Contracts: parse amounts exactly, not via f64

Custom output amounts (--make-outputs) and the CLI amount parser converted
grin to nanogrin with `(g * GRIN_BASE as f64) as u64`, which can't represent
all values exactly. Use core::amount_from_hr_string — the same exact integer
parser already used by `send` and `invoice`.

- contract OutputSelectionArgs::output_amounts (covers selection.rs).
- wallet_args::parse_grin_amount.

Addresses PR #754 review (types.rs, selection.rs, wallet_args.rs).

libwallet/src/contract/types.rs

@@ -15,7 +15,6 @@
 //! Types related to a contract
 
 use crate::error::Error;
-use crate::grin_core::consensus;
 use crate::slate_versions::ser as dalek_ser;
 use ed25519_dalek::PublicKey as DalekPublicKey;
 
@@ -56,11 +55,10 @@ impl OutputSelectionArgs {
 			Some(s) => s
 				.split(",")
 				.map(|amt| {
-					amt.parse::<f64>()
-						.map(|g| (g * consensus::GRIN_BASE as f64) as u64)
-						.map_err(|e| {
-							Error::GenericError(format!("Invalid output amount '{}': {}", amt, e))
-						})
+					// Exact decimal parsing (integer nanogrin), not f64.
+					crate::grin_core::core::amount_from_hr_string(amt).map_err(|e| {
+						Error::GenericError(format!("Invalid output amount '{}': {}", amt, e))
+					})
 				})
 				.collect(),
 			None => Ok(vec![]),

src/cmd/wallet_args.rs

@@ -13,7 +13,6 @@
 // limitations under the License.
 
 /// Argument parsing and error handling for wallet commands
-use self::core::consensus;
 use crate::api::TLSConfig;
 use crate::cli::command_loop;
 use crate::config::GRIN_WALLET_DIR;
@@ -290,13 +289,13 @@ fn parse_u64_or_none(arg: Option<&str>) -> Option<u64> {
 
 // Parse a value expressed in Grin (e.g. "1.5") into nanograms.
 fn parse_grin_amount(arg: &str, name: &str) -> Result<u64, ParseError> {
-	match arg.parse::<f64>() {
-		Ok(g) => Ok((g * consensus::GRIN_BASE as f64) as u64),
-		Err(e) => Err(ParseError::ArgumentError(format!(
+	// Exact decimal parsing (integer nanogrin), not f64.
+	core::core::amount_from_hr_string(arg).map_err(|e| {
+		ParseError::ArgumentError(format!(
 			"Could not parse {} '{}' as a number. e={}",
 			name, arg, e
-		))),
-	}
+		))
+	})
 }
 
 pub fn parse_global_args(