logarchiver/internal/cli/filter.go

package cli

import (
	"bytes"
	"io"
	"strings"
	"time"

	"git.unkin.net/unkin/logarchiver/internal/event"
)

// lineFilter is a predicate over a single NDJSON event line.
type lineFilter func(raw []byte) bool

// newLineFilter builds a predicate from optional host/time constraints. A nil
// filter (all constraints empty) means "pass everything".
func newLineFilter(host string, from, to time.Time) lineFilter {
	if host == "" && from.IsZero() && to.IsZero() {
		return nil
	}
	return func(raw []byte) bool {
		meta := event.Extract(raw)
		if host != "" && !globMatch(host, meta.Host) {
			return false
		}
		if !from.IsZero() || !to.IsZero() {
			// Events without a parseable timestamp are kept (we cannot exclude
			// them on time grounds without dropping data).
			if meta.Ok {
				if !from.IsZero() && meta.Timestamp.Before(from) {
					return false
				}
				if !to.IsZero() && meta.Timestamp.After(to) {
					return false
				}
			}
		}
		return true
	}
}

// filterWriter forwards only complete NDJSON lines that satisfy filter. It
// buffers a trailing partial line across Writes so streaming decryption can feed
// it arbitrary chunks. Flush must be called at end to emit any final unterminated
// line. A nil filter forwards bytes verbatim.
type filterWriter struct {
	dst    io.Writer
	filter lineFilter
	buf    bytes.Buffer
}

func newFilterWriter(dst io.Writer, filter lineFilter) *filterWriter {
	return &filterWriter{dst: dst, filter: filter}
}

func (w *filterWriter) Write(p []byte) (int, error) {
	if w.filter == nil {
		return w.dst.Write(p)
	}
	w.buf.Write(p)
	for {
		data := w.buf.Bytes()
		i := bytes.IndexByte(data, '\n')
		if i < 0 {
			break
		}
		line := data[:i]
		if len(bytes.TrimSpace(line)) > 0 && w.filter(line) {
			if _, err := w.dst.Write(line); err != nil {
				return 0, err
			}
			if _, err := w.dst.Write([]byte{'\n'}); err != nil {
				return 0, err
			}
		}
		w.buf.Next(i + 1)
	}
	return len(p), nil
}

// Flush emits a trailing line that had no terminating newline.
func (w *filterWriter) Flush() error {
	if w.filter == nil {
		return nil
	}
	line := bytes.TrimRight(w.buf.Bytes(), "\n")
	w.buf.Reset()
	if len(bytes.TrimSpace(line)) > 0 && w.filter(line) {
		if _, err := w.dst.Write(line); err != nil {
			return err
		}
		if _, err := w.dst.Write([]byte{'\n'}); err != nil {
			return err
		}
	}
	return nil
}

// globMatch matches pattern against s where '*' matches any run of characters.
// With no '*', it is an exact match.
func globMatch(pattern, s string) bool {
	if !strings.Contains(pattern, "*") {
		return pattern == s
	}
	parts := strings.Split(pattern, "*")
	// Anchor first part.
	if !strings.HasPrefix(s, parts[0]) {
		return false
	}
	s = s[len(parts[0]):]
	for _, part := range parts[1 : len(parts)-1] {
		if part == "" {
			continue
		}
		idx := strings.Index(s, part)
		if idx < 0 {
			return false
		}
		s = s[idx+len(part):]
	}
	// Anchor last part.
	return strings.HasSuffix(s, parts[len(parts)-1])
}