Bolt11Invoice.fromString skips p, h and s fields of the wrong length

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
84/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
scala
Domain
backend, payments

Research direction

Read eclair-core/src/main/scala/fr/acinq/eclair/payment/Bolt11Invoice.scala around the InvalidTag1, InvalidTag23 and InvalidTag16 decoding branches, then review the related tests in eclair-core/src/test/scala/fr/acinq/eclair/payment/Bolt11InvoiceSpec.scala. Run ./mvnw test -pl eclair-core -Dsuites='*Bolt11InvoiceSpec'; done means invoices with 51-group p, h or s fields fail to decode, as the supplied test expects.

Written by the indexing model from the issue text.

Description

Bolt11Invoice.fromString skips a 51-group p, h or s field and decodes the invoice instead of failing. This happens on master at 06716fce and in v0.14.5.

The case below, added to eclair-core/src/test/scala/fr/acinq/eclair/payment/Bolt11InvoiceSpec.scala, builds three invoices from the BOLT 11 cup of coffee example, each with one wrong-length field: a 51-group h, a 51-group p and a 51-group s.

// BOLT 11 example "Please send $3 for a cup of coffee to the same peer, within one minute".
val cupOfCoffee: Bolt11Invoice = Bolt11Invoice.fromString("lnbc2500u1pvjluezsp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygspp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jsxqzpu9qrsgquk0rl77nj30yxdy8j9vdx85fkpmdla2087ne0xh8nhedh8w27kyke0lp53ut353s06fv3qfegext0eh0ymjpf39tuven09sam30g4vgpfna3rh").get

test("reject p, h or s fields with an invalid length") {
  // Bolt11: a reader MUST fail an invoice whose p, h, s or n field does not have the correct length.
  def groups(i: Int) = BitVector.fill(i * 5)(high = false)
  val wrongLength = List(InvalidTag23(groups(51)), InvalidTag1(groups(51)), InvalidTag16(groups(51)))
  for (bad <- wrongLength) {
    val invoice = cupOfCoffee.copy(tags = cupOfCoffee.tags :+ bad).sign(priv)
    assert(Bolt11Invoice.fromString(invoice.toString).isFailure)
  }
}

./mvnw test -pl eclair-core -Dsuites='*Bolt11InvoiceSpec' reports the case failing.

- reject p, h or s fields with an invalid length *** FAILED ***
  Bolt11Invoice.fromString(invoice.toString).isFailure was false (Bolt11InvoiceSpec.scala:686)
Tests: succeeded 37, failed 1, canceled 0, ignored 0, pending 0

The codec reads those fields as InvalidTag1, InvalidTag23 and InvalidTag16 at lines 411-414, 439-442 and 429-432. The constructor counts only the fields of the right length, so a wrong-length field does not stop the decode. The test "ignore hash tags with invalid length" at Bolt11InvoiceSpec.scala:450-451 still quotes the earlier skip rule, which BOLT 11 replaced in commit 68881992 in June 2025.

fromString should fail on all three. BOLT 11, Tagged Fields, line 214 says a reader "MUST fail the payment if any field with fixed data_length (p, h, s, n) does not have the correct length (52, 52, 52, 53)".

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