Crate apollo_smith

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A test case generator for GraphQL language. Download docs


The goal of apollo-smith is to generate valid GraphQL documents by sampling from all available possibilities of GraphQL grammar.

We’ve written apollo-smith to use in fuzzing, but you may wish to use it for anything that requires GraphQL document generation.

apollo-smith is inspired by bytecodealliance’s wasm-smith crate, and the article written by Nick Fitzgerald on writing test case generators in Rust.

This is still a work in progress, for outstanding issues, checkout out the apollo-smith label in our issue tracker.

Rust versions

apollo-smith is tested on the latest stable version of Rust. Older version may or may not be compatible.

Using apollo-smith with cargo fuzz

Define a new target with cargo fuzz,

$ cargo fuzz add my_apollo_smith_fuzz_target

and add apollo-smith to your Cargo.toml:

## fuzz/Cargo.toml

apollo-smith = "0.3.2"

It can then be used in a fuzz_target along with the arbitrary crate,

// fuzz/fuzz_targets/


use libfuzzer_sys::fuzz_target;
use arbitrary::Unstructured;
use apollo_smith::DocumentBuilder;

fuzz_target!(|input: &[u8]| {
    let mut u = Unstructured::new(input);
    let gql_doc = DocumentBuilder::new(&mut u)?;
    let document = gql_doc.finish();
    let document_str = String::from(document);


and fuzzed with the following command:

$ cargo +nightly fuzz run my_apollo_smith_fuzz_target

Using apollo-smith with apollo-parser

You can use apollo-parser to generate valid operations in apollo-smith. This can be done with the parser-impl feature flag.

## Cargo.toml

apollo-smith = { version = "0.3.1", features = ["parser-impl"] }
use std::fs;

use apollo_parser::Parser;
use apollo_smith::{Document, DocumentBuilder};

use libfuzzer_sys::arbitrary::{Result, Unstructured};

/// This generate an arbitrary valid GraphQL operation
pub fn generate_valid_operation(input: &[u8]) {

    let parser = Parser::new(&fs::read_to_string("supergraph.graphql").expect("cannot read file"));

    let tree = parser.parse();
    if !tree.errors().is_empty() {
        panic!("cannot parse the graphql file");

    let mut u = Unstructured::new(input);

    // Convert `apollo_parser::Document` into `apollo_smith::Document`.
    let apollo_smith_doc = Document::from(tree.document());

    // Create a `DocumentBuilder` given an existing document to match a schema.
    let mut gql_doc = DocumentBuilder::with_document(&mut u, apollo_smith_doc)?;
    let operation_def = gql_doc.operation_definition()?.unwrap();


Feature flags

Enable parser-impl feature in apollo-smith is used to convert apollo-parser types to apollo-smith types. This is useful when you require the test-case generator to generate documents based on a given schema.

## Cargo.toml

apollo-smith = { version = "0.3.1", features = ["parser-impl"] }


  • Recursive object type not yet supported (example : myType { inner: myType })


Licensed under either of

  • Apache License, Version 2.0 (LICENSE-APACHE or
  • MIT license (LICENSE-MIT or

at your option.


The __DirectiveDef type represents a Directive definition.
The __Document type represents a GraphQL document.A GraphQL Document describes a complete file or request string operated on by a GraphQL service or client. A document contains multiple definitions, either executable or representative of a GraphQL type system.
DocumentBuilder is a struct to build an arbitrary valid GraphQL document
Enums are special scalars that can only have a defined set of values.
The __fragmentDef type represents a fragment definition
Input objects are composite types used as inputs into queries defined as a list of named input values..
InterfaceTypeDef is an abstract type where there are common fields declared.
Object types represent concrete instantiations of sets of fields.
The __operationDef type represents an operation definition
Represents scalar types such as Int, String, and Boolean. Scalars cannot have fields.
A GraphQL service’s collective type system capabilities are referred to as that service’s “schema”.
UnionDefs are an abstract type where no common fields are declared.

Type Definitions

A Result with the error type fixed as arbitrary::Error.