terraform/internal/providercache/dir.go

package providercache

import (
	"io/ioutil"
	"log"
	"path/filepath"
	"sort"
	"strings"

	"github.com/hashicorp/terraform/addrs"
	"github.com/hashicorp/terraform/internal/getproviders"
)

// Dir represents a single local filesystem directory containing cached
// provider plugin packages that can be both read from (to find providers to
// use for operations) and written to (during provider installation).
//
// The contents of a cache directory follow the same naming conventions as a
// getproviders.FilesystemMirrorSource, except that the packages are always
// kept in the "unpacked" form (a directory containing the contents of the
// original distribution archive) so that they are ready for direct execution.
//
// A Dir also pays attention only to packages for the current host platform,
// silently ignoring any cached packages for other platforms.
//
// Various Dir methods return values that are technically mutable due to the
// restrictions of the Go typesystem, but callers are not permitted to mutate
// any part of the returned data structures.
type Dir struct {
	baseDir        string
	targetPlatform getproviders.Platform

	// metaCache is a cache of the metadata of relevant packages available in
	// the cache directory last time we scanned it. This can be nil to indicate
	// that the cache is cold. The cache will be invalidated (set back to nil)
	// by any operation that modifies the contents of the cache directory.
	//
	// We intentionally don't make effort to detect modifications to the
	// directory made by other codepaths because the contract for NewDir
	// explicitly defines using the same directory for multiple purposes
	// as undefined behavior.
	metaCache map[addrs.Provider][]CachedProvider
}

// NewDir creates and returns a new Dir object that will read and write
// provider plugins in the given filesystem directory.
//
// If two instances of Dir are concurrently operating on a particular base
// directory, or if a Dir base directory is also used as a filesystem mirror
// source directory, the behavior is undefined.
func NewDir(baseDir string) *Dir {
	return &Dir{
		baseDir:        baseDir,
		targetPlatform: getproviders.CurrentPlatform,
	}
}

// newDirWithPlatform is a variant of NewDir that allows selecting a specific
// target platform, rather than taking the current one where this code is
// running.
//
// This is primarily intended for portable unit testing and not particularly
// useful in "real" callers.
func newDirWithPlatform(baseDir string, platform getproviders.Platform) *Dir {
	return &Dir{
		baseDir:        baseDir,
		targetPlatform: platform,
	}
}

// AllAvailablePackages returns a description of all of the packages already
// present in the directory. The cache entries are grouped by the provider
// they relate to and then sorted by version precedence, with highest
// precedence first.
//
// This function will return an empty result both when the directory is empty
// and when scanning the directory produces an error.
//
// The caller is forbidden from modifying the returned data structure in any
// way, even though the Go type system permits it.
func (d *Dir) AllAvailablePackages() map[addrs.Provider][]CachedProvider {
	if err := d.fillMetaCache(); err != nil {
		log.Printf("[WARN] Failed to scan provider cache directory %s: %s", d.baseDir, err)
		return nil
	}

	return d.metaCache
}

// ProviderVersion returns the cache entry for the requested provider version,
// or nil if the requested provider version isn't present in the cache.
func (d *Dir) ProviderVersion(provider addrs.Provider, version getproviders.Version) *CachedProvider {
	if err := d.fillMetaCache(); err != nil {
		return nil
	}

	for _, entry := range d.metaCache[provider] {
		// We're intentionally comparing exact version here, so if either
		// version number contains build metadata and they don't match then
		// this will not return true. The rule of ignoring build metadata
		// applies only for handling version _constraints_ and for deciding
		// version precedence.
		if entry.Version == version {
			return &entry
		}
	}

	return nil
}

// ProviderLatestVersion returns the cache entry for the latest
// version of the requested provider already available in the cache, or nil if
// there are no versions of that provider available.
func (d *Dir) ProviderLatestVersion(provider addrs.Provider) *CachedProvider {
	if err := d.fillMetaCache(); err != nil {
		return nil
	}

	entries := d.metaCache[provider]
	if len(entries) == 0 {
		return nil
	}

	return &entries[0]
}

func (d *Dir) fillMetaCache() error {
	// For d.metaCache we consider nil to be different than a non-nil empty
	// map, so we can distinguish between having scanned and got an empty
	// result vs. not having scanned successfully at all yet.
	if d.metaCache != nil {
		log.Printf("[TRACE] providercache.fillMetaCache: using cached result from previous scan of %s", d.baseDir)
		return nil
	}
	log.Printf("[TRACE] providercache.fillMetaCache: scanning directory %s", d.baseDir)

	allData, err := getproviders.SearchLocalDirectory(d.baseDir)
	if err != nil {
		return err
	}

	// The getproviders package just returns everything it found, but we're
	// interested only in a subset of the results:
	// - those that are for the current platform
	// - those that are in the "unpacked" form, ready to execute
	// ...so we'll filter in these ways while we're constructing our final
	// map to save as the cache.
	//
	// We intentionally always make a non-nil map, even if it might ultimately
	// be empty, because we use that to recognize that the cache is populated.
	data := make(map[addrs.Provider][]CachedProvider)

	for providerAddr, metas := range allData {
		for _, meta := range metas {
			if meta.TargetPlatform != d.targetPlatform {
				log.Printf("[TRACE] providercache.fillMetaCache: ignoring %s because it is for %s, not %s", meta.Location, meta.TargetPlatform, d.targetPlatform)
				continue
			}
			if _, ok := meta.Location.(getproviders.PackageLocalDir); !ok {
				// PackageLocalDir indicates an unpacked provider package ready
				// to execute.
				log.Printf("[TRACE] providercache.fillMetaCache: ignoring %s because it is not an unpacked directory", meta.Location)
				continue
			}

			packageDir := filepath.Clean(string(meta.Location.(getproviders.PackageLocalDir)))
			execFile := findProviderExecutableInLocalPackage(meta)
			if execFile == "" {
				// If the package doesn't contain a suitable executable then
				// it isn't considered to be part of our cache.
				log.Printf("[TRACE] providercache.fillMetaCache: ignoring %s because it is does not seem to contain a suitable plugin executable", meta.Location)
				continue
			}

			log.Printf("[TRACE] providercache.fillMetaCache: including %s as a candidate package for %s %s", meta.Location, providerAddr, meta.Version)
			data[providerAddr] = append(data[providerAddr], CachedProvider{
				Provider:       providerAddr,
				Version:        meta.Version,
				PackageDir:     filepath.ToSlash(packageDir),
				ExecutableFile: filepath.ToSlash(execFile),
			})
		}
	}

	// After we've built our lists per provider, we'll also sort them by
	// version precedence so that the newest available version is always at
	// index zero. If there are two versions that differ only in build metadata
	// then it's undefined but deterministic which one we will select here,
	// because we're preserving the order returned by SearchLocalDirectory
	// in that case..
	for _, entries := range data {
		sort.SliceStable(entries, func(i, j int) bool {
			// We're using GreaterThan rather than LessThan here because we
			// want these in _decreasing_ order of precedence.
			return entries[i].Version.GreaterThan(entries[j].Version)
		})
	}

	d.metaCache = data
	return nil
}

// This is a helper function to peep into the unpacked directory associated
// with the given package meta and find something that looks like it's intended
// to be the executable file for the plugin.
//
// This is a bit messy and heuristic-y because historically Terraform used the
// filename itself for local filesystem discovery, allowing some variance in
// the filenames to capture extra metadata, whereas now we're using the
// directory structure leading to the executable instead but need to remain
// compatible with the executable names bundled into existing provider packages.
//
// It will return a zero-length string if it can't find a file following
// the expected convention in the given directory.
func findProviderExecutableInLocalPackage(meta getproviders.PackageMeta) string {
	packageDir, ok := meta.Location.(getproviders.PackageLocalDir)
	if !ok {
		// This should never happen because the providercache package only
		// uses the local unpacked directory layout. If anything else ends
		// up in here then we'll indicate that no executable is available,
		// because all other locations require a fetch/unpack step first.
		return ""
	}

	infos, err := ioutil.ReadDir(string(packageDir))
	if err != nil {
		// If the directory itself doesn't exist or isn't readable then we
		// can't access an executable in it.
		return ""
	}

	// For a provider named e.g. tf.example.com/awesomecorp/happycloud, we
	// expect an executable file whose name starts with
	// "terraform-provider-happycloud", followed by zero or more additional
	// characters. If there _are_ additional characters then the first one
	// must be an underscore or a period, like in thse examples:
	// - terraform-provider-happycloud_v1.0.0
	// - terraform-provider-happycloud.exe
	//
	// We don't require the version in the filename to match because the
	// executable's name is no longer authoritative, but packages of "official"
	// providers may continue to use versioned executable names for backward
	// compatibility with Terraform 0.12.
	//
	// We also presume that providers packaged for Windows will include the
	// necessary .exe extension on their filenames but do not explicitly check
	// for that. If there's a provider package for Windows that has a file
	// without that suffix then it will be detected as an executable but then
	// we'll presumably fail later trying to run it.
	wantPrefix := "terraform-provider-" + meta.Provider.Type

	// We'll visit all of the directory entries and take the first (in
	// name-lexical order) that looks like a plausible provider executable
	// name. A package with multiple files meeting these criteria is degenerate
	// but we will tolerate it by ignoring the subsequent entries.
	for _, info := range infos {
		if info.IsDir() {
			continue // A directory can never be an executable
		}
		name := info.Name()
		if !strings.HasPrefix(name, wantPrefix) {
			continue
		}
		remainder := name[len(wantPrefix):]
		if len(remainder) > 0 && (remainder[0] != '_' && remainder[0] != '.') {
			continue // subsequent characters must be delimited by _
		}
		return filepath.Join(string(packageDir), name)
	}

	// If we fall out here then nothing has matched.
	return ""
}