receiver/prometheusremotewritereceiver: add MetricIdentity with xxhash-based Hash method.

Creates MetricIdentity struct for uniquely identifying metrics and adds
a deterministic Hash method using xxhash with proper field separation.

partly fixes open-telemetry#37277.

Author: sujalshah-bit

.chloggen/metric-identity-hash.yaml

@@ -0,0 +1,27 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusremotewritereciever
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Introduced `MetricIdentity` struct with xxhash-based hashing for uniquely identifying metrics."
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [37277]
+
+# (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: |
+  The hash method ensures consistent, deterministic identification of metrics by using
+  proper field separation and xxhash, which is already utilized in other parts of the code.
+
+# 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]

receiver/prometheusremotewritereceiver/receiver.go

@@ -49,6 +49,47 @@ type prometheusRemoteWriteReceiver struct {
 	wg     sync.WaitGroup
 }
 
+// MetricIdentity contains all the components that uniquely identify a metric
+// according to the OpenTelemetry Protocol data model.
+type MetricIdentity struct {
+	ResourceID   string
+	ScopeName    string
+	ScopeVersion string
+	MetricName   string
+	Unit         string
+	Type         writev2.Metadata_MetricType
+}
+
+// CreateMetricIdentity creates a MetricIdentity struct from the required components
+func CreateMetricIdentity(resourceID string, scopeName, scopeVersion, metricName, unit string, metricType writev2.Metadata_MetricType) MetricIdentity {
+	return MetricIdentity{
+		ResourceID:   resourceID,
+		ScopeName:    scopeName,
+		ScopeVersion: scopeVersion,
+		MetricName:   metricName,
+		Unit:         unit,
+		Type:         metricType,
+	}
+}
+
+// Hash generates a unique hash for the metric identity
+func (mi MetricIdentity) Hash() string {
+	const separator = "\xff"
+
+	combined := strings.Join([]string{
+		mi.ResourceID,
+		mi.ScopeName,
+		mi.ScopeVersion,
+		mi.MetricName,
+		mi.Unit,
+		fmt.Sprintf("%d", mi.Type),
+	}, separator)
+
+	hash := xxhash.Sum64String(combined)
+
+	return fmt.Sprintf("%x", hash)
+}
+
 func (prw *prometheusRemoteWriteReceiver) Start(ctx context.Context, host component.Host) error {
 	mux := http.NewServeMux()
 	mux.HandleFunc("/api/v1/write", prw.handlePRW)
@@ -221,16 +262,17 @@ func (prw *prometheusRemoteWriteReceiver) translateV2(_ context.Context, req *wr
 		description := req.Symbols[ts.Metadata.HelpRef]
 
 		resourceID := identity.OfResource(rm.Resource())
-		// Temporary approach to generate the metric key.
-		// TODO: Replace this with a proper hashing function.
-		// The definition of the metric uniqueness is based on the following document. Ref: https://opentelemetry.io/docs/specs/otel/metrics/data-model/#opentelemetry-protocol-data-model
-		metricKey := fmt.Sprintf("%s:%s:%s:%s:%s:%d",
+
+		metricIdentity := CreateMetricIdentity(
 			resourceID.String(), // Resource identity
 			scopeName,           // Scope name
 			scopeVersion,        // Scope version
 			metricName,          // Metric name
 			unit,                // Unit
-			ts.Metadata.Type)    // Metric type
+			ts.Metadata.Type,    // Metric type
+		)
+
+		metricKey := metricIdentity.Hash()
 
 		var scope pmetric.ScopeMetrics
 		var foundScope bool