[Cli] Retrieve a waypoint value from a given url

Summary:
Added a waypoint-url cmd line argument to download the waypoint value from.
These are still optional but we might consider making it a non-optional value with a default pointing to https://developers.libra.org/testnet_waypoint.txt.

Testing:
```
./scripts/cli/start_cli_testnet.sh -- --waypoint-url https://developers.libra.org/testnet_waypoint.txt
./scripts/cli/start_cli_testnet.sh
./scripts/cli/start_cli_testnet.sh -- --waypoint 0:997acd1b112a19eb1d2d3dff78677a0009343727926071c3858aeff2ea3499bf
```

Issues: ref #2425

Closes: #2446
Approved by: dmitri-perelman

client/cli/Cargo.toml

@@ -23,6 +23,7 @@ reqwest = { version = "0.10.1", features = ["blocking"], default-features = fals
 serde = { version = "1.0.96", features = ["derive"] }
 serde_json = "1.0.40"
 structopt = "0.3.2"
+ureq = { version = "0.11.3"}
 
 admission-control-proto = { path = "../../admission_control/admission-control-proto", version = "0.1.0" }
 libra-config = { path = "../../config", version = "0.1.0" }

client/cli/src/main.rs

@@ -14,9 +14,13 @@ use cli::{
 use libra_logger::set_default_global_logger;
 use libra_types::waypoint::Waypoint;
 use rustyline::{config::CompletionType, error::ReadlineError, Config, Editor};
-use std::num::NonZeroU16;
-use std::time::{Duration, UNIX_EPOCH};
+use std::{
+    num::NonZeroU16,
+    str::FromStr,
+    time::{Duration, UNIX_EPOCH},
+};
 use structopt::StructOpt;
+use ureq;
 
 #[derive(Debug, StructOpt)]
 #[structopt(
@@ -51,8 +55,18 @@ struct Args {
     #[structopt(short = "r", long = "sync")]
     pub sync: bool,
     /// If set, a client uses the waypoint parameter for its initial LedgerInfo verification.
-    #[structopt(name = "waypoint", short, long)]
+    #[structopt(
+        name = "waypoint",
+        long,
+        help = "Explicitly specify the waypoint to use"
+    )]
     pub waypoint: Option<Waypoint>,
+    #[structopt(
+        name = "waypoint_url",
+        long,
+        help = "URL for a file with the waypoint to use"
+    )]
+    pub waypoint_url: Option<String>,
     /// Verbose output.
     #[structopt(short = "v", long = "verbose")]
     pub verbose: bool,
@@ -70,14 +84,25 @@ fn main() {
         .clone()
         .unwrap_or_else(|| "".to_string());
     let mnemonic_file = args.mnemonic_file.clone();
+
+    // If waypoint is given explicitly, use its value,
+    // otherwise if waypoint_url is given, try to retrieve the waypoint from the URL,
+    // otherwise waypoint is None.
+    let waypoint = args.waypoint.or_else(|| {
+        args.waypoint_url.as_ref().map(|url_str| {
+            retrieve_waypoint(url_str.as_str()).unwrap_or_else(|e| {
+                panic!("Failure to retrieve a waypoint from {}: {}", url_str, e)
+            })
+        })
+    });
     let mut client_proxy = ClientProxy::new(
         &args.host,
         args.port.get(),
         &faucet_account_file,
         args.sync,
         args.faucet_server.clone(),
         mnemonic_file,
-        args.waypoint,
+        waypoint,
     )
     .expect("Failed to construct client.");
 
@@ -181,6 +206,22 @@ fn print_help(client_info: &str, commands: &[std::sync::Arc<dyn Command>]) {
     println!("\n");
 }
 
+/// Retrieve a waypoint given the URL.
+fn retrieve_waypoint(url_str: &str) -> anyhow::Result<Waypoint> {
+    let response = ureq::get(url_str).timeout_connect(10_000).call();
+    match response.status() {
+        200 => response
+            .into_string()
+            .map_err(|_| anyhow::format_err!("Failed to parse waypoint from URL {}", url_str))
+            .and_then(|r| Waypoint::from_str(r.trim())),
+        _ => Err(anyhow::format_err!(
+            "URL {} returned {}",
+            url_str,
+            response.status_line()
+        )),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

types/src/waypoint.rs

@@ -45,9 +45,21 @@ impl Waypoint {
 
     /// Errors in case the given ledger info does not match the waypoint.
     pub fn verify(&self, ledger_info: &LedgerInfo) -> Result<()> {
-        ensure!(ledger_info.version() == self.version(), "Version mismatch");
+        ensure!(
+            ledger_info.version() == self.version(),
+            "Waypoint version mismatch: waypoint version = {}, given version = {}",
+            self.version(),
+            ledger_info.version()
+        );
         let converter = Ledger2WaypointConverter::new(ledger_info)?;
-        ensure!(converter.hash() == self.value(), "HashValue mismatch");
+        ensure!(
+            converter.hash() == self.value(),
+            format!(
+                "Waypoint value mismatch: waypoint value = {}, given value = {}",
+                self.value().to_hex(),
+                converter.hash().to_hex()
+            )
+        );
         Ok(())
     }
 }