Use sections encoding for db_next

Author: webmaster128

CHANGELOG.md

@@ -42,6 +42,9 @@ and this project adheres to
 
 - all: The `query` enpoint is now optional. It is still highly recommended to
   expose it an almost any use case though.
+- all: Change the encoding of the key/value region of the `db_next` import to a
+  more generic encoding that supports an arbitrary number of sections. This
+  encoding can then be reused for other multi value regions.
 - cosmwasm-std: Remove `from_address` from `BankMsg::Send`, as it always sends
   from the contract address, and this is consistent with other `CosmosMsg`
   variants.

packages/std/src/imports.rs

@@ -5,6 +5,7 @@ use crate::binary::Binary;
 use crate::errors::{StdError, StdResult, SystemError};
 use crate::memory::{alloc, build_region, consume_region, Region};
 use crate::results::SystemResult;
+use crate::sections::decode_sections2;
 use crate::serde::from_slice;
 use crate::traits::{Api, Querier, QuerierResult, Storage};
 #[cfg(feature = "iterator")]
@@ -120,23 +121,13 @@ impl Iterator for ExternalIterator {
     fn next(&mut self) -> Option<Self::Item> {
         let next_result = unsafe { db_next(self.iterator_id) };
         let kv_region_ptr = next_result as *mut Region;
-        let mut kv = unsafe { consume_region(kv_region_ptr) };
-
-        // The KV region uses the format value || key || keylen, where keylen is a fixed size big endian u32 value
-        let keylen = u32::from_be_bytes([
-            kv[kv.len() - 4],
-            kv[kv.len() - 3],
-            kv[kv.len() - 2],
-            kv[kv.len() - 1],
-        ]) as usize;
-        if keylen == 0 {
-            return None;
+        let kv = unsafe { consume_region(kv_region_ptr) };
+        let (key, value) = decode_sections2(kv);
+        if key.len() == 0 {
+            None
+        } else {
+            Some((key, value))
         }
-
-        kv.truncate(kv.len() - 4);
-        let key = kv.split_off(kv.len() - keylen);
-        let value = kv;
-        Some((key, value))
     }
 }
 

packages/vm/src/imports.rs

@@ -298,13 +298,7 @@ fn do_next<A: Api, S: Storage, Q: Querier>(
     // Empty key will later be treated as _no more element_.
     let (key, value) = result?.unwrap_or_else(|| (Vec::<u8>::new(), Vec::<u8>::new()));
 
-    // Build value || key || keylen
-    let keylen_bytes = to_u32(key.len())?.to_be_bytes();
-    let mut out_data = value;
-    out_data.reserve(key.len() + 4);
-    out_data.extend(key);
-    out_data.extend_from_slice(&keylen_bytes);
-
+    let out_data = encode_sections(&[key, value])?;
     write_to_contract::<A, S, Q>(env, &out_data)
 }
 
@@ -1158,19 +1152,19 @@ mod tests {
         let kv_region_ptr = do_next::<MA, MS, MQ>(&env, id).unwrap();
         assert_eq!(
             force_read(&env, kv_region_ptr),
-            [VALUE1, KEY1, b"\0\0\0\x03"].concat()
+            [KEY1, b"\0\0\0\x03", VALUE1, b"\0\0\0\x06"].concat()
         );
 
         // Entry 2
         let kv_region_ptr = do_next::<MA, MS, MQ>(&env, id).unwrap();
         assert_eq!(
             force_read(&env, kv_region_ptr),
-            [VALUE2, KEY2, b"\0\0\0\x04"].concat()
+            [KEY2, b"\0\0\0\x04", VALUE2, b"\0\0\0\x05"].concat()
         );
 
         // End
         let kv_region_ptr = do_next::<MA, MS, MQ>(&env, id).unwrap();
-        assert_eq!(force_read(&env, kv_region_ptr), b"\0\0\0\0");
+        assert_eq!(force_read(&env, kv_region_ptr), b"\0\0\0\0\0\0\0\0");
         // API makes no guarantees for value_ptr in this case
     }