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test: avoid sporadic MINIMALDATA failure in feature_taproot.py (fixes #27595)

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The functional test feature_taproot.py fails in some rare cases on the
execution of the `"branched_codesep"` spending script. The problem
occurs if the first data-push (having random content with a random
length in the range [0, 510]) has a length of 1 and the single byte has
value of [1...16] or [-1]; in this case, the data-push is not minimally
encoded by test framework's CScript class (i.e. doesn't use the special
op-codes OP_1...OP_16 or OP_1NEGATE) and the script interpreter throws
an SCRIPT_ERR_MINIMALDATA error:

```
test_framework.authproxy.JSONRPCException: non-mandatory-script-verify-flag (Data push larger than necessary) (-26)
```

Background:
The functional test framework's CScript class translates passed
bytes/bytearrays always to data pushes using OP_PUSHx/OP_PUSHDATA{1,2,4}
op-codes. E.g. the expression `CScript(bytes([1]))` yields
`bytes([OP_PUSH1, 1])` instead of the minimal-encoded `bytes([OP_1])`.

Fix this by adapting the random-size range to [2,...], i.e. never pass
byte-arrays below length two to be pushed.

Closes #27595.
This commit is contained in:
Sebastian Falbesoner 2023-05-11 19:54:03 +02:00
parent 7f2019755d
commit 54877253c8
1 changed files with 5 additions and 1 deletions
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6
test/functional/feature_taproot.py
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@ -738,7 +738,11 @@ def spenders_taproot_active():
scripts = [
("pk_codesep", CScript(random_checksig_style(pubs[1]) + bytes([OP_CODESEPARATOR]))), # codesep after checksig
("codesep_pk", CScript(bytes([OP_CODESEPARATOR]) + random_checksig_style(pubs[1]))), # codesep before checksig
("branched_codesep", CScript([random_bytes(random.randrange(511)), OP_DROP, OP_IF, OP_CODESEPARATOR, pubs[0], OP_ELSE, OP_CODESEPARATOR, pubs[1], OP_ENDIF, OP_CHECKSIG])), # branch dependent codesep
("branched_codesep", CScript([random_bytes(random.randrange(2, 511)), OP_DROP, OP_IF, OP_CODESEPARATOR, pubs[0], OP_ELSE, OP_CODESEPARATOR, pubs[1], OP_ENDIF, OP_CHECKSIG])), # branch dependent codesep
# Note that the first data push in the "branched_codesep" script has the purpose of
# randomizing the sighash, both by varying script size and content. In order to
# avoid MINIMALDATA script verification errors caused by not-minimal-encoded data
# pushes (e.g. `OP_PUSH1 1` instead of `OP_1`), we set a minimum data size of 2 bytes.
]
random.shuffle(scripts)
tap = taproot_construct(pubs[0], scripts)