From f1a3dc67197990865f4c2c5d18e8ecbb645f63e7 Mon Sep 17 00:00:00 2001
From: Martin Habovstiak <martin.habovstiak@gmail.com>
Date: Sun, 7 May 2023 08:45:25 +0200
Subject: [PATCH] Allow parsing sub-sat denoms with decimal points

Numbers with only zeros after decimal points are valid if they are also
multiples of `10^precision` (e.g. 1000 for msats). These were
artificially disallowed as "too precise" which was at least misleading.

This change allows parsing such numbers.
---
 bitcoin/src/amount.rs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/bitcoin/src/amount.rs b/bitcoin/src/amount.rs
index d513feb4..80dc06ea 100644
--- a/bitcoin/src/amount.rs
+++ b/bitcoin/src/amount.rs
@@ -199,7 +199,13 @@ impl std::error::Error for ParseAmountError {
 }
 
 fn is_too_precise(s: &str, precision: usize) -> bool {
-    s.contains('.') || precision >= s.len() || s.chars().rev().take(precision).any(|d| d != '0')
+    match s.find('.') {
+        Some(pos) =>
+            s[(pos + 1)..].chars().any(|d| d != '0')
+                || precision >= pos
+                || s[..pos].chars().rev().take(precision).any(|d| d != '0'),
+        None => precision >= s.len() || s.chars().rev().take(precision).any(|d| d != '0'),
+    }
 }
 
 /// Parse decimal string in the given denomination into a satoshi value and a
@@ -227,7 +233,7 @@ fn parse_signed_to_satoshi(
         // The difference in precision between native (satoshi)
         // and desired denomination.
         let precision_diff = -denom.precision();
-        if precision_diff < 0 {
+        if precision_diff <= 0 {
             // If precision diff is negative, this means we are parsing
             // into a less precise amount. That is not allowed unless
             // there are no decimals and the last digits are zeroes as
@@ -239,7 +245,7 @@ fn parse_signed_to_satoshi(
                     _ => return Err(ParseAmountError::TooPrecise),
                 }
             }
-            s = &s[0..s.len() - last_n];
+            s = &s[0..s.find('.').unwrap_or(s.len()) - last_n];
             0
         } else {
             precision_diff
@@ -267,6 +273,7 @@ fn parse_signed_to_satoshi(
                 };
             }
             '.' => match decimals {
+                None if max_decimals <= 0 => break,
                 None => decimals = Some(0),
                 // Double decimal dot.
                 _ => return Err(ParseAmountError::InvalidFormat),