feat(data-pipeline): encode structured values

[lloeki]

AI-generated code disclosure: this PR was implemented with substantial AI assistance and manually reviewed and validated.

What does this PR do?

Introduces a validated, language-neutral structured-value token ABI and standalone MessagePack encoder. It supports nil, booleans, signed and unsigned integers, floats, UTF-8 strings, binary strings, arrays, and maps, with depth and shape validation.

Motivation

The opaque blob API in DataDog/libdatadog PR 2303 restores transitional parity but still requires every consumer to encode MessagePack. This stage moves validated structured-value encoding into libdatadog as part of APMSP-3219.

Additional Notes

Stack position: L4, current PR: DataDog/libdatadog PR 2304, stacked on L1 DataDog/libdatadog PR 2303.

These open L0-L5 changes are not included in libdatadog v38.0.0. They are planned to ship together in a single libdatadog v39 release, with the common dd-trace-rb uptake tracked by R3 DataDog/dd-trace-rb PR 6143.

Complete expected libdatadog review and merge order for that single v39 release:

Level	libdatadog PR	Matching dd-trace-rb consumer
L0	DataDog/libdatadog PR 2302	Release prerequisite; no payload API consumer
L1	DataDog/libdatadog PR 2303	R4 DataDog/dd-trace-rb PR 6130
L2	DataDog/libdatadog PR 2305	R5 DataDog/dd-trace-rb PR 6129
L3	DataDog/libdatadog PR 2301	R6 DataDog/dd-trace-rb PR 6134
L4 (current)	DataDog/libdatadog PR 2304	R7 DataDog/dd-trace-rb PR 6132
L5	DataDog/libdatadog PR 2300	R8 DataDog/dd-trace-rb PR 6133

L0-L3 are independent and can be reviewed in parallel. Merging them in the listed order is still recommended because it reduces integration and release-branch conflicts, and lands panic containment before the new payload surfaces. L4 is stacked on L1, and L5 is stacked on L4.

The matching payload consumers are R4 DataDog/dd-trace-rb PR 6130, R5 DataDog/dd-trace-rb PR 6129, R6 DataDog/dd-trace-rb PR 6134, R7 DataDog/dd-trace-rb PR 6132, and R8 DataDog/dd-trace-rb PR 6133. All depend through the common v39 uptake in R3 DataDog/dd-trace-rb PR 6143. The downstream review and merge order after R3 is R4, R5, R6, R7, then R8; R7 also depends on R4, and R8 depends on R7.

DataDog/libdatadog-rb v37 PR 65 and DataDog/libdatadog-rb v38 PR 66 are separate ordered prerequisite releases only for R2 DataDog/dd-trace-rb PR 6131 and its ForkSafeRuntime uptake. They do not contain the open L0-L5 changes or payload APIs. R3 is stacked on R2, but R3, rather than either prerequisite package, is the common v39 payload-API uptake.

This PR remains a draft because its review and final rebase depend on L1. Its matching consumer R7 DataDog/dd-trace-rb PR 6132 is also a draft pending this API, the v39 package, and R3 DataDog/dd-trace-rb PR 6143. L5 remains draft until this PR is ready.

L0 tracks APMSP-3830; L1-L5 implement the payload work tracked by APMSP-3219.

How to test the change?

Prior local validation completed successfully:

• nix develop -c cargo test -p libdd-data-pipeline-ffi structured_value passed structured-value encoding, ownership, malformed-stream, shape, and depth-limit tests.
• nix develop -c cargo test -p libdd-data-pipeline-ffi passed the complete data-pipeline FFI suite.
• nix develop -c cargo clippy -p libdd-data-pipeline-ffi --all-targets -- -D warnings passed.
• nix develop .#nightly -c cargo fmt --all -- --check passed.
• The release artifact built successfully with nix develop -c cargo run -p builder --bin release -- --out /tmp/opencode/libdatadog-m2/x86_64-linux.
• The matching consumer's native suite passed 122 examples, AppSec passed 807 examples, and AI Guard passed 125 examples against the local artifact.
• Full Standard and Steep checks passed on the matching consumer branch.

[github-actions]

📚 Documentation Check Results

⚠️ 1346 documentation warning(s) found

📦 libdd-data-pipeline-ffi - 1346 warning(s)

---

Updated: 2026-08-05 21:36:56 UTC | Commit: e66bb87 | missing-docs job results

[github-actions]

🔒 Cargo Deny Results

⚠️ 3 issue(s) found, showing only errors (advisories, bans, sources)

📦 libdd-data-pipeline-ffi - 3 error(s)

Show output

error[vulnerability]: Invalid pointer dereference in `fmt::Pointer` impl for `Atomic` and `Shared` when the underlying pointer is invalid
   ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:78:1
   │
78 │ crossbeam-epoch 0.9.18 registry+https://github.com/rust-lang/crates.io-index
   │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ security vulnerability detected
   │
   ├ ID: RUSTSEC-2026-0204
   ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0204
   ├ Affected versions of `fmt::Display` dereference the underlying pointer. This causes a invalid pointer dereference e.g., when a pointer created with `Atomic::null` or `Shared::null`. `fmt::Debug` impls and pre-0.9 `fmt::Display` impls, which do not dereference pointers, are not affected by this issue.
   ├ Announcement: https://github.com/crossbeam-rs/crossbeam/pull/1276
   ├ Solution: Upgrade to >=0.9.20 (try `cargo update -p crossbeam-epoch`)
   ├ crossbeam-epoch v0.9.18
     └── crossbeam-deque v0.8.5
         └── rayon-core v1.12.1
             └── rayon v1.10.0
                 └── criterion v0.5.1
                     ├── libdd-common v5.1.0
                     │   ├── libdd-capabilities-impl v3.0.0
                     │   │   ├── libdd-data-pipeline v7.0.0
                     │   │   │   └── libdd-data-pipeline-ffi v38.0.0
                     │   │   ├── libdd-data-pipeline-ffi v38.0.0 (*)
                     │   │   ├── libdd-shared-runtime v2.0.0
                     │   │   │   ├── libdd-data-pipeline v7.0.0 (*)
                     │   │   │   ├── libdd-data-pipeline-ffi v38.0.0 (*)
                     │   │   │   ├── libdd-dogstatsd-client v4.0.0
                     │   │   │   │   ├── libdd-data-pipeline v7.0.0 (*)
                     │   │   │   │   └── libdd-trace-stats v6.0.0
                     │   │   │   │       └── libdd-data-pipeline v7.0.0 (*)
                     │   │   │   ├── libdd-telemetry v6.0.0
                     │   │   │   │   ├── libdd-data-pipeline v7.0.0 (*)
                     │   │   │   │   └── libdd-trace-stats v6.0.0 (*)
                     │   │   │   └── libdd-trace-stats v6.0.0 (*)
                     │   │   ├── (dev) libdd-telemetry v6.0.0 (*)
                     │   │   ├── libdd-trace-stats v6.0.0 (*)
                     │   │   └── libdd-trace-utils v9.0.0
                     │   │       ├── libdd-data-pipeline v7.0.0 (*)
                     │   │       ├── (dev) libdd-data-pipeline-ffi v38.0.0 (*)
                     │   │       ├── libdd-trace-obfuscation v5.0.0
                     │   │       │   └── libdd-trace-stats v6.0.0 (*)
                     │   │       ├── libdd-trace-stats v6.0.0 (*)
                     │   │       └── (dev) libdd-trace-utils v9.0.0 (*)
                     │   ├── libdd-common-ffi v38.0.0
                     │   │   └── libdd-data-pipeline-ffi v38.0.0 (*)
                     │   ├── libdd-data-pipeline v7.0.0 (*)
                     │   ├── libdd-dogstatsd-client v4.0.0 (*)
                     │   ├── libdd-shared-runtime v2.0.0 (*)
                     │   ├── libdd-telemetry v6.0.0 (*)
                     │   ├── libdd-trace-obfuscation v5.0.0 (*)
                     │   ├── libdd-trace-stats v6.0.0 (*)
                     │   └── libdd-trace-utils v9.0.0 (*)
                     ├── (dev) libdd-data-pipeline v7.0.0 (*)
                     ├── (dev) libdd-ddsketch v1.1.0
                     │   ├── libdd-data-pipeline v7.0.0 (*)
                     │   ├── libdd-telemetry v6.0.0 (*)
                     │   └── libdd-trace-stats v6.0.0 (*)
                     ├── (dev) libdd-trace-normalization v3.0.0
                     │   ├── libdd-data-pipeline v7.0.0 (*)
                     │   └── libdd-trace-utils v9.0.0 (*)
                     ├── (dev) libdd-trace-obfuscation v5.0.0 (*)
                     ├── (dev) libdd-trace-stats v6.0.0 (*)
                     └── (dev) libdd-trace-utils v9.0.0 (*)

error[unsound]: Rand is unsound with a custom logger using `rand::rng()`
    ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:228:1
    │
228 │ rand 0.8.5 registry+https://github.com/rust-lang/crates.io-index
    │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ unsound advisory detected
    │
    ├ ID: RUSTSEC-2026-0097
    ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0097
    ├ It has been reported (by [@lopopolo](https://github.com/lopopolo)) that the `rand` library is [unsound](https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#soundness-of-code--of-a-library) (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:
      
      - The `log` and `thread_rng` features are enabled
      - A [custom logger](https://docs.rs/log/latest/log/#implementing-a-logger) is defined
      - The custom logger accesses `rand::rng()` (previously `rand::thread_rng()`) and calls any `TryRng` (previously `RngCore`) methods on `ThreadRng`
      - The `ThreadRng` (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
      - Trace-level logging is enabled or warn-level logging is enabled and the random source (the `getrandom` crate) is unable to provide a new seed
      
      `TryRng` (previously `RngCore`) methods for `ThreadRng` use `unsafe` code to cast `*mut BlockRng<ReseedingCore>` to `&mut BlockRng<ReseedingCore>`. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of [aliased mutable references is Undefined Behaviour](https://doc.rust-lang.org/stable/nomicon/references.html), the behaviour of optimized builds is hard to predict.
    ├ Announcement: https://github.com/rust-random/rand/pull/1763
    ├ Solution: Upgrade to >=0.10.1 OR <0.10.0, >=0.9.3 OR <0.9.0, >=0.8.6 (try `cargo update -p rand`)
    ├ rand v0.8.5
      ├── libdd-common v5.1.0
      │   ├── libdd-capabilities-impl v3.0.0
      │   │   ├── libdd-data-pipeline v7.0.0
      │   │   │   └── libdd-data-pipeline-ffi v38.0.0
      │   │   ├── libdd-data-pipeline-ffi v38.0.0 (*)
      │   │   ├── libdd-shared-runtime v2.0.0
      │   │   │   ├── libdd-data-pipeline v7.0.0 (*)
      │   │   │   ├── libdd-data-pipeline-ffi v38.0.0 (*)
      │   │   │   ├── libdd-dogstatsd-client v4.0.0
      │   │   │   │   ├── libdd-data-pipeline v7.0.0 (*)
      │   │   │   │   └── libdd-trace-stats v6.0.0
      │   │   │   │       └── libdd-data-pipeline v7.0.0 (*)
      │   │   │   ├── libdd-telemetry v6.0.0
      │   │   │   │   ├── libdd-data-pipeline v7.0.0 (*)
      │   │   │   │   └── libdd-trace-stats v6.0.0 (*)
      │   │   │   └── libdd-trace-stats v6.0.0 (*)
      │   │   ├── (dev) libdd-telemetry v6.0.0 (*)
      │   │   ├── libdd-trace-stats v6.0.0 (*)
      │   │   └── libdd-trace-utils v9.0.0
      │   │       ├── libdd-data-pipeline v7.0.0 (*)
      │   │       ├── (dev) libdd-data-pipeline-ffi v38.0.0 (*)
      │   │       ├── libdd-trace-obfuscation v5.0.0
      │   │       │   └── libdd-trace-stats v6.0.0 (*)
      │   │       ├── libdd-trace-stats v6.0.0 (*)
      │   │       └── (dev) libdd-trace-utils v9.0.0 (*)
      │   ├── libdd-common-ffi v38.0.0
      │   │   └── libdd-data-pipeline-ffi v38.0.0 (*)
      │   ├── libdd-data-pipeline v7.0.0 (*)
      │   ├── libdd-dogstatsd-client v4.0.0 (*)
      │   ├── libdd-shared-runtime v2.0.0 (*)
      │   ├── libdd-telemetry v6.0.0 (*)
      │   ├── libdd-trace-obfuscation v5.0.0 (*)
      │   ├── libdd-trace-stats v6.0.0 (*)
      │   └── libdd-trace-utils v9.0.0 (*)
      ├── (dev) libdd-data-pipeline v7.0.0 (*)
      ├── (dev) libdd-ddsketch v1.1.0
      │   ├── libdd-data-pipeline v7.0.0 (*)
      │   ├── libdd-telemetry v6.0.0 (*)
      │   └── libdd-trace-stats v6.0.0 (*)
      ├── (dev) libdd-trace-normalization v3.0.0
      │   ├── libdd-data-pipeline v7.0.0 (*)
      │   └── libdd-trace-utils v9.0.0 (*)
      ├── (dev) libdd-trace-stats v6.0.0 (*)
      ├── libdd-trace-utils v9.0.0 (*)
      └── proptest v1.5.0
          └── (dev) libdd-tinybytes v1.1.1
              ├── libdd-data-pipeline v7.0.0 (*)
              ├── libdd-data-pipeline-ffi v38.0.0 (*)
              ├── (dev) libdd-tinybytes v1.1.1 (*)
              └── libdd-trace-utils v9.0.0 (*)

error[vulnerability]: Denial of Service via Stack Exhaustion
    ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:298:1
    │
298 │ time 0.3.41 registry+https://github.com/rust-lang/crates.io-index
    │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ security vulnerability detected
    │
    ├ ID: RUSTSEC-2026-0009
    ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0009
    ├ ## Impact
      
      When user-provided input is provided to any type that parses with the RFC 2822 format, a denial of
      service attack via stack exhaustion is possible. The attack relies on formally deprecated and
      rarely-used features that are part of the RFC 2822 format used in a malicious manner. Ordinary,
      non-malicious input will never encounter this scenario.
      
      ## Patches
      
      A limit to the depth of recursion was added in v0.3.47. From this version, an error will be returned
      rather than exhausting the stack.
      
      ## Workarounds
      
      Limiting the length of user input is the simplest way to avoid stack exhaustion, as the amount of
      the stack consumed would be at most a factor of the length of the input.
    ├ Announcement: https://github.com/time-rs/time/blob/main/CHANGELOG.md#0347-2026-02-05
    ├ Solution: Upgrade to >=0.3.47 (try `cargo update -p time`)
    ├ time v0.3.41
      └── tracing-appender v0.2.3
          └── libdd-log v1.0.0
              └── (dev) libdd-data-pipeline v7.0.0
                  └── libdd-data-pipeline-ffi v38.0.0

advisories FAILED, bans ok, sources ok

---

Updated: 2026-08-05 21:36:56 UTC | Commit: e66bb87 | dependency-check job results

[pr-commenter]

Benchmarks

Comparison

Benchmark execution time: 2026-08-05 22:10:08

Comparing candidate commit b3952ec in PR branch lloeki/native-meta-struct-m2 with baseline commit 9ac89b9 in branch main.

Found 2 performance improvements and 4 performance regressions! Performance is the same for 162 metrics, 10 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:alloc_free/system/4096

• 🟥 execution_time [+3.713ns; +3.818ns] or [+4.650%; +4.781%]

scenario:no_profiler/short_circuit/4096

• 🟩 execution_time [-4.519ns; -4.373ns] or [-4.632%; -4.483%]

scenario:profiler_attached/fast_path_system/4096

• 🟥 execution_time [+4.297ns; +4.445ns] or [+4.265%; +4.412%]

scenario:profiler_attached/slow_path_system/4096

• 🟩 execution_time [-11.953ns; -11.817ns] or [-7.654%; -7.567%]

scenario:trace_buffer/4_senders/no_delay

• 🟥 execution_time [+194.135µs; +216.856µs] or [+8.448%; +9.437%]
• 🟥 throughput [-137694.830op/s; -122365.277op/s] or [-8.780%; -7.803%]

Candidate

Omitted due to size.

Baseline

Omitted due to size.

[datadog-official]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 94.60%
• Overall Coverage: 75.21% (+0.07%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: a6fe6f2 | Docs | Datadog PR Page | Give us feedback!}

[dd-octo-sts]

Artifact Size Benchmark Report

aarch64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.so	8.14 MB	8.14 MB	+0% (+72 B) 👌
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.a	88.19 MB	88.23 MB	+.04% (+41.20 KB) 🔍

aarch64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.so	10.96 MB	10.96 MB	+.02% (+2.39 KB) 🔍
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.a	99.33 MB	99.38 MB	+.04% (+45.84 KB) 🔍

libdatadog-x64-windows

Artifact	Baseline	Commit	Change
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.dll	26.32 MB	26.34 MB	+.07% (+19.50 KB) 🔍
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.lib	93.42 KB	94.26 KB	+.89% (+860 B) 🔍
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.pdb	189.36 MB	189.51 MB	+.07% (+152.00 KB) 🔍
/libdatadog-x64-windows/debug/static/datadog_profiling_ffi.lib	986.64 MB	987.16 MB	+.05% (+529.04 KB) 🔍
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.dll	8.61 MB	8.61 MB	+.06% (+5.50 KB) 🔍
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.lib	93.42 KB	94.26 KB	+.89% (+860 B) 🔍
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.pdb	25.31 MB	25.33 MB	+.06% (+16.00 KB) 🔍
/libdatadog-x64-windows/release/static/datadog_profiling_ffi.lib	50.42 MB	50.45 MB	+.06% (+32.35 KB) 🔍

libdatadog-x86-windows

Artifact	Baseline	Commit	Change
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.dll	22.94 MB	22.96 MB	+.06% (+16.00 KB) 🔍
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.lib	94.89 KB	95.74 KB	+.89% (+872 B) 🔍
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.pdb	194.18 MB	194.31 MB	+.06% (+136.00 KB) 🔍
/libdatadog-x86-windows/debug/static/datadog_profiling_ffi.lib	976.07 MB	975.46 MB	--.06% (-622.43 KB) 💪
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.dll	6.65 MB	6.65 MB	+.06% (+4.50 KB) 🔍
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.lib	94.89 KB	95.74 KB	+.89% (+872 B) 🔍
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.pdb	27.22 MB	27.23 MB	+.05% (+16.00 KB) 🔍
/libdatadog-x86-windows/release/static/datadog_profiling_ffi.lib	48.01 MB	48.04 MB	+.06% (+30.51 KB) 🔍

x86_64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.a	78.55 MB	78.58 MB	+.04% (+38.71 KB) 🔍
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.so	9.04 MB	9.04 MB	+.08% (+8.09 KB) 🔍

x86_64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.a	94.18 MB	94.22 MB	+.04% (+43.12 KB) 🔍
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.so	11.02 MB	11.02 MB	+.05% (+5.66 KB) 🔍

[lloeki]

Draft dd-trace-rb example consumer: DataDog/dd-trace-rb#6132.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Validate blob slices before copying

When C callers pass a malformed ddog_ByteSlice for value (for example a null pointer with a nonzero length), value.as_bytes() panics via Slice::as_slice().expect(...) instead of returning an ExporterError. In builds where this crate is aggregated without its catch_panic feature, that aborts the host at this FFI entry point; even with containment enabled it reports Panic rather than a validation error, unlike the new structured encoder's try_as_bytes() path. Please use try_as_bytes() here and return an input error before inserting.

AGENTS.md reference: AGENTS.md:L72-L76

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[ekump]

These values need to be kept in sync here and in cbindgen.toml. Any reason why we can't use a #[repr(u8)] pub enum similar to what we do for ExporterErrorCode? I wanted to ask first since that would change the public API.

CC @hoolioh