From a02b657f3cf22ff7e82b3be722d53be89fff8e7f Mon Sep 17 00:00:00 2001
From: Carson McManus <dyc3@users.noreply.github.com>
Date: Tue, 11 Oct 2022 14:10:04 -0400
Subject: [PATCH] clamp `ItemStack` item count to range 1-127 (#110)

---
 src/item.rs          | 46 +++++++++++++++++++++++++++++++++++++-------
 src/protocol/slot.rs | 12 ++++++------
 2 files changed, 45 insertions(+), 13 deletions(-)

diff --git a/src/item.rs b/src/item.rs
index cc5e0c8..4738692 100644
--- a/src/item.rs
+++ b/src/item.rs
@@ -8,13 +8,6 @@ use crate::protocol::{Decode, Encode, VarInt};
 
 include!(concat!(env!("OUT_DIR"), "/item.rs"));
 
-#[derive(Debug, Clone, PartialEq)]
-pub struct ItemStack {
-    pub item: ItemKind,
-    pub item_count: u8,
-    pub nbt: Option<Compound>,
-}
-
 impl Encode for ItemKind {
     fn encode(&self, w: &mut impl std::io::Write) -> anyhow::Result<()> {
         VarInt(self.to_raw() as i32).encode(w)
@@ -30,6 +23,37 @@ impl Decode for ItemKind {
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub struct ItemStack {
+    pub item: ItemKind,
+    item_count: u8,
+    pub nbt: Option<Compound>,
+}
+
+impl ItemStack {
+    const STACK_MIN: u8 = 1;
+    const STACK_MAX: u8 = 127;
+
+    pub fn new(item: ItemKind, count: u8, nbt: Option<Compound>) -> Self {
+        Self {
+            item,
+            item_count: count.clamp(Self::STACK_MIN, Self::STACK_MAX),
+            nbt,
+        }
+    }
+
+    /// Gets the number of items in this stack.
+    pub fn count(&self) -> u8 {
+        self.item_count
+    }
+
+    /// Sets the number of items in this stack. Values are clamped to 1-127,
+    /// which are the positive values accepted by clients.
+    pub fn set_count(&mut self, count: u8) {
+        self.item_count = count.clamp(Self::STACK_MIN, Self::STACK_MAX)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -52,4 +76,12 @@ mod tests {
 
         assert_eq!(BlockKind::NetherPortal.to_item_kind(), ItemKind::Air);
     }
+
+    #[test]
+    fn item_stack_clamps_count() {
+        let mut stack = ItemStack::new(ItemKind::Stone, 200, None);
+        assert_eq!(stack.item_count, ItemStack::STACK_MAX);
+        stack.set_count(201);
+        assert_eq!(stack.item_count, ItemStack::STACK_MAX);
+    }
 }
diff --git a/src/protocol/slot.rs b/src/protocol/slot.rs
index 47098bf..9541903 100644
--- a/src/protocol/slot.rs
+++ b/src/protocol/slot.rs
@@ -18,7 +18,7 @@ impl Encode for Slot {
             Some(s) => {
                 true.encode(w)?;
                 s.item.encode(w)?;
-                s.item_count.encode(w)?;
+                s.count().encode(w)?;
                 match &s.nbt {
                     Some(n) => n.encode(w),
                     None => 0u8.encode(w),
@@ -34,15 +34,15 @@ impl Decode for Slot {
         if !present {
             return Ok(None);
         }
-        Ok(Some(ItemStack {
-            item: ItemKind::decode(r)?,
-            item_count: u8::decode(r)?,
-            nbt: if r.first() == Some(&0) {
+        Ok(Some(ItemStack::new(
+            ItemKind::decode(r)?,
+            u8::decode(r)?,
+            if r.first() == Some(&0) {
                 r.read_u8()?;
                 None
             } else {
                 Some(Compound::decode(r)?)
             },
-        }))
+        )))
     }
 }