Add build scheduler DB interface, dumb in-memory impl, cache

build_scheduler/go/db/db.go

Index: build_scheduler/go/db/db.go
diff --git a/build_scheduler/go/db/db.go b/build_scheduler/go/db/db.go
new file mode 100644
index 0000000000000000000000000000000000000000..e1867022c2b568c00e52c24ab18296d145fbdba4
--- /dev/null
+++ b/build_scheduler/go/db/db.go
@@ -0,0 +1,68 @@
+package db
+
+import (
+	"errors"
+	"time"
+
+	"go.skia.org/infra/go/buildbucket"
+)
+
+const (
+	// Maximum number of simultaneous GetModifiedBuilds users.
+	MAX_MODIFIED_BUILDS_USERS = 10
+
+	// Expiration for GetModifiedBuilds users.
+	MODIFIED_BUILDS_TIMEOUT = 10 * time.Minute
+)
+
+var (
+	ErrTooManyUsers = errors.New("Too many users")
+	ErrUnknownId    = errors.New("Unknown ID")
+)
+
+func IsTooManyUsers(e error) bool {
+	return e != nil && e.Error() == ErrTooManyUsers.Error()
+}
+
+func IsUnknownId(e error) bool {
+	return e != nil && e.Error() == ErrUnknownId.Error()
+}
+
+type Build struct {
+	*buildbucket.Build
+	Commits []string
+}
+
+func (b *Build) Copy() *Build {
+	commits := make([]string, len(b.Commits))
+	copy(commits, b.Commits)
+	rv := &Build{
+		Build:   b.Build.Copy(),
+		Commits: commits,
+	}
+	return rv
+}
+
+type DB interface {
+	// Close the [connection to the] DB.
+	Close() error
+
+	// GetBuildsFromDateRange retrieves all builds which started in the given date range.
+	GetBuildsFromDateRange(time.Time, time.Time) ([]*Build, error)
+
+	// GetModifiedBuilds returns all builds modified since the last time
+	// GetModifiedBuilds was run with the given id.
+	GetModifiedBuilds(string) ([]*Build, error)
+
+	// PutBuild inserts or updates the Build in the database.
+	PutBuild(*Build) error
+
+	// PutBuilds inserts or updates the Builds in the database.
+	PutBuilds([]*Build) error
+
+	// StartTrackingModifiedBuilds initiates tracking of modified builds for
+	// the current caller. Returns a unique ID which can be used by the caller
+	// to retrieve builds which have been modified since the last query. The ID
+	// expires after a period of inactivity.
+	StartTrackingModifiedBuilds() (string, error)
+}