Implement fee calculator

Reviewed-on: #80

librustzcash-wrapper/src/lib.rs

@@ -1643,6 +1643,7 @@ pub extern "C" fn rust_wrapper_create_transaction(
     sapoutput_len: usize,
     net: bool,
     bl_height: u32,
+    build: bool,
     out: *mut u8,
     out_len: &mut usize){
     let sap_wit_in: Vec<u8> = marshall_from_haskell_var(sap_wit, sap_wit_len, RW);
@@ -1794,6 +1795,7 @@ pub extern "C" fn rust_wrapper_create_transaction(
             }
         }
     }
+    if build {
         let spend_params_in: Vec<u8> = marshall_from_haskell_var(sapspend, sapspend_len, RW);
         let spend_params_reader = Cursor::new(spend_params_in);
         let spend_prover = SpendParameters::read(spend_params_reader, false).unwrap();
@@ -1861,4 +1863,21 @@ pub extern "C" fn rust_wrapper_create_transaction(
                 }
             }
         }
+    } else {
+        let result = if net {
+            main_builder.get_fee(&FeeRule::standard())
+        } else {
+            test_builder.get_fee(&FeeRule::standard())
+        };
+        match result {
+            Ok(r) => {
+                let x = Hhex {bytes: r.to_i64_le_bytes().to_vec()};
+                marshall_to_haskell_var(&x, out, out_len, RW);
+            },
+            Err(e) => {
+                let x = Hhex {bytes: vec![2]};
+                marshall_to_haskell_var(&x, out, out_len, RW);
+            }
+        }
+    }
 }

src/C/Zcash.chs

@@ -287,6 +287,7 @@ import ZcashHaskell.Types
      , toBorshVar* `BS.ByteString'&
      , `Bool'
      , `Word64'
+     , `Bool'
      , getVarBuffer `Buffer HexString'&
      }
   -> `()'

src/ZcashHaskell/Utils.hs

@@ -133,8 +133,9 @@ createTransaction ::
   -> SaplingOutputParams -- ^ the Sapling circuit output parameters
   -> ZcashNet -- ^ the network to be used
   -> Int -- ^ target block height
+  -> Bool -- ^ True to build, False to estimate fee
   -> Either TxError HexString
-createTransaction sapAnchor orchAnchor tSpend sSpend oSpend outgoing sParams oParams znet bh =
+createTransaction sapAnchor orchAnchor tSpend sSpend oSpend outgoing sParams oParams znet bh build =
   if BS.length (hexBytes txResult) > 1
     then Right txResult
     else case head (BS.unpack $ hexBytes txResult) of
@@ -168,3 +169,4 @@ createTransaction sapAnchor orchAnchor tSpend sSpend oSpend outgoing sParams oPa
         (sapOParams oParams)
         (znet == MainNet)
         (fromIntegral bh)
+        build