Adding StdXObserver Docs (#2311)

* Adding StdXObserver Docs

* fixing docs

* code cleanup

* moving example

* improving exclusion rules

* adding impls for features

* adding test exclusions

* excluding miri from OS including tests

* fixing CI

---------

Co-authored-by: Dongjia "toka" Zhang <tokazerkje@outlook.com>

libafl/src/fuzzer/mod.rs

@@ -772,7 +772,7 @@ where
         }
     }
 
-    /// Runs the input and triggers observers and feedback
+    /// Runs the input and triggers observers
     pub fn execute_input<E, EM>(
         &mut self,
         state: &mut <Self as UsesState>::State,

libafl/src/mutators/mod.rs

@@ -33,7 +33,7 @@ pub use multi::*;
 #[cfg(feature = "nautilus")]
 pub mod nautilus;
 
-use alloc::{boxed::Box, vec::Vec};
+use alloc::{borrow::Cow, boxed::Box, vec::Vec};
 
 use libafl_bolts::{tuples::IntoVec, HasLen, Named};
 #[cfg(feature = "nautilus")]
@@ -407,3 +407,35 @@ impl<I, S> IntoVec<Box<dyn Mutator<I, S>>> for Vec<Box<dyn Mutator<I, S>>> {
         self
     }
 }
+
+/// [`Mutator`] that does nothing, used for testing.
+///
+/// Example:
+///
+/// ```rust,ignore
+/// let mut stages = tuple_list!(StdMutationalStage::new(NopMutator(MutationResult::Mutated)));
+/// ```
+#[derive(Debug, Clone)]
+pub struct NopMutator {
+    result: MutationResult,
+}
+
+impl NopMutator {
+    /// The passed argument is returned every time the mutator is called.
+    #[must_use]
+    pub fn new(result: MutationResult) -> Self {
+        Self { result }
+    }
+}
+
+impl<I, S> Mutator<I, S> for NopMutator {
+    fn mutate(&mut self, _state: &mut S, _input: &mut I) -> Result<MutationResult, Error> {
+        Ok(self.result)
+    }
+}
+
+impl Named for NopMutator {
+    fn name(&self) -> &Cow<'static, str> {
+        &Cow::Borrowed("NopMutator")
+    }
+}

libafl/src/observers/stdio.rs

@@ -12,6 +12,159 @@ use crate::{inputs::UsesInput, observers::Observer, state::State, Error};
 
 /// An observer that captures stdout of a target.
 /// Only works for supported executors.
+///
+/// # Example usage
+#[cfg_attr(all(feature = "std", target_os = "linux", not(miri)), doc = " ```")] // miri doesn't like the Command crate, linux as a shorthand for the availability of base64
+#[cfg_attr(
+    not(all(feature = "std", target_os = "linux", not(miri))),
+    doc = " ```ignore"
+)]
+/// use std::borrow::Cow;
+///
+/// use libafl::{
+///     corpus::{Corpus, InMemoryCorpus, Testcase},
+///     events::{EventFirer, NopEventManager},
+///     executors::{CommandExecutor, ExitKind},
+///     feedbacks::Feedback,
+///     inputs::{BytesInput, UsesInput},
+///     mutators::{MutationResult, NopMutator},
+///     observers::{ObserversTuple, StdErrObserver, StdOutObserver},
+///     schedulers::QueueScheduler,
+///     stages::StdMutationalStage,
+///     state::{HasCorpus, State, StdState},
+///     Error, Fuzzer, StdFuzzer,
+/// };
+///
+/// use libafl_bolts::{
+///     current_nanos,
+///     rands::StdRand,
+///     tuples::{tuple_list, Handle, Handled, MatchNameRef},
+///     Named,
+/// };
+///
+/// static mut STDOUT: Option<Vec<u8>> = None;
+/// static mut STDERR: Option<Vec<u8>> = None;
+///
+/// #[derive(Clone)]
+/// struct ExportStdXObserver {
+///     stdout_observer: Handle<StdOutObserver>,
+///     stderr_observer: Handle<StdErrObserver>,
+/// }
+///
+/// impl<S> Feedback<S> for ExportStdXObserver
+/// where
+///     S: State
+/// {
+///     fn is_interesting<EM, OT>(
+///         &mut self,
+///         _state: &mut S,
+///         _manager: &mut EM,
+///         _input: &<S>::Input,
+///         observers: &OT,
+///         _exit_kind: &ExitKind,
+///     ) -> Result<bool, Error>
+///     where
+///         EM: EventFirer<State = S>,
+///         OT: ObserversTuple<S>,
+///     {
+///         unsafe {
+///             STDOUT = observers.get(&self.stdout_observer).unwrap().stdout.clone();
+///             STDERR = observers.get(&self.stderr_observer).unwrap().stderr.clone();
+///         }
+///         Ok(true)
+///     }
+///
+/// #[cfg(feature = "track_hit_feedbacks")]
+///     fn last_result(&self) -> Result<bool, Error> {
+///         Ok(true)
+///     }
+/// }
+///
+/// impl Named for ExportStdXObserver {
+///     fn name(&self) -> &Cow<'static, str> {
+///         &Cow::Borrowed("ExportStdXObserver")
+///     }
+/// }
+///
+/// fn main() {
+///     let input_text = "Hello, World!";
+///     let encoded_input_text = "SGVsbG8sIFdvcmxkIQo=";
+///
+///     let stdout_observer = StdOutObserver::new("stdout-observer");
+///     let stderr_observer = StdErrObserver::new("stderr-observer");
+///
+///     let mut feedback = ExportStdXObserver {
+///         stdout_observer: stdout_observer.handle(),
+///         stderr_observer: stderr_observer.handle(),
+///     };
+///
+///     let mut objective = ();
+///
+///     let mut executor = CommandExecutor::builder()
+///         .program("base64")
+///         .arg("--decode")
+///         .stdout_observer(stdout_observer.handle())
+///         .stderr_observer(stderr_observer.handle())
+///         .build(tuple_list!(stdout_observer, stderr_observer))
+///         .unwrap();
+///
+///     let mut state = StdState::new(
+///         StdRand::with_seed(current_nanos()),
+///         InMemoryCorpus::new(),
+///         InMemoryCorpus::new(),
+///         &mut feedback,
+///         &mut objective,
+///     )
+///     .unwrap();
+///
+///     let scheduler = QueueScheduler::new();
+///     let mut fuzzer = StdFuzzer::new(scheduler, feedback, objective);
+///     let mut manager = NopEventManager::new();
+///
+///     let mut stages = tuple_list!(StdMutationalStage::new(NopMutator::new(
+///         MutationResult::Mutated
+///     )));
+///
+///     state
+///         .corpus_mut()
+///         .add(Testcase::new(BytesInput::from(
+///             encoded_input_text.as_bytes().to_vec(),
+///         )))
+///         .unwrap();
+///
+///     let corpus_id = fuzzer
+///         .fuzz_one(&mut stages, &mut executor, &mut state, &mut manager)
+///         .unwrap();
+///
+///     unsafe {
+///         assert!(input_text
+///             .as_bytes()
+///             .iter()
+///             .zip(STDOUT.as_ref().unwrap().iter().filter(|e| **e != 10)) // ignore newline chars
+///             .all(|(&a, &b)| a == b));
+///         assert!(STDERR.as_ref().unwrap().is_empty());
+///     }
+///
+///     state
+///         .corpus()
+///         .get(corpus_id)
+///         .unwrap()
+///         .replace(Testcase::new(BytesInput::from(
+///             encoded_input_text.bytes().skip(1).collect::<Vec<u8>>(), // skip one char to make it invalid code
+///         )));
+///
+///     fuzzer
+///         .fuzz_one(&mut stages, &mut executor, &mut state, &mut manager)
+///         .unwrap();
+///
+///     unsafe {
+///         let compare_vec: Vec<u8> = Vec::new();
+///         assert_eq!(compare_vec, *STDERR.as_ref().unwrap());
+///         // stdout will still contain data, we're just checking that there is an error message
+///     }
+/// }
+/// ```
+
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct StdOutObserver {
     /// The name of the observer.
@@ -55,10 +208,17 @@ where
         self.stdout = None;
         Ok(())
     }
+
+    fn pre_exec(&mut self, _state: &mut S, _input: &<S as UsesInput>::Input) -> Result<(), Error> {
+        self.stdout = None;
+        Ok(())
+    }
 }
 
 /// An observer that captures stderr of a target.
 /// Only works for supported executors.
+///
+/// Check docs for [`StdOutObserver`] for example.
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct StdErrObserver {
     /// The name of the observer.
@@ -102,4 +262,9 @@ where
         self.stderr = None;
         Ok(())
     }
+
+    fn pre_exec(&mut self, _state: &mut S, _input: &<S as UsesInput>::Input) -> Result<(), Error> {
+        self.stderr = None;
+        Ok(())
+    }
 }