feat(iota-graphql-rpc-client): add checkpoint graphql example (#3925)

* feat(iota-graphql-rpc-client): add checkpoint graphql example

* feat(iota-graphql-rpc-client): add ensure to catch errors

---------

Co-authored-by: Thibault Martinez <[email protected]>

crates/iota-graphql-rpc-client/Cargo.toml

@@ -17,3 +17,7 @@ thiserror.workspace = true
 
 # internal dependencies
 iota-graphql-rpc-headers.workspace = true
+
+[dev-dependencies]
+anyhow.workspace = true
+tokio = { workspace = true, features = ["macros", "rt-multi-thread"] }

crates/iota-graphql-rpc-client/examples/checkpoint.rs

@@ -0,0 +1,67 @@
+// Copyright (c) 2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
+//! This example showcases how to use the GraphQL API by querying data about the
+//! latest checkpoint.
+//!
+//! cargo run --example checkpoint
+
+use iota_graphql_rpc_client::simple_client::SimpleClient;
+
+#[tokio::main]
+async fn main() -> Result<(), anyhow::Error> {
+    let graphql_client = SimpleClient::new("http://127.0.0.1:8000");
+    let query = r#"{
+            checkpoint {
+                digest
+                sequenceNumber
+                validatorSignatures
+                previousCheckpointDigest
+                networkTotalTransactions
+                rollingGasSummary {
+                    computationCost
+                    storageCost
+                    storageRebate
+                    nonRefundableStorageFee
+                    }
+                epoch {
+                    epochId
+                    referenceGasPrice
+                    startTimestamp
+                    endTimestamp
+                }
+                transactionBlocks(first: 2) {
+                    edges {
+                        node {
+                            kind {
+                                __typename
+                            }
+                            digest
+                            sender {
+                                address
+                            }
+                        }
+                    }
+                }
+            }
+        }"#;
+    let res = graphql_client
+        .execute_to_graphql(query.to_string(), true, vec![], vec![])
+        .await?;
+    anyhow::ensure!(res.errors().is_empty(), "{:?}", res.errors());
+
+    let resp_body = res.response_body().data.clone().into_json()?;
+    // Access a nested field
+    println!(
+        "Selected data for checkpoint {}:",
+        resp_body
+            .get("checkpoint")
+            .ok_or(anyhow::anyhow!("missing checkpoint"))?
+            .get("sequenceNumber")
+            .ok_or(anyhow::anyhow!("missing sequenceNumber"))?
+    );
+    // Full response
+    println!("{:#?}", resp_body);
+
+    Ok(())
+}