Add OTLP http/json trace export (OTEL_TRACES_EXPORTER=otlp)

[bm1549]

What does this PR do?

Adds OTLP http/json trace export to the datadog gem. When OTEL_TRACES_EXPORTER=otlp is set, finished traces are exported over OTLP http/json to an OpenTelemetry collector instead of the Datadog agent. The exporter is hand-rolled in pure Ruby (no new heavy dependency), wired into Tracing::Component#build_writer as an alternate transport, mirroring dd-trace-js.

Configuration (tracing.otlp settings + env mapping):

• OTEL_TRACES_EXPORTER — otlp enables OTLP export; none disables tracing
• OTEL_EXPORTER_OTLP_TRACES_ENDPOINT → fallback OTEL_EXPORTER_OTLP_ENDPOINT + /v1/traces → default http://<agent_host>:4318/v1/traces
• OTEL_EXPORTER_OTLP_TRACES_HEADERS / _TIMEOUT (10s) / _PROTOCOL (only http/json honored this phase; warns otherwise)
• OTEL_TRACES_SAMPLER / _ARG (reuses the existing mapping)

Behavior: DD_TRACE_AGENT_PROTOCOL_VERSION disables OTLP; DD_TRACE_SAMPLE_RATE/rules take precedence; only sampled spans are exported; the agent transport (and Remote Config / /info) is unaffected when OTLP is off.

Motivation:

Part of the cross-language OTLP Traces Export effort (RFC "OTLP Traces Export 2026Q1", Phase 1): let the Datadog SDK emit traces over OTLP for users running an OpenTelemetry collector.

Change log entry

Yes. Add OTLP trace export: set OTEL_TRACES_EXPORTER=otlp to export traces over OTLP (http/json) to an OpenTelemetry collector.

Additional Notes:

Yes — the AI-generated code was read and understood. 47+ OTLP-specific specs plus config/gate specs (374 examples in the combined run, 0 failures); RBS signatures added; StandardRB/Steep clean. Scope is RFC Phase 1: http/json only (no gRPC, no W3C TraceContext L2 / probability sampling, no trace stats, no OTel semantic conventions).

How to test the change?

Covered by new RSpec specs under spec/datadog/tracing/transport/otlp*. End-to-end coverage is added in system-tests (Test_Otel_Tracing_OTLP, activated for ruby). Manually: set OTEL_TRACES_EXPORTER=otlp and OTEL_EXPORTER_OTLP_TRACES_ENDPOINT to a collector and confirm spans arrive as OTLP http/json.

Related PRs (cross-language OTLP traces export):

• dd-trace-rs (Rust): feat(traces): add OTLP http/json trace export dd-trace-rs#251
• dd-trace-rb (Ruby): Add OTLP http/json trace export (OTEL_TRACES_EXPORTER=otlp) #5888
• dd-trace-php (PHP): Add OTLP trace export via the sidecar (OTEL_TRACES_EXPORTER=otlp) dd-trace-php#3971
• libdatadog (sidecar OTLP path — merge-order gate for dd-trace-php): feat(sidecar): export session traces over OTLP via TraceExporter libdatadog#2101
• system-tests (e2e tests + Rust weblog): Add OTLP trace export tests + Rust weblog [rust@brian.marks/otlp-trace-export][ruby@brian.marks/otlp-trace-export][php@brian.marks/otlp-trace-export] system-tests#7121

Merge order: libdatadog #2101 → dd-trace-php #3971 (re-bump the submodule to the released libdatadog commit). system-tests #7121 validates rust/ruby/php once the tracer branches are available.

🤖 Generated with Claude Code

[dd-octo-sts]

Typing analysis

Note: Ignored files are excluded from the next sections.

steep:ignore comments

This PR introduces 1 steep:ignore comment.

steep:ignore comments (+1-0)

❌ Introduced:

lib/datadog/tracing/transport/otlp/exporter.rb:38

Untyped methods

This PR introduces 23 partially typed methods. It decreases the percentage of typed methods from 65.14% to 64.63% (-0.51%).

Partially typed methods (+23-0)

❌ Introduced:

sig/datadog/tracing/transport/otlp/encoder.rbs:33
└── def initialize: (resource_attributes: Array[Hash[Symbol, untyped]], ?scope_version: String?, ?default_service: String?) -> void
sig/datadog/tracing/transport/otlp/encoder.rbs:35
└── def encode: (untyped trace) -> String
sig/datadog/tracing/transport/otlp/encoder.rbs:37
└── def payload: (untyped trace) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:41
└── def encode_span: (untyped span, String? trace_id_high) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:43
└── def attributes: (untyped span) -> Array[Hash[Symbol, untyped]]
sig/datadog/tracing/transport/otlp/encoder.rbs:45
└── def encode_link: (untyped link) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:47
└── def encode_event: (untyped event) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:49
└── def any_value: (untyped value) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:51
└── def numeric_value: (Numeric value) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:53
└── def integer_value: (Integer value) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:55
└── def span_kind: (untyped span) -> Integer
sig/datadog/tracing/transport/otlp/encoder.rbs:57
└── def status: (untyped span) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/encoder.rbs:63
└── def start_time_nano: (untyped span) -> Integer
sig/datadog/tracing/transport/otlp/encoder.rbs:65
└── def end_time_nano: (untyped span) -> Integer
sig/datadog/tracing/transport/otlp/encoder.rbs:67
└── def string_attribute: (String key, untyped value) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp/exporter.rbs:18
└── def initialize: (endpoint: String, headers: Hash[String, String]?, timeout_millis: Integer, logger: untyped) -> void
sig/datadog/tracing/transport/otlp.rbs:5
└── def self?.build: (settings: untyped, agent_settings: untyped, ?logger: untyped) -> Transport
sig/datadog/tracing/transport/otlp.rbs:7
└── def self?.resolve_endpoint: (untyped otlp, untyped agent_settings) -> String
sig/datadog/tracing/transport/otlp.rbs:9
└── def self?.resource_attributes: (untyped settings) -> Array[Hash[Symbol, untyped]]
sig/datadog/tracing/transport/otlp.rbs:11
└── def self?.string_attribute: (String key, untyped value) -> Hash[Symbol, untyped]
sig/datadog/tracing/transport/otlp.rbs:24
└── def initialize: (exporter: Exporter, encoder: Encoder, logger: untyped) -> void
sig/datadog/tracing/transport/otlp.rbs:26
└── def send_traces: (untyped traces) -> Array[Response]
sig/datadog/tracing/transport/otlp.rbs:30
└── def drop?: (untyped trace) -> bool

Untyped other declarations

This PR introduces 4 untyped other declarations and 1 partially typed other declaration. It increases the percentage of typed other declarations from 82.59% to 82.7% (+0.11%).

Untyped other declarations (+4-0)

❌ Introduced:

sig/datadog/tracing/transport/otlp/exporter.rbs:11
└── @logger: untyped
sig/datadog/tracing/transport/otlp/exporter.rbs:16
└── attr_reader logger: untyped
sig/datadog/tracing/transport/otlp.rbs:16
└── @logger: untyped
sig/datadog/tracing/transport/otlp.rbs:21
└── attr_reader logger: untyped

Partially typed other declarations (+1-0)

❌ Introduced:

sig/datadog/tracing/transport/otlp/encoder.rbs:29
└── @resource_attributes: Array[Hash[Symbol, untyped]]

If you believe a method or an attribute is rightfully untyped or partially typed, you can add # untyped:accept on the line before the definition to remove it from the stats.

[datadog-prod-us1-4]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 46.38%
• Overall Coverage: 89.80% (-0.27%)

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