Implement a per-output fixed size metric buffer

Also moved some objects out of config.go and put them in their own
package, internal/models

fixes #568
closes #285

internal/models/filter.go

@@ -0,0 +1,92 @@
+package models
+
+import (
+	"strings"
+
+	"github.com/influxdata/influxdb/client/v2"
+	"github.com/influxdata/telegraf/internal"
+)
+
+// TagFilter is the name of a tag, and the values on which to filter
+type TagFilter struct {
+	Name   string
+	Filter []string
+}
+
+// Filter containing drop/pass and tagdrop/tagpass rules
+type Filter struct {
+	Drop []string
+	Pass []string
+
+	TagDrop []TagFilter
+	TagPass []TagFilter
+
+	IsActive bool
+}
+
+func (f Filter) ShouldPointPass(point *client.Point) bool {
+	if f.ShouldPass(point.Name()) && f.ShouldTagsPass(point.Tags()) {
+		return true
+	}
+	return false
+}
+
+// ShouldPass returns true if the metric should pass, false if should drop
+// based on the drop/pass filter parameters
+func (f Filter) ShouldPass(key string) bool {
+	if f.Pass != nil {
+		for _, pat := range f.Pass {
+			// TODO remove HasPrefix check, leaving it for now for legacy support.
+			// Cam, 2015-12-07
+			if strings.HasPrefix(key, pat) || internal.Glob(pat, key) {
+				return true
+			}
+		}
+		return false
+	}
+
+	if f.Drop != nil {
+		for _, pat := range f.Drop {
+			// TODO remove HasPrefix check, leaving it for now for legacy support.
+			// Cam, 2015-12-07
+			if strings.HasPrefix(key, pat) || internal.Glob(pat, key) {
+				return false
+			}
+		}
+
+		return true
+	}
+	return true
+}
+
+// ShouldTagsPass returns true if the metric should pass, false if should drop
+// based on the tagdrop/tagpass filter parameters
+func (f Filter) ShouldTagsPass(tags map[string]string) bool {
+	if f.TagPass != nil {
+		for _, pat := range f.TagPass {
+			if tagval, ok := tags[pat.Name]; ok {
+				for _, filter := range pat.Filter {
+					if internal.Glob(filter, tagval) {
+						return true
+					}
+				}
+			}
+		}
+		return false
+	}
+
+	if f.TagDrop != nil {
+		for _, pat := range f.TagDrop {
+			if tagval, ok := tags[pat.Name]; ok {
+				for _, filter := range pat.Filter {
+					if internal.Glob(filter, tagval) {
+						return false
+					}
+				}
+			}
+		}
+		return true
+	}
+
+	return true
+}