internal/sourcemap/chained.go

// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you under
// the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package sourcemap

import (
	"context"
	"errors"

	"github.com/go-sourcemap/sourcemap"

	"github.com/elastic/apm-server/internal/logs"
	"github.com/elastic/elastic-agent-libs/logp"
)

// ChainedFetcher is a Fetcher that attempts fetching from each Fetcher in sequence.
type ChainedFetcher struct {
	fetchers []Fetcher
	logger   *logp.Logger
}

func NewChainedFetcher(fetchers []Fetcher, logger *logp.Logger) *ChainedFetcher {
	return &ChainedFetcher{logger: logger.Named(logs.Sourcemap), fetchers: fetchers}
}

// Fetch fetches a source map from Kibana.
//
// Fetch calls Fetch on each Fetcher in the chain, in sequence, until one returns
// a non-nil Consumer and nil error. If no Fetch call succeeds, then the last error
// will be returned.
func (c *ChainedFetcher) Fetch(ctx context.Context, name, version, path string) (*sourcemap.Consumer, error) {
	var lastErr error
	for _, f := range c.fetchers {
		consumer, err := f.Fetch(ctx, name, version, path)
		// log a message if the previous fetcher failed
		if lastErr != nil {
			c.logger.With(logp.Error(lastErr)).Debug("failed to fetch sourcemap, falling back to the next fetcher")
		}
		// if there are no errors or the error is not errFetcherUnvailable
		// then the fetcher is working/available.
		// Return the result: error and consumer.
		if !errors.Is(err, errFetcherUnvailable) {
			return consumer, err
		}

		// err is errFetcherUnvailable
		// store it in a tmp variable and try the next fetcher
		lastErr = err
	}
	return nil, lastErr
}