Add fuzzing tests

fuzz/fuzz_targets/fuzz_dateparse.rs

@@ -0,0 +1,10 @@
+use bolero::check;
+
+fn main() {
+    check!().for_each(|data: &[u8]| match std::str::from_utf8(data) {
+        Ok(input) => {
+            mailparse::dateparse(input).ok();
+        }
+        Err(_err) => {}
+    });
+}

fuzz/fuzz_targets/fuzz_format_flowed.rs

@@ -0,0 +1,25 @@
+use bolero::check;
+use format_flowed::{format_flowed, unformat_flowed};
+
+fn round_trip(input: &str) -> String {
+    let mut input = format_flowed(input);
+    input.retain(|c| c != '\r');
+    unformat_flowed(&input, false)
+}
+
+fn main() {
+    check!().for_each(|data: &[u8]| {
+        if let Ok(input) = std::str::from_utf8(data.into()) {
+            let mut input = input.to_string();
+
+            // Only consider inputs that don't contain quotes.
+            input.retain(|c| c != '>');
+
+            // Only consider inputs that are the result of unformatting format=flowed text.
+            // At least this means that lines don't contain any trailing whitespace.
+            let input = round_trip(&input);
+            let output = round_trip(&input);
+            assert_eq!(input, output);
+        }
+    });
+}

fuzz/fuzz_targets/fuzz_mailparse.rs

@@ -0,0 +1,7 @@
+use bolero::check;
+
+fn main() {
+    check!().for_each(|data: &[u8]| {
+        mailparse::parse_mail(data).ok();
+    });
+}

fuzz/fuzz_targets/fuzz_simplify.rs

@@ -0,0 +1,13 @@
+use bolero::check;
+
+use deltachat::fuzzing::simplify;
+
+fn main() {
+    check!().for_each(|data: &[u8]| match String::from_utf8(data.to_vec()) {
+        Ok(input) => {
+            simplify(input.clone(), true);
+            simplify(input, false);
+        }
+        Err(_err) => {}
+    });
+}