test: cover PSBT unknown field merging #35310

This PR adds functional coverage for combinepsbt preserving unknown PSBT fields across global, input, and output maps, as suggested by @Bicaru20 in #34893 (comment).

The test covers both PSBTv0 and PSBTv2 by creating valid base PSBTs with createpsbt, injecting unknown key-value pairs into two copies, combining them, and asserting that all unknown fields are retained in the decoded result.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35310.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #34893 (psbt: preserve proprietary fields when combining PSBTs by w0xlt)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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While thinking about how to implement this test, I saw that in the bip 174 there is an specific example on how to combine two psbt with unknown fields. I think that since this example is given we could use it for this test.

I re-wrote the test for that specific example in case you also think it is better to do it this way:

diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index a88b4773f5..f10fdc0b44 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -304,0 +305,8 @@ class PSBTTest(BitcoinTestFramework):
+       
+        unknown_psbt_key_a = unknown_key(0xf0, bytes.fromhex("010203040506070809"))
+        unknown_psbt_key_b = unknown_key(0xf0, bytes.fromhex("010203040506070810"))
+
+        unknown_psbt_value= bytes.fromhex("0102030405060708090a0b0c0d0e0f")
+
+        inputs = [{"txid": "ff" * 32, "vout": 0, "sequence":0xffffffff}]
+        outputs = [{"data": "00"}]
@@ -306,17 +313,0 @@ class PSBTTest(BitcoinTestFramework):
-        unknown_key_type = 0xda
-        global_key_a = unknown_key(unknown_key_type, b"global-a")
-        global_key_b = unknown_key(unknown_key_type, b"global-b")
-        input_key_a = unknown_key(unknown_key_type, b"input-a")
-        input_key_b = unknown_key(unknown_key_type, b"input-b")
-        output_key_a = unknown_key(unknown_key_type, b"output-a")
-        output_key_b = unknown_key(unknown_key_type, b"output-b")
-
-        global_value_a = b"\xaa"
-        global_value_b = b"\xdd"
-        input_value_a = b"\xbb"
-        input_value_b = b"\xee"
-        output_value_a = b"\xcc"
-        output_value_b = b"\xff"
-
-        inputs = [{"txid": "aa" * 32, "vout": 0}]
-        outputs = [{self.nodes[0].getnewaddress(): Decimal("1")}]
@@ -327,3 +318,3 @@ class PSBTTest(BitcoinTestFramework):
-            psbt1.g.map[global_key_a] = global_value_a
-            psbt1.i[0].map[input_key_a] = input_value_a
-            psbt1.o[0].map[output_key_a] = output_value_a
+            psbt1.g.map[unknown_psbt_key_a] = unknown_psbt_value
+            psbt1.i[0].map[unknown_psbt_key_a] = unknown_psbt_value
+            psbt1.o[0].map[unknown_psbt_key_a] = unknown_psbt_value
@@ -332,3 +323,3 @@ class PSBTTest(BitcoinTestFramework):
-            psbt2.g.map[global_key_b] = global_value_b
-            psbt2.i[0].map[input_key_b] = input_value_b
-            psbt2.o[0].map[output_key_b] = output_value_b
+            psbt2.g.map[unknown_psbt_key_b] = unknown_psbt_value
+            psbt2.i[0].map[unknown_psbt_key_b] = unknown_psbt_value
+            psbt2.o[0].map[unknown_psbt_key_b] = unknown_psbt_value
@@ -339,2 +330,2 @@ class PSBTTest(BitcoinTestFramework):
-                (global_key_a, global_value_a),
-                (global_key_b, global_value_b),
+                (unknown_psbt_key_a, unknown_psbt_value),
+                (unknown_psbt_key_b, unknown_psbt_value),
@@ -343,2 +334,2 @@ class PSBTTest(BitcoinTestFramework):
-                (input_key_a, input_value_a),
-                (input_key_b, input_value_b),
+                (unknown_psbt_key_a, unknown_psbt_value),
+                (unknown_psbt_key_b, unknown_psbt_value),
@@ -347,2 +338,2 @@ class PSBTTest(BitcoinTestFramework):
-                (output_key_a, output_value_a),
-                (output_key_b, output_value_b),
+                (unknown_psbt_key_a, unknown_psbt_value),
+                (unknown_psbt_key_b, unknown_psbt_value),

PS: Thanks for putting me as co-author :)

Thanks, this makes sense. I adapted the test to use the unknown key/value bytes from the BIP174 example, while keeping the existing PSBTv0 and PSBTv2 coverage.

I did not use the BIP174 serialized PSBTs directly because that vector is PSBTv0-specific; instead the test still creates valid base PSBTs with createpsbt for each supported version, injects the BIP174-style unknown fields into the global/input/output maps, combines them, and checks that they are preserved.

Rebased