[−][src]Trait fuzzcheck_traits::Mutator
A Mutator is an object capable of mutating a value for the purpose of fuzz-testing.
For example, a mutator could change the value
v1 = [1, 4, 2, 1]
to v1' = [1, 5, 2, 1]
.
The idea is that if v1 is an “interesting” value to test, then v1' also
has a high chance of being “interesting” to test.
Complexity
A mutator is also responsible for keeping track of the complexity of a value. The complexity is, roughly speaking, how large the value is.
For example, the complexity of a vector is the complexity of its length,
plus the sum of the complexities of its elements. So vec![]
would have a
complexity of 0.0
and vec![76]
would have a complexity of 9.0
: 1.0
for its short length and 8.0
for the 8-bit integer “76”. But there is no
fixed rule for how to compute the complexity of a value, and it is up to you
to judge how “large” something is.
Cache
In order to mutate values efficiently, the mutator is able to make use of a per-value cache. The Cache contains information associated with the value that will make it faster to compute its complexity or apply a mutation to it. For a vector, its cache is its total complexity, along with a vector of the cache of each of its element.
MutationStep
The same values will be passed to the mutator many times, so that it is mutated in many different ways. There are different strategies to choose what mutation to apply to a value. The first one is to create a list of mutation operations, and choose one to apply randomly from this list.
However, one may want to have better control over which mutation operation
is used. For example, if the value to be mutated is of type Option<T>
,
then you may want to first mutate it to None
, and then always mutate it
to another Some(t)
. This is where MutationStep
comes in. The mutation
step is a type you define to allow you to keep track of which mutation
operation has already been tried. This allows you to deterministically
apply mutations to a value such that better mutations are tried first, and
duplicate mutations are avoided.
Unmutate
Finally, it is important to note that values and caches are mutated in-place. The fuzzer does not clone them before handing them to the mutator. Therefore, the mutator also needs to know how to reverse each mutation it performed. To do so, each mutation needs to return a token describing how to reverse it. The unmutate method will later be called with that token to get the original value and cache back.
For example, if the value is [[1, 3], [5], [9, 8]]
, the mutator may
mutate it to [[1, 3], [5], [9, 1, 8]]
and return the token:
Element(2, Remove(1))
, which means that in order to reverse the
mutation, the element at index 2 has to be unmutated by removing
its element at index 1. In pseudocode:
value = [[1, 3], [5], [9, 8]]; cache: c1 (ommitted from example) step: s1 (ommitted from example) let unmutate_token = self.mutate(&mut value, &mut cache, &mut step, max_cplx); // value = [[1, 3], [5], [9, 1, 8]] // token = Element(2, Remove(1)) // cache = c2 // step = s2 test(&value); self.unmutate(&mut value, &mut cache, unmutate_token); // value = [[1, 3], [5], [9, 8]] // cache = c1 (back to original cache) // step = s2 (step has not been reversed)
Associated Types
type Value: Clone
type Cache: Clone
type MutationStep: Clone
type ArbitraryStep: Clone + Default
type UnmutateToken
Required methods
fn cache_from_value(&self, value: &Self::Value) -> Self::Cache
Compute the cache for the given value
fn initial_step_from_value(&self, value: &Self::Value) -> Self::MutationStep
Compute the initial mutation step for the given value
fn max_complexity(&self) -> f64
The maximum complexity of an input of this type
fn min_complexity(&self) -> f64
The minimum complexity of an input of this type
fn complexity(&self, value: &Self::Value, cache: &Self::Cache) -> f64
The complexity of the current input
fn ordered_arbitrary(
&mut self,
step: &mut Self::ArbitraryStep,
max_cplx: f64
) -> Option<(Self::Value, Self::Cache)>
&mut self,
step: &mut Self::ArbitraryStep,
max_cplx: f64
) -> Option<(Self::Value, Self::Cache)>
fn random_arbitrary(&mut self, max_cplx: f64) -> (Self::Value, Self::Cache)
fn ordered_mutate(
&mut self,
value: &mut Self::Value,
cache: &mut Self::Cache,
step: &mut Self::MutationStep,
max_cplx: f64
) -> Option<Self::UnmutateToken>
&mut self,
value: &mut Self::Value,
cache: &mut Self::Cache,
step: &mut Self::MutationStep,
max_cplx: f64
) -> Option<Self::UnmutateToken>
fn random_mutate(
&mut self,
value: &mut Self::Value,
cache: &mut Self::Cache,
max_cplx: f64
) -> Self::UnmutateToken
&mut self,
value: &mut Self::Value,
cache: &mut Self::Cache,
max_cplx: f64
) -> Self::UnmutateToken
fn unmutate(
&self,
value: &mut Self::Value,
cache: &mut Self::Cache,
t: Self::UnmutateToken
)
&self,
value: &mut Self::Value,
cache: &mut Self::Cache,
t: Self::UnmutateToken
)