render_server.rs

// Copyright 2019-2021 Parity Technologies (UK) Ltd.
//
// Permission is hereby granted, free of charge, to any
// person obtaining a copy of this software and associated
// documentation files (the "Software"), to deal in the
// Software without restriction, including without
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// publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software
// is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice
// shall be included in all copies or substantial portions
// of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
// ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
// TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
// PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
// SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

use std::collections::HashSet;

use super::RpcDescription;
use crate::attributes::Resource;
use crate::helpers::{generate_where_clause, is_option};
use proc_macro2::{Span, TokenStream as TokenStream2};
use quote::{quote, quote_spanned};
use syn::punctuated::Punctuated;
use syn::{parse_quote, ReturnType, Token};

impl RpcDescription {
	pub(super) fn render_server(&self) -> Result<TokenStream2, syn::Error> {
		let trait_name = quote::format_ident!("{}Server", &self.trait_def.ident);
		let generics = self.trait_def.generics.clone();
		let (impl_generics, _, where_clause) = generics.split_for_impl();

		let method_impls = self.render_methods()?;
		let into_rpc_impl = self.render_into_rpc()?;
		let async_trait = self.jrps_server_item(quote! { core::__reexports::async_trait });

		// Doc-comment to be associated with the server.
		let doc_comment = format!("Server trait implementation for the `{}` RPC API.", &self.trait_def.ident);

		let trait_impl = quote! {
			#[#async_trait]
			#[doc = #doc_comment]
			pub trait #trait_name #impl_generics: Sized + Send + Sync + 'static #where_clause {
				#method_impls
				#into_rpc_impl
			}
		};

		Ok(trait_impl)
	}

	fn render_methods(&self) -> Result<TokenStream2, syn::Error> {
		let methods = self.methods.iter().map(|method| {
			let docs = &method.docs;
			let method_sig = &method.signature;
			quote! {
				#docs
				#method_sig
			}
		});

		let subscriptions = self.subscriptions.iter().map(|sub| {
			let docs = &sub.docs;
			let subscription_sink_ty = self.jrps_server_item(quote! { SubscriptionSink });
			// Add `SubscriptionSink` as the second input parameter to the signature.
			let subscription_sink: syn::FnArg = syn::parse_quote!(subscription_sink: #subscription_sink_ty);
			let mut sub_sig = sub.signature.clone();

			// For ergonomic reasons, the server's subscription method should return `SubscriptionResult`.
			let return_ty = self.jrps_server_item(quote! { types::SubscriptionResult });
			let output: ReturnType = parse_quote! { -> #return_ty };
			sub_sig.sig.output = output;

			sub_sig.sig.inputs.insert(1, subscription_sink);
			quote! {
				#docs
				#sub_sig
			}
		});

		Ok(quote! {
			#(#methods)*
			#(#subscriptions)*
		})
	}

	fn render_into_rpc(&self) -> Result<TokenStream2, syn::Error> {
		let rpc_module = self.jrps_server_item(quote! { RpcModule });

		let mut registered = HashSet::new();
		let mut errors = Vec::new();
		let mut check_name = |name: &str, span: Span| {
			if registered.contains(name) {
				let message = format!("{:?} is already defined", name);
				errors.push(quote_spanned!(span => compile_error!(#message);));
			} else {
				registered.insert(name.to_string());
			}
		};

		/// Helper that will ignore results of `register_*` method calls, and panic
		/// if there have been any errors in debug builds.
		///
		/// The debug assert is a safeguard should the contract that guarantees the method
		/// names to never conflict in the macro be broken in the future.
		fn handle_register_result(tokens: TokenStream2) -> TokenStream2 {
			quote! {{
				let res = #tokens;
				debug_assert!(res.is_ok(), "RPC macro method names should never conflict, this is a bug, please report it.");
			}}
		}

		/// Helper that will parse the resources passed to the macro and call the appropriate resource
		/// builder to register the resource limits.
		fn handle_resource_limits(resources: &Punctuated<Resource, Token![,]>) -> TokenStream2 {
			// Nothing to be done if no resources were set.
			if resources.is_empty() {
				return quote! {};
			}

			// Transform each resource into a call to `.resource(name, value)`.
			let resources = resources.iter().map(|resource| {
				let Resource { name, value, .. } = resource;
				quote! { .resource(#name, #value)? }
			});

			quote! {
				.and_then(|resource_builder| {
					resource_builder #(#resources)*;
					Ok(())
				})
			}
		}

		let methods = self
			.methods
			.iter()
			.map(|method| {
				// Rust method to invoke (e.g. `self.<foo>(...)`).
				let rust_method_name = &method.signature.sig.ident;
				// Name of the RPC method (e.g. `foo_makeSpam`).
				let rpc_method_name = self.rpc_identifier(&method.name);
				// `parsing` is the code associated with parsing structure from the
				// provided `Params` object.
				// `params_seq` is the comma-delimited sequence of parameters we're passing to the rust function
				// called..
				let (parsing, params_seq) = self.render_params_decoding(&method.params, None);

				check_name(&rpc_method_name, rust_method_name.span());

				let resources = handle_resource_limits(&method.resources);

				if method.signature.sig.asyncness.is_some() {
					handle_register_result(quote! {
						rpc.register_async_method(#rpc_method_name, |params, context| async move {
							#parsing
							context.as_ref().#rust_method_name(#params_seq).await
						})
						#resources
					})
				} else {
					let register_kind =
						if method.blocking { quote!(register_blocking_method) } else { quote!(register_method) };

					handle_register_result(quote! {
						rpc.#register_kind(#rpc_method_name, |params, context| {
							#parsing
							context.#rust_method_name(#params_seq)
						})
						#resources
					})
				}
			})
			.collect::<Vec<_>>();

		let subscriptions = self
			.subscriptions
			.iter()
			.map(|sub| {
				// Rust method to invoke (e.g. `self.<foo>(...)`).
				let rust_method_name = &sub.signature.sig.ident;
				// Name of the RPC method to subscribe to (e.g. `foo_sub`).
				let rpc_sub_name = self.rpc_identifier(&sub.name);
				// Name of `method` in the subscription response.
				let rpc_notif_name_override = sub.notif_name_override.as_ref().map(|m| self.rpc_identifier(m));
				// Name of the RPC method to unsubscribe (e.g. `foo_sub`).
				let rpc_unsub_name = self.rpc_identifier(&sub.unsubscribe);
				// `parsing` is the code associated with parsing structure from the
				// provided `Params` object.
				// `params_seq` is the comma-delimited sequence of parameters.
				let pending = proc_macro2::Ident::new("subscription_sink", rust_method_name.span());
				let (parsing, params_seq) = self.render_params_decoding(&sub.params, Some(pending));

				check_name(&rpc_sub_name, rust_method_name.span());
				check_name(&rpc_unsub_name, rust_method_name.span());

				let rpc_notif_name = match rpc_notif_name_override {
					Some(notif) => {
						check_name(&notif, rust_method_name.span());
						notif
					}
					None => rpc_sub_name.clone(),
				};

				let resources = handle_resource_limits(&sub.resources);

				handle_register_result(quote! {
					rpc.register_subscription(#rpc_sub_name, #rpc_notif_name, #rpc_unsub_name, |params, subscription_sink, context| {
						#parsing
						context.as_ref().#rust_method_name(subscription_sink, #params_seq)
					})
					#resources
				})
			})
			.collect::<Vec<_>>();

		let method_aliases = self
			.methods
			.iter()
			.map(|method| {
				let rpc_name = self.rpc_identifier(&method.name);
				let rust_method_name = &method.signature.sig.ident;

				// Rust method to invoke (e.g. `self.<foo>(...)`).
				let aliases: Vec<TokenStream2> = method
					.aliases
					.iter()
					.map(|alias| {
						check_name(alias, rust_method_name.span());
						handle_register_result(quote! {
							rpc.register_alias(#alias, #rpc_name)
						})
					})
					.collect();

				quote!( #(#aliases)* )
			})
			.collect::<Vec<_>>();

		let subscription_aliases = self
			.subscriptions
			.iter()
			.map(|method| {
				let sub_name = self.rpc_identifier(&method.name);
				let unsub_name = self.rpc_identifier(&method.unsubscribe);
				let rust_method_name = &method.signature.sig.ident;

				let sub: Vec<TokenStream2> = method
					.aliases
					.iter()
					.map(|alias| {
						check_name(alias, rust_method_name.span());
						handle_register_result(quote! {
							rpc.register_alias(#alias, #sub_name)
						})
					})
					.collect();
				let unsub: Vec<TokenStream2> = method
					.unsubscribe_aliases
					.iter()
					.map(|alias| {
						check_name(alias, rust_method_name.span());
						handle_register_result(quote! {
							rpc.register_alias(#alias, #unsub_name)
						})
					})
					.collect();

				quote! (
					#(#sub)*
					#(#unsub)*
				)
			})
			.collect::<Vec<_>>();

		let doc_comment = "Collects all the methods and subscriptions defined in the trait \
								and adds them into a single `RpcModule`.";

		let sub_tys: Vec<syn::Type> = self.subscriptions.clone().into_iter().map(|s| s.item).collect();
		let where_clause = generate_where_clause(&self.trait_def, &sub_tys, false);

		// NOTE(niklasad1): empty where clause is valid rust syntax.
		Ok(quote! {
			#[doc = #doc_comment]
			fn into_rpc(self) -> #rpc_module<Self> where #(#where_clause,)* {
				let mut rpc = #rpc_module::new(self);

				#(#errors)*
				#(#methods)*
				#(#subscriptions)*
				#(#method_aliases)*
				#(#subscription_aliases)*

				rpc
			}
		})
	}

	fn render_params_decoding(
		&self,
		params: &[(syn::PatIdent, syn::Type)],
		sub: Option<proc_macro2::Ident>,
	) -> (TokenStream2, TokenStream2) {
		if params.is_empty() {
			return (TokenStream2::default(), TokenStream2::default());
		}

		let params_fields_seq = params.iter().map(|(name, _)| name);
		let params_fields = quote! { #(#params_fields_seq),* };
		let tracing = self.jrps_server_item(quote! { tracing });
		let err = self.jrps_server_item(quote! { core::Error });
		let sub_err = self.jrps_server_item(quote! { types::SubscriptionEmptyError });

		// Code to decode sequence of parameters from a JSON array.
		let decode_array = {
			let decode_fields = params.iter().map(|(name, ty)| match (is_option(ty), sub.as_ref()) {
				(true, Some(pending)) => {
					quote! {
						let #name: #ty = match seq.optional_next() {
							Ok(v) => v,
							Err(e) => {
								#tracing::error!(concat!("Error parsing optional \"", stringify!(#name), "\" as \"", stringify!(#ty), "\": {:?}"), e);
								let _e: #err = e.into();
								#pending.reject(_e);
								return Err(#sub_err);
							}
						};
					}
				}
				(true, None) => {
					quote! {
						let #name: #ty = match seq.optional_next() {
							Ok(v) => v,
							Err(e) => {
								#tracing::error!(concat!("Error parsing optional \"", stringify!(#name), "\" as \"", stringify!(#ty), "\": {:?}"), e);
								return Err(e.into())
							}
						};
					}
				}
				(false, Some(pending)) => {
					quote! {
						let #name: #ty = match seq.next() {
							Ok(v) => v,
							Err(e) => {
								#tracing::error!(concat!("Error parsing \"", stringify!(#name), "\" as \"", stringify!(#ty), "\": {:?}"), e);
								let _e: #err = e.into();
								#pending.reject(_e);
								return Err(#sub_err);
							}
						};
					}
				}
				(false, None) => {
					quote! {
						let #name: #ty = match seq.next() {
							Ok(v) => v,
							Err(e) => {
								#tracing::error!(concat!("Error parsing \"", stringify!(#name), "\" as \"", stringify!(#ty), "\": {:?}"), e);
								return Err(e.into())
							}
						};
					}
				}
			});

			quote! {
				let mut seq = params.sequence();
				#(#decode_fields);*
				(#params_fields)
			}
		};

		// Code to decode sequence of parameters from a JSON object (aka map).
		let decode_map = {
			let generics = (0..params.len()).map(|n| quote::format_ident!("G{}", n));

			let serde = self.jrps_server_item(quote! { core::__reexports::serde });
			let serde_crate = serde.to_string();
			let fields = params.iter().zip(generics.clone()).map(|((name, _), ty)| {
				quote! { #name: #ty, }
			});
			let destruct = params.iter().map(|(name, _)| quote! { parsed.#name });
			let types = params.iter().map(|(_, ty)| ty);

			if let Some(pending) = sub {
				quote! {
					#[derive(#serde::Deserialize)]
					#[serde(crate = #serde_crate)]
					struct ParamsObject<#(#generics,)*> {
						#(#fields)*
					}

					let parsed: ParamsObject<#(#types,)*> = match params.parse() {
						Ok(p) => p,
						Err(e) => {
							#tracing::error!("Failed to parse JSON-RPC params as object: {}", e);
							let _e: #err = e.into();
							#pending.reject(_e);
							return Err(#sub_err);
						}
					};

					(#(#destruct),*)
				}
			} else {
				quote! {
					#[derive(#serde::Deserialize)]
					#[serde(crate = #serde_crate)]
					struct ParamsObject<#(#generics,)*> {
						#(#fields)*
					}

					let parsed: ParamsObject<#(#types,)*> = params.parse().map_err(|e| {
						#tracing::error!("Failed to parse JSON-RPC params as object: {}", e);
						e
					})?;
					(#(#destruct),*)
				}
			}
		};

		let parsing = quote! {
			let (#params_fields) = if params.is_object() {
				#decode_map
			} else {
				#decode_array
			};
		};

		(parsing, params_fields)
	}
}