Merge #633

633: Add first fuzz target for fuzzing simplify algorithm. r=michaelkirk a=frewsxcv

- [x] I agree to follow the project's [code of conduct](https://github.com/georust/geo/blob/master/CODE_OF_CONDUCT.md).
- ~I added an entry to `CHANGES.md` if knowledge of this change could be valuable to users.~
---

Based off of #532.

Fuzzing allows us to find buggy edge cases and  alsocheck the validity of our algorithms (by comparing results against the result of other libraries like GEOS). This pull request just adds one fuzz target for fuzzing our `Simplify` algorithm to get us started.

How to fuzz:

```sh
cargo install cargo-fuzz
cd geo
cargo fuzz run simplify # cargo fuzz run <fuzz target>
```


Co-authored-by: Corey Farwell <coreyf@rwell.org>

.github/workflows/test.yml

@@ -15,6 +15,7 @@ jobs:
       - geo_types
       - geo
       - geo_postgis
+      - geo_fuzz
       - coverage
       - bench
     steps:
@@ -24,6 +25,7 @@ jobs:
       - name: Mark the job as a failure
         if: "!success()"
         run: exit 1
+
   geo_types:
     name: geo-types
     runs-on: ubuntu-latest
@@ -80,6 +82,24 @@ jobs:
       - run: cargo install cargo-all-features
       - run: cargo build-all-features
       - run: cargo test-all-features
+
+  geo_fuzz:
+    name: geo-fuzz
+    runs-on: ubuntu-latest
+    if: "!contains(github.event.head_commit.message, '[skip ci]')"
+    defaults:
+      run:
+        working-directory: geo/fuzz
+    strategy:
+      matrix:
+        container_image: ["georust/geo-ci:rust-1.49", "georust/geo-ci:rust-1.50"]
+    container:
+      image: ${{ matrix.container_image }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - run: cargo build --bins
+
   coverage:
     name: coverage
     runs-on: ubuntu-latest

geo/fuzz/.gitignore

@@ -0,0 +1,3 @@
+target
+corpus
+artifacts

geo/fuzz/Cargo.toml

@@ -0,0 +1,29 @@
+[package]
+name = "geo-fuzz"
+version = "0.0.0"
+authors = ["Automatically generated"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[dependencies.geo]
+path = ".."
+
+[dependencies.geo-types]
+path = "../../geo-types"
+features = ["arbitrary"]
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "simplify"
+path = "fuzz_targets/simplify.rs"
+test = false
+doc = false

geo/fuzz/fuzz_targets/simplify.rs

@@ -0,0 +1,23 @@
+#![no_main]
+
+use geo::algorithm::euclidean_length::EuclideanLength;
+use geo::algorithm::simplify::Simplify;
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|tuple: (geo_types::Polygon<f32>, f32)| {
+    let (polygon, epsilon) = tuple;
+
+    let simplified = polygon.simplify(&epsilon);
+
+    check_result(polygon, simplified);
+});
+
+fn check_result(original: geo_types::Polygon<f32>, simplified: geo_types::Polygon<f32>) {
+    assert!(simplified.exterior().0.len() <= original.exterior().0.len());
+    assert!(simplified.exterior().euclidean_length() <= original.exterior().euclidean_length());
+
+    for interior in simplified.interiors() {
+        assert!(simplified.exterior().0.len() <= interior.0.len());
+        assert!(simplified.exterior().euclidean_length() <= interior.euclidean_length());
+    }
+}