fix: accept fib flags as string or array

nft 1.1.4 changed the json output to return only a single string if
there is only one flag set.[1,2]

The same logic applies to some other types as well which I update in the
following commits.

[1] https://github.com/nftables-rs/nftables-rs/issues/183
[2] https://bugzilla.netfilter.org/show_bug.cgi?id=1806

Fixes #183

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

resources/test/fixtures/README.md

@@ -0,0 +1 @@
+These files are where either generated by a specific nftables version or by hand to test specific json parsing behavior.

resources/test/fixtures/single-fib-flag-1.json

@@ -0,0 +1,53 @@
+{
+  "nftables": [
+    {
+      "metainfo": {
+        "version": "1.1.0",
+        "release_name": "some name",
+        "json_schema_version": 1
+      }
+    },
+    {
+      "table": {
+        "family": "ip",
+        "name": "test",
+        "handle": 1
+      }
+    },
+    {
+      "chain": {
+        "family": "ip",
+        "table": "test",
+        "name": "prerouting",
+        "handle": 1
+      }
+    },
+    {
+      "rule": {
+        "family": "ip",
+        "table": "test",
+        "chain": "prerouting",
+        "handle": 2,
+        "expr": [
+          {
+            "match": {
+              "op": "==",
+              "left": {
+                "fib": {
+                  "result": "type",
+                  "flags": [
+                    "daddr"
+                  ]
+                }
+              },
+              "right": "local"
+            }
+          },
+          {
+            "accept": null
+          }
+        ]
+      }
+    }
+  ]
+}

resources/test/fixtures/single-fib-flag-2.json

@@ -0,0 +1,51 @@
+{
+  "nftables": [
+    {
+      "metainfo": {
+        "version": "1.1.0",
+        "release_name": "some name",
+        "json_schema_version": 1
+      }
+    },
+    {
+      "table": {
+        "family": "ip",
+        "name": "test",
+        "handle": 1
+      }
+    },
+    {
+      "chain": {
+        "family": "ip",
+        "table": "test",
+        "name": "prerouting",
+        "handle": 1
+      }
+    },
+    {
+      "rule": {
+        "family": "ip",
+        "table": "test",
+        "chain": "prerouting",
+        "handle": 2,
+        "expr": [
+          {
+            "match": {
+              "op": "==",
+              "left": {
+                "fib": {
+                  "result": "type",
+                  "flags": "daddr"
+                }
+              },
+              "right": "local"
+            }
+          },
+          {
+            "accept": null
+          }
+        ]
+      }
+    }
+  ]
+}

src/expr.rs

@@ -3,6 +3,8 @@ use serde::{Deserialize, Serialize};
 use std::{borrow::Cow, collections::HashSet};
 
 use crate::stmt::{Counter, JumpTarget, Statement};
+use crate::visitor::deserialize_flags;
+use strum_macros::EnumString;
 
 #[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize, JsonSchema)]
 #[serde(untagged)]
@@ -300,7 +302,7 @@ pub struct SctpChunk<'a> {
 #[serde(rename = "meta")]
 /// Create a reference to packet meta data.
 ///
-/// See [this page](https://wiki.nftables.org/wiki-nftables/index.php/Matching_packet_metainformation)  
+/// See [this page](https://wiki.nftables.org/wiki-nftables/index.php/Matching_packet_metainformation)
 /// for more information.
 pub struct Meta {
     /// The packet [meta data key](MetaKey).
@@ -589,6 +591,7 @@ impl Default for SymHash {
 pub struct Fib {
     /// The data to be queried by fib lookup.
     pub result: FibResult,
+    #[serde(deserialize_with = "deserialize_flags")]
     /// The tuple of elements ([FibFlags](FibFlag)) that is used as input to the
     /// fib lookup functions.
     pub flags: HashSet<FibFlag>,
@@ -618,8 +621,11 @@ pub enum FibResult {
     Type,
 }
 
-#[derive(Debug, Clone, Copy, Eq, PartialEq, Serialize, Deserialize, Hash, JsonSchema)]
+#[derive(
+    Debug, Clone, Copy, Eq, PartialEq, Serialize, Deserialize, EnumString, Hash, JsonSchema,
+)]
 #[serde(rename_all = "lowercase")]
+#[strum(serialize_all = "lowercase")]
 /// Represents flags for `fib` lookup.
 pub enum FibFlag {
     /// Consider the source address of a packet.

src/visitor.rs

@@ -113,3 +113,49 @@ where
         None => s.serialize_some(&0_usize),
     }
 }
+
+/// Deserialize string or array of strings into the given HashSet type.
+pub fn deserialize_flags<'de, D, T>(deserializer: D) -> Result<HashSet<T>, D::Error>
+where
+    D: de::Deserializer<'de>,
+    T: FromStr + Eq + core::hash::Hash + Deserialize<'de>,
+    <T as FromStr>::Err: std::fmt::Display,
+{
+    struct FlagSet<T>(PhantomData<T>);
+    impl<'de, T> de::Visitor<'de> for FlagSet<T>
+    where
+        T: FromStr + Eq + core::hash::Hash + Deserialize<'de>,
+        <T as FromStr>::Err: std::fmt::Display,
+    {
+        type Value = HashSet<T>;
+
+        fn expecting(&self, formatter: &mut Formatter) -> std::fmt::Result {
+            formatter.write_str("single string or list of strings")
+        }
+
+        fn visit_none<E>(self) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            Ok(HashSet::default())
+        }
+
+        fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+            <T as FromStr>::Err: std::fmt::Display,
+        {
+            let mut h: HashSet<T> = HashSet::new();
+            h.insert(T::from_str(value).map_err(<E>::custom)?);
+            Ok(h)
+        }
+
+        fn visit_seq<S>(self, visitor: S) -> Result<Self::Value, S::Error>
+        where
+            S: de::SeqAccess<'de>,
+        {
+            Deserialize::deserialize(de::value::SeqAccessDeserializer::new(visitor))
+        }
+    }
+    deserializer.deserialize_any(FlagSet(PhantomData))
+}

tests/fixtures.rs

@@ -0,0 +1,26 @@
+use std::{fs::File, io::BufReader};
+
+use nftables::schema::Nftables;
+
+// nft 1.1.4 changed behavior where the flag is printed as single string instead of array
+// As such this lib should be able to parse both and return the same result.
+// https://bugzilla.netfilter.org/show_bug.cgi?id=1806
+#[test]
+fn test_parse_fib_flags() {
+    let file1 = BufReader::new(
+        File::open("resources/test/fixtures/single-fib-flag-1.json").expect("Cannot open file1"),
+    );
+    let json1: Nftables =
+        serde_path_to_error::deserialize(&mut serde_json::Deserializer::from_reader(file1))
+            .expect("failed to parse json1");
+
+    let file2 = BufReader::new(
+        File::open("resources/test/fixtures/single-fib-flag-2.json").expect("Cannot open file2"),
+    );
+
+    let json2: Nftables =
+        serde_path_to_error::deserialize(&mut serde_json::Deserializer::from_reader(file2))
+            .expect("failed to parse json2");
+
+    assert_eq!(json1, json2, "Both parsed files should be identical")
+}