From 4ee16d0ff0cfec6c9a9db7811a79349c34c99aac Mon Sep 17 00:00:00 2001
From: SoorajDevadiga <sooraj.devadiga9380@gmail.com>
Date: Tue, 26 May 2026 18:57:07 +0530
Subject: [PATCH] Fix: recoverable diagnostics for truncated TLV value

---
 sigflow/parsers/tlv.py | 11 +++++++++++
 tests/test_parsers.py  | 14 ++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/sigflow/parsers/tlv.py b/sigflow/parsers/tlv.py
index c05746c..ae00549 100644
--- a/sigflow/parsers/tlv.py
+++ b/sigflow/parsers/tlv.py
@@ -14,16 +14,27 @@ def parse(self, data: bytes, context: ExecutionContext) -> list[Frame]:
         offset = 0
         seq = 0
         while offset < len(data):
+            # Need at least the TLV header (tag + length)
             if len(data) - offset < TLV.size:
                 context.warn("tlv-truncated", "partial tlv header", offset)
                 break
+
             tag, length = TLV.unpack_from(data, offset)
             offset += TLV.size
+
             if length > self.max_payload:
                 context.warn("tlv-large", f"tag {tag} exceeds max payload", offset)
                 break
+
+            # If the TLV header is present, but the declared value bytes are truncated,
+            # downgrade to a recoverable diagnostic (consistent with BinaryFrameParser).
+            if offset + length > len(data):
+                context.warn("tlv-truncated", "truncated tlv value", offset)
+                break
+
             value = self.require(data, offset, length)
             frames.append(Frame(tag, seq, value, metadata={"tag": tag}))
             seq += 1
             offset += length
         return frames
+
diff --git a/tests/test_parsers.py b/tests/test_parsers.py
index 638db7a..68c0e50 100644
--- a/tests/test_parsers.py
+++ b/tests/test_parsers.py
@@ -2,6 +2,7 @@
 from sigflow.core.context import ExecutionContext
 from sigflow.core.exceptions import ParseError
 from sigflow.parsers.binary import BinaryFrameParser
+from sigflow.parsers.tlv import TLVParser
 
 
 def test_binary_parser_reads_frames(sample_stream):
@@ -19,3 +20,16 @@ def test_binary_parser_reports_truncation(sample_stream):
 def test_invalid_magic_raises():
     with pytest.raises(ParseError):
         BinaryFrameParser().parse(b"NOPE" + b"0" * 32, ExecutionContext({}))
+
+
+def test_tlv_truncated_value_is_recoverable():
+    # TLV format: >HH (tag, length)
+    # Provide header declaring length=4 but only 2 bytes for value.
+    data = b"\x00\x01" + b"\x00\x04" + b"AB"
+    ctx = ExecutionContext({})
+    frames = TLVParser().parse(data, ctx)
+
+    # No ParseError should be raised; parsing should stop and emit a diagnostic.
+    assert frames == []
+    assert any(d.code == "tlv-truncated" for d in ctx.diagnostics)
+