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fix(server): bound preview snapshot metadata #7408

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fix(server): bound preview snapshot metadata #7408

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72 changes: 72 additions & 0 deletions apps/server/src/mcp/McpHttpServer.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import * as NodeServices from "@effect/platform-node/NodeServices";
import { EnvironmentId, PreviewTabId, ProviderInstanceId, ThreadId } from "@t3tools/contracts";
import * as Effect from "effect/Effect";
import * as Layer from "effect/Layer";
import * as Schema from "effect/Schema";
import * as Stream from "effect/Stream";
import { McpProtocol, McpSchema, McpServer } from "effect/unstable/ai";
import { HttpBody, HttpClient, HttpRouter, HttpServerResponse } from "effect/unstable/http";
Expand Down Expand Up @@ -38,6 +39,17 @@ const TestLayer = McpHttpServer.PreviewToolkitRegistrationLive.pipe(
Layer.provideMerge(McpServer.McpServer.layer),
Layer.provideMerge(PreviewAutomationBroker.layer.pipe(Layer.provide(NodeServices.layer))),
);
const BoundedSnapshotMetadata = Schema.Struct({
visibleText: Schema.String,
accessibilityTree: Schema.Struct({ truncated: Schema.Boolean }),
truncation: Schema.Struct({
truncated: Schema.Boolean,
reason: Schema.String,
}),
});
const decodeBoundedSnapshotMetadata = Schema.decodeUnknownSync(
Schema.fromJsonString(BoundedSnapshotMetadata),
);

it("normalizes empty successful notification responses to accepted", () => {
const notificationResponse = McpHttpServer.normalizeMcpHttpResponse(
Expand Down Expand Up @@ -97,6 +109,66 @@ it.effect("returns bounded structural preview snapshot failures", () =>
).pipe(Effect.provide(TestLayer)),
);

it.effect("bounds successful preview snapshot metadata before returning it to providers", () =>
Effect.scoped(
Effect.gen(function* () {
const server = yield* McpServer.McpServer;
const broker = yield* PreviewAutomationBroker.PreviewAutomationBroker;
const events = yield* broker.connect({
clientId: "mcp-oversized-snapshot-client",
environmentId,
});
yield* Stream.runForEach(events, (event) =>
event.type === "connected"
? Effect.void
: broker.respond({
clientId: "mcp-oversized-snapshot-client",
connectionId: event.connectionId,
requestId: event.request.requestId,
ok: true,
result: {
url: "http://example.test/large",
title: "Large page",
loading: false,
visibleText: "visible ".repeat(20_000),
interactiveElements: [],
accessibilityTree: { nodes: [{ name: "accessible ".repeat(50_000) }] },
consoleEntries: [],
networkEntries: [],
actionTimeline: [],
screenshot: {
mimeType: "image/png",
data: Buffer.from("png").toString("base64"),
width: 10,
height: 5,
},
},
}),
).pipe(Effect.forkScoped);
yield* Effect.yieldNow;

const snapshot = yield* server
.callTool({ name: "preview_snapshot", arguments: {} })
.pipe(
Effect.provideService(McpInvocationContext.McpInvocationContext, invocation),
Effect.provideService(McpSchema.McpServerClient, client),
);
const text = snapshot.content.find((content) => content.type === "text")?.text;

expect(text).toBeDefined();
expect(Buffer.byteLength(text!, "utf8")).toBeLessThanOrEqual(64_000);
const metadata = decodeBoundedSnapshotMetadata(text!);
expect(metadata.accessibilityTree).toMatchObject({ truncated: true });
expect(metadata.truncation).toMatchObject({
truncated: true,
reason: "metadata_size_limit",
});
expect(metadata.visibleText.length).toBeLessThan(160_000);
expect(snapshot.structuredContent).toMatchObject(metadata);
}),
).pipe(Effect.provide(TestLayer)),
);

it.effect("terminates HTTP MCP sessions with DELETE", () =>
Effect.scoped(
Effect.gen(function* () {
Expand Down
94 changes: 73 additions & 21 deletions apps/server/src/mcp/McpHttpServer.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import * as Stream from "effect/Stream";
import type * as Types from "effect/Types";
import { McpProtocol, McpSchema, McpServer, Tool } from "effect/unstable/ai";
import { HttpRouter, HttpServerRequest, HttpServerResponse } from "effect/unstable/http";
import type { PreviewAutomationSnapshot } from "@t3tools/contracts";

import packageJson from "../../package.json" with { type: "json" };
import * as McpInvocationContext from "./McpInvocationContext.ts";
Expand All @@ -23,6 +24,73 @@ import {
PreviewStandardToolkit,
} from "./toolkits/preview/tools.ts";

const PREVIEW_SNAPSHOT_METADATA_MAX_BYTES = 64_000;
const PREVIEW_SNAPSHOT_FALLBACK_VISIBLE_TEXT_LENGTH = 8_000;

const previewSnapshotMetadata = (snapshot: PreviewAutomationSnapshot) => {
const { screenshot, ...page } = snapshot;
const metadata = {
...page,
screenshot: {
mimeType: screenshot.mimeType,
width: screenshot.width,
height: screenshot.height,
},
};
const serialized = JSON.stringify(metadata);
const originalBytes = Buffer.byteLength(serialized, "utf8");
if (originalBytes <= PREVIEW_SNAPSHOT_METADATA_MAX_BYTES) {
return { metadata, serialized };
}

const withoutAccessibilityTree = {
...metadata,
accessibilityTree: { truncated: true },
truncation: {
truncated: true,
reason: "metadata_size_limit",
originalBytes,
omitted: ["accessibilityTree"],
},
};
const withoutAccessibilityTreeSerialized = JSON.stringify(withoutAccessibilityTree);
if (
Buffer.byteLength(withoutAccessibilityTreeSerialized, "utf8") <=
PREVIEW_SNAPSHOT_METADATA_MAX_BYTES
) {
return {
metadata: withoutAccessibilityTree,
serialized: withoutAccessibilityTreeSerialized,
};
}

const fallback = {
url: snapshot.url.slice(0, 2_048),
title: snapshot.title.slice(0, 512),
loading: snapshot.loading,
visibleText: snapshot.visibleText.slice(0, PREVIEW_SNAPSHOT_FALLBACK_VISIBLE_TEXT_LENGTH),
interactiveElements: [],
accessibilityTree: { truncated: true },
consoleEntries: [],
networkEntries: [],
actionTimeline: [],
screenshot: metadata.screenshot,
truncation: {
truncated: true,
reason: "metadata_size_limit",
originalBytes,
omitted: [
"accessibilityTree",
"interactiveElements",
"consoleEntries",
"networkEntries",
"actionTimeline",
],
},
};
return { metadata: fallback, serialized: JSON.stringify(fallback) };
};

const unauthorized = HttpServerResponse.jsonUnsafe(
{
error: "invalid_mcp_credential",
Expand Down Expand Up @@ -164,34 +232,18 @@ const registerPreviewSnapshot = Effect.fn("McpHttpServer.registerPreviewSnapshot
Effect.matchCauseEffect({
onFailure: previewSnapshotFailure,
onSuccess: ({ encodedResult }) => {
const snapshot = encodedResult as {
readonly screenshot: {
readonly mimeType: "image/png";
readonly data: string;
readonly width: number;
readonly height: number;
};
readonly [key: string]: unknown;
};
const { screenshot, ...page } = snapshot;
const metadata = {
...page,
screenshot: {
mimeType: screenshot.mimeType,
width: screenshot.width,
height: screenshot.height,
},
};
const snapshot = encodedResult as PreviewAutomationSnapshot;
const { metadata, serialized } = previewSnapshotMetadata(snapshot);
return Effect.succeed(
new McpSchema.CallToolResult({
isError: false,
structuredContent: metadata,
content: [
{ type: "text", text: JSON.stringify(metadata) },
{ type: "text", text: serialized },
{
type: "image",
data: new Uint8Array(Buffer.from(screenshot.data, "base64")),
mimeType: screenshot.mimeType,
data: new Uint8Array(Buffer.from(snapshot.screenshot.data, "base64")),
mimeType: snapshot.screenshot.mimeType,
},
],
}),
Expand Down
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