Interface update, per-method Contexts.

service/memcache/interface.go

Index: service/memcache/interface.go
diff --git a/service/memcache/interface.go b/service/memcache/interface.go
index 6d4d33b2d880660f5b499adce34836c6d57bb7e1..5167667587da615f095f0827977a3dd127969776 100644
--- a/service/memcache/interface.go
+++ b/service/memcache/interface.go
@@ -4,72 +4,177 @@
 
 package memcache
 
-// Interface is the full interface to the memcache service.
+import (
+	"github.com/luci/luci-go/common/errors"
+	"golang.org/x/net/context"
+)
+
+func filterItems(lme errors.LazyMultiError, items []Item, nilErr error) ([]Item, []int) {
+	idxMap := make([]int, 0, len(items))
+	retItems := make([]Item, 0, len(items))
+	for i, itm := range items {
+		if itm != nil {
+			idxMap = append(idxMap, i)
+			retItems = append(retItems, itm)
+		} else {
+			lme.Assign(i, nilErr)
+		}
+	}
+	return retItems, idxMap
+}
+
+func multiCall(items []Item, nilErr error, inner func(items []Item, cb RawCB) error) error {
+	lme := errors.NewLazyMultiError(len(items))
+	realItems, idxMap := filterItems(lme, items, nilErr)
+	j := 0
+	err := inner(realItems, func(err error) {
+		lme.Assign(idxMap[j], err)
+		j++
+	})
+	if err == nil {
+		err = lme.Get()
+		if len(items) == 1 {
+			err = errors.SingleError(err)
+		}
+	}
+	return err
+}
+
+// NewItem creates a new, mutable, memcache item.
+func NewItem(c context.Context, key string) Item {
+	return Raw(c).NewItem(key)
+}
+
+// Add writes items to memcache iff they don't already exist.
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func Add(c context.Context, items ...Item) error {
+	return multiCall(items, ErrNotStored, Raw(c).AddMulti)
+}
+
+// Set writes items into memcache unconditionally.
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func Set(c context.Context, items ...Item) error {
+	return multiCall(items, ErrNotStored, Raw(c).SetMulti)
+}
+
+func getMultiImpl(raw RawInterface, items []Item) error {
+	lme := errors.NewLazyMultiError(len(items))
+	realItems, idxMap := filterItems(lme, items, ErrCacheMiss)
+	if len(realItems) == 0 {
+		return lme.Get()
+	}
+
+	keys := make([]string, len(realItems))
+	for i, itm := range realItems {
+		keys[i] = itm.Key()
+	}
+
+	j := 0
+	err := raw.GetMulti(keys, func(item Item, err error) {
+		i := idxMap[j]
+		if !lme.Assign(i, err) {
+			items[i].SetAll(item)
+		}
+		j++
+	})
+	if err == nil {
+		err = lme.Get()
+		if len(items) == 1 {
+			err = errors.SingleError(err)
+		}
+	}
+	return err
+}
+
+// Get retrieves items from memcache.
+func Get(c context.Context, items ...Item) error {
+	return getMultiImpl(Raw(c), items)
+}
+
+// GetKey is a convenience method for generating and retrieving an Item instance
+// for the specified from memcache key.
+//
+// On a cache miss ErrCacheMiss will be returned. Item will always be
+// returned, even on a miss, but it's value may be empty if it was a miss.
+func GetKey(c context.Context, key string) (Item, error) {
+	raw := Raw(c)
+	ret := raw.NewItem(key)
+	err := getMultiImpl(raw, []Item{ret})
+	return ret, err
+}
+
+// Delete deletes items from memcache.
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func Delete(c context.Context, keys ...string) error {
+	lme := errors.NewLazyMultiError(len(keys))
+	i := 0
+	err := Raw(c).DeleteMulti(keys, func(err error) {
+		lme.Assign(i, err)
+		i++
+	})
+	if err == nil {
+		err = lme.Get()
+		if len(keys) == 1 {
+			err = errors.SingleError(err)
+		}
+	}
+	return err
+}
+
+// CompareAndSwap writes the given item that was previously returned by Get, if
+// the value was neither modified or evicted between the Get and the
+// CompareAndSwap calls.
+//
+// Example:
+//   itm := memcache.NewItem(context, "aKey")
+//   memcache.Get(context, itm) // check error
+//   itm.SetValue(append(itm.Value(), []byte("more bytes")))
+//   memcache.CompareAndSwap(context, itm) // check error
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func CompareAndSwap(c context.Context, items ...Item) error {
+	return multiCall(items, ErrNotStored, Raw(c).CompareAndSwapMulti)
+}
+
+// Increment adds delta to the uint64 contained at key. If the memcache key
+// is missing, it's populated with initialValue before applying delta (i.e.
+// the final value would be initialValue+delta).
+//
+// Underflow caps at 0, overflow wraps back to 0.
 //
-// The *Multi methods may return a "github.com/luci/luci-go/common/errors".MultiError
-// if the rpc to the server was successful, but, e.g. some of the items were
-// missing. They may also return a regular error, if, for example, the rpc
-// failed outright.
-type Interface interface {
-	// NewItem creates a new, mutable, memcache item.
-	NewItem(key string) Item
-
-	// Add puts a single item into memcache, but only if it didn't exist in
-	// memcache before.
-	Add(item Item) error
-
-	// Set the item in memcache, whether or not it exists.
-	Set(item Item) error
-
-	// Get retrieves an item from memcache.
-	//
-	// On a cache miss ErrCacheMiss will be returned. Item will always be
-	// returned, even on a miss, but it's value may be empty if it was a miss.
-	Get(key string) (Item, error)
-
-	// Delete removes an item from memcache.
-	Delete(key string) error
-
-	// CompareAndSwap accepts an item which is the result of Get() or GetMulti().
-	// The Get functions add a secret field to item ('CasID'), which is used as
-	// the "compare" value for the "CompareAndSwap". The actual "Value" field of
-	// the object set by the Get functions is the "swap" value.
-	//
-	// Example:
-	//   mc := memcache.Get(context)
-	//   itm := mc.NewItem("aKey")
-	//   mc.Get(itm) // check error
-	//   itm.SetValue(append(itm.Value(), []byte("more bytes")))
-	//   mc.CompareAndSwap(itm) // check error
-	CompareAndSwap(item Item) error
-
-	// Batch operations; GetMulti takes a []Item instead of []string to improve
-	// ergonomics when streamlining these operations.
-	AddMulti(items []Item) error
-	SetMulti(items []Item) error
-	GetMulti(items []Item) error
-	DeleteMulti(keys []string) error
-	CompareAndSwapMulti(items []Item) error
-
-	// Increment adds delta to the uint64 contained at key. If the memcache key
-	// is missing, it's populated with initialValue before applying delta (i.e.
-	// the final value would be initialValue+delta).
-	//
-	// Underflow caps at 0, overflow wraps back to 0.
-	//
-	// If key contains a value which is not exactly 8 bytes, it's assumed to
-	// contain non-number data and this method will return an error.
-	Increment(key string, delta int64, initialValue uint64) (newValue uint64, err error)
-
-	// IncrementExisting is like Increment, except that the valu must exist
-	// already.
-	IncrementExisting(key string, delta int64) (newValue uint64, err error)
-
-	// Flush dumps the entire memcache state.
-	Flush() error
-
-	// Stats gets some best-effort statistics about the current state of memcache.
-	Stats() (*Statistics, error)
-
-	Raw() RawInterface
+// If key contains a value which is not exactly 8 bytes, it's assumed to
+// contain non-number data and this method will return an error.
+func Increment(c context.Context, key string, delta int64, initialValue uint64) (uint64, error) {
+	return Raw(c).Increment(key, delta, &initialValue)
+}
+
+// IncrementExisting is like Increment, except that the valu must exist
+// already.
+func IncrementExisting(c context.Context, key string, delta int64) (uint64, error) {
+	return Raw(c).Increment(key, delta, nil)
+}
+
+// Flush dumps the entire memcache state.
+func Flush(c context.Context) error {
+	return Raw(c).Flush()
+}
+
+// Stats gets some best-effort statistics about the current state of memcache.
+func Stats(c context.Context) (*Statistics, error) {
+	return Raw(c).Stats()
 }