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Glossary

Terms used throughout the ndn-rs codebase and NDN literature. Organized alphabetically.

Action
Enum returned by each PipelineStage to control packet flow. Variants: Continue (pass to next stage), Send (forward to faces and exit), Satisfy (satisfy PIT entries), Drop (discard), Nack (send negative acknowledgement).
InProcFace
An in-process face that connects an application to the ndn-rs engine. Implemented as a pair of shared-memory ring buffers with a Unix socket control channel. Applications interact with the forwarder through InProcFace rather than opening network sockets.
CanBePrefix
An Interest selector indicating that the Interest name may be a proper prefix of the Data name. Without this flag, the Data name must exactly match the Interest name.
CS (Content Store)
A per-node cache of Data packets. Any router can serve a cached Data to a future Interest without forwarding upstream. In ndn-rs, CS is a trait (ContentStore) with pluggable backends: LruCs, ShardedCs, PersistentCs.
Data
One of the two NDN network-layer packet types. A Data packet carries a name, content, and a cryptographic signature. Data is always a response to an Interest and travels the reverse path.
Face
An NDN communication interface, analogous to a network interface in IP. A face can be a UDP tunnel, TCP connection, Ethernet link, Unix socket, in-process channel, or any transport that implements the Face trait (recv() + send()). Each face has a unique FaceId.
FaceId
A u32 identifier assigned to each face when it is created. Used throughout PIT records, FIB nexthops, and pipeline dispatch. Application code does not use raw FaceId values directly.
FIB (Forwarding Information Base)
Maps name prefixes to sets of nexthop faces with costs. Implemented as a NameTrie with Arc<RwLock<TrieNode>> per level for concurrent longest-prefix match. Analogous to an IP routing table.
ForwardingAction
Enum returned by a Strategy to tell the pipeline what to do with an Interest. Variants: Forward (send to faces), ForwardAfter (delayed forward for probing), Nack (reject), Suppress (do not forward).
FreshnessPeriod
A field in a Data packet specifying how long (in milliseconds) the Data should be considered “fresh” after arrival. Used by the CS to honor MustBeFresh selectors. Decoded once at CS insert time and stored as a stale_at timestamp.
HopLimit
An optional field in an Interest packet, decremented at each hop. When it reaches zero the Interest is dropped. Prevents Interests from looping indefinitely in misconfigured networks.
Interest
One of the two NDN network-layer packet types. An Interest packet carries a name and optional selectors (CanBePrefix, MustBeFresh, Nonce, Lifetime, HopLimit). It requests a Data packet matching the given name.
MustBeFresh
An Interest selector requesting that the returned Data must not be stale (its FreshnessPeriod must not have expired). A CS entry whose stale_at has passed will not satisfy a MustBeFresh Interest.
Nack (Network Nack)
A negative acknowledgement sent by a router when it cannot satisfy or forward an Interest. Carries a reason code (NoRoute, Congestion, Duplicate). Nacks travel the reverse Interest path, same as Data.
Name
A hierarchical identifier for NDN content. Composed of a sequence of NameComponent values. Example: /ndn/example/data/v1. In ndn-rs, names use SmallVec<[NameComponent; 8]> for stack allocation in the common case and are shared via Arc<Name>.
NameComponent
A single segment of an NDN name. Components are typed (GenericNameComponent, ImplicitSha256DigestComponent, ParametersSha256DigestComponent, etc.) and carry arbitrary bytes, not just UTF-8 strings.
A link-layer protocol that fragments, reassembles, and annotates NDN packets on a single hop. Carries hop-by-hop fields such as PIT tokens, Nack reasons, congestion marks, and fragmentation headers. In ndn-rs, NDNLPv2 headers are parsed before the packet enters the forwarding pipeline.
Nonce
A random 32-bit value carried in every Interest packet. Used for loop detection: if a PIT entry already contains the same nonce, the Interest is a loop and is Nacked. Stored in SmallVec<[u32; 4]> per PIT entry.
PacketContext
The per-packet state object passed by value through the pipeline. Contains raw bytes, decoded packet, face ID, name, PIT token, output face list, and extensible tags. Fields are populated progressively as stages execute.
PipelineStage
A trait representing one step in the forwarding pipeline. Each stage receives a PacketContext and returns an Action. Built-in stages are monomorphized for zero-cost dispatch; plugin stages use dynamic dispatch via BoxedStage.
PIT (Pending Interest Table)
Records outstanding Interests that have been forwarded but not yet satisfied. Keyed by name + selector hash. Implemented as a DashMap for sharded concurrent access. Each entry tracks in-records (downstream faces), out-records (upstream faces), and nonces seen.
PitToken
A hash derived from the Interest name and selectors, used as the PIT lookup key. Distinct from the NDNLPv2 wire-protocol PIT token (an opaque hop-by-hop value echoed in Data/Nack responses).
SafeData
A newtype wrapper around Data that can only be constructed by the Validator after successful signature verification. Application callbacks and the Content Store receive SafeData, not raw Data. This enforces at compile time that unverified data cannot be forwarded or consumed.
ShmFace
A shared-memory face for high-throughput communication between an application and the ndn-rs router on the same host. Uses a ring buffer in a shared memory segment with a Unix socket control channel for signaling.
Strategy
A per-prefix forwarding policy that decides how to handle Interests and Data. Implements the Strategy trait with methods like after_receive_interest and after_receive_data. Strategies receive an immutable StrategyContext and return ForwardingAction values. A name trie parallel to the FIB maps prefixes to strategy instances.
TrustSchema
A declarative specification of which keys are allowed to sign which names. Uses name pattern matching with capture groups. The Validator checks incoming Data against the trust schema before constructing SafeData.