VCL Parser for Go

A VCL (Varnish Configuration Language) parser implemented in Go that parses VCL files into Abstract Syntax Trees (AST).

Features

• Complete lexical analysis of VCL syntax
• Recursive descent parser with error recovery
• Type-safe AST representation
• Post-parse resolution of include statements
• Symbol table and semantic analysis
• Visitor pattern for AST traversal
• VMOD and variable semantics loaded from varnishd build

Semantics

Semantics like what variables are available in a given context are defined in the metadata package, in a JSON file that is generated by the generate.py script inside varnishd. This file is embedded into the library at compile time.

VMOD semantics are loaded from a collection of VCC files in vcclib. These are embedded into the library at compile time.

Usage

package main

import (
	"fmt"
	"log"

	"github.com/varnish/vclparser/pkg/parser"
)

func main() {
	vclCode := `
    vcl 4.0;

    backend default {
        .host = "127.0.0.1";
        .port = "8080";
    }

    sub vcl_recv {
        if (req.method == "GET") {
            return (hash);
        }
    }
    `

	ast, err := parser.Parse(vclCode)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Parsed VCL with %d declarations\n", len(ast.Declarations))
}

Architecture

• pkg/lexer/ - Lexical analysis and tokenization
• pkg/ast/ - AST node definitions and visitor pattern
• pkg/parser/ - Recursive descent parser implementation
• pkg/types/ - Type system and symbol table
• examples/ - Usage examples
• tests/testdata/ - Test VCL files

VCL Language Support

This parser supports the full VCL language including:

• Version declarations (vcl 4.0;)
• Backend definitions with properties
• Access Control Lists (ACLs)
• Probe definitions
• Subroutine definitions
• All VCL statements (if/else, set, unset, call, return, etc.)
• Expression parsing with proper operator precedence
• Built-in variables and functions
• C-code blocks (C{ }C)

Testing

go test ./...