sign: inline write_tx_header, write_tx_middle and write_tx_footer functions

they are semantically incorrect and obfuscating what's really being done

src/apps/common/signtx.py

@@ -129,7 +129,9 @@ async def sign_tx(tx: SignTx, root):
         key_sign = None
         key_sign_pub = None
 
-        write_tx_header(h_sign, tx_version, tx_inputs_count)
+        write_uint32(h_sign, tx_version)
+
+        write_varint(h_sign, tx_inputs_count)
 
         for i in range(tx_inputs_count):
             # STAGE_REQUEST_4_INPUT
@@ -145,7 +147,7 @@ async def sign_tx(tx: SignTx, root):
                 txi.script_sig = bytes()
             write_tx_input(h_sign, txi)
 
-        write_tx_middle(h_sign, tx_outputs_count)
+        write_varint(h_sign, tx_outputs_count)
 
         for o in range(tx_outputs_count):
             # STAGE_REQUEST_4_OUTPUT
@@ -155,7 +157,9 @@ async def sign_tx(tx: SignTx, root):
             write_tx_output(h_second, txo_bin)
             write_tx_output(h_sign, txo_bin)
 
-        write_tx_footer(h_sign, tx_lock_time, True)
+        write_uint32(h_sign, tx_lock_time)
+
+        write_uint32(h_sign, 0x0000001) # hash_type
 
         import ubinascii
 
@@ -172,8 +176,9 @@ async def sign_tx(tx: SignTx, root):
         txi_sign.script_sig = input_derive_script_post_sign(
             txi_sign, key_sign_pub, signature)
         w_txi_sign = BufferWriter()
-        if i_sign == 0:
-            write_tx_header(w_txi_sign, tx_version, tx_inputs_count)
+        if i_sign == 0: # serializing first input => prepend tx version and inputs count
+            write_uint32(w_txi_sign, tx_version)
+            write_varint(w_txi_sign, tx_inputs_count)
         write_tx_input(w_txi_sign, txi_sign)
         tx_ser.serialized_tx = w_txi_sign.getvalue()
 
@@ -187,11 +192,11 @@ async def sign_tx(tx: SignTx, root):
 
         # serialize output
         w_txo_bin = BufferWriter()
-        if o == 0:
-            write_tx_middle(w_txo_bin, tx_outputs_count)
+        if o == 0: # serializing first output => prepend outputs count
+            write_varint(w_txo_bin, tx_outputs_count)
         write_tx_output(w_txo_bin, txo_bin)
-        if o == tx_outputs_count - 1:
-            write_tx_footer(w_txo_bin, tx_lock_time, False)
+        if o == tx_outputs_count - 1: # serializing last output => append tx lock_time
+            write_uint32(w_txo_bin, tx_lock_time)
         tx_ser.signature_index = None
         tx_ser.signature = None
         tx_ser.serialized_tx = w_txo_bin.getvalue()
@@ -214,14 +219,16 @@ async def get_prevtx_output_value(tx_req: TxRequest, prev_hash: bytes, prev_inde
 
     txh = HashWriter(sha256)
 
-    write_tx_header(txh, tx_version, tx_inputs_count)
+    write_uint32(txh, tx_version)
+
+    write_varint(txh, tx_inputs_count)
 
     for i in range(tx_inputs_count):
         # STAGE_REQUEST_2_PREV_INPUT
         txi = await request_tx_input(tx_req, i, prev_hash)
         write_tx_input(txh, txi)
 
-    write_tx_middle(txh, tx_outputs_count)
+    write_varint(txh, tx_outputs_count)
 
     for o in range(tx_outputs_count):
         # STAGE_REQUEST_2_PREV_OUTPUT
@@ -230,11 +237,12 @@ async def get_prevtx_output_value(tx_req: TxRequest, prev_hash: bytes, prev_inde
         if o == prev_index:
             total_out += txo_bin.amount
 
-    write_tx_footer(txh, tx_lock_time, False)
+    write_uint32(txh, tx_lock_time)
 
     prev_hash_rev = bytes(reversed(prev_hash))  # TODO: improve performance
     if tx_hash_digest(txh, True) != prev_hash_rev:
         raise ValueError('Encountered invalid prev_hash')
+
     return total_out
 
 
@@ -352,12 +360,6 @@ def script_spendaddress_new(pubkey: bytes, signature: bytes) -> bytearray:
 # TX Serialization
 # ===
 
-
-def write_tx_header(w, version: int, inputs_count: int):
-    write_uint32(w, version)
-    write_varint(w, inputs_count)
-
-
 def write_tx_input(w, i: TxInputType):
     i_sequence = getattr(i, 'sequence', 4294967295)
     write_bytes_rev(w, i.prev_hash)
@@ -377,22 +379,12 @@ def write_tx_input_check(w, i: TxInputType):
     write_uint32(w, i_sequence)
 
 
-def write_tx_middle(w, outputs_count: int):
-    write_varint(w, outputs_count)
-
-
 def write_tx_output(w, o: TxOutputBinType):
     write_uint64(w, o.amount)
     write_varint(w, len(o.script_pubkey))
     write_bytes(w, o.script_pubkey)
 
 
-def write_tx_footer(w, locktime: int, add_hash_type: bool):
-    write_uint32(w, locktime)
-    if add_hash_type:
-        write_uint32(w, 1)
-
-
 def write_op_push(w, n: int):
     wb = w.writebyte
     if n < 0x4C: