sentry-span-streaming-dart

name	sentry-span-streaming-dart
description	Migrate Dart/Flutter SDK to Sentry span streaming (span-first trace lifecycle). Use when asked to "enable span streaming", "migrate to span streaming", "use traceLifecycle stream", "use Sentry.startSpan", or switch from transaction-based to streamed span delivery in a Dart or Flutter project.
license	Apache-2.0
category	feature-setup
parent	sentry-feature-setup
disable-model-invocation	true
allowed-tools	Bash, Read, Edit, Write, Grep, Glob

All Skills > Feature Setup > Span Streaming (Dart)

Sentry Span Streaming Migration (Dart/Flutter)

Migrate from the default transaction-based trace lifecycle (SentryTraceLifecycle.static) to span streaming (SentryTraceLifecycle.stream), where spans are sent individually as they complete instead of being batched into a transaction at the end.

This skill covers the Dart and Flutter SDKs (sentry, sentry_flutter, and integration packages such as sentry_dio, sentry_sqflite, sentry_drift). For JavaScript, see Span Streaming (JavaScript). For Python, see Span Streaming (Python).

Invoke This Skill When

• User asks to "enable span streaming" or "migrate to span streaming" in a Dart or Flutter project
• User wants to switch from transaction-based to streamed span delivery
• User mentions traceLifecycle, SentryTraceLifecycle.stream, Sentry.startSpan, or SentrySpanV2
• User wants lower latency span delivery or per-span processing

---

Phase 1: Detect

1.1 Detect SDK and Version

# Which Sentry packages does the project use?
grep -n "sentry" pubspec.yaml 2>/dev/null

# Resolved versions — span streaming requires >= 9.19.0
grep -A8 '^  sentry:' pubspec.lock 2>/dev/null | grep -m1 version
grep -A8 '^  sentry_flutter:' pubspec.lock 2>/dev/null | grep -m1 version

Span streaming requires sentry / sentry_flutter >=9.19.0.

1.2 Find Existing Sentry Config and Tracing Usage

# Find init calls
grep -rn "SentryFlutter\.init\|Sentry\.init" lib/ bin/ test/ --include="*.dart" 2>/dev/null | head -10

# Find old transaction API usage (these become no-ops in streaming mode)
grep -rn "startTransaction\|\.startChild(" lib/ bin/ test/ --include="*.dart" 2>/dev/null | head -20

# Find callbacks affected by the migration
grep -rn "beforeSendTransaction\|beforeSendSpan\|ignoreSpans" lib/ bin/ test/ --include="*.dart" 2>/dev/null

# Find untyped span data/tag usage on transactions
grep -rn "\.setData(\|\.setTag(" lib/ bin/ test/ --include="*.dart" 2>/dev/null | head -20

1.3 Classify the Migration Work

Finding	Migration Work
Sentry.startTransaction(...) calls	Replace with Sentry.startSpan / Sentry.startSpanSync / Sentry.startInactiveSpan
span.startChild(...) calls	Replace with nested Sentry.startSpan calls — parenting is automatic via zones
setData / setTag on spans	Replace with typed span.setAttribute(...) / SentryAttribute
beforeSendTransaction callback	Never called in streaming mode — migrate logic to beforeSendSpan or ignoreSpans
Existing beforeSendSpan / ignoreSpans usage	Review against streaming semantics — beforeSendSpan is mutation-only, ignoreSpans matches names only (see 2.5/2.6)
Only auto-instrumentation (no manual spans)	Just enable the option — integrations switch automatically

---

Phase 2: Migrate

Prerequisites: sentry / sentry_flutter >=9.19.0 with tracing enabled (tracesSampleRate or tracesSampler configured).

2.1 Enable Span Streaming

Set traceLifecycle in the init options. This is the only required config change.

// Flutter
await SentryFlutter.init((options) {
  options.dsn = '__DSN__';
  options.tracesSampleRate = 1.0;
  options.traceLifecycle = SentryTraceLifecycle.stream;
}, appRunner: () => runApp(const MyApp()));

// Plain Dart
await Sentry.init((options) {
  options.dsn = '__DSN__';
  options.tracesSampleRate = 1.0;
  options.traceLifecycle = SentryTraceLifecycle.stream;
});

You can only use one tracing system at a time:

• In stream mode, the transaction APIs (Sentry.startTransaction, ISentrySpan.startChild) do nothing and log a warning.
• In static mode (the default), the new span APIs (Sentry.startSpan) do nothing.
• Auto-instrumentations automatically switch to the correct API based on this setting.

2.2 Replace Transactions with Spans

Sentry.startSpan runs an async callback and ends the span when the returned future completes. Nested calls auto-parent through zones — there is no startChild equivalent to migrate to; just nest.

// Before (static mode)
final transaction = Sentry.startTransaction('checkout', 'task');
try {
  final child = transaction.startChild('db.query', description: 'load cart');
  final cart = await loadCart();
  await child.finish();
  transaction.setData('cart.item_count', cart.items.length);
  transaction.status = const SpanStatus.ok();
} catch (exception) {
  transaction.status = const SpanStatus.internalError(); // -> span.status (see below)
  rethrow;
} finally {
  await transaction.finish();
}

// After (streaming mode)
await Sentry.startSpan('checkout', (span) async {
  final cart = await Sentry.startSpan('load cart', (_) => loadCart());
  span.setAttribute('cart.item_count', SentryAttribute.int(cart.items.length));
});

Error handling is automatic: if the callback throws (or the future errors), the span status is set to SentrySpanStatusV2.error before the span ends, and the error is rethrown. Otherwise the status defaults to ok.

You can also set the status manually via the status setter:

span.status = SentrySpanStatusV2.error;

There is no untyped SpanStatus string equivalent. Explicit statuses from the old API (e.g. transaction.status = const SpanStatus.internalError()) migrate to span.status = SentrySpanStatusV2.error — though error is set automatically on throw and ok automatically otherwise, so manual assignment is only needed to override the default.

For synchronous work, use Sentry.startSpanSync:

final config = Sentry.startSpanSync('parse-config', (_) {
  return Config.parse(raw);
});

Both variants can be freely nested — parent-child relationships resolve correctly across sync/async boundaries. If a span is not sampled, the callback still runs and receives a no-op span, so all span operations are safe.

2.3 Spans That Outlive a Callback

Use Sentry.startInactiveSpan when the work cannot be wrapped in a single callback — widget lifecycles, stream subscriptions, platform channel round-trips. You must call end() manually, and other spans do not automatically become its children.

final paymentSpan = Sentry.startInactiveSpan('payment',
    attributes: {'payment.provider': SentryAttribute.string('stripe')});

// ...later, from a different entry point
void onDeepLink(Uri uri) {
  paymentSpan.end();
}

Parenting. parentSpan defaults to an internal unset sentinel (const UnsetSentrySpanV2()), which means "inherit the currently active span." This is explicitly distinct from passing parentSpan: null, which forces a root span with no parent. Pass an explicit SentrySpanV2 to parent under a specific span. (The same default applies to startSpan / startSpanSync.)

Retroactive timing. startSpan and startSpanSync accept an optional startTimestamp, and span.end(endTimestamp: ...) accepts an explicit end time. Use these when the real start or end of the work happened before you could create or end the span — for example, a duration measured by a platform channel:

final paymentSpan = Sentry.startInactiveSpan('payment');
// ...native reports it started at `nativeStart` and ended at `nativeEnd`
paymentSpan.end(endTimestamp: nativeEnd);

// startTimestamp is available on the callback variants:
Sentry.startSpanSync('replay-import', (_) => importRows(),
    startTimestamp: measuredStart);

2.4 Migrate setData / setTag to Typed Attributes

Streamed spans use typed attributes instead of untyped data and tags:

// Before
transaction.setData('retry_count', 3);
transaction.setTag('payment.provider', 'stripe');

// After
span.setAttribute('retry_count', SentryAttribute.int(3));
span.setAttributes({
  'payment.provider': SentryAttribute.string('stripe'),
  'cache.hit': SentryAttribute.bool(true),
  'response_time_ms': SentryAttribute.double(12.5),
});
span.removeAttribute('old_key');

Factory	Dart Type
SentryAttribute.string(v)	String
SentryAttribute.int(v)	int
SentryAttribute.bool(v)	bool
SentryAttribute.double(v)	double

2.5 Migrate beforeSendTransaction

beforeSendTransaction has no effect in streaming mode — transactions are never created, so the callback is never invoked. Migrate its logic:

Use Case	Streaming Replacement
Drop spans by name	ignoreSpans with IgnoreSpanRule
Scrub sensitive data / PII	beforeSendSpan
Modify span data before send	beforeSendSpan

beforeSendSpan receives each SentrySpanV2 before it is sent. Unlike other beforeSend callbacks, it cannot drop spans — it is mutation-only (FutureOr<void> return). Use ignoreSpans to drop.

await Sentry.init((options) {
  options.traceLifecycle = SentryTraceLifecycle.stream;
  options.beforeSendSpan = (span) {
    span.removeAttribute('http.request.body');
  };
});

Remove the beforeSendTransaction option after migrating its logic.

2.6 Configure ignoreSpans (Optional)

ignoreSpans drops spans by name before sampling. Matching is name-only (attribute matching is not yet supported in the Dart SDK).

options.ignoreSpans = [
  IgnoreSpanRule.nameEquals('health-check'),
  IgnoreSpanRule.nameStartsWith('internal.'),
  IgnoreSpanRule.nameContains('metrics'),
  IgnoreSpanRule.nameEndsWith('.bg'),
];

Factory	Matches
IgnoreSpanRule.nameEquals(String)	Exact span name
IgnoreSpanRule.nameStartsWith(Pattern)	Name prefix (String or RegExp)
IgnoreSpanRule.nameContains(Pattern)	Name substring (String or RegExp)
IgnoreSpanRule.nameEndsWith(String)	Name suffix

When an ignored span has children, the children are re-parented to the nearest recording ancestor rather than dropped.

2.7 Flutter Auto-Instrumentation

No code changes needed: frames tracking, app start, TTID/TTFD, navigation, user interaction, HTTP, database, and GraphQL instrumentations all switch to the streaming API automatically when traceLifecycle is stream.

2.8 Sampling

tracesSampleRate and tracesSampler work unchanged. Only root spans are sampled; child spans inherit the root's decision. When a root span is not sampled, the callback still executes with a no-op span.

---

Phase 3: Verify

3.1 Static Check

dart analyze 2>&1 | head -30
# or for Flutter projects
flutter analyze 2>&1 | head -30

Expect no new analyzer errors from the migration.

3.2 Runtime Verification

Instruct the user to verify with options.debug = true or network inspection:

1. Envelope content type: span envelopes are sent with content type application/vnd.sentry.items.span.v2+json instead of transaction envelopes. Spans are buffered briefly and flushed in batches, so expect a short delay before envelopes appear.
2. Sentry dashboard: spans appear in the Traces view shortly after each span completes, without waiting for a whole transaction to finish.
3. No-op warnings: a log line startTransaction is not supported when traceLifecycle is 'stream' means old transaction API calls remain — find and migrate them.

3.3 Common Issues

Symptom	Cause	Fix
Log: startTransaction is not supported when traceLifecycle is 'stream'	Old transaction API still called in streaming mode	Replace with Sentry.startSpan / startSpanSync
Sentry.startSpan produces no spans	traceLifecycle still static (the default), or tracing disabled	Set options.traceLifecycle = SentryTraceLifecycle.stream and a tracesSampleRate
beforeSendTransaction never called	Expected in streaming mode	Migrate logic to beforeSendSpan or ignoreSpans, then remove it
Returning a value from beforeSendSpan to drop a span does nothing	beforeSendSpan is mutation-only (FutureOr<void> return)	Use ignoreSpans to drop spans
Compile error: startSpan callback type mismatch	Callback must return Future<T> for startSpan	Use startSpanSync for synchronous work

---

Quick Reference

Minimal Flutter Setup

import 'package:flutter/widgets.dart';
import 'package:sentry_flutter/sentry_flutter.dart';

Future<void> main() async {
  await SentryFlutter.init((options) {
    options.dsn = '__DSN__';
    options.tracesSampleRate = 1.0;
    options.traceLifecycle = SentryTraceLifecycle.stream;
  }, appRunner: () => runApp(const MyApp()));

  await Sentry.startSpan('load-config', (span) async {
    span.setAttribute('source', SentryAttribute.string('remote'));
    await loadConfig();
  });
}

Minimal Dart Setup

import 'package:sentry/sentry.dart';

Future<void> main() async {
  await Sentry.init((options) {
    options.dsn = '__DSN__';
    options.tracesSampleRate = 1.0;
    options.traceLifecycle = SentryTraceLifecycle.stream;
  });

  await Sentry.startSpan('main-task', (span) async {
    span.setAttribute('job.id', SentryAttribute.string('42'));
    await doWork();
  });
}

Span Control Reference

// Status (auto-set to error on throw, ok otherwise)
span.status = SentrySpanStatusV2.error; // error | ok

// Retroactive timing
Sentry.startSpanSync('task', (_) => work(), startTimestamp: start); // also on startSpan
span.end(endTimestamp: end);                                        // on any span

// Parenting (startSpan / startSpanSync / startInactiveSpan)
// default: inherit active span | parentSpan: someSpan -> explicit parent | parentSpan: null -> root

Full Migration Checklist

• SDK version is >=9.19.0 (sentry / sentry_flutter)
• options.traceLifecycle = SentryTraceLifecycle.stream set in every init call
• All Sentry.startTransaction calls replaced with Sentry.startSpan / startSpanSync / startInactiveSpan
• All startChild calls replaced with nested Sentry.startSpan calls
• setData / setTag on spans replaced with typed setAttribute / SentryAttribute
• beforeSendTransaction logic migrated to beforeSendSpan or ignoreSpans, option removed
• startInactiveSpan spans have a guaranteed end() call path
• dart analyze / flutter analyze passes
• Spans visible in Sentry Traces view