A complete NGAP (NG Application Protocol) codec for 5G, auto-generated from 3GPP ASN.1 definitions (TS 38.413) using Aligned PER (APER) encoding.

Part of the OxiRush project — a 5G Core Network testing framework.

• Full TS 38.413 coverage — every NGAP procedure, IE, and PDU type
• Auto-generated from ASN.1 — the codec is rebuilt at cargo build from the canonical 3GPP ASN.1 files, tracking spec updates automatically
• APER encoding/decoding — standards-compliant Aligned PER via asn1-codecs
• Serde support — all generated types derive Serialize/Deserialize
• Round-trip fidelity — encode then decode produces identical structures
• Builder macros — build_ngap! and build_ngap_ie! eliminate the deeply nested ProtocolIEs boilerplate
• Extraction macro — extract_ngap_ies! pulls typed fields from decoded messages with req/opt semantics
• Auto-derived IE IDs and procedure codes — no manual constants needed, derived at build time from ASN.1 #[asn(key = N)] attributes
• Encode/decode convenience — pdu.encode() and NGAP_PDU::decode(&bytes) wrap the raw APER codec
• PDU inspection — pdu.procedure_name(), pdu.direction(), pdu.procedure_code(), pdu.is_initiating()
• Display impl — format!("{pdu}") → "InitiatingMessage NGSetup (code=21)"
• Type builders — plmn(), guami(), tai(), nr_cgi(), global_gnb_id(), s_nssai() for common NGAP IEs
• Bitvec helpers — int_to_bitvec(), bytes_to_bitvec() for AMF identity, security keys, cell IDs

[dependencies]
oxirush-ngap = "0.3"

The auto-generated types are deeply nested. The build_ngap! macro provides a concise DSL:

use oxirush_ngap::{build_ngap, ngap::*};
use oxirush_ngap::helpers::*;

// Simple: UEContextReleaseRequest with a cause
let pdu = build_ngap!(InitiatingMessage, UEContextReleaseRequest,
    REJECT, UEContextReleaseRequest,
    REJECT AMF_UE_NGAP_ID(1u64),
    REJECT RAN_UE_NGAP_ID(0u32),
    IGNORE Cause(Cause::RadioNetwork(CauseRadioNetwork(CauseRadioNetwork::USER_INACTIVITY))),
);

// Complex: InitialContextSetupRequest with GUAMI, NSSAI, security key helpers
let pdu = build_ngap!(InitiatingMessage, InitialContextSetup,
    REJECT, InitialContextSetupRequest,
    REJECT AMF_UE_NGAP_ID(1u64),
    REJECT RAN_UE_NGAP_ID(0u32),
    REJECT UEAggregateMaximumBitRate(UEAggregateMaximumBitRate {
        ue_aggregate_maximum_bit_rate_dl: BitRate(1_000_000_000),
        ue_aggregate_maximum_bit_rate_ul: BitRate(1_000_000_000),
        ie_extensions: None,
    }),
    REJECT GUAMI(guami(plmn("208", "93"), 1, 1, 0)),
    REJECT AllowedNSSAI(vec![AllowedNSSAI_Item {
        s_nssai: s_nssai(1, Some([0x00, 0x00, 0x01])),
        ie_extensions: None,
    }]),
    REJECT SecurityKey(bytes_to_bitvec(&[0u8; 32])),
    IGNORE NAS_PDU(vec![0x7e, 0x00, 0x42]),
);

// Encode to APER wire format
let wire_bytes = pdu.encode().unwrap();

// Inspect the PDU
println!("{pdu}");                        // "InitiatingMessage InitialContextSetup (code=14)"
assert_eq!(pdu.procedure_name(), "InitialContextSetup");
assert!(pdu.is_initiating());

build_ngap! arguments: (Direction, Procedure, Criticality, MessageType, IEs...)

Each IE: Criticality IeName(value) — IE IDs and procedure codes are auto-derived at build time. Raw values (e.g. u64) auto-convert to newtypes via .into().

Build individual IEs when you need conditional logic:

use oxirush_ngap::{build_ngap_ie, ngap::*};

let cause_ie = build_ngap_ie!(UEContextReleaseRequest, IGNORE
    Cause(Cause::RadioNetwork(CauseRadioNetwork(CauseRadioNetwork::USER_INACTIVITY)))
);

The extract_ngap_ies! macro pulls typed fields from a decoded message. Required fields that are missing cause the enclosing function to return Err(MissingIeError). Optional fields stay as Option<T>.

use oxirush_ngap::{extract_ngap_ies, ngap::*, macros::MissingIeError};

// Simple: extract UE IDs and an optional cause
fn handle_release(req: UEContextReleaseRequest) -> Result<(), MissingIeError> {
    extract_ngap_ies!(req, UEContextReleaseRequest,
        req amf_id: u64     = AMF_UE_NGAP_ID(id),           // required, default .0
        req ran_id: u32     = RAN_UE_NGAP_ID(id),           // required, default .0
        opt cause:  String  = Cause(c) => format!("{c:?}"), // optional + custom expr
    );
    // amf_id: u64, ran_id: u32, cause: Option<String>
    println!("AMF={amf_id} RAN={ran_id} cause={cause:?}");
    Ok(())
}

// Complex: extract many IEs with pattern matching and type conversions
fn handle_handover(req: HandoverRequired) -> Result<(), MissingIeError> {
    extract_ngap_ies!(req, HandoverRequired,
        req amf_id: u64 = AMF_UE_NGAP_ID(id),
        req ran_id: u32 = RAN_UE_NGAP_ID(id),
        opt cause_rn: u8 = Cause(c) =>
            if let Cause::RadioNetwork(rn) = c { rn.0 } else { 0 },
        opt ho_type: u8 = HandoverType(ht),           // default .0
        opt container: Vec<u8> =
            SourceToTarget_TransparentContainer(c) => c.0.clone(),
    );
    println!("HO UE {} type {:?} cause {:?}", amf_id, ho_type, cause_rn);
    Ok(())
}

extract_ngap_ies! arguments: (msg_var, MessageType, fields...)

Each field: req|opt name: Type = IeName(binding) with optional => custom_expr

When => expr is omitted, defaults to binding.0 (newtype unwrap).

use oxirush_ngap::ngap::NGAP_PDU;

// Encode NGAP_PDU to APER bytes
let bytes = pdu.encode().unwrap();

// Decode APER bytes to NGAP_PDU
let decoded = NGAP_PDU::decode(&bytes).unwrap();

use oxirush_ngap::helpers::*;

let p = plmn("208", "93");                          // PLMNIdentity (3-byte TBCD)
let g = guami(plmn("208", "93"), 1, 1, 0);          // GUAMI (PLMN + AMF identity)
let t = tai(plmn("208", "93"), &[0x00, 0x00, 0x01]); // TAI (PLMN + TAC)
let cgi = nr_cgi(plmn("208", "93"), 0x000001, 1);    // NR-CGI (36-bit cell ID)
let gnb = global_gnb_id(plmn("208", "93"), 0x000001); // GlobalGNB-ID (24-bit gNB-ID)
let nssai = s_nssai(1, Some([0x00, 0x00, 0x01]));    // S-NSSAI (SST + optional SD)
let sec = ue_security_capabilities(&[0xE0, 0xE0]);   // UESecurityCapabilities

// Bitvec conversion for NGAP bitstring fields
let key = bytes_to_bitvec(&[0u8; 32]);               // SecurityKey (256 bits)
let region = int_to_bitvec(1, 8);                     // AMFRegionID (8 bits)

The auto-generated types are fully usable without macros — you can construct NGAP_PDU values directly and pattern-match on decoded ones. The macros simply eliminate the repetitive ProtocolIE_ID(...), Criticality(...), and {Msg}ProtocolIEs_EntryValue::Id_... boilerplate. See examples/decode_manually.rs for a complete encode → decode → inspect example without macros.

The build script (build/main.rs) runs at cargo build time:

1. ASN.1 compilation — reads the 3GPP ASN.1 source files from ngap/ (NGAP-PDU-Descriptions.asn, NGAP-PDU-Contents.asn, NGAP-IEs.asn, NGAP-CommonDataTypes.asn, NGAP-Constants.asn, NGAP-Containers.asn) and compiles them to Rust using asn1-compiler
2. Post-processing — the build script then parses the generated code to emit:
   • From<InnerType> impls for all single-field newtypes (enables .into() auto-conversion in build_ngap!)
   • __ngap_ie_id! macro — maps IE variant names to numeric IDs by parsing #[asn(key = N)] attributes on ProtocolIEs_EntryValue enums (207 arms)
   • __ngap_proc_code! macro — maps procedure names to codes by parsing {Direction}Value enums (66 arms)
   • impl NGAP_PDU — procedure_code(), direction(), procedure_name(), is_initiating() / is_successful() / is_unsuccessful()
   • impl Display for NGAP_PDU — human-readable PDU formatting
3. Output — src/ngap.rs, the complete APER codec with helper macros and impls (~21K lines)

Do not edit src/ngap.rs manually. Modify the ASN.1 files in ngap/ or the build script in build/ instead.

build_ngap! and build_ngap_ie! auto-derive IE IDs, procedure codes, and Id_ variant names. Raw values auto-convert to newtypes via .into(). extract_ngap_ies! accesses .protocol_i_es.0 internally — pass the message variable directly.

cargo run --example build_pdu         # Build NGAP PDUs using build_ngap! and build_ngap_ie!
cargo run --example extract_ies       # Extract IEs from a decoded PDU using extract_ngap_ies!
cargo run --example decode_manually   # Encode/decode without macros (raw types)

• TS 38.413 — NGAP specification (procedures, messages, IEs)
• ITU-T X.691 — ASN.1 Packed Encoding Rules (PER)

Contributions welcome! See CONTRIBUTING.md for guidelines.

All commits must be signed off (git commit -s) per the Developer Certificate of Origin.

By contributing to this project, you agree to the Developer Certificate of Origin (DCO). This means that you have the right to submit your contributions and you agree to license them according to the project's license.

All commits should be signed-off with git commit -s to indicate your agreement to the DCO.

Copyright 2026 Valentin D'Emmanuele

Licensed under the Apache License, Version 2.0. See LICENSE for details.