[pbs-devel] [RFC PATCH proxmox 2/4] promxox-router: add SerializableReturn Trait

[Dominik Csapak]

this will be useful as a generic return type for api calls which
must implement Serialize.

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
 proxmox-router/Cargo.toml                 |  2 +
 proxmox-router/src/lib.rs                 |  2 +
 proxmox-router/src/serializable_return.rs | 62 +++++++++++++++++++++++
 3 files changed, 66 insertions(+)
 create mode 100644 proxmox-router/src/serializable_return.rs

diff --git a/proxmox-router/Cargo.toml b/proxmox-router/Cargo.toml
index 28616d8..d460772 100644
--- a/proxmox-router/Cargo.toml
+++ b/proxmox-router/Cargo.toml
@@ -15,6 +15,7 @@ hyper = { version = "0.14", features = [ "full" ] }
 nix = "0.19.1"
 percent-encoding = "2.1"
 serde_json = "1.0"
+serde = "1.0"
 unicode-width ="0.1.8"
 
 # cli:
@@ -24,6 +25,7 @@ libc = { version = "0.2", optional = true }
 
 proxmox-lang = { path = "../proxmox-lang", version = "1.0" }
 proxmox-schema = { path = "../proxmox-schema", version = "1.1" }
+proxmox-async = { path = "../proxmox-async", version = "0.3" }
 
 [features]
 default = [ "cli" ]
diff --git a/proxmox-router/src/lib.rs b/proxmox-router/src/lib.rs
index dadb917..84f39f8 100644
--- a/proxmox-router/src/lib.rs
+++ b/proxmox-router/src/lib.rs
@@ -12,6 +12,7 @@ pub mod error;
 mod permission;
 mod router;
 mod rpc_environment;
+mod serializable_return;
 
 #[doc(inline)]
 pub use error::HttpError;
@@ -19,6 +20,7 @@ pub use error::HttpError;
 pub use permission::*;
 pub use router::*;
 pub use rpc_environment::{RpcEnvironment, RpcEnvironmentType};
+pub use serializable_return::SerializableReturn;
 
 // make list_subdirs_api_method! work without an explicit proxmox-schema dependency:
 #[doc(hidden)]
diff --git a/proxmox-router/src/serializable_return.rs b/proxmox-router/src/serializable_return.rs
new file mode 100644
index 0000000..51f6c3c
--- /dev/null
+++ b/proxmox-router/src/serializable_return.rs
@@ -0,0 +1,62 @@
+use serde::Serializer;
+use serde_json::Value;
+
+/// This defines a *fixed* serializer (iow. also where/how to write out the data).
+///
+/// (Note that `serde::Serializer` is implemented for `__&mut__ serde_json::Serializer`.
+type SenderSerializer<'a> = &'a mut serde_json::Serializer<
+    &'a mut std::io::BufWriter<proxmox_async::blocking::SenderWriter>,
+>;
+
+/// This is an object-safe trait which requires the ability to serialize into particular
+/// Serializer instances.
+pub trait SerializableReturn {
+    /// Serializes self into a [`proxmox_async::blocking::SenderWriter`] wrapped
+    /// into a [`std::io::BufWriter`]
+    ///
+    /// If `value` is an Object/Map, serializes that first and puts the value of
+    /// `self` into the `data` property.
+    fn sender_serialize(
+        &self,
+        serializer: SenderSerializer,
+        value: Value,
+    ) -> Result<
+        <SenderSerializer as serde::Serializer>::Ok,
+        <SenderSerializer as serde::Serializer>::Error,
+    >;
+
+    /// Returns a value again from self
+    fn to_value(&self) -> Result<Value, serde_json::error::Error>;
+}
+
+impl<T> SerializableReturn for T
+where
+    T: serde::Serialize,
+{
+    fn sender_serialize(
+        &self,
+        serializer: SenderSerializer,
+        value: Value,
+    ) -> Result<
+        <SenderSerializer as serde::Serializer>::Ok,
+        <SenderSerializer as serde::Serializer>::Error,
+    > {
+        use serde::ser::SerializeMap;
+        if let Some(original) = value.as_object() {
+            let mut map = serializer.serialize_map(None)?;
+            for (k, v) in original {
+                map.serialize_entry(k, v)?;
+            }
+
+            map.serialize_key("data")?;
+            map.serialize_value(&self)?;
+            map.end()
+        } else {
+            self.serialize(serializer)
+        }
+    }
+
+    fn to_value(&self) -> Result<Value, serde_json::error::Error> {
+        serde_json::to_value(self)
+    }
+}
-- 
2.30.2