[connector/signaltometrics] Add boilerplate for the connector (open-telemetry#36454)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

Adds boilerplate code for a new signal to metrics connector.

<!-- Issue number (e.g. open-telemetry#1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Part of
open-telemetry#35930

<!--Describe what testing was performed and which tests were added.-->
#### Testing

Unit tests provided as required.

<!--Describe the documentation added.-->
#### Documentation

Added basic README. Will add more details with future commits.
<!--Please delete paragraphs that you did not use before submitting.-->


CC: @ChrsMark

---------

Co-authored-by: Christos Markou <[email protected]>

Author: 2 people

.chloggen/add-signaltometrics-connector.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: new_component
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: signaltometricsconnector
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: New component for generating metrics from raw signals using user defined OTTL expressions.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35930]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

.github/CODEOWNERS

@@ -34,6 +34,7 @@ connector/otlpjsonconnector/                      @open-telemetry/collector-cont
 connector/roundrobinconnector/                    @open-telemetry/collector-contrib-approvers @bogdandrutu
 connector/routingconnector/                       @open-telemetry/collector-contrib-approvers @jpkrohling @mwear
 connector/servicegraphconnector/                  @open-telemetry/collector-contrib-approvers @jpkrohling @mapno @JaredTan95
+connector/signaltometricsconnector/               @open-telemetry/collector-contrib-approvers @ChrsMark @lahsivjar
 connector/spanmetricsconnector/                   @open-telemetry/collector-contrib-approvers @portertech @Frapschen
 connector/sumconnector/                           @open-telemetry/collector-contrib-approvers @greatestusername @shalper2 @crobert-1
 

.github/ISSUE_TEMPLATE/bug_report.yaml

@@ -35,6 +35,7 @@ body:
       - connector/roundrobin
       - connector/routing
       - connector/servicegraph
+      - connector/signaltometrics
       - connector/spanmetrics
       - connector/sum
       - examples/demo

.github/ISSUE_TEMPLATE/feature_request.yaml

@@ -29,6 +29,7 @@ body:
       - connector/roundrobin
       - connector/routing
       - connector/servicegraph
+      - connector/signaltometrics
       - connector/spanmetrics
       - connector/sum
       - examples/demo

.github/ISSUE_TEMPLATE/other.yaml

@@ -29,6 +29,7 @@ body:
       - connector/roundrobin
       - connector/routing
       - connector/servicegraph
+      - connector/signaltometrics
       - connector/spanmetrics
       - connector/sum
       - examples/demo

.github/ISSUE_TEMPLATE/unmaintained.yaml

@@ -34,6 +34,7 @@ body:
       - connector/roundrobin
       - connector/routing
       - connector/servicegraph
+      - connector/signaltometrics
       - connector/spanmetrics
       - connector/sum
       - examples/demo

connector/signaltometricsconnector/Makefile

@@ -0,0 +1 @@
+include ../../Makefile.Common

connector/signaltometricsconnector/README.md

@@ -0,0 +1,227 @@
+# Signal to metrics connector
+
+Signal to metrics connector produces metrics from all signal types (traces,
+logs, or metrics).
+
+<!-- status autogenerated section -->
+| Status        |           |
+| ------------- |-----------|
+| Distributions | [] |
+| Issues        | [![Open issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector-contrib?query=is%3Aissue%20is%3Aopen%20label%3Aconnector%2Fsignaltometrics%20&label=open&color=orange&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues?q=is%3Aopen+is%3Aissue+label%3Aconnector%2Fsignaltometrics) [![Closed issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector-contrib?query=is%3Aissue%20is%3Aclosed%20label%3Aconnector%2Fsignaltometrics%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues?q=is%3Aclosed+is%3Aissue+label%3Aconnector%2Fsignaltometrics) |
+| [Code Owners](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CONTRIBUTING.md#becoming-a-code-owner)    | [@ChrsMark](https://www.github.com/ChrsMark), [@lahsivjar](https://www.github.com/lahsivjar) |
+
+[development]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#development
+
+## Supported Pipeline Types
+
+| [Exporter Pipeline Type] | [Receiver Pipeline Type] | [Stability Level] |
+| ------------------------ | ------------------------ | ----------------- |
+| traces | metrics | [development] |
+| logs | metrics | [development] |
+| metrics | metrics | [development] |
+
+[Exporter Pipeline Type]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/connector/README.md#exporter-pipeline-type
+[Receiver Pipeline Type]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/connector/README.md#receiver-pipeline-type
+[Stability Level]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#stability-levels
+<!-- end autogenerated section -->
+
+## Configuration
+
+The component can produce metrics from spans, datapoints (for metrics), and logs.
+At least one of the metrics for one signal type MUST be specified correctly for
+the component to work.
+
+All signal types can be configured to produce metrics with the same configuration
+structure. For example, the below configuration will produce delta temporality counters
+for counting number of events for each of the configured signals:
+
+```yaml
+signaltometrics:
+  spans:
+    - name: span.count
+      description: Count of spans
+      sum:
+        value: Int(AbsoluteCount()) # Count of total spans represented by each span
+  datapoints:
+    - name: datapoint.count
+      description: Count of datapoints
+      sum:
+        value: "1" # increment by 1 for each datapoint
+  logs:
+    - name: logrecord.count
+      description: Count of log records
+      sum:
+        value: "1" # increment by 1 for each log record
+```
+
+### Metrics types
+
+`signaltometrics` produces a variety of metric types by utilizing [OTTL](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/ottl/README.md)
+to extract the relevant data for a metric type from the incoming data. The
+component can produce the following metric types for each signal types:
+
+- [Sum](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#sums)
+- [Histogram](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#histogram)
+- [Exponential Histogram](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponentialhistogram)
+
+The component does NOT perform any stateful or time based aggregations. The metric
+types are aggregated for the payload sent in each `Consume*` call. The final metric
+is then sent forward in the pipeline.
+
+#### Sum
+
+Sum metrics have the following configurations:
+
+```yaml
+sum:
+  value: <ottl_value_expression>
+```
+
+- [**Required**] `value` represents an OTTL expression to extract a value from the
+  incoming data. Only OTTL expressions that return a value are accepted. The
+  returned value determines the value type of the `sum` metric (`int` or `double`).
+  [OTTL converters](https://pkg.go.dev/github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs#readme-converters)
+  can be used to transform the data.
+
+#### Histogram
+
+Histogram metrics have the following configurations:
+
+```yaml
+histogram:
+  buckets: []float64
+  count: <ottl_value_expression>
+  value: <ottl_value_expression>
+```
+
+- [**Optional**] `buckets` represents the buckets to be used for the histogram.
+  If no buckets are configured then it defaults to:
+
+  ```go
+  []float64{2, 4, 6, 8, 10, 50, 100, 200, 400, 800, 1000, 1400, 2000, 5000, 10_000, 15_000}
+  ```
+
+- [**Optional**] `count` represents an OTTL expression to extract the count to be
+  recorded in the histogram from the incoming data. If no expression is provided
+  then it defaults to the count of the signal i.e. [adjusted count](https://opentelemetry.io/docs/specs/otel/trace/tracestate-probability-sampling-experimental/#adjusted-count)
+  for spans and count for others. [OTTL converters](https://pkg.go.dev/github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs#readme-converters)
+  can be used to transform the data.
+- [**Required**] `value` represents an OTTL expression to extract the value to be
+  recorded in the histogram from the incoming data. [OTTL converters](https://pkg.go.dev/github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs#readme-converters)
+  can be used to transform the data.
+
+#### Exponential Histogram
+
+Exponential histogram metrics have the following configurations:
+
+```yaml
+exponential_histogram:
+  max_size: <int64>
+  count: <ottl_value_expression>
+  value: <ottl_value_expression>
+```
+
+- [**Optional**] `max_size` represents the maximum number of buckets per positive
+  or negative number range. Defaults to `160`.
+- [**Optional**] `count` represents an OTTL expression to extract the count to be
+  recorded in the exponential histogram from the incoming data. If no expression
+  is provided then it defaults to the count of the signal i.e. [adjusted count](https://opentelemetry.io/docs/specs/otel/trace/tracestate-probability-sampling-experimental/#adjusted-count)
+  for spans and count for others.
+  [OTTL converters](https://pkg.go.dev/github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs#readme-converters) can be used to transform the data.
+- [**Required**] `value` represents an OTTL expression to extract the value to be recorded
+  in the exponential histogram from the incoming data.
+  [OTTL converters](https://pkg.go.dev/github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs#readme-converters) can be used to transform the data.
+
+### Attributes
+
+The component can produce metrics categorized by the attributes (span attributes
+for traces, datapoint attributes for datapoints, or log record attributes for logs)
+from the incoming data by configuring `attributes` for the configured metrics.
+
+If no `attributes` are configured then the metrics are produced without any attributes.
+
+```yaml
+attributes:
+  - key: datapoint.foo
+  - key: datapoint.bar
+    default_value: bar
+```
+
+If attributes are specified then a separate metric will be generated for each unique
+set of attribute values. Optionally, a `default_value` can be used to always include
+the attribute with the value of the attribute defaulting to the value specified in
+`default_value` if the incoming data is missing that attribute.
+
+### Conditions
+
+Conditions are an optional list of OTTL conditions that are evaluated on the incoming
+data and are ORed together. For example:
+
+```yaml
+signaltometrics:
+  datapoints:
+    - name: datapoint.bar.sum
+      description: Count total number of datapoints as per datapoint.bar attribute
+      conditions:
+        - resource.attributes["foo"] != nil
+        - resource.attributes["bar"] != nil
+      sum:
+        value: "1"
+```
+
+The above configuration will produce sum metrics from datapoints with either `foo`
+OR `bar` resource attribute defined.
+
+Conditions can also be ANDed together, for example:
+
+```yaml
+signaltometrics:
+  datapoints:
+    - name: gauge.to.exphistogram
+      conditions:
+        - metric.type == 1 AND resource.attributes["resource.foo"] != nil
+      exponential_histogram:
+        count: "1" # 1 count for each datapoint
+        value: Double(value_int) + value_double # handle both int and double
+```
+
+The above configuration produces exponential histogram from gauge metrics with resource
+attributes `resource.foo` set.
+
+### Customizing resource attributes
+
+The component allows customizing the resource attributes for the produced metrics
+by specifying a list of attributes that should be included in the final metrics.
+If no attributes are specified for `include_resource_attributes` then no filtering
+is performed i.e. all resource attributes of the incoming data is considered.
+
+```yaml
+include_resource_attributes:
+  - key: resource.foo # Include resource.foo attribute if present
+  - key: resource.bar # Always include resource.bar attribute, default to bar
+    default_value: bar
+```
+
+With the above configuration the produced metrics would only have the couple of
+resource attributes specified in the list:
+
+- `resource.foo` will be present for the produced metrics if the incoming data also
+  has the attribute defined.
+- `resource.bar` will always be present because of the `default_value`. If the incoming
+  data does not have a resource attribute with name `resource.bar` then the configured
+  `default_value` of `bar` will be used.
+
+### Single writer
+
+Metrics data streams MUST obey [single-writer](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#single-writer)
+principle. However, since `signaltometrics` component produces metrics from all signal
+types and also allows customizing the resource attributes, there is a possibility
+of violating the single-writer principle. To keep the single-writer principle intact,
+the component adds collector instance information as resource attributes. The following
+resource attributes are added to each produced metrics:
+
+```yaml
+signaltometrics.service.name: <service_name_of_the_otel_collector>
+signaltometrics.service.namespace: <service_namespace_of_the_otel_collector>
+signaltometrics.service.instance.id: <service_instance_id_of_the_otel_collector>
+```

connector/signaltometricsconnector/config/config.go

@@ -0,0 +1,62 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package config // import "github.com/open-telemetry/opentelemetry-collector-contrib/connector/signaltometricsconnector/config"
+
+import "fmt"
+
+// Config for the connector. Each configuration field describes the metrics
+// to produce from a specific signal.
+type Config struct {
+	Spans      []MetricInfo `mapstructure:"spans"`
+	Datapoints []MetricInfo `mapstructure:"datapoints"`
+	Logs       []MetricInfo `mapstructure:"logs"`
+}
+
+func (c *Config) Validate() error {
+	if len(c.Spans) == 0 && len(c.Datapoints) == 0 && len(c.Logs) == 0 {
+		return fmt.Errorf("no configuration provided, at least one should be specified")
+	}
+	return nil
+}
+
+// MetricInfo defines the structure of the metric produced by the connector.
+type MetricInfo struct {
+	Name        string `mapstructure:"name"`
+	Description string `mapstructure:"description"`
+	// Unit, if not-empty, will set the unit associated with the metric.
+	// See: https://github.com/open-telemetry/opentelemetry-collector/blob/b06236cc794982916cc956f20828b3e18eb33264/pdata/pmetric/generated_metric.go#L72-L81
+	Unit string `mapstructure:"unit"`
+	// IncludeResourceAttributes is a list of resource attributes that
+	// needs to be included in the generated metric. If no resource
+	// attribute is included in the list then all attributes are included.
+	IncludeResourceAttributes []Attribute `mapstructure:"include_resource_attributes"`
+	Attributes                []Attribute `mapstructure:"attributes"`
+	// Conditions are a set of OTTL condtions which are ORed. Data is
+	// processed into metrics only if the sequence evaluates to true.
+	Conditions           []string              `mapstructure:"conditions"`
+	Histogram            *Histogram            `mapstructure:"histogram"`
+	ExponentialHistogram *ExponentialHistogram `mapstructure:"exponential_histogram"`
+	Sum                  *Sum                  `mapstructure:"sum"`
+}
+
+type Attribute struct {
+	Key          string `mapstructure:"key"`
+	DefaultValue any    `mapstructure:"default_value"`
+}
+
+type Histogram struct {
+	Buckets []float64 `mapstructure:"buckets"`
+	Count   string    `mapstructure:"count"`
+	Value   string    `mapstructure:"value"`
+}
+
+type ExponentialHistogram struct {
+	MaxSize int32  `mapstructure:"max_size"`
+	Count   string `mapstructure:"count"`
+	Value   string `mapstructure:"value"`
+}
+
+type Sum struct {
+	Value string `mapstructure:"value"`
+}