Provide proposed timestamp along with tx

When values are proposed to SCP, a timestamp is provided with the
proposed value. These timestamps are validated and consolidated to
populate the timestamp field of the `Block`.

api/proto/blockchain.proto

@@ -43,6 +43,9 @@ message Block {
 
     // Hash of the block's contents.
     BlockContentsHash contents_hash = 7;
+
+    // The block's timestamp. ms since Unix epoch
+    uint64 timestamp = 8;
 }
 
 message BlockContents {

api/src/convert/block.rs

@@ -17,6 +17,7 @@ impl From<&Block> for blockchain::Block {
         block.set_cumulative_txo_count(other.cumulative_txo_count);
         block.set_root_element((&other.root_element).into());
         block.set_contents_hash(blockchain::BlockContentsHash::from(&other.contents_hash));
+        block.set_timestamp(other.timestamp);
         block
     }
 }
@@ -39,6 +40,7 @@ impl TryFrom<&blockchain::Block> for Block {
             cumulative_txo_count: value.cumulative_txo_count,
             root_element,
             contents_hash,
+            timestamp: value.timestamp,
         };
         Ok(block)
     }
@@ -65,6 +67,7 @@ mod tests {
                 hash: TxOutMembershipHash::from([12u8; 32]),
             },
             contents_hash: BlockContentsHash::try_from(&[66u8; 32][..]).unwrap(),
+            timestamp: 357,
         };
 
         let block = blockchain::Block::from(&source_block);
@@ -77,6 +80,7 @@ mod tests {
         assert_eq!(block.get_root_element().get_range().get_to(), 20);
         assert_eq!(block.get_root_element().get_hash().get_data(), &[12u8; 32]);
         assert_eq!(block.get_contents_hash().get_data(), [66u8; 32]);
+        assert_eq!(block.get_timestamp(), 357);
     }
 
     #[test]
@@ -103,6 +107,7 @@ mod tests {
         source_block.set_index(2);
         source_block.set_root_element(root_element);
         source_block.set_contents_hash(contents_hash);
+        source_block.set_timestamp(411);
 
         let block = Block::try_from(&source_block).unwrap();
         assert_eq!(block.id.as_ref(), [10u8; 32]);
@@ -113,6 +118,7 @@ mod tests {
         assert_eq!(block.root_element.range.to, 20);
         assert_eq!(block.root_element.hash.as_ref(), &[13u8; 32]);
         assert_eq!(block.contents_hash.as_ref(), [66u8; 32]);
+        assert_eq!(block.timestamp, 411);
     }
 
     #[test]
@@ -131,6 +137,7 @@ mod tests {
                 hash: TxOutMembershipHash::from([12u8; 32]),
             },
             contents_hash: BlockContentsHash::try_from(&[66u8; 32][..]).unwrap(),
+            timestamp: 911,
         };
 
         // Encode using `protobuf`, decode using `prost`.

blockchain/test-utils/src/lib.rs

@@ -111,7 +111,18 @@ pub fn get_blocks_with_recipients<R: RngCore + CryptoRng>(
 
         let block = match &prev_block {
             Some(parent) => {
-                Block::new_with_parent(block_version, parent, &Default::default(), &block_contents)
+                let timestamp = if block_version.timestamps_are_supported() {
+                    parent.timestamp + 1
+                } else {
+                    0
+                };
+                Block::new_with_parent(
+                    block_version,
+                    parent,
+                    &Default::default(),
+                    &block_contents,
+                    timestamp,
+                )
             }
             None => Block::new_origin_block(&block_contents.outputs),
         };
@@ -242,6 +253,7 @@ mod tests {
                 block.cumulative_txo_count,
                 &block.root_element,
                 &block.contents_hash,
+                block.timestamp,
             );
             assert_eq!(derived_block_id, block.id);