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gRPC events: disprove transport hypothesis (native HTTP/2 also returns zero rows)

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Tested grpc-event-query-capture.md's leading next-session hypothesis — that the
native client's Grpc.Core HTTP/2 transport (vs our Grpc.Net.Client + GrpcWebHandler
gRPC-Web) is why event reads return zero rows. Added HistorianGrpcChannelFactory
.CreateHttp2 (plain HTTP/2 over SocketsHttpHandler, no gRPC-Web wrap) and an
HISTORIAN_GRPC_EVENT_HTTP2 switch on the event orchestrator (event path only; reads
stay gRPC-Web).

Live side-by-side against the event-bearing 2023 R2 server, everything else held
constant: the full v8 chain (ExchangeKey auth, CM_EVENT RegisterTags/EnsureTags=True,
StartEventQuery with a valid handle) runs end-to-end over BOTH native HTTP/2 and
gRPC-Web, and the server returns the byte-identical version-11 rowCount-0 terminal
(0B00000000001E000000) on both transports. Transport choice makes no difference —
the leading hypothesis is disproven and the zero-row scoping sits above the gRPC
transport layer.

Also confirmed the native capture-event harness queries a 30-day historical window
(returns 50 rows), so the native read is connection-scoped historical retrieval,
not a live subscription.

CreateHttp2 + the env switch + the EventChannelMode diagnostic are retained for
further connection-level probing. 44 offline tests pass; orchestrator stays on the
no-row throw.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC
This commit is contained in:
Joseph Doherty
2026-06-23 12:55:09 -04:00
parent 1161c40fd3
commit b0388e7a40
4 changed files with 78 additions and 10 deletions
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src/AVEVA.Historian.Client/Grpc/HistorianGrpcEventOrchestrator.cs
+13 -1
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@@ -58,6 +58,9 @@ internal sealed class HistorianGrpcEventOrchestrator
/// <summary>Diagnostic: type+code description of the most recent error/terminal buffer.</summary>
public string LastErrorBufferDescription { get; private set; } = string.Empty;
/// <summary>Diagnostic: which transport the event channel used (<c>grpc-web</c> or <c>http2</c>).</summary>
public string EventChannelMode { get; private set; } = string.Empty;
/// <summary>Diagnostic: hex of the most recent result buffer (first 48 bytes).</summary>
public string LastResultBufferHex { get; private set; } = string.Empty;
@@ -143,7 +146,16 @@ internal sealed class HistorianGrpcEventOrchestrator
private List<HistorianEvent> RunEventChain(DateTime startUtc, DateTime endUtc, HistorianEventFilter? filter, CancellationToken cancellationToken)
{
using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(_options);
// Hypothesis #1 (server-side/connection angle, grpc-event-query-capture.md): the native client
// uses Grpc.Core native HTTP/2, while our default channel wraps gRPC-Web over HTTP/1.1. Reads
// work over gRPC-Web, but the connection-scoped event query may require a true HTTP/2 connection.
// Opt in via HISTORIAN_GRPC_EVENT_HTTP2=1 to use a plain HTTP/2 channel for the event path only.
bool useHttp2 = string.Equals(
Environment.GetEnvironmentVariable("HISTORIAN_GRPC_EVENT_HTTP2"), "1", StringComparison.Ordinal);
EventChannelMode = useHttp2 ? "http2" : "grpc-web";
using HistorianGrpcConnection connection = useHttp2
? HistorianGrpcChannelFactory.CreateHttp2(_options)
: HistorianGrpcChannelFactory.Create(_options);
// Event reads need an Event-type (v8) connection. OpenSession(eventConnection: true) runs the
// full v8 path: HistoryService.ExchangeKey (P-256 ECDH) -> client key = SHA256(secret) -> v8
// OpenConnection with ConnectionType=Event and the credential token RC4(password, MD5(clientKey)).