improved error messages

btclib/base58.py

@@ -121,8 +121,12 @@ def b58decode(v: String, out_size: Optional[int] = None) -> bytes:
         v = v.encode("ascii")
 
     result = _b58decode(v)
-    result, checksum = result[:-4], result[-4:]
+    if len(result) < 4:
+        m = "not enough bytes for checksum, "
+        m += f"invalid base58 decoded size: {len(result)}"
+        raise ValueError(m)
 
+    result, checksum = result[:-4], result[-4:]
     h256 = hash256(result)
     if checksum != h256[:4]:
         m = f"invalid checksum: 0x{checksum.hex()} instead of 0x{h256[:4].hex()}"
@@ -131,6 +135,6 @@ def b58decode(v: String, out_size: Optional[int] = None) -> bytes:
     if out_size is None or len(result) == out_size:
         return result
 
-    m = "Invalid base58 decoded size: "
+    m = "valid checksum, invalid decoded size: "
     m += f"{len(result)} bytes instead of {out_size}"
     raise ValueError(m)

btclib/tests/test_base58.py

@@ -25,20 +25,26 @@ def test_empty():
     assert _b58encode(b"") == b""
     assert _b58decode(_b58encode(b"")) == b""
 
+    assert b58decode(b58encode(b""), 0) == b""
+
 
 def test_hello_world():
     assert _b58encode(b"hello world") == b"StV1DL6CwTryKyV"
     assert _b58decode(b"StV1DL6CwTryKyV") == b"hello world"
     assert _b58decode(_b58encode(b"hello world")) == b"hello world"
     assert _b58encode(_b58decode(b"StV1DL6CwTryKyV")) == b"StV1DL6CwTryKyV"
 
+    assert b58decode(b58encode(b"hello world"), 11) == b"hello world"
+
 
 def test_trailing_zeros():
     assert _b58encode(b"\x00\x00hello world") == b"11StV1DL6CwTryKyV"
     assert _b58decode(b"11StV1DL6CwTryKyV") == b"\x00\x00hello world"
-    assert _b58decode(_b58encode(b"\0\0hello world")) == b"\x00\x00hello world"
+    assert _b58decode(_b58encode(b"\x00\x00hello world")) == b"\x00\x00hello world"
     assert _b58encode(_b58decode(b"11StV1DL6CwTryKyV")) == b"11StV1DL6CwTryKyV"
 
+    assert b58decode(b58encode(b"\x00\x00hello world")) == b"\x00\x00hello world"
+
 
 def test_exceptions():
 
@@ -48,7 +54,7 @@ def test_exceptions():
     encoded = b58encode(b"test")
 
     wrong_length = len(encoded) - 1
-    with pytest.raises(ValueError, match="Invalid base58 decoded size: "):
+    with pytest.raises(ValueError, match="invalid decoded size: "):
         b58decode(encoded, wrong_length)
 
     invalidChecksum = encoded[:-4] + b"1111"
@@ -58,6 +64,10 @@ def test_exceptions():
     with pytest.raises(ValueError, match="'ascii' codec can't encode character "):
         b58decode("hèllo world")
 
+    err_msg = "not enough bytes for checksum, invalid base58 decoded size: "
+    with pytest.raises(ValueError, match=err_msg):
+        b58decode(_b58encode(b"123"))
+
 
 def test_wif():
     # https://en.bitcoin.it/wiki/Wallet_import_format