new driver: kubernetes

Tested with `kind` and GKE.

Note: "nodes" shown in `docker buildx ls` are unrelated to Kubernetes "nodes".
Probably buildx should come up with an alternative term.

Usage:

  $ kind create cluster
  $ export KUBECONFIG="$(kind get kubeconfig-path --name="kind")"

  $ docker buildx create --driver kubernetes --driver-opt replicas=3 --use
  $ docker buildx build -t foo --load .

`--load` loads the image into the local Docker.

Driver opts:

  - `image=IMAGE` - Sets the container image to be used for running buildkit.
  - `namespace=NS` - Sets the Kubernetes namespace. Defaults to the current namespace.
  - `replicas=N` - Sets the number of `Pod` replicas. Defaults to 1.
  - `rootless=(true|false)` - Run the container as a non-root user without `securityContext.privileged`. Defaults to false.
  - `loadbalance=(sticky|random)` - Load-balancing strategy. If set to "sticky", the pod is chosen using the hash of the context path. Defaults to "sticky"

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/github.com/peterbourgon/diskv/index.go

@@ -0,0 +1,115 @@
+package diskv
+
+import (
+	"sync"
+
+	"github.com/google/btree"
+)
+
+// Index is a generic interface for things that can
+// provide an ordered list of keys.
+type Index interface {
+	Initialize(less LessFunction, keys <-chan string)
+	Insert(key string)
+	Delete(key string)
+	Keys(from string, n int) []string
+}
+
+// LessFunction is used to initialize an Index of keys in a specific order.
+type LessFunction func(string, string) bool
+
+// btreeString is a custom data type that satisfies the BTree Less interface,
+// making the strings it wraps sortable by the BTree package.
+type btreeString struct {
+	s string
+	l LessFunction
+}
+
+// Less satisfies the BTree.Less interface using the btreeString's LessFunction.
+func (s btreeString) Less(i btree.Item) bool {
+	return s.l(s.s, i.(btreeString).s)
+}
+
+// BTreeIndex is an implementation of the Index interface using google/btree.
+type BTreeIndex struct {
+	sync.RWMutex
+	LessFunction
+	*btree.BTree
+}
+
+// Initialize populates the BTree tree with data from the keys channel,
+// according to the passed less function. It's destructive to the BTreeIndex.
+func (i *BTreeIndex) Initialize(less LessFunction, keys <-chan string) {
+	i.Lock()
+	defer i.Unlock()
+	i.LessFunction = less
+	i.BTree = rebuild(less, keys)
+}
+
+// Insert inserts the given key (only) into the BTree tree.
+func (i *BTreeIndex) Insert(key string) {
+	i.Lock()
+	defer i.Unlock()
+	if i.BTree == nil || i.LessFunction == nil {
+		panic("uninitialized index")
+	}
+	i.BTree.ReplaceOrInsert(btreeString{s: key, l: i.LessFunction})
+}
+
+// Delete removes the given key (only) from the BTree tree.
+func (i *BTreeIndex) Delete(key string) {
+	i.Lock()
+	defer i.Unlock()
+	if i.BTree == nil || i.LessFunction == nil {
+		panic("uninitialized index")
+	}
+	i.BTree.Delete(btreeString{s: key, l: i.LessFunction})
+}
+
+// Keys yields a maximum of n keys in order. If the passed 'from' key is empty,
+// Keys will return the first n keys. If the passed 'from' key is non-empty, the
+// first key in the returned slice will be the key that immediately follows the
+// passed key, in key order.
+func (i *BTreeIndex) Keys(from string, n int) []string {
+	i.RLock()
+	defer i.RUnlock()
+
+	if i.BTree == nil || i.LessFunction == nil {
+		panic("uninitialized index")
+	}
+
+	if i.BTree.Len() <= 0 {
+		return []string{}
+	}
+
+	btreeFrom := btreeString{s: from, l: i.LessFunction}
+	skipFirst := true
+	if len(from) <= 0 || !i.BTree.Has(btreeFrom) {
+		// no such key, so fabricate an always-smallest item
+		btreeFrom = btreeString{s: "", l: func(string, string) bool { return true }}
+		skipFirst = false
+	}
+
+	keys := []string{}
+	iterator := func(i btree.Item) bool {
+		keys = append(keys, i.(btreeString).s)
+		return len(keys) < n
+	}
+	i.BTree.AscendGreaterOrEqual(btreeFrom, iterator)
+
+	if skipFirst && len(keys) > 0 {
+		keys = keys[1:]
+	}
+
+	return keys
+}
+
+// rebuildIndex does the work of regenerating the index
+// with the given keys.
+func rebuild(less LessFunction, keys <-chan string) *btree.BTree {
+	tree := btree.New(2)
+	for key := range keys {
+		tree.ReplaceOrInsert(btreeString{s: key, l: less})
+	}
+	return tree
+}