mm::node::ParameterCache Class Reference

On-disk cache of CoE parameter definitions, keyed by device identity. More...

#include <parameter_cache.h>

Classes
struct	CacheEntry
	Summary of one cache file on disk, for the management UI. More...

Public Member Functions
	ParameterCache ()=default
	ParameterCache (ParameterCacheConfig config)
void	configure (ParameterCacheConfig config)
	Replaces the active policy/location. Called by DeviceManager::init.
bool	enabledForVendor (uint32_t vendorId) const
	Whether the cache is active for vendorId under the current policy.
std::optional< std::vector< DeviceParameter > >	load (uint32_t vendorId, uint32_t productCode, uint32_t revisionNumber) const
	Loads the cached parameter definitions for an identity.
void	store (uint32_t vendorId, uint32_t productCode, uint32_t revisionNumber, const std::vector< DeviceParameter > &parameters) const
	Persists parameter definitions for an identity (atomic temp-file + rename).
std::vector< CacheEntry >	list () const
	Lists every valid cache file in the cache directory.
std::expected< std::vector< uint8_t >, std::string >	readRaw (std::string_view id) const
	Reads the raw JSON bytes of one cache file, addressed by its id (for download).
std::expected< void, std::string >	remove (std::string_view id) const
	Deletes one cache file addressed by its id. Policy-independent.

Static Public Member Functions
static std::string	makeId (uint32_t vendorId, uint32_t productCode, uint32_t revisionNumber)
	Builds the opaque id a client uses to address one cache file, from an identity triple. The single place the id encoding lives; list reports it and readRaw / remove parse it back, so neither the HTTP layer nor the UI ever formats the key itself.

Static Public Attributes
static constexpr int	kFormatVersion = 2
	Bumped when an older file's contents can no longer be trusted, whatever its shape.

Detailed Description

On-disk cache of CoE parameter definitions, keyed by device identity.

Enumerating a drive's object dictionary over the SDO-Information service is hundreds of mailbox round-trips and takes seconds; the result — the set of DeviceParameter definitions (index, subindex, name, data type, bit length, access, unit, and the static default/min/max bounds) — is identical for every device of the same (vendorId, productCode, revisionNumber) and, for a vendor with stable revision discipline, stays valid across power cycles. This cache persists those definitions to a human-readable JSON file per identity so a later scan of the same hardware skips the round-trips.

Only the definition is cached — never the live value or syncState. On load each parameter's value is reset to the type-appropriate default and read live from the device, so a stale cache can at most cost a re-enumeration, never show a stale value as if current. The cached file is a definition/schema snapshot, intended to be readable and (in future) enriched with ESI-derived metadata such as descriptions and enum option labels.

All operations are best-effort and never throw: a missing, unreadable, corrupt, or wrong-format-version file is a miss (the caller falls back to a live enumeration); a write failure is logged, not propagated. Owned by DeviceManager (it outlives the Device set, which is rebuilt on every scan) and handed to each Device by pointer.

Constructor & Destructor Documentation

ParameterCache() [1/2]

mm::node::ParameterCache::ParameterCache ( )

default

ParameterCache() [2/2]

mm::node::ParameterCache::ParameterCache ( ParameterCacheConfig  config )

explicit

Member Function Documentation

configure()

void mm::node::ParameterCache::configure

(

ParameterCacheConfig

config

)

Replaces the active policy/location. Called by DeviceManager::init.

enabledForVendor()

bool mm::node::ParameterCache::enabledForVendor

(

uint32_t

vendorId

)

const

Whether the cache is active for vendorId under the current policy.

True when the master switch is on and either cacheAllVendors is set or vendorId is Synapticon's. The single gate consulted by both load and store.

list()

std::vector< ParameterCache::CacheEntry > mm::node::ParameterCache::list

(

)

const

Lists every valid cache file in the cache directory.

Unlike load / store, listing/management ignores the enabled/vendor policy — you must be able to inspect and clean up files even with caching disabled or after turning it off. Files that do not parse or carry a different formatVersion are skipped. Returns an empty list when the directory does not exist.

load()

std::optional< std::vector< DeviceParameter > > mm::node::ParameterCache::load	(	uint32_t	vendorId,
		uint32_t	productCode,
		uint32_t	revisionNumber
	)		const

Loads the cached parameter definitions for an identity.

Each returned DeviceParameter has its definition fields populated, its value set to the type-appropriate default, and its syncState left Unknown (the caller reads live values).

Returns

The cached definitions on a hit, or std::nullopt when the cache is disabled for the vendor, no file exists, or the file is unreadable / corrupt / for a different identity or format version (all treated as a miss).

makeId()

std::string mm::node::ParameterCache::makeId ( uint32_t  vendorId, uint32_t  productCode, uint32_t  revisionNumber  )

static

Builds the opaque id a client uses to address one cache file, from an identity triple. The single place the id encoding lives; list reports it and readRaw / remove parse it back, so neither the HTTP layer nor the UI ever formats the key itself.

readRaw()

std::expected< std::vector< uint8_t >, std::string > mm::node::ParameterCache::readRaw

(

std::string_view

id

)

const

Reads the raw JSON bytes of one cache file, addressed by its id (for download).

Parses id and reads the file; policy-independent. The HTTP layer passes the path parameter straight through — the id encoding and its validation live here, not in the server.

Returns

The file bytes, or an error string if id is malformed or the file does not exist.

remove()

std::expected< void, std::string > mm::node::ParameterCache::remove

(

std::string_view

id

)

const

Deletes one cache file addressed by its id. Policy-independent.

Returns

Void on success, or an error string if id is malformed or the file does not exist.

store()

void mm::node::ParameterCache::store	(	uint32_t	vendorId,
		uint32_t	productCode,
		uint32_t	revisionNumber,
		const std::vector< DeviceParameter > &	parameters
	)		const

Persists parameter definitions for an identity (atomic temp-file + rename).

The live value and syncState of each parameter are intentionally not written. No-op when the cache is disabled for the vendor. Best-effort: directory-creation or write failures are logged at warn level and otherwise ignored.

Member Data Documentation

kFormatVersion

constexpr int mm::node::ParameterCache::kFormatVersion = 2

staticconstexpr

Bumped when an older file's contents can no longer be trusted, whatever its shape.

Two things invalidate a file, and the second is easy to miss. One is the on-disk field set or a field's meaning: adding a new optional field needs no bump (missing keys default and unknown keys are ignored), changing what a field means does. The other is a change to how the dictionary is enumerated, because a file records what the enumeration of the day produced and is never checked against the device again.

Nothing detects the second case, so it has to be remembered here. A file is keyed on vendor, product and revision alone, so an enumeration fix that is not accompanied by a bump reaches every host except the ones that already had the bug — where a stale file keeps being served and the fix looks like it never shipped. That is a fault only one machine can reproduce and nothing corrects.

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The documentation for this class was generated from the following files:

• libs/node/parameter_cache.h
• libs/node/parameter_cache.cc