Fastly VCL Interpreters in Rust

A tree-walk interpreter for Fastly VCL

Install project

• Install rust - curl https://sh.rustup.rs -sSf | sh
• Clone project - git clone https://github.com/JakeChampion/vcl-local.git && cd vcl-local
• Build project - cargo build
• Test project - cargo test
• Install project cargo install --path .
• Try out new command - vcl-local examples/polyfill/main.vcl --show-ast

Examples

Now consider hello.vcl

log "hello world";

We can tokenize this with

cargo run --release --quiet -- hello.vcl --show-tokens

Which gives output

tokens: [
    Token { ty: Log, lexeme: "log", literal: None, line: 1, col: 2},
    Token { ty: String, lexeme: ""hello world"", literal: Some(Str("hello world")), line: 1, col: 16},
    Token { ty: Semicolon, lexeme: ";", literal: None, line: 1, col: 17},
    Token { ty: Eof, lexeme: "", literal: None, line: 1, col: 17},
]

We can show the AST with

cargo run --release --quiet -- hello.vcl --show-ast

Which gives

AST: [
    Log(
        Literal(
            String(
                "hello world",
            ),
        ),
    ),
]

TODO

Scanner

• Add comments to the scan result

Parser

• Pragmas
• Macros
• ACL
• Includes
• string concat without requiring + sign. e.g. - set req.http.a = "url:"req.url;
• heredoc syntax for long strings
• short strings need percent decoding
• long strings do not need percent decoding
• typed tables
• subfield lookup using colon -- set client.identity = req.http.cookie:user_id;

Interpreter

• The integer variants of the +=, -=, and *= operators wrap around as if they were unsigned 64-bit integers.
• FLOAT arithmetic has special cases for operands which are NaN: Arithmetic operators evaluate to NaN when either operand is NaN.
• fastly.error = "EDOM" when Domain error. This occurs for a mathematical function which is not defined for a particular value; formally, that value is not considered part of its input domain. For example, division by zero, or var.x %= 5; where var.x is a floating point infinity.