terraform/remote/remote.go

package remote

import (
	"bytes"
	"crypto/md5"
	"fmt"
	"io"
	"io/ioutil"
	"net/url"
	"os"
	"path/filepath"

	"github.com/hashicorp/terraform/terraform"
)

const (
	// LocalDirectory is the directory created in the working
	// dir to hold the remote state file.
	LocalDirectory = ".terraform"

	// HiddenStateFile is the name of the state file in the
	// LocalDirectory
	HiddenStateFile = "terraform.tfstate"

	// BackupHiddenStateFile is the path we backup the state
	// file to before modifications are made
	BackupHiddenStateFile = "terraform.tfstate.backup"

	// DefaultServer is used when no server is provided. We use
	// the hosted cloud URL.
	DefaultServer = "http://www.hashicorp.com/"
)

// StateChangeResult is used to communicate to a caller
// what actions have been taken when updating a state file
type StateChangeResult int

const (
	// StateChangeNoop indicates nothing has happened,
	// but that does not indicate an error. Everything is
	// just up to date. (Push/Pull)
	StateChangeNoop StateChangeResult = iota

	// StateChangeInit indicates that there is no local or
	// remote state, and that the state was initialized
	StateChangeInit

	// StateChangeUpdateLocal indicates the local state
	// was updated. (Pull)
	StateChangeUpdateLocal

	// StateChangeUpdateRemote indicates the remote state
	// was updated. (Push)
	StateChangeUpdateRemote

	// StateChangeLocalNewer means the pull was a no-op
	// because the local state is newer than that of the
	// server. This means a Push should take place. (Pull)
	StateChangeLocalNewer

	// StateChangeRemoteNewer means the push was a no-op
	// because the remote state is newer than that of the
	// local state. This means a Pull should take place.
	// (Push)
	StateChangeRemoteNewer

	// StateChangeConflict means that the push or pull
	// was a no-op because there is a conflict. This means
	// there are multiple state definitions at the same
	// serial number with different contents. This requires
	// an operator to intervene and resolve the conflict.
	// Shame on the user for doing concurrent apply.
	// (Push/Pull)
	StateChangeConflict
)

func (sc StateChangeResult) String() string {
	switch sc {
	case StateChangeNoop:
		return "Local and remote state in sync"
	case StateChangeInit:
		return "Local state initialized"
	case StateChangeUpdateLocal:
		return "Local state updated"
	case StateChangeUpdateRemote:
		return "Remote state updated"
	case StateChangeLocalNewer:
		return "Local state is newer than remote state, push required"
	case StateChangeRemoteNewer:
		return "Remote state is newer than local state, pull required"
	case StateChangeConflict:
		return "Local and remote state conflict, manual resolution required"
	default:
		return fmt.Sprintf("Unknown state change type: %d", sc)
	}
}

// SuccessfulPull is used to clasify the StateChangeResult for
// a pull operation. This is different by operation, but can be used
// to determine a proper exit code.
func (sc StateChangeResult) SuccessfulPull() bool {
	switch sc {
	case StateChangeNoop:
		return true
	case StateChangeInit:
		return true
	case StateChangeUpdateLocal:
		return true
	case StateChangeLocalNewer:
		return false
	case StateChangeConflict:
		return false
	default:
		return false
	}
}

// EnsureDirectory is used to make sure the local storage
// directory exists
func EnsureDirectory() error {
	cwd, err := os.Getwd()
	if err != nil {
		return fmt.Errorf("Failed to get current directory: %v", err)
	}
	path := filepath.Join(cwd, LocalDirectory)
	if err := os.Mkdir(path, 0770); err != nil {
		if os.IsExist(err) {
			return nil
		}
		return fmt.Errorf("Failed to make directory '%s': %v", path, err)
	}
	return nil
}

// HiddenStatePath is used to return the path to the hidden state file,
// should there be one.
func HiddenStatePath() (string, error) {
	cwd, err := os.Getwd()
	if err != nil {
		return "", fmt.Errorf("Failed to get current directory: %v", err)
	}
	path := filepath.Join(cwd, LocalDirectory, HiddenStateFile)
	return path, nil
}

// validConfig does a purely logical validation of the remote config
func validConfig(conf *terraform.RemoteState) error {
	// Verify the remote server configuration is sane
	if (conf.Server != "" || conf.AuthToken != "") && conf.Name == "" {
		return fmt.Errorf("Name must be provided for remote state storage")
	}
	if conf.Server != "" {
		if _, err := url.Parse(conf.Server); err != nil {
			return fmt.Errorf("Remote Server URL invalid: %v", err)
		}
	} else {
		// Fill in the default server
		conf.Server = DefaultServer
	}
	return nil
}

// ValidateConfig is used to take a remote state configuration,
// ensure the local directory exists and that the remote state
// does not conflict with an existing state file.
func ValidateConfig(conf *terraform.RemoteState) error {
	// Logical validation first
	if err := validConfig(conf); err != nil {
		return err
	}

	// Ensure the hidden directory
	if err := EnsureDirectory(); err != nil {
		return fmt.Errorf(
			"Remote state setup failed: %s", err)
	}

	// Get the path to the state file
	path, err := HiddenStatePath()
	if err != nil {
		return err
	}

	// Open the existing file
	f, err := os.Open(path)
	if err != nil {
		if !os.IsNotExist(err) {
			return fmt.Errorf("Failed to open state file '%s': %s", path, err)
		}
		return nil
	}
	defer f.Close()

	// Decode the state
	state, err := terraform.ReadState(f)
	if err != nil {
		return fmt.Errorf("Failed to read state file '%s': %v", path, err)
	}

	// If the hidden state file has no remote info, something
	// is definitely wrong...
	if state.Remote == nil {
		return fmt.Errorf(`State file '%s' missing remote storage information.
This is likely a bug, please report it.`)
	}

	// Check if there is a conflict
	if !state.Remote.Equals(conf) {
		return fmt.Errorf(
			"Conflicting definitions for remote storage in existing state file '%s'", path)
	}
	return nil
}

// RefreshState is used to read the remote state given
// the configuration for the remote endpoint, and update
// the local state if necessary.
func RefreshState(conf *terraform.RemoteState) (StateChangeResult, error) {
	// Read the state from the server
	client := &remoteStateClient{conf: conf}
	payload, err := client.GetState()
	if err != nil {
		return StateChangeNoop,
			fmt.Errorf("Failed to read remote state: %v", err)
	}

	// Parse the remote state
	var remoteState *terraform.State
	if payload != nil {
		remoteState, err = terraform.ReadState(bytes.NewReader(payload.State))
		if err != nil {
			return StateChangeNoop,
				fmt.Errorf("Failed to parse remote state: %v", err)
		}

		// Ensure we understand the remote version!
		if remoteState.Version > terraform.StateVersion {
			return StateChangeNoop, fmt.Errorf(
				`Remote state is version %d, this version of Terraform only understands up to %d`, remoteState.Version, terraform.StateVersion)
		}
	}

	// Get the path to the state file
	path, err := HiddenStatePath()
	if err != nil {
		return StateChangeNoop, err
	}

	// Get the existing state file
	raw, err := ioutil.ReadFile(path)
	if err != nil && !os.IsNotExist(err) {
		return StateChangeNoop, fmt.Errorf("Failed to read local state: %v", err)
	}

	// Decode the state
	var localState *terraform.State
	if raw != nil {
		localState, err = terraform.ReadState(bytes.NewReader(raw))
		if err != nil {
			return StateChangeNoop,
				fmt.Errorf("Failed to decode state file '%s': %v", path, err)
		}
	}

	// We need to handle the matrix of cases in reconciling
	// the local and remote state. Primarily the concern is
	// around the Serial number which should grow monotonically.
	// Additionally, we use the MD5 to detect a conflict for
	// a given Serial.
	switch {
	case remoteState == nil && localState == nil:
		// Initialize a blank state
		out, _ := blankState(conf)
		if err := Persist(bytes.NewReader(out)); err != nil {
			return StateChangeNoop,
				fmt.Errorf("Failed to persist state: %v", err)
		}
		return StateChangeInit, nil

	case remoteState == nil && localState != nil:
		fallthrough
	case remoteState.Serial < localState.Serial:
		// User should probably do a push, nothing to do
		return StateChangeLocalNewer, nil

	case remoteState != nil && localState == nil:
		fallthrough
	case remoteState.Serial > localState.Serial:
		// Update the local state from the remote state
		if err := Persist(bytes.NewReader(payload.State)); err != nil {
			return StateChangeNoop,
				fmt.Errorf("Failed to persist state: %v", err)
		}
		return StateChangeUpdateLocal, nil

	case remoteState.Serial == localState.Serial:
		// Check for a hash collision on the local/remote state
		localMD5 := md5.Sum(raw)
		if bytes.Equal(localMD5[:md5.Size], payload.MD5) {
			// Hash collision, everything is up-to-date
			return StateChangeNoop, nil
		} else {
			// This is very bad. This means we have 2 state files
			// with the same Serial but a different hash. Most probably
			// explaination is two parallel apply operations. This
			// requires a manual reconciliation.
			return StateChangeConflict, nil
		}
	}

	// We should not reach this point
	panic("Unhandled remote update case")
}

// blankState is used to return a serialized form of a blank state
// with only the remote info.
func blankState(conf *terraform.RemoteState) ([]byte, error) {
	blank := terraform.NewState()
	blank.Remote = conf
	buf := bytes.NewBuffer(nil)
	err := terraform.WriteState(blank, buf)
	return buf.Bytes(), err
}

// Persist is used to write out the state given by a reader (likely
// being streamed from a remote server) to the local storage.
func Persist(r io.Reader) error {
	cwd, err := os.Getwd()
	if err != nil {
		return fmt.Errorf("Failed to get current directory: %v", err)
	}
	statePath := filepath.Join(cwd, LocalDirectory, HiddenStateFile)
	backupPath := filepath.Join(cwd, LocalDirectory, BackupHiddenStateFile)

	// Backup the old file if it exists
	if err := copyFile(statePath, backupPath); err != nil {
		return fmt.Errorf("Failed to backup state file '%s' to '%s': %v", statePath, backupPath, err)
	}

	// Open the state path
	fh, err := os.Create(statePath)
	if err != nil {
		return fmt.Errorf("Failed to open state file '%s': %v", statePath, err)
	}

	// Copy the new state
	_, err = io.Copy(fh, r)
	fh.Close()
	if err != nil {
		os.Remove(statePath)
		return fmt.Errorf("Failed to persist state file: %v", err)
	}
	return nil
}

// copyFile is used to copy from a source file if it exists to a destination.
// This is used to create a backup of the state file.
func copyFile(src, dst string) error {
	srcFH, err := os.Open(src)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return err
	}
	defer srcFH.Close()

	dstFH, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer dstFH.Close()

	_, err = io.Copy(dstFH, srcFH)
	return err
}