refactor Offchain Worker examples

Cargo.toml

@@ -108,7 +108,8 @@ members = [
 	"frame/election-provider-support/solution-type/fuzzer",
 	"frame/examples",
 	"frame/examples/basic",
-	"frame/examples/offchain-worker",
+	"frame/examples/offchain-worker-ping-pong",
+	"frame/examples/offchain-worker-price-oracle",
 	"frame/examples/kitchensink",
 	"frame/examples/dev-mode",
 	"frame/examples/default-config",

frame/examples/Cargo.toml

@@ -14,7 +14,8 @@ targets = ["x86_64-unknown-linux-gnu"]
 [dependencies]
 pallet-example-basic = { default-features = false, path = "./basic" }
 pallet-default-config-example = { default-features = false, path = "./default-config" }
-pallet-example-offchain-worker = { default-features = false, path = "./offchain-worker" }
+pallet-example-offchain-worker-ping-pong = { default-features = false, path = "./offchain-worker-ping-pong" }
+pallet-example-offchain-worker-price-oracle = { default-features = false, path = "./offchain-worker-price-oracle" }
 pallet-example-kitchensink = { default-features = false, path = "./kitchensink" }
 pallet-dev-mode = { default-features = false, path = "./dev-mode" }
 
@@ -23,14 +24,16 @@ default = [ "std" ]
 std = [
     "pallet-example-basic/std",
     "pallet-default-config-example/std",
-    "pallet-example-offchain-worker/std",
+    "pallet-example-offchain-worker-ping-pong/std",
+    "pallet-example-offchain-worker-price-oracle/std",
     "pallet-example-kitchensink/std",
     "pallet-dev-mode/std",
 ]
 try-runtime = [
     "pallet-example-basic/try-runtime",
     "pallet-default-config-example/try-runtime",
-    "pallet-example-offchain-worker/try-runtime",
+    "pallet-example-offchain-worker-ping-pong/try-runtime",
+    "pallet-example-offchain-worker-price-oracle/try-runtime",
     "pallet-example-kitchensink/try-runtime",
     "pallet-dev-mode/try-runtime",
 ]

frame/examples/offchain-worker-ping-pong/Cargo.toml

@@ -0,0 +1,43 @@
+[package]
+name = "pallet-example-offchain-worker-ping-pong"
+version = "4.0.0-dev"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2021"
+license = "MIT-0"
+homepage = "https://substrate.io"
+repository = "https://github.com/paritytech/substrate/"
+description = "FRAME example pallet for offchain worker (ping-pong)"
+readme = "README.md"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+codec = { package = "parity-scale-codec", version = "3.2.2", default-features = false }
+lite-json = { version = "0.2.0", default-features = false }
+log = { version = "0.4.17", default-features = false }
+scale-info = { version = "2.5.0", default-features = false, features = ["derive"] }
+frame-support = { version = "4.0.0-dev", default-features = false, path = "../../support" }
+frame-system = { version = "4.0.0-dev", default-features = false, path = "../../system" }
+sp-core = { version = "21.0.0", default-features = false, path = "../../../primitives/core" }
+sp-io = { version = "23.0.0", default-features = false, path = "../../../primitives/io" }
+sp-keystore = { version = "0.27.0", optional = true, path = "../../../primitives/keystore" }
+sp-runtime = { version = "24.0.0", default-features = false, path = "../../../primitives/runtime" }
+sp-std = { version = "8.0.0", default-features = false, path = "../../../primitives/std" }
+
+[features]
+default = ["std"]
+std = [
+    "codec/std",
+    "frame-support/std",
+    "frame-system/std",
+    "lite-json/std",
+    "log/std",
+    "scale-info/std",
+    "sp-core/std",
+    "sp-io/std",
+    "sp-keystore",
+    "sp-runtime/std",
+    "sp-std/std",
+]
+try-runtime = ["frame-support/try-runtime"]

frame/examples/offchain-worker-ping-pong/README.md

@@ -0,0 +1,52 @@
+# Ping-Pong Offchain Worker Example Pallet
+
+A simple pallet demonstrating concepts, APIs and structures common to most offchain workers.
+
+Run `cargo doc --package pallet-example-offchain-worker-ping-pong --open` to view this module's
+documentation.
+
+This is a simple example pallet to showcase how the runtime can and should interact with an offchain worker asynchronously.
+It also showcases the potential pitfalls and security considerations that come with it.
+
+It is based on [this example by `gnunicorn`](https://gnunicorn.github.io/substrate-offchain-cb/),
+although an updated version with a few modifications.
+
+The example plays simple ping-pong with off-chain workers:
+Once a signed transaction to `ping` is submitted (by any user), Ping request is written into Storage.
+Each ping request has a `nonce`, which is arbitrarily chosen by the user (not necessarily unique).
+
+After every block, the offchain worker is triggered. If it sees a Ping request in the current
+block, it reacts by sending a transaction to send a Pong with the corresponding `nonce`. When `pong_*` extrinsics are executed,
+they emit an `PongAck*` event so we can track with existing UIs.
+
+The `PongAck*` events come in two different flavors:
+- `PongAckAuthenticated`: emitted when the call was made by an **authenticated** offchain worker (whitelisted via `Authorities` storage)
+- `PongAckUnauthenticated`: emitted when the call was made by an **unauthenticated** offchain worker (or potentially malicious actors)
+
+The security implications of `PongAckUnauthenticated` should be obvious: not **ONLY** offchain workers can
+call `pong_unsigned_*`. **ANYONE** can do it, and they can actually use a different `nonce`
+from the original ping (try it yourself!). If the `nonce` actually had an important meaning to the state of our chain, this would be a **VULNERABILITY**!
+
+This is meant to highlight the importance of solid security assumptions when using unsigned transactions.
+In other words: 
+
+⚠️ **DO NOT USE UNSIGNED TRANSACTIONS UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING!** ⚠️
+
+Here's an example of how a node admin can inject some keys into the keystore, so that the OCW
+can call `pong_signed`:
+
+```bash
+$ curl --location --request POST 'http://localhost:9944' \
+--header 'Content-Type: application/json' \
+--data-raw '{
+    "jsonrpc": "2.0",
+    "method": "author_insertKey",
+    "params": ["pong","bread tongue spell stadium clean grief coin rent spend total practice document","0xb6a8b4b6bf796991065035093d3265e314c3fe89e75ccb623985e57b0c2e0c30"],
+    "id": 1
+}'
+```
+
+Then make sure that the corresponding address (`5GCCgshTQCfGkXy6kAkFDW1TZXAdsbCNZJ9Uz2c7ViBnwcVg`) has funds and is added to `Authorities` in the runtime by adding it via `add_authority` extrinsic (from `root`).
+
+More complex management models and session
+based key rotations should be considered, but that's outside the scope of this example.