Roll back PgArgumentBuffer if encoding fails

sqlx-postgres/src/arguments.rs

@@ -64,13 +64,19 @@ impl PgArguments {
     where
         T: Encode<'q, Postgres> + Type<Postgres>,
     {
-        // remember the type information for this value
-        self.types
-            .push(value.produces().unwrap_or_else(T::type_info));
+        let type_info = value.produces().unwrap_or_else(T::type_info);
+
+        let buffer_snapshot = self.buffer.snapshot();
 
         // encode the value into our buffer
-        self.buffer.encode(value)?;
+        if let Err(error) = self.buffer.encode(value) {
+            // reset the value buffer to its previous value if encoding failed so we don't leave a half-encoded value behind
+            self.buffer.reset_to_snapshot(buffer_snapshot);
+            return Err(error);
+        };
 
+        // remember the type information for this value
+        self.types.push(type_info);
         // increment the number of arguments we are tracking
         self.buffer.count += 1;
 
@@ -176,6 +182,44 @@ impl PgArgumentBuffer {
         self.extend_from_slice(&0_u32.to_be_bytes());
         self.type_holes.push((offset, type_name.clone()));
     }
+
+    fn snapshot(&self) -> PgArgumentBufferSnapshot {
+        let Self {
+            buffer,
+            count,
+            patches,
+            type_holes,
+        } = self;
+
+        PgArgumentBufferSnapshot {
+            buffer_length: buffer.len(),
+            count: *count,
+            patches_length: patches.len(),
+            type_holes_length: type_holes.len(),
+        }
+    }
+
+    fn reset_to_snapshot(
+        &mut self,
+        PgArgumentBufferSnapshot {
+            buffer_length,
+            count,
+            patches_length,
+            type_holes_length,
+        }: PgArgumentBufferSnapshot,
+    ) {
+        self.buffer.truncate(buffer_length);
+        self.count = count;
+        self.patches.truncate(patches_length);
+        self.type_holes.truncate(type_holes_length);
+    }
+}
+
+struct PgArgumentBufferSnapshot {
+    buffer_length: usize,
+    count: usize,
+    patches_length: usize,
+    type_holes_length: usize,
 }
 
 impl Deref for PgArgumentBuffer {