From 997babafbfa0645a8aa331e223a53f8cc7b2698a Mon Sep 17 00:00:00 2001
From: Lev Kokotov <lev.kokotov@gmail.com>
Date: Tue, 20 Jan 2026 14:03:55 -0800
Subject: [PATCH] fix: handle null sharding key in COPY parser

---
 pgdog/src/frontend/router/parser/copy.rs | 50 +++++++++++++++++++++---
 1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/pgdog/src/frontend/router/parser/copy.rs b/pgdog/src/frontend/router/parser/copy.rs
index 0d512b8e..169c1598 100644
--- a/pgdog/src/frontend/router/parser/copy.rs
+++ b/pgdog/src/frontend/router/parser/copy.rs
@@ -72,6 +72,8 @@ pub struct CopyParser {
     sharded_column: usize,
     /// Schema shard.
     schema_shard: Option<Shard>,
+    /// String representing NULL values in text/CSV format.
+    null_string: String,
 }
 
 impl Default for CopyParser {
@@ -86,6 +88,7 @@ impl Default for CopyParser {
             sharded_table: None,
             sharded_column: 0,
             schema_shard: None,
+            null_string: "\\N".to_owned(),
         }
     }
 }
@@ -187,6 +190,7 @@ impl CopyParser {
             )))
         };
         parser.sharding_schema = cluster.sharding_schema();
+        parser.null_string = null_string;
 
         Ok(parser)
     }
@@ -234,12 +238,16 @@ impl CopyParser {
                                 .get(self.sharded_column)
                                 .ok_or(Error::NoShardingColumn)?;
 
-                            let ctx = ContextBuilder::new(table)
-                                .data(key)
-                                .shards(self.sharding_schema.shards)
-                                .build()?;
+                            if key == self.null_string {
+                                Shard::All
+                            } else {
+                                let ctx = ContextBuilder::new(table)
+                                    .data(key)
+                                    .shards(self.sharding_schema.shards)
+                                    .build()?;
 
-                            ctx.apply()?
+                                ctx.apply()?
+                            }
                         } else if let Some(schema_shard) = self.schema_shard.clone() {
                             schema_shard
                         } else {
@@ -443,6 +451,38 @@ mod test {
         assert_eq!(sharded[2].shard(), &Shard::All);
     }
 
+    #[test]
+    fn test_copy_text_null_sharding_key() {
+        // pg_dump text format uses `\N` to represent NULL values.
+        // When the sharding key is NULL, route to all shards.
+        // When a non-sharding column is NULL, route normally based on the key.
+        let copy = "COPY sharded (id, value) FROM STDIN";
+        let stmt = parse(copy).unwrap();
+        let stmt = stmt.protobuf.stmts.first().unwrap();
+        let copy = match stmt.stmt.clone().unwrap().node.unwrap() {
+            NodeEnum::CopyStmt(copy) => copy,
+            _ => panic!("not a copy"),
+        };
+
+        let mut copy = CopyParser::new(&copy, &Cluster::new_test(&config())).unwrap();
+
+        let one = CopyData::new("1\tAlice\n".as_bytes());
+        let two = CopyData::new("\\N\tBob\n".as_bytes());
+        let three = CopyData::new("11\tCharlie\n".as_bytes());
+        let four = CopyData::new("6\t\\N\n".as_bytes());
+
+        let sharded = copy.shard(&[one, two, three, four]).unwrap();
+        assert_eq!(sharded.len(), 4);
+        assert_eq!(sharded[0].message().data(), b"1\tAlice\n");
+        assert_eq!(sharded[0].shard(), &Shard::Direct(0));
+        assert_eq!(sharded[1].message().data(), b"\\N\tBob\n");
+        assert_eq!(sharded[1].shard(), &Shard::All);
+        assert_eq!(sharded[2].message().data(), b"11\tCharlie\n");
+        assert_eq!(sharded[2].shard(), &Shard::Direct(1));
+        assert_eq!(sharded[3].message().data(), b"6\t\\N\n");
+        assert_eq!(sharded[3].shard(), &Shard::Direct(1));
+    }
+
     #[test]
     fn test_copy_binary() {
         let copy = "COPY sharded (id, value) FROM STDIN (FORMAT 'binary')";