attribute: add String method for Value type - #8142

…emetry#5028)

### What

Adds in-development guidance for representing a single OpenTelemetry
attribute as a string in non-OTLP protocols.

The recommended form is a single-entry JSON object, for example:

```json
{"http.request.method":"GET"}
```

**Implementation:**
- open-telemetry/opentelemetry-go#8205 in OTel
Go we are using non-OTLP string represnetation for debugging

### Why

- open-telemetry/opentelemetry-go#7810

The narrower purpose is to fill a gap in the existing non-OTLP string
representation guidance. The specification already has stable guidance
for representing `AnyValue` values as strings when a non-OTLP protocol
cannot represent some `AnyValue` types natively. What is missing is the
corresponding representation for a single `Attribute`, which is a key
plus an `AnyValue`. This PR proposes that the single attribute is
represented as a single-member JSON object, with the member value
following the existing non-OTLP `AnyValue` representation rules.

I originally thought about `key:value` (and even `key=value`
beforehand), but it is ambiguous when `:` appears in keys or string
values and is not a robust debugging representation.

Using a JSON object improves clarity for debugging output by:

- aligning with existing non-OTLP, JSON-based guidance for complex
`AnyValue` types
- making the representation easier to read and copy when needed

This also is consistent with how OTel Java, .NET, Python, Go are
representing attributes in standard output exporters. Therefore, I think
it would be most familiar representation for the users.

Why not OTLP/JSON?
For the OTel Go use case, the compact (lossy) non-OTLP representation is
practical for human-readable output such as test failures. `String()` is
intended for debugging and logging, and its output is not expected to be
lossless nor suitable for deserialization. A canonical OTLP JSON
`KeyValue` would need wrapper fields such as
`{"key":"http.request.method","value":{"stringValue":"GET"}}`, which is
much more verbose than `{"http.request.method":"GET"}` and harder to
scan in failure messages.
Moreover, OTel Go `attribute.Value.String()` already follows the
non-OTLP `AnyValue` rules:
<open-telemetry/opentelemetry-go#8142> (as OTel
Go maintainers, we want to use an OTel-wide representation even for
debugging output). We want `attribute.KeyValue.String()` to follow the
same rules, but the string representation of a single attribute is not
yet specified; this PR fills that gap and is currently blocking
<open-telemetry/opentelemetry-go#8205>.

### Added

- Add `ByteSlice` and `ByteSliceValue` functions for new `BYTESLICE`
attribute type in `go.opentelemetry.io/otel/attribute`. (#7948)
- Apply attribute value limit to the `KindBytes` attribute type in
`go.opentelemetry.io/otel/sdk/log`. (#7990)
- Apply attribute value limit to the `BYTESLICE` attribute type in
`go.opentelemetry.io/otel/sdk/trace`. (#7990)
- Support `BYTESLICE` attributes in `go.opentelemetry.io/otel/trace`.
(#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace`. (#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlplog`. (#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric`. (#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/zipkin`. (#8153)
- Add `String` method for `Value` type in
`go.opentelemetry.io/otel/attribute`. (#8142)
- Add `Slice` and `SliceValue` functions for new `SLICE` attribute type
in `go.opentelemetry.io/otel/attribute`. (#8166)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace`. (#8216)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlplog`. (#8216)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric`. (#8216)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/zipkin`. (#8216)
- Apply `AttributeValueLengthLimit` to `attribute.SLICE` type attribute
values in `go.opentelemetry.io/otel/sdk/trace`, recursively truncating
contained string values. (#8217)
- Add `Error` field on `Record` type in
`go.opentelemetry.io/otel/log/logtest`. (#8148)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`. (#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8157)
- Add `Settable` to `go.opentelemetry.io/otel/metric/x` to allow reusing
attribute options. (#8178)
- Add experimental support for splitting metric data across multiple
batches in `go.opentelemetry.io/otel/sdk/metric`.
Set `OTEL_GO_X_METRIC_EXPORT_BATCH_SIZE=<max_size>` to enable for all
periodic readers.
See `go.opentelemetry.io/otel/sdk/metric/internal/x` for feature
documentation. (#8071)
- Add experimental self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`.
  Enable with `OTEL_GO_X_SELF_OBSERVABILITY=true` environment variable.
See
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc/internal/x`
for feature documentation. (#8192)
- Add experimental self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
  Enable with `OTEL_GO_X_SELF_OBSERVABILITY=true` environment variable.
See
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp/internal/x`
for feature documentation. (#8194)
- Add experimental self-observability metrics in
`go.opentelemetry.io/otel/exporters/stdout/stdoutlog`.
  Enable with `OTEL_GO_X_SELF_OBSERVABILITY=true` environment variable.
See `go.opentelemetry.io/otel/stdout/stdoutlog/internal/x` for feature
documentation. (#8263)
- Add `WithDefaultAttributes` to `go.opentelemetry.io/otel/metric/x` to
support setting default attributes on instruments. (#8135)
- Add `go.opentelemetry.io/otel/semconv/v1.41.0` package.
The package contains semantic conventions from the `v1.41.0` version of
the OpenTelemetry Semantic Conventions.
See the [migration documentation](./semconv/v1.41.0/MIGRATION.md) for
information on how to upgrade from
`go.opentelemetry.io/otel/semconv/v1.40.0`. (#8324)
- Add Observable variants of instruments to
`go.opentelemetry.io/otel/semconv/v1.41.0` package. (#8350)
- Generate explicit histogram bucket boundaries from weaver
configuration for HTTP and RPC duration instruments in
`go.opentelemetry.io/otel/semconv/v1.41.0`. (#8002)

### Changed

- ⚠️ **Breaking Change:** `go.opentelemetry.io/otel/sdk/metric` now
applies a default cardinality limit of 2000 to comply with the Metrics
SDK specification recommendation.
New attribute sets are dropped when the cardinality limit is reached.
The measurement of these sets are aggregated into a special attribute
set containing `attribute.Bool("otel.metric.overflow", true)`.
  This can break users who relied on the previous unlimited default.
Set `WithCardinalityLimit(0)` or the deprecated
`OTEL_GO_X_CARDINALITY_LIMIT=0` environment variable to preserve
unlimited cardinality.
Note that support for `OTEL_GO_X_CARDINALITY_LIMIT` may be removed in a
future release. (#8247)
- `ErrorType` in `go.opentelemetry.io/otel/semconv` now unwraps errors
created with `fmt.Errorf` when deriving the `error.type` attribute.
(#8133)
- `go.opentelemetry.io/otel/sdk/log` now unwraps error chains created
with `fmt.Errorf` when deriving the `error.type` attribute from errors
on log records. (#8133)
- `Set.MarshalLog` method in `go.opentelemetry.io/otel/attribute` now
uses `Value.String` formatting following the [OpenTelemetry AnyValue
representation for non-OTLP
protocols](https://opentelemetry.io/docs/specs/otel/common/#anyvalue).
(#8169)
- Optimize `go.opentelemetry.io/otel/sdk/metric` to return a drop
reservoir and short-circuit `Offer` calls to the exemplar reservoir when
`exemplar.AlwaysOffFilter` is configured. (#8211) (#8267)
- Optimize `go.opentelemetry.io/otel/sdk/metric` to return a drop
reservoir for asynchronous instruments when `exemplar.TraceBasedFilter`
is configured. (#8286)

### Deprecated

- Deprecate `Value.Emit` method in `go.opentelemetry.io/otel/attribute`.
  Use `Value.String` instead. (#8176)

### Fixed

- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Fix gzipped request body replay on redirect in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
(#8135)
- Fix gzipped request body replay on redirect in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8152)
- `go.opentelemetry.io/otel/exporters/prometheus` now uses
`Value.String` formatting for label values following the [OpenTelemetry
AnyValue representation for non-OTLP
protocols](https://opentelemetry.io/docs/specs/otel/common/#anyvalue).
(#8170)
- Propagate errors from the exporter when calling `Shutdown` on
`BatchSpanProcessor` in `go.opentelemetry.io/otel/sdk/trace`. (#8197)
- Fix stale status code reporting on self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp` and
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8226)
- Fix a concurrent `Collect` data race and potential panic in
`go.opentelemetry.io/otel/exporters/prometheus` when
`WithResourceAsConstantLabels` option is used. (#8227)
- Fix race condition in `FixedSizeReservoir` in
`go.opentelemetry.io/otel/sdk/metric/exemplar` by reverting #7447.
(#8249)
- Fix `FixedSizeReservoir` in
`go.opentelemetry.io/otel/sdk/metric/exemplar` to safely handle zero
size.
A capacity check in the constructor initializes the reservoir safely and
skips initialization for zero-cap; early returns in `Offer()` and
`Collect()` ensure no-op behavior. (#8295)
- Fix counting of spans and logs in self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`,
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`,
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`, and
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8254)
- Drop conflicting scope attributes named `name`, `version`, or
`schema_url` from metric labels in
`go.opentelemetry.io/otel/exporters/prometheus`, preserving the
dedicated `otel_scope_name`, `otel_scope_version`, and
`otel_scope_schema_url` labels. (#8264)
- Close schema files opened by `ParseFile` in
`go.opentelemetry.io/otel/schema/v1.0` and
`go.opentelemetry.io/otel/schema/v1.1`.
([GHSA-995v-fvrw-c78m](GHSA-995v-fvrw-c78m))
- Enforce the 8192-byte baggage size limit during extraction/parsing,
changing behavior when the limit is exceeded in
`go.opentelemetry.io/otel/baggage` and
`go.opentelemetry.io/otel/propagation`. (#8222)
- Fix `go.opentelemetry.io/otel/semconv/v1.41.0` to include `Attr*`
helper methods for required attributes on observable instruments.
(#8361)
- Limit baggage extraction error reporting in
`go.opentelemetry.io/otel/propagation` to prevent malformed or oversized
baggage headers from flooding logs.
([GHSA-5wrp-cwcj-q835](GHSA-5wrp-cwcj-q835))

…emetry#5028)

### What

Adds in-development guidance for representing a single OpenTelemetry
attribute as a string in non-OTLP protocols.

The recommended form is a single-entry JSON object, for example:

```json
{"http.request.method":"GET"}
```

**Implementation:**
- open-telemetry/opentelemetry-go#8205 in OTel
Go we are using non-OTLP string represnetation for debugging

### Why

- open-telemetry/opentelemetry-go#7810

The narrower purpose is to fill a gap in the existing non-OTLP string
representation guidance. The specification already has stable guidance
for representing `AnyValue` values as strings when a non-OTLP protocol
cannot represent some `AnyValue` types natively. What is missing is the
corresponding representation for a single `Attribute`, which is a key
plus an `AnyValue`. This PR proposes that the single attribute is
represented as a single-member JSON object, with the member value
following the existing non-OTLP `AnyValue` representation rules.

I originally thought about `key:value` (and even `key=value`
beforehand), but it is ambiguous when `:` appears in keys or string
values and is not a robust debugging representation.

Using a JSON object improves clarity for debugging output by:

- aligning with existing non-OTLP, JSON-based guidance for complex
`AnyValue` types
- making the representation easier to read and copy when needed

This also is consistent with how OTel Java, .NET, Python, Go are
representing attributes in standard output exporters. Therefore, I think
it would be most familiar representation for the users.

Why not OTLP/JSON?
For the OTel Go use case, the compact (lossy) non-OTLP representation is
practical for human-readable output such as test failures. `String()` is
intended for debugging and logging, and its output is not expected to be
lossless nor suitable for deserialization. A canonical OTLP JSON
`KeyValue` would need wrapper fields such as
`{"key":"http.request.method","value":{"stringValue":"GET"}}`, which is
much more verbose than `{"http.request.method":"GET"}` and harder to
scan in failure messages.
Moreover, OTel Go `attribute.Value.String()` already follows the
non-OTLP `AnyValue` rules:
<open-telemetry/opentelemetry-go#8142> (as OTel
Go maintainers, we want to use an OTel-wide representation even for
debugging output). We want `attribute.KeyValue.String()` to follow the
same rules, but the string representation of a single attribute is not
yet specified; this PR fills that gap and is currently blocking
<open-telemetry/opentelemetry-go#8205>.

…l 1.44

otel 1.44.0 deprecates attribute.Value.Emit in favor of Value.String
(open-telemetry/opentelemetry-go#8142). The JSONL exporter flattened span
and event attributes via Emit at jsonl_exporter.go:114,127, which trips the
staticcheck deprecation lint once otel is bumped to 1.44.

String is the otel-sanctioned drop-in replacement; for STRING-typed
attributes (the common case here) the output is byte-identical, and numeric
and slice types adopt the new canonical formatting.

Bumps otel, otel/sdk, otel/trace (and transitive otel/metric) to 1.44.0 in
the same change because Value.String does not exist in 1.43 — the code and
the bump must land together. This unblocks the otel 1.44 dependency bumps
(#170, #173, #175).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

…l 1.44

otel 1.44.0 deprecates attribute.Value.Emit in favor of Value.String
(open-telemetry/opentelemetry-go#8142). The JSONL exporter flattened span
and event attributes via Emit at jsonl_exporter.go:114,127, which trips the
staticcheck deprecation lint once otel is bumped to 1.44.

String is the otel-sanctioned drop-in replacement; for STRING-typed
attributes (the common case here) the output is byte-identical, and numeric
and slice types adopt the new canonical formatting.

Bumps otel, otel/sdk, otel/trace (and transitive otel/metric) to 1.44.0 in
the same change because Value.String does not exist in 1.43 — the code and
the bump must land together. This unblocks the otel 1.44 dependency bumps
(#170, #173, #175).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

…l 1.44 (#184)

otel 1.44.0 deprecates attribute.Value.Emit in favor of Value.String
(open-telemetry/opentelemetry-go#8142). The JSONL exporter flattened span
and event attributes via Emit at jsonl_exporter.go:114,127, which trips the
staticcheck deprecation lint once otel is bumped to 1.44.

String is the otel-sanctioned drop-in replacement; for STRING-typed
attributes (the common case here) the output is byte-identical, and numeric
and slice types adopt the new canonical formatting.

Bumps otel, otel/sdk, otel/trace (and transitive otel/metric) to 1.44.0 in
the same change because Value.String does not exist in 1.43 — the code and
the bump must land together. This unblocks the otel 1.44 dependency bumps
(#170, #173, #175).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>