 3986 where RFC 3987 delegates syntax

⚠️ This project is not affiliated with or endorsed by the authors of RFC 3987 or the rfc3987 Python package.

⚠️ Limitations

The grammar and parser enforce only the ABNF syntax defined in RFC 3987 (and referenced RFC 3986 productions where applicable).
The following are not validated and must be handled separately for full compliance:

Unicode Normalization Form C (NFC)
Bidirectional text (BiDi) constraints (RFC 3987 §4.1)
Port number ranges (must be 0–65535)
Context-aware percent-encoding requirements
Additional host/network semantics beyond ABNF syntax (for example, canonical representation expectations)

ChatGPT 40 was used during the original development process. Errors may exist due to this assistance. Additional review, testing, and bug fixes by human experts is welcome.

📦 Installation

pip install rfc3987-syntax2

📚 Documentation

Complete documentation is available on Read the Docs. This includes:

Responsibilities & Capabilities
Install Instructions
API Reference
Usage Examples

🛠 Usage

List all supported “terms” (i.e., non-terminals and terminals within ABNF production rules) used to validate the syntax of an IRI according to RFC 3987

from rfc3987_syntax2 import RFC3987_SYNTAX_TERMS

print("Supported terms:")
for term in RFC3987_SYNTAX_TERMS:
    print(term)

Syntactically validate a string using the general-purpose validator

from rfc3987_syntax2 import is_valid_syntax

if is_valid_syntax(term='iri', value='http://github.com'):
    print("✓ Valid IRI syntax")

if not is_valid_syntax(term='iri', value='bob'):
    print("✗ Invalid IRI syntax")

if is_valid_syntax(term='iri_reference', value='bob'):
    print("✓ Valid IRI-reference syntax")

Alternatively, use term-specific helpers to validate RFC 3987 syntax.

from rfc3987_syntax2 import is_valid_syntax_iri
from rfc3987_syntax2 import is_valid_syntax_iri_reference

if is_valid_syntax_iri('http://github.com'):
    print("✓ Valid IRI syntax")

if not is_valid_syntax_iri('bob'):
    print("✗ Invalid IRI syntax")

if is_valid_syntax_iri_reference('bob'):
    print("✓ Valid IRI-reference syntax")

Get the Lark parse tree for a syntax validation (useful for additional semantic validation)

from rfc3987_syntax2 import parse

ptree: ParseTree = parse(term="iri", value="http://github.com")

print(ptree)

📚 Sources

This grammar was derived from:

RFC 3987 – Internationalized Resource Identifiers (IRIs)
→ Defines IRI syntax and extensions to URI (e.g. Unicode characters, ucschar)
→ https://datatracker.ietf.org/doc/html/rfc3987
RFC 3986 – Uniform Resource Identifier (URI): Generic Syntax
→ Provides reusable components like scheme, authority, ipv4address, etc.
→ https://datatracker.ietf.org/doc/html/rfc3986

📝 When RFC 3986 is listed as the source, it is used in accordance with RFC 3987, which explicitly references it for foundational elements.

Rule-to-Source Mapping

Rule/Component	Source	Notes
`iri`	RFC 3987	Top-level IRI rule
`iri_reference`	RFC 3987	Top-level IRI Reference rule
`absolute_iri`	RFC 3987	Top-level Absolute IRI rule
`scheme`	RFC 3986	Referenced by RFC 3987 §2.2
`ihier_part`	RFC 3987	IRI-specific hierarchy
`irelative_ref`	RFC 3987	IRI-specific relative ref
`irelative_part`	RFC 3987	IRI-specific relative part
`iauthority`	RFC 3987	IRI authority production
`iuserinfo`	RFC 3987	IRI userinfo production
`ihost`	RFC 3987	IRI host production
`ireg_name`	RFC 3987	IRI reg-name production
`ipath`	RFC 3987	Union of IRI path variants
`ipath_abempty`	RFC 3987	IRI path format variant
`ipath_absolute`	RFC 3987	Absolute path
`ipath_noscheme`	RFC 3987	Path disallowing scheme prefix
`ipath_rootless`	RFC 3987	Used in non-scheme contexts
`ipath_empty`	RFC 3987	Empty IRI path
`iquery`	RFC 3987	Query extension to URI
`ifragment`	RFC 3987	Fragment extension to URI
`ipchar`, `isegment`	RFC 3987	IRI path characters and segments
`isegment_nz_nc`	RFC 3987	IRI-specific path constraint
`iunreserved`	RFC 3987	Includes `ucschar`
`ucschar`, `iprivate`	RFC 3987	Unicode support
`sub_delims`	RFC 3986	Reserved characters
`ip_literal`	RFC 3986	IPv6 or IPvFuture in `[]`
`ipv6address`	RFC 3986	RFC 3986 IPv6address production; syntax-level validation only
`ipvfuture`	RFC 3986	Forward-compatible
`ipv4address`	RFC 3986	Dotted-decimal IPv4
`ls32`	RFC 3986	Final 32 bits of IPv6
`h16`, `dec_octet`	RFC 3986	Hex and decimal chunks
`port`	RFC 3986	Optional numeric
`pct_encoded`	RFC 3986	Percent encoding (e.g. `%20`)
`alpha`, `digit`, `hexdig`	RFC 3986	Character classes
`non_zero`	Project helper	Local helper token used in `dec_octet`
`unreserved`	RFC 3986	Used by `ipvfuture` production

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