* Fix JA4 ALPN fingerprint to use first and last characters
According to the JA4 specification (line 2139), the ALPN field should
contain the first and last characters of the first ALPN extension value.
Currently, nDPI uses the first and second characters (alpn[0] and alpn[1]),
which produces incorrect fingerprints that don't match other JA4
implementations like Wireshark.
For example, with ALPN 'http/1.1':
- Current (incorrect): 'ht' (first + second char)
- Fixed (correct): 'h1' (first + last char)
This change ensures nDPI's JA4 implementation conforms to the official
specification and maintains interoperability with other JA4 tools.
Fixes: Incorrect JA4 ALPN fingerprint generation
* Fix JA4 ALPN implementation to correctly parse first ALPN protocol
The previous fix attempted to use strlen(ja->client.alpn)-1 but this was
insufficient because nDPI modifies the ALPN string by:
1. Adding null terminators that truncate the last character
2. Converting semicolons to dashes, affecting multi-protocol ALPNs
This complete fix:
- Adds alpn_original_last field to store the true last character
- Captures the last character of the FIRST ALPN protocol only (before ;/,)
- Preserves the original character before nDPI's string modifications
Now correctly implements JA4 spec: first + last characters of first ALPN protocol
Examples:
- ALPN 'h2;http/1.1' -> 'h2' (not 'h.' or 'h1')
- ALPN 'http/1.1' -> 'h1' (not 'ht' or 'h.')
Fixes: #2914
* Fix JA4 SNI detection to properly handle missing SNI extensions
Previously, nDPI incorrectly set JA4 SNI flag to 'd' (domain present) for
flows without any SNI extension. This was because the logic only checked
for NDPI_NUMERIC_IP_HOST risk (set when SNI contains IP) but didn't
distinguish between missing SNI and domain SNI.
Now properly detects:
- No SNI extension → 'i' flag
- SNI with IP address → 'i' flag
- SNI with domain → 'd' flag
This matches the JA4 specification.
This function is always called once for every flow, as last code
processing the flow itself.
As a first usage example, check here if the flow is unidirectional
(instead of checking it at every packets)
