[wip] add config lib

Signed-off-by: Alex Boten <aboten@lightstep.com>

config/config.go

@@ -0,0 +1,143 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package config // import "go.opentelemetry.io/contrib/config"
+
+import (
+	"fmt"
+
+	"go.opentelemetry.io/collector/confmap"
+)
+
+func (sp *SpanProcessor) Unmarshal(conf *confmap.Conf) error {
+	if conf == nil {
+		return nil
+	}
+
+	if err := conf.Unmarshal(sp); err != nil {
+		return fmt.Errorf("invalid span processor configuration: %w", err)
+	}
+
+	if sp.Batch != nil {
+		return sp.Batch.Exporter.Validate()
+	}
+	return fmt.Errorf("unsupported span processor type %s", conf.AllKeys())
+}
+
+// Validate checks for valid exporters to be configured for the SpanExporter
+func (se *SpanExporter) Validate() error {
+	if se.Console == nil && se.Otlp == nil {
+		return fmt.Errorf("invalid exporter configuration")
+	}
+	return nil
+}
+
+func (mr *MetricReader) Unmarshal(conf *confmap.Conf) error {
+	if conf == nil {
+		return nil
+	}
+
+	if err := conf.Unmarshal(mr); err != nil {
+		return fmt.Errorf("invalid metric reader configuration: %w", err)
+	}
+
+	if mr.Pull != nil {
+		return mr.Pull.Validate()
+	}
+	if mr.Periodic != nil {
+		return mr.Periodic.Validate()
+	}
+
+	return fmt.Errorf("unsupported metric reader type %s", conf.AllKeys())
+}
+
+// Validate checks for valid exporters to be configured for the PullMetricReader
+func (pmr *PullMetricReader) Validate() error {
+	if pmr.Exporter.Prometheus == nil {
+		return fmt.Errorf("invalid exporter configuration")
+	}
+	return nil
+}
+
+// Validate checks for valid exporters to be configured for the PeriodicMetricReader
+func (pmr *PeriodicMetricReader) Validate() error {
+	if pmr.Exporter.Otlp == nil && pmr.Exporter.Console == nil {
+		return fmt.Errorf("invalid exporter configuration")
+	}
+	return nil
+}
+
+func (v *View) Unmarshal(conf *confmap.Conf) error {
+	if conf == nil {
+		return nil
+	}
+
+	if err := conf.Unmarshal(v); err != nil {
+		return fmt.Errorf("invalid view configuration: %w", err)
+	}
+
+	return v.Validate()
+}
+
+func (v *View) Validate() error {
+	if v.Selector == nil || v.Stream == nil {
+		return fmt.Errorf("invalid view configuration")
+	}
+	return nil
+}
+
+func (s *ViewSelector) InstrumentNameStr() string {
+	if s.InstrumentName == nil {
+		return ""
+	}
+	return *s.InstrumentName
+}
+
+func (s *ViewSelector) InstrumentTypeStr() string {
+	if s.InstrumentType == nil {
+		return ""
+	}
+	return *s.InstrumentType
+}
+
+func (s *ViewSelector) MeterNameStr() string {
+	if s.MeterName == nil {
+		return ""
+	}
+	return *s.MeterName
+}
+
+func (s *ViewSelector) MeterVersionStr() string {
+	if s.MeterVersion == nil {
+		return ""
+	}
+	return *s.MeterVersion
+}
+
+func (s *ViewSelector) MeterSchemaUrlStr() string {
+	if s.MeterSchemaUrl == nil {
+		return ""
+	}
+	return *s.MeterSchemaUrl
+}
+
+func (s *ViewStream) NameStr() string {
+	if s.Name == nil {
+		return ""
+	}
+	return *s.Name
+}
+
+func (s *ViewStream) DescriptionStr() string {
+	if s.Description == nil {
+		return ""
+	}
+	return *s.Description
+}
+
+func (e *ViewStreamAggregationExplicitBucketHistogram) RecordMinMaxBool() bool {
+	if e.RecordMinMax == nil {
+		return false
+	}
+	return *e.RecordMinMax
+}