accounts: cache key addresses

In order to avoid disk thrashing for Accounts and HasAccount,
address->key file mappings are now cached in memory. This makes it no
longer necessary to keep the key address in the file name. The address
of each key is derived from file content instead.

There are minor user-visible changes:

- "geth account list" now reports key file paths alongside the address.
- If multiple keys are present for an address, unlocking by address is
  not possible. Users are directed to remove the duplicate files
  instead. Unlocking by index is still possible.
- Key files are overwritten written in place when updating the password.

accounts/key.go

@@ -21,8 +21,13 @@ import (
 	"crypto/ecdsa"
 	"encoding/hex"
 	"encoding/json"
+	"fmt"
 	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"strings"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
@@ -44,13 +49,12 @@ type Key struct {
 }
 
 type keyStore interface {
-	// create new key using io.Reader entropy source and optionally using auth string
-	GenerateNewKey(io.Reader, string) (*Key, error)
-	GetKey(common.Address, string) (*Key, error) // get key from addr and auth string
-	GetKeyAddresses() ([]common.Address, error)  // get all addresses
-	StoreKey(*Key, string) error                 // store key optionally using auth string
-	DeleteKey(common.Address, string) error      // delete key by addr and auth string
-	Cleanup(keyAddr common.Address) (err error)
+	// Loads and decrypts the key from disk.
+	GetKey(addr common.Address, filename string, auth string) (*Key, error)
+	// Writes and encrypts the key.
+	StoreKey(filename string, k *Key, auth string) error
+	// Joins filename with the key directory unless it is already absolute.
+	JoinPath(filename string) string
 }
 
 type plainKeyJSON struct {
@@ -142,21 +146,6 @@ func newKeyFromECDSA(privateKeyECDSA *ecdsa.PrivateKey) *Key {
 	return key
 }
 
-func NewKey(rand io.Reader) *Key {
-	randBytes := make([]byte, 64)
-	_, err := rand.Read(randBytes)
-	if err != nil {
-		panic("key generation: could not read from random source: " + err.Error())
-	}
-	reader := bytes.NewReader(randBytes)
-	privateKeyECDSA, err := ecdsa.GenerateKey(secp256k1.S256(), reader)
-	if err != nil {
-		panic("key generation: ecdsa.GenerateKey failed: " + err.Error())
-	}
-
-	return newKeyFromECDSA(privateKeyECDSA)
-}
-
 // generate key whose address fits into < 155 bits so it can fit into
 // the Direct ICAP spec. for simplicity and easier compatibility with
 // other libs, we retry until the first byte is 0.
@@ -177,3 +166,64 @@ func NewKeyForDirectICAP(rand io.Reader) *Key {
 	}
 	return key
 }
+
+func newKey(rand io.Reader) (*Key, error) {
+	privateKeyECDSA, err := ecdsa.GenerateKey(secp256k1.S256(), rand)
+	if err != nil {
+		return nil, err
+	}
+	return newKeyFromECDSA(privateKeyECDSA), nil
+}
+
+func storeNewKey(ks keyStore, rand io.Reader, auth string) (*Key, Account, error) {
+	key, err := newKey(rand)
+	if err != nil {
+		return nil, Account{}, err
+	}
+	a := Account{Address: key.Address, File: ks.JoinPath(keyFileName(key.Address))}
+	if err := ks.StoreKey(a.File, key, auth); err != nil {
+		zeroKey(key.PrivateKey)
+		return nil, a, err
+	}
+	return key, a, err
+}
+
+func writeKeyFile(file string, content []byte) error {
+	// Create the keystore directory with appropriate permissions
+	// in case it is not present yet.
+	const dirPerm = 0700
+	if err := os.MkdirAll(filepath.Dir(file), dirPerm); err != nil {
+		return err
+	}
+	// Atomic write: create a temporary hidden file first
+	// then move it into place. TempFile assigns mode 0600.
+	f, err := ioutil.TempFile(filepath.Dir(file), "."+filepath.Base(file)+".tmp")
+	if err != nil {
+		return err
+	}
+	if _, err := f.Write(content); err != nil {
+		f.Close()
+		os.Remove(f.Name())
+		return err
+	}
+	f.Close()
+	return os.Rename(f.Name(), file)
+}
+
+// keyFileName implements the naming convention for keyfiles:
+// UTC--<created_at UTC ISO8601>-<address hex>
+func keyFileName(keyAddr common.Address) string {
+	ts := time.Now().UTC()
+	return fmt.Sprintf("UTC--%s--%s", toISO8601(ts), hex.EncodeToString(keyAddr[:]))
+}
+
+func toISO8601(t time.Time) string {
+	var tz string
+	name, offset := t.Zone()
+	if name == "UTC" {
+		tz = "Z"
+	} else {
+		tz = fmt.Sprintf("%03d00", offset/3600)
+	}
+	return fmt.Sprintf("%04d-%02d-%02dT%02d-%02d-%02d.%09d%s", t.Year(), t.Month(), t.Day(), t.Hour(), t.Minute(), t.Second(), t.Nanosecond(), tz)
+}