[pve-devel] [PATCH proxmox-firewall 18/37] nftables: add helpers

[Stefan Hanreich <s.hanreich@proxmox.com>]

Several objects, statements and expressions in nftables-json require
null values, for instance:

    { "flush": { "ruleset": null }}

For this purpose we define our own Null type, which we can then easily
use for defining types that accept Null as value.

Several keys accept as value either a singular element (string or
object) if there is only one object, but an array if there are
multiple objects. For instance when adding a single element to a set:

           { "element": {
	       ...
	       "elem": "element1"
           }}

but when adding multiple elements:

           { "element": {
	       ...
	       "elem": ["element1", "element2"]
           }}

NfVec<T> is a wrapper for Vec<T> that serializes into T iff Vec
contains one element, otherwise it serializes like a Vec would
normally do.

Co-authored-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
---
 proxmox-nftables/Cargo.toml    |   4 +
 proxmox-nftables/src/helper.rs | 190 +++++++++++++++++++++++++++++++++
 proxmox-nftables/src/lib.rs    |   1 +
 3 files changed, 195 insertions(+)
 create mode 100644 proxmox-nftables/src/helper.rs

diff --git a/proxmox-nftables/Cargo.toml b/proxmox-nftables/Cargo.toml
index 764e231..ebece9d 100644
--- a/proxmox-nftables/Cargo.toml
+++ b/proxmox-nftables/Cargo.toml
@@ -13,4 +13,8 @@ license = "AGPL-3"
 [dependencies]
 log = "0.4"
 
+serde = { version = "1", features = [ "derive" ] }
+serde_json = "1"
+serde_plain = "1"
+
 proxmox-ve-config = { path = "../proxmox-ve-config", optional = true }
diff --git a/proxmox-nftables/src/helper.rs b/proxmox-nftables/src/helper.rs
new file mode 100644
index 0000000..77ce347
--- /dev/null
+++ b/proxmox-nftables/src/helper.rs
@@ -0,0 +1,190 @@
+use std::fmt;
+use std::marker::PhantomData;
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Copy, Debug)]
+pub struct Null;
+
+impl<'de> Deserialize<'de> for Null {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de::Error;
+
+        match Option::<()>::deserialize(deserializer)? {
+            None => Ok(Self),
+            Some(_) => Err(D::Error::custom("expected null")),
+        }
+    }
+}
+
+impl Serialize for Null {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_none()
+    }
+}
+
+impl fmt::Display for Null {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("null")
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct NfVec<T>(pub(crate) Vec<T>);
+
+impl<T> Default for NfVec<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T> NfVec<T> {
+    pub const fn new() -> Self {
+        Self(Vec::new())
+    }
+
+    pub fn one(value: T) -> Self {
+        Self(vec![value])
+    }
+}
+
+impl<T> From<Vec<T>> for NfVec<T> {
+    fn from(v: Vec<T>) -> Self {
+        Self(v)
+    }
+}
+
+impl<T> From<NfVec<T>> for Vec<T> {
+    fn from(v: NfVec<T>) -> Self {
+        v.0
+    }
+}
+
+impl<T> FromIterator<T> for NfVec<T> {
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
+impl<T> std::ops::Deref for NfVec<T> {
+    type Target = Vec<T>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T> std::ops::DerefMut for NfVec<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<T: Serialize> Serialize for NfVec<T> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        if self.len() == 1 {
+            self[0].serialize(serializer)
+        } else {
+            self.0.serialize(serializer)
+        }
+    }
+}
+
+macro_rules! visit_value {
+    ($( ($visit:ident, $($ty:tt)+), )+) => {
+        $(
+            fn $visit<E>(self, value: $($ty)+) -> Result<Self::Value, E>
+            where
+                E: Error,
+            {
+                T::deserialize(value.into_deserializer()).map(NfVec::one)
+            }
+        )+
+    };
+}
+
+impl<'de, T: Deserialize<'de>> Deserialize<'de> for NfVec<T> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de::{Error, IntoDeserializer};
+
+        struct V<T>(PhantomData<T>);
+
+        impl<'de, T: Deserialize<'de>> serde::de::Visitor<'de> for V<T> {
+            type Value = NfVec<T>;
+
+            fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                f.write_str("an array or single element")
+            }
+
+            fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: serde::de::SeqAccess<'de>,
+            {
+                Vec::<T>::deserialize(serde::de::value::SeqAccessDeserializer::new(seq)).map(NfVec)
+            }
+
+            fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
+            where
+                A: serde::de::MapAccess<'de>,
+            {
+                T::deserialize(serde::de::value::MapAccessDeserializer::new(map)).map(NfVec::one)
+            }
+
+            fn visit_none<E>(self) -> Result<Self::Value, E>
+            where
+                E: Error,
+            {
+                Ok(NfVec::new())
+            }
+
+            fn visit_unit<E>(self) -> Result<Self::Value, E>
+            where
+                E: Error,
+            {
+                Ok(NfVec::new())
+            }
+
+            fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+            where
+                D: serde::Deserializer<'de>,
+            {
+                deserializer.deserialize_any(self)
+            }
+
+            visit_value! {
+                (visit_bool, bool),
+                (visit_borrowed_bytes, &'de [u8]),
+                (visit_borrowed_str, &'de str),
+                (visit_byte_buf, Vec<u8>),
+                (visit_bytes, &[u8]),
+                (visit_char, char),
+                (visit_f32, f32),
+                (visit_f64, f64),
+                (visit_i8, i8),
+                (visit_i16, i16),
+                (visit_i32, i32),
+                (visit_i64, i64),
+                (visit_u8, u8),
+                (visit_u16, u16),
+                (visit_u32, u32),
+                (visit_u64, u64),
+                (visit_str, &str),
+                (visit_string, String),
+            }
+        }
+
+        deserializer.deserialize_any(V::<T>(PhantomData))
+    }
+}
diff --git a/proxmox-nftables/src/lib.rs b/proxmox-nftables/src/lib.rs
index e69de29..485bb81 100644
--- a/proxmox-nftables/src/lib.rs
+++ b/proxmox-nftables/src/lib.rs
@@ -0,0 +1 @@
+pub mod helper;
-- 
2.39.2