Second draft: configmiddleware and extensionlimiter

config/configmiddleware/Makefile

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+include ../../Makefile.Common

config/configmiddleware/README.md

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+# Middleware configuration
+
+**Status: development**
+
+This module defines necessary interfaces to configure middleware
+extensions for use in components. Multiple kinds of middleware may be
+defined, however middlewares are configured through a single list, and
+middleware components are invoked in order. Specific kinds of
+middleware are be configured as specific extension types, and more
+than one extension type is supported:
+
+- `Limiter`: a weighted protocol-agnostic form of middleware, meant
+  for use in receivers.  To implement a limiter extension, components
+  should implement the interface in
+  [`extension/extensionlimiter`](#../../extension/extensionlimiter/README.md).
+- `Interceptor`: a protocol-specific form of middleware, may be client
+  or server, stream or unary. To implement an interceptor extension,
+  components should implement the interface in
+  [`extension/extensioninterceptor`](#../../extension/extensioninterceptor/README.md).
+
+Middleware is included in the basic HTTP and gRPC Server Config
+structs, making it so that exporters and receivers in push-based
+protocols automatically through `confighttp` and `configgrpc`.
+
+The currently known extensions are listed below.
+
+## Limiter implementations
+
+- [Memory Limiter Extension](../../extension/memorylimiterextension/README.md)
+- [Admission Limiter Extension](../../extension/admissionlimiterextension/README.md)
+
+Example:
+
+```yaml
+extensions:
+  # Used with gRPC traffic, consults GC statistics.
+  memory_limiter/cold
+    request_limit_mib: 100
+	waiting_limit_mib: 10
+
+  # Used with HTTP traffic, counts request bytes in flight.
+  admission_limiter/warm:
+    request_limit_mib: 10
+    waiting_limit_mib: 10
+
+receivers:
+  otlp:
+    protocols:
+	  http:
+	    # ...
+	    middleware:
+		- limiter: admission_limiter/warm
+      grpc:
+	    # ...
+        middleware:
+        - limiter: memory_limiter/cold
+```

config/configmiddleware/configmiddleware.go

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+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package configauth implements the configuration settings to
+// ensure authentication on incoming requests, and allows
+// exporters to add authentication on outgoing requests.
+package configmiddleware // import "go.opentelemetry.io/collector/config/configmiddleware"
+
+import (
+	"context"
+	"fmt"
+
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/extension/extensionlimiter"
+)
+
+var (
+	errExactlyOneID       = fmt.Errorf("middleware must configure a single one component")
+	errNotALimiter        = fmt.Errorf("middleware must configure a single one component")
+	errMiddlewareNotFound = fmt.Errorf("middleware not found")
+
+	emptyID = component.ID{}
+)
+
+// Middleware defines the a middleware component.  Middleware can be more than
+// one type of extension.  Each extension uses a single field, and exactly one
+// field should be set.
+//
+// The typical way Middleware configuration is used will be in a list contained
+// within another configuration object.  For example, the `configgrpc.ServerConfig`
+// inside the OTLP receiver lists middleware:
+//
+//	otlp:
+//	  protocols:
+//	    grpc:
+//	      middleware:
+//	      - interceptor: blocker
+//	      - limiter: admission
+//	      - interceptor: decorator
+type Middleware struct {
+	// LimiterID specifies the name of a limiter extension to be used.
+	LimiterID component.ID `mapstructure:"limiter,omitempty"`
+
+	// InterceptorID specifies the name of an interceptor extension to be used.
+	InterceptorID component.ID `mapstructure:"interceptor,omitempty"`
+}
+
+// Validate ensures that exactly one IDis set.
+func (m Middleware) Validate() error {
+	hasLim := m.LimiterID.String() != ""
+	hasInt := m.InterceptorID.String() != ""
+	if hasLim == hasInt {
+		return errExactlyOneID
+	}
+	return nil
+}
+
+// GetLimiter requests to locate a named limiter extension.
+func (m Middleware) GetLimiter(_ context.Context, extensions map[component.ID]component.Component) (extensionlimiter.Limiter, error) {
+	if m.LimiterID == emptyID {
+		return nil, errNotALimiter
+	}
+	if ext, found := extensions[m.LimiterID]; found {
+		if ext, ok := ext.(extensionlimiter.Limiter); ok {
+			return ext, nil
+		}
+		return nil, errNotALimiter
+	}
+	return nil, fmt.Errorf("failed to resolve limiter %q: %w", m.LimiterID, errMiddlewareNotFound)
+}

config/configmiddleware/go.mod

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+module go.opentelemetry.io/collector/config/configmiddleware
+
+go 1.23.0
+
+require (
+	go.opentelemetry.io/collector/component v1.27.0
+	go.opentelemetry.io/collector/extension/extensionlimiter v1.27.0
+)
+
+require (
+	github.com/gogo/protobuf v1.3.2 // indirect
+	go.opentelemetry.io/collector/extension v1.27.0 // indirect
+	go.opentelemetry.io/collector/pdata v1.27.0 // indirect
+	go.opentelemetry.io/otel v1.35.0 // indirect
+	go.opentelemetry.io/otel/metric v1.35.0 // indirect
+	go.opentelemetry.io/otel/trace v1.35.0 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
+	go.uber.org/zap v1.27.0 // indirect
+	golang.org/x/net v0.34.0 // indirect
+	golang.org/x/sys v0.30.0 // indirect
+	golang.org/x/text v0.21.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20250115164207-1a7da9e5054f // indirect
+	google.golang.org/grpc v1.71.0 // indirect
+	google.golang.org/protobuf v1.36.5 // indirect
+)
+
+replace go.opentelemetry.io/collector/pdata => ../../pdata
+
+replace go.opentelemetry.io/collector/component => ../../component
+
+replace go.opentelemetry.io/collector/component/componenttest => ../../component/componenttest
+
+replace go.opentelemetry.io/collector/extension => ../../extension
+
+replace go.opentelemetry.io/collector/extension/extensionlimiter => ../../extension/extensionlimiter

extension/extensionlimiter/README.md

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+# Limiter extension
+
+The limiter extension interface supports components that limit
+requests by several measures of weight.  Extension components are able
+to limit entry to pipeline by the number of requests, the
+(signal-specific) number of items, and/or the number of bytes of
+network and memory consumed as they transit the pipeline.
+
+The limiter interface supports a single method, `Acquire(ctx,
+settings, weight)` accepting context, settings, and weight
+parameters. 
+
+## Limiter context
+
+The context passed to a Limiter is the one created following the Auth
+extension, and it includes the `client.Metadata` of the
+request. 
+
+## Limiter settings
+
+Secondary information, including the signal kind of the request, is
+included in the settings.  Other information may be included in this
+struct in the future, for example the ID of the calling component.
+
+## Limiter weight
+
+The `Weight` struct includes three fields for three different ways to
+limit requests, including by request count, by item count, and by
+bytes.
+
+The weight `Bytes` field is particularly important for memory-based
+limiters. For measuring bytes, components are encouraged to be
+approximate. The goal is to estimate the amount of actual memory that
+will be used by pipeline data as the request is in transit, so
+components may use the uncompressed size of the data as a proxy for
+the amount of memory that will be used. The corresponding pipeline
+data `Sizer` class may be used.
+
+In cases where components allocate memory in multiple steps, they can
+make multiple calls to Acquire to report additional bytes used.

extension/extensionlimiter/go.mod

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+module go.opentelemetry.io/collector/extension/extensionlimiter
+
+go 1.23.0
+
+require (
+	go.opentelemetry.io/collector/component v1.27.0
+	go.opentelemetry.io/collector/extension v1.27.0
+)
+
+require (
+	github.com/gogo/protobuf v1.3.2 // indirect
+	go.opentelemetry.io/collector/pdata v1.27.0 // indirect
+	go.opentelemetry.io/otel v1.35.0 // indirect
+	go.opentelemetry.io/otel/metric v1.35.0 // indirect
+	go.opentelemetry.io/otel/sdk/metric v1.35.0 // indirect
+	go.opentelemetry.io/otel/trace v1.35.0 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
+	go.uber.org/zap v1.27.0 // indirect
+	golang.org/x/net v0.34.0 // indirect
+	golang.org/x/sys v0.30.0 // indirect
+	golang.org/x/text v0.21.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20250115164207-1a7da9e5054f // indirect
+	google.golang.org/grpc v1.71.0 // indirect
+	google.golang.org/protobuf v1.36.5 // indirect
+)
+
+replace go.opentelemetry.io/collector/component => ../../component
+
+replace go.opentelemetry.io/collector/component/componenttest => ../../component/componenttest
+
+replace go.opentelemetry.io/collector/extension => ../
+
+replace go.opentelemetry.io/collector/pdata => ../../pdata