rfc3987-syntax 1.1.0
Helper functions to syntactically validate strings according to RFC 3987.
Requires Python: >=3.9
Keywords: RFC 3987, RFC3987, parser, syntax, validator

# rfc3987-syntax

Helper functions to parse and validate the **syntax** of terms defined in **[RFC 3987](https://www.rfc-editor.org/info/rfc3987)** — the IETF standard for Internationalized Resource Identifiers (IRIs).


## 🎯 Purpose

The goal of `rfc3987-syntax` 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](https://github.com/lark-parser/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 must be enforced separately.


## 📄 License, Attribution, and Citation

**`rfc3987-syntax`** is licensed under the [MIT License](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`](https://github.com/lark-parser/lark), licensed under MIT
- ✅ Implements grammar from **[RFC 3987](https://datatracker.ietf.org/doc/html/rfc3987)**, using **[RFC 3986](https://datatracker.ietf.org/doc/html/rfc3986)** where RFC 3987 delegates syntax

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

Please cite this software in accordance with the enclosed CITATION.cff file.


## ⚠️ Limitations

The grammar and parser enforce **only the ABNF syntax** defined in RFC 3987. 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)
- ✅ Valid **IPv6 compression** (only one `::`, max segments)
- ✅ Context-aware **percent-encoding** requirements

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

```bash
pip install rfc3987-syntax
```

## 🛠 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

```python
from rfc3987_syntax import RFC3987_SYNTAX_TERMS

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

### Syntactically validate a string using the general-purpose validator

```python
from rfc3987_syntax 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 not is_valid_syntax(term='iri_reference', value='bob'):
    print("✓ Valid IRI-reference syntax")
```

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

```python
from rfc3987_syntax import is_valid_syntax_iri
from rfc3987_syntax 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)

```python
from rfc3987_syntax 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 3986   | Standard URI authority |
| `ipath_abempty`      | RFC 3986   | Path format variant |
| `ipath_absolute`     | RFC 3986   | Absolute path |
| `ipath_noscheme`     | RFC 3986   | Path disallowing scheme prefix |
| `ipath_rootless`     | RFC 3986   | Used in non-scheme contexts |
| `iquery`             | RFC 3987   | Query extension to URI |
| `ifragment`          | RFC 3987   | Fragment extension to URI |
| `ipchar`, `isegment` | RFC 3986   | 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   | Expanded forms 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 |