21 KiB
Code Review — InboundAPI
| Field | Value |
|---|---|
| Module | src/ScadaLink.InboundAPI |
| Design doc | docs/requirements/Component-InboundAPI.md |
| Status | Reviewed |
| Last reviewed | 2026-05-16 |
| Reviewer | claude-agent |
| Commit reviewed | 9c60592 |
| Open findings | 10 |
Summary
The InboundAPI module is small (8 source files) and the happy-path flow — extract
key, validate, deserialize parameters, execute script, serialize result — is clean
and readable. However the review surfaced several real problems concentrated in two
themes: concurrency and security. The InboundScriptExecutor is a singleton
that mutates a plain Dictionary from concurrent ASP.NET request threads with no
synchronization, which can corrupt the handler cache or crash the process under load.
On the security side, API-key comparison is a non-constant-time database string
match (timing oracle), compiled scripts run with no enforcement of the documented
script trust model (forbidden APIs such as System.IO/Process/Reflection are
fully reachable), there is no request-body size limit, and the executor's catch-all
swallows OperationCanceledException from genuine client disconnects as a "timeout".
Design-doc adherence is also incomplete: the Database.Connection() script API
described in the design doc is entirely absent from InboundScriptContext, and the
endpoint never enforces that the API is central-only. Testing covers the validators
well but there is no coverage of the HTTP endpoint, concurrency, or recompilation.
None of the findings are data-loss-class, but the concurrency and trust-model issues
are High severity and should be addressed before production use.
Checklist coverage
| # | Category | Examined | Notes |
|---|---|---|---|
| 1 | Correctness & logic bugs | ☑ | CoerceValue returns null for legitimately-null/String values indistinguishably; parameter-definition edge cases noted. |
| 2 | Akka.NET conventions | ☑ | Module is ASP.NET-hosted, no actors of its own; routes to actors via CommunicationService. No correlation-ID issues — IDs are set in RouteHelper. |
| 3 | Concurrency & thread safety | ☑ | Singleton InboundScriptExecutor mutates a non-thread-safe Dictionary from concurrent request threads — see InboundAPI-001/002. |
| 4 | Error handling & resilience | ☑ | Catch-all conflates client cancellation with timeout (InboundAPI-004); compilation-failure path repeats work on every request (InboundAPI-009). |
| 5 | Security | ☑ | Non-constant-time key comparison, no trust-model enforcement, no body-size limit, missing-method enumeration oracle — see InboundAPI-003/005/006/011. |
| 6 | Performance & resource management | ☑ | Up to 3 separate DB round-trips per request in ApiKeyValidator; uncapped lazy recompilation. |
| 7 | Design-document adherence | ☑ | Database.Connection() script API missing; central-only hosting not enforced; lazy-compile diverges from "compiled at startup". |
| 8 | Code organization & conventions | ☑ | ParameterDefinition is an API-shaped POCO declared in the component project rather than Commons; otherwise conventions followed. |
| 9 | Testing coverage | ☑ | Good unit coverage of the two validators; no endpoint, concurrency, recompilation, or timeout-vs-cancel tests. |
| 10 | Documentation & comments | ☑ | ApiKeyValidationResult.NotFound XML/name says "NotFound" but returns HTTP 400 — misleading (InboundAPI-013). |
Findings
InboundAPI-001 — Singleton script handler cache mutated without synchronization
| Severity | High |
| Category | Concurrency & thread safety |
| Status | Resolved |
| Location | src/ScadaLink.InboundAPI/InboundScriptExecutor.cs:17, :32, :40, :89, :123-128 |
Description
InboundScriptExecutor is registered as a singleton (ServiceCollectionExtensions.cs:11)
and its handler cache is a plain Dictionary<string, Func<...>> (InboundScriptExecutor.cs:17).
RegisterHandler, RemoveHandler, CompileAndRegister, and the lazy-compile path in
ExecuteAsync all read and write this dictionary with no lock. ASP.NET serves inbound
API requests on concurrent thread-pool threads, so two requests for an as-yet-uncompiled
method (or a request racing a CLI-triggered CompileAndRegister) can mutate the
dictionary concurrently. Dictionary is explicitly not safe for concurrent
read/write — this can corrupt internal buckets, throw InvalidOperationException,
or return a torn/null handler, crashing the request or the process.
Recommendation
Replace the Dictionary with a ConcurrentDictionary<string, Func<...>>, or guard all
access with a lock. For the lazy-compile path use GetOrAdd so concurrent first-callers
compile at most once.
Resolution
Resolved 2026-05-16 (commit <pending>): replaced the plain Dictionary handler
cache with a ConcurrentDictionary; RemoveHandler now uses TryRemove; the
lazy-compile path in ExecuteAsync compiles outside the cache and inserts atomically
via GetOrAdd so concurrent first-callers share one handler. Regression tests
ConcurrentLazyCompile_SameMethod_DoesNotCorruptCache and
ConcurrentRegisterAndExecute_DoesNotThrow added.
InboundAPI-002 — Lazy compilation is a check-then-act race with no atomicity
| Severity | Medium |
| Category | Concurrency & thread safety |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/InboundScriptExecutor.cs:123-129 |
Description
ExecuteAsync does if (!_scriptHandlers.TryGetValue(...)) { CompileAndRegister(method); handler = _scriptHandlers[method.Name]; }.
Even setting aside the unsynchronized dictionary (InboundAPI-001), this is a
check-then-act sequence: between TryGetValue failing and the re-read on line 128,
another thread could RemoveHandler the entry, causing the indexer on line 128 to
throw KeyNotFoundException — an unhandled-in-context exception that is then caught
only by the broad catch on line 143 and reported to the caller as "Internal script
error". Multiple concurrent first-callers will also each compile the same script
redundantly (wasted Roslyn work).
Recommendation
Make compile-and-fetch a single atomic operation (ConcurrentDictionary.GetOrAdd
with a lazily-evaluated factory, or a per-method lock), and have CompileAndRegister
return the handler it produced rather than requiring a separate dictionary read.
Resolution
Unresolved.
InboundAPI-003 — API key compared with non-constant-time string equality
| Severity | High |
| Category | Security |
| Status | Resolved |
| Location | src/ScadaLink.ConfigurationDatabase/Repositories/InboundApiRepository.cs:22-23, consumed by src/ScadaLink.InboundAPI/ApiKeyValidator.cs:33 |
Description
API-key authentication resolves the key with
FirstOrDefaultAsync(k => k.KeyValue == keyValue) — an ordinary equality match
translated to a SQL WHERE KeyValue = @p comparison. The secret is matched with
ordinary (early-exit) string/SQL comparison rather than a constant-time comparison,
which is a classic timing side-channel for secret material. Combined with the design's
explicit "no rate limiting" decision, an attacker with network access to the central
API can mount a timing attack to recover valid keys. The API key is the sole
credential for the inbound API, so this is the primary authentication path.
Recommendation
Look the key up by a non-secret indexed identifier (e.g. a key prefix/id) or fetch
candidate rows, then verify the secret in-process using
CryptographicOperations.FixedTimeEquals over the UTF-8 bytes. Preferably store only
a salted hash of the key value and compare hashes. Avoid leaking secret-length and
match-position timing.
Resolution
Resolved 2026-05-16 (commit <pending>): ApiKeyValidator no longer calls the
secret-equality lookup GetApiKeyByValueAsync (the SQL WHERE KeyValue = @secret
timing oracle). It now fetches all keys via GetAllApiKeysAsync and matches the
secret in-process with CryptographicOperations.FixedTimeEquals over the UTF-8 bytes,
scanning every candidate so neither match position nor secret length is observable.
Regression tests ValidateAsync_DoesNotUseSecretEqualityLookup,
ValidateAsync_WrongKey_ConstantTimePath_Returns401, and
ValidateAsync_KeyOfDifferentLength_Returns401 added. Note: the timing-oracle method
GetApiKeyByValueAsync remains on IInboundApiRepository (it is outside this module);
removing it from the repository is left as separate follow-up since the validator no
longer depends on it.
InboundAPI-004 — Client disconnect is misreported as a script timeout
| Severity | Medium |
| Category | Error handling & resilience |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/InboundScriptExecutor.cs:117-141 |
Description
ExecuteAsync creates a linked CTS from httpContext.RequestAborted and the method
timeout, then catches OperationCanceledException and unconditionally returns
"Script execution timed out". When the client aborts the request (RequestAborted
fires), the same exception type is thrown, so a normal client disconnect is logged as
a timeout (_logger.LogWarning("Script execution timed out ...")) and an attempt is
made to write a 500 timeout body to an already-gone connection. This pollutes the
failure log (which the design says is reserved for genuine script errors) and obscures
real timeout incidents.
Recommendation
Distinguish the two cancellation sources: if cancellationToken (the request token)
is cancelled, treat it as a client abort — do not log a timeout and do not attempt to
write a response. Only when the timeout CTS fired should the result be "timed out".
Check cts.Token.IsCancellationRequested && !cancellationToken.IsCancellationRequested
or use a dedicated timeout CancellationTokenSource so the two are separable.
Resolution
Unresolved.
InboundAPI-005 — Compiled API scripts run with no script-trust-model enforcement
| Severity | High |
| Category | Security |
| Status | Resolved |
| Location | src/ScadaLink.InboundAPI/InboundScriptExecutor.cs:56-93 |
Description
CLAUDE.md's Akka.NET conventions state the script trust model forbids System.IO,
Process, Threading, Reflection, and raw network access. CompileAndRegister
compiles arbitrary C# with CSharpScript.Create and only restricts the default
imports (WithImports("System", ...)). Imports are a convenience, not a sandbox — a
script can still fully-qualify any type (System.IO.File.Delete(...),
System.Diagnostics.Process.Start(...), System.Reflection, raw Socket) because
the core framework assemblies are referenced and Roslyn scripting performs no API
allow/deny-listing. Inbound API scripts execute on the central node with the host
process's privileges, so a malicious or buggy method definition has full host access.
Note the Design role authors these scripts (less trusted than Admin), making
enforcement material.
Recommendation
Add a compile-time analyzer/SyntaxWalker (as the Site Runtime does for instance
scripts) that rejects forbidden namespaces/types before registering a handler, and/or
run scripts under a constrained boundary. At minimum, share the Site Runtime's
forbidden-API checker so the trust model is enforced consistently. Reject the method
(and log) when a violation is found instead of registering it.
Resolution
Resolved 2026-05-16 (commit <pending>): added ForbiddenApiChecker, a Roslyn
CSharpSyntaxWalker that statically rejects scripts referencing forbidden namespaces
(System.IO, System.Diagnostics, System.Threading except Tasks,
System.Reflection, System.Net, System.Runtime.InteropServices, Microsoft.Win32)
whether reached via a using directive or a fully-qualified name. CompileAndRegister
now runs the check before Roslyn compilation and refuses to register (and logs) a
violating method; ExecuteAsync's lazy-compile path is gated by the same check.
Regression tests CompileAndRegister_ForbiddenApi_RejectsScript (theory),
ExecuteAsync_ForbiddenApiScript_DoesNotRunAndReturnsFailure, and
CompileAndRegister_PermittedScript_StillRegisters added.
InboundAPI-006 — No request body size limit on the inbound endpoint
| Severity | Medium |
| Category | Security |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/EndpointExtensions.cs:54-62 |
Description
HandleInboundApiRequest calls JsonDocument.ParseAsync(httpContext.Request.Body, ...)
with no explicit body-size cap and no [RequestSizeLimit]/endpoint metadata. Although
Kestrel has a default max request body size, this endpoint accepts arbitrary JSON from
external systems, fully buffers it into a JsonDocument, and then Clone()s the
root element (:61) which materializes the entire document on the heap. With no rate
limiting (a deliberate design choice) a single caller can drive large allocations.
Deep/wide JSON also makes the CoerceValue object/list deserialization
(ParameterValidator.cs:113,117) expensive.
Recommendation
Set an explicit, modest body-size limit on the endpoint
(.WithMetadata(new RequestSizeLimitAttribute(...)) or
IHttpMaxRequestBodySizeFeature) and consider a JsonDocumentOptions MaxDepth.
Reject oversized bodies with 413 before buffering.
Resolution
Unresolved.
InboundAPI-007 — Database.Connection() script API from the design doc is not implemented
| Severity | Medium |
| Category | Design-document adherence |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/InboundScriptExecutor.cs:155-170 |
Description
Component-InboundAPI.md ("Script Runtime API -> Database Access") specifies
Database.Connection("connectionName") as an available script capability for
querying the configuration/machine-data databases. InboundScriptContext exposes only
Parameters, Route, and CancellationToken — there is no Database member. Any
method script that follows the documented API will fail to compile. Either the code
is incomplete or the design doc is stale; the two must be reconciled.
Recommendation
If database access is in scope, add a Database property to InboundScriptContext
backed by a connection-factory service. If it is not, remove the "Database Access"
section from Component-InboundAPI.md so the design doc stops advertising an absent
API.
Resolution
Unresolved.
InboundAPI-008 — Inbound API endpoint not restricted to the active central node
| Severity | Medium |
| Category | Design-document adherence |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/EndpointExtensions.cs:19-23, src/ScadaLink.Host/Program.cs:149 |
Description
The design states the Inbound API is "Central cluster only (active node)" and "fails
over with it". MapInboundAPI registers POST /api/{methodName} unconditionally, and
Program.cs maps it inside the central-role branch but with no active-node gating —
unlike /health/active which has an active-node predicate. A standby central node
will happily serve inbound API calls, executing scripts and Route.To() calls from a
non-leader, which can race the active node or run against stale singleton state.
Recommendation
Gate the endpoint on active-node status (reuse the cluster active-node health check
or a leader-state check) and return 503 on the standby, so Traefik/clients only reach
the live node — consistent with how the Management API and /health/active are
treated.
Resolution
Unresolved.
InboundAPI-009 — Failed compilation is retried on every subsequent request
| Severity | Low |
| Category | Performance & resource management |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/InboundScriptExecutor.cs:123-128 |
Description
When a method's script fails to compile, CompileAndRegister returns false and
nothing is stored in _scriptHandlers. Every subsequent call to that method re-enters
the lazy-compile branch and recompiles the broken script via Roslyn from scratch.
Roslyn compilation is expensive; a single broken method definition repeatedly invoked
by an external caller (no rate limiting) becomes a CPU amplification vector.
Recommendation
Cache the compilation failure (e.g. store a sentinel handler that immediately
returns the compile error, or keep a HashSet of known-bad method names with the
diagnostic) so a broken script is compiled at most once until the definition is
updated via CompileAndRegister.
Resolution
Unresolved.
InboundAPI-010 — ParameterValidator ignores extra body fields and cannot validate Object/List element types
| Severity | Low |
| Category | Correctness & logic bugs |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/ParameterValidator.cs:64-90, :112-118 |
Description
Two related correctness gaps: (1) The validator iterates only over defined
parameters; any extra top-level fields in the request body are silently ignored
rather than reported, so callers get no feedback on typo'd parameter names. (2) For
Object and List types the validator only checks the JSON kind (Object/Array)
and then blindly JsonSerializer.Deserializes the raw text — the design's extended
type system describes Objects as "named structure with typed fields" and Lists as
collections "of objects or primitive types", but no field-level or element-level type
validation is performed. Invalid nested structures pass validation and surface only
as runtime script errors.
Recommendation
Optionally warn/400 on unexpected body fields. For the extended types, either parse a
richer ParameterDefinition (with nested field definitions / element type) and
validate recursively, or document explicitly that Object/List are validated only for
shape — and update the design doc to match.
Resolution
Unresolved.
InboundAPI-011 — Method-existence check leaks to unapproved callers (enumeration oracle)
| Severity | Low |
| Category | Security |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/ApiKeyValidator.cs:39-52 |
Description
ValidateAsync returns 400 Method '{methodName}' not found when the method does not
exist, but 403 API key not approved for this method when it exists but the key is
not approved. A caller holding any valid enabled key can therefore enumerate which
method names exist on the central API by observing 400-vs-403 responses. The error
message also echoes the caller-supplied methodName back verbatim into the JSON
response (EndpointExtensions.cs:47), a minor reflected-input concern.
Recommendation
Return an indistinguishable response (e.g. 403/404) for both "method not found" and "key not approved" so existence is not observable to unapproved callers. Avoid echoing raw caller input in error bodies, or sanitize it.
Resolution
Unresolved.
InboundAPI-012 — ParameterDefinition POCO declared in the component project, not Commons
| Severity | Low |
| Category | Code organization & conventions |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/ParameterValidator.cs:128-133 |
Description
ParameterDefinition is a persistence-/contract-shaped POCO: it is the deserialized
form of ApiMethod.ParameterDefinitions (a column in the configuration database) and
describes the public API contract. CLAUDE.md's code-organization rules place
persistence-ignorant entity/contract types in ScadaLink.Commons. Defining it inside
the InboundAPI project means any other component that needs to read or produce method
parameter definitions (e.g. Central UI's method editor, CLI, Management Service)
cannot share the type and will duplicate it.
Recommendation
Move ParameterDefinition (and a matching return-definition type, if added) to
ScadaLink.Commons under the InboundApi entity/types namespace so it is shared by all
components that work with method definitions.
Resolution
Unresolved.
InboundAPI-013 — ApiKeyValidationResult.NotFound factory returns HTTP 400, contradicting its name
| Severity | Low |
| Category | Documentation & comments |
| Status | Open |
| Location | src/ScadaLink.InboundAPI/ApiKeyValidator.cs:78-79 |
Description
The static factory is named NotFound and is used for the "method not found" case,
but it builds a result with StatusCode = 400 (Bad Request), not 404. The name
strongly implies 404 and will mislead future maintainers; EndpointExtensions
faithfully propagates whatever status code the factory sets, so the misnaming directly
affects the wire contract.
Recommendation
Rename the factory to match its behaviour (e.g. BadRequest) or change the status
code to 404 if that is the intended contract — and document the chosen "method not
found" status in Component-InboundAPI.md's Error Handling section, which currently
does not list it.
Resolution
Unresolved.