Implement filter in status, website and uri in CLI and Frontend

cmd/frontend/filter.go

@@ -0,0 +1,175 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	st "git.ipng.ch/ipng/nginx-logtail/internal/store"
+)
+
+// andRe splits a filter expression on AND (case-insensitive, surrounded by whitespace).
+var andRe = regexp.MustCompile(`(?i)\s+and\s+`)
+
+// ParseFilterExpr parses a mini filter expression into a filterState.
+//
+// Syntax: TERM [AND TERM ...]
+//
+// Terms:
+//
+//	status=200  status!=200  status>=400  status>400  status<=500  status<500
+//	website=example.com      — exact match
+//	website~=gouda.*         — RE2 regex
+//	uri=/api/v1/             — exact match
+//	uri~=^/api/.*            — RE2 regex
+//	prefix=1.2.3.0/24        — exact match
+//
+// Values may be enclosed in double or single quotes.
+func ParseFilterExpr(s string) (filterState, error) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return filterState{}, nil
+	}
+	terms := andRe.Split(s, -1)
+	var fs filterState
+	for _, term := range terms {
+		term = strings.TrimSpace(term)
+		if term == "" {
+			continue
+		}
+		if err := applyTerm(term, &fs); err != nil {
+			return filterState{}, err
+		}
+	}
+	return fs, nil
+}
+
+// applyTerm parses a single "field op value" term into fs.
+func applyTerm(term string, fs *filterState) error {
+	// Find the first operator character: ~, !, >, <, =
+	opIdx := strings.IndexAny(term, "~!><=")
+	if opIdx <= 0 {
+		return fmt.Errorf("invalid term %q: expected field=value, field>=value, field~=regex, etc.", term)
+	}
+
+	field := strings.ToLower(strings.TrimSpace(term[:opIdx]))
+	rest := term[opIdx:]
+
+	var op, value string
+	switch {
+	case strings.HasPrefix(rest, "~="):
+		op, value = "~=", rest[2:]
+	case strings.HasPrefix(rest, "!="):
+		op, value = "!=", rest[2:]
+	case strings.HasPrefix(rest, ">="):
+		op, value = ">=", rest[2:]
+	case strings.HasPrefix(rest, "<="):
+		op, value = "<=", rest[2:]
+	case strings.HasPrefix(rest, ">"):
+		op, value = ">", rest[1:]
+	case strings.HasPrefix(rest, "<"):
+		op, value = "<", rest[1:]
+	case strings.HasPrefix(rest, "="):
+		op, value = "=", rest[1:]
+	default:
+		return fmt.Errorf("unrecognised operator in %q", term)
+	}
+
+	value = unquote(strings.TrimSpace(value))
+
+	switch field {
+	case "status":
+		if op == "~=" {
+			return fmt.Errorf("status does not support ~=; use =, !=, >=, >, <=, <")
+		}
+		expr := op + value
+		if op == "=" {
+			expr = value // ParseStatusExpr accepts bare "200"
+		}
+		if _, _, ok := st.ParseStatusExpr(expr); !ok {
+			return fmt.Errorf("invalid status expression %q", expr)
+		}
+		fs.Status = expr
+	case "website":
+		switch op {
+		case "=":
+			fs.Website = value
+		case "~=":
+			fs.WebsiteRe = value
+		default:
+			return fmt.Errorf("website only supports = and ~=, not %q", op)
+		}
+	case "uri":
+		switch op {
+		case "=":
+			fs.URI = value
+		case "~=":
+			fs.URIRe = value
+		default:
+			return fmt.Errorf("uri only supports = and ~=, not %q", op)
+		}
+	case "prefix":
+		if op != "=" {
+			return fmt.Errorf("prefix only supports =, not %q", op)
+		}
+		fs.Prefix = value
+	default:
+		return fmt.Errorf("unknown field %q; valid: status, website, uri, prefix", field)
+	}
+	return nil
+}
+
+// unquote strips surrounding double or single quotes.
+func unquote(s string) string {
+	if len(s) >= 2 {
+		if (s[0] == '"' && s[len(s)-1] == '"') || (s[0] == '\'' && s[len(s)-1] == '\'') {
+			return s[1 : len(s)-1]
+		}
+	}
+	return s
+}
+
+// FilterExprString serialises a filterState back into the mini filter expression language.
+// Returns "" when no filters are active.
+func FilterExprString(f filterState) string {
+	var parts []string
+	if f.Website != "" {
+		parts = append(parts, "website="+quoteMaybe(f.Website))
+	}
+	if f.WebsiteRe != "" {
+		parts = append(parts, "website~="+quoteMaybe(f.WebsiteRe))
+	}
+	if f.Prefix != "" {
+		parts = append(parts, "prefix="+quoteMaybe(f.Prefix))
+	}
+	if f.URI != "" {
+		parts = append(parts, "uri="+quoteMaybe(f.URI))
+	}
+	if f.URIRe != "" {
+		parts = append(parts, "uri~="+quoteMaybe(f.URIRe))
+	}
+	if f.Status != "" {
+		parts = append(parts, statusTermStr(f.Status))
+	}
+	return strings.Join(parts, " AND ")
+}
+
+// statusTermStr converts a stored status expression (">=400", "200") to a
+// full filter term ("status>=400", "status=200").
+func statusTermStr(expr string) string {
+	if expr == "" {
+		return ""
+	}
+	if len(expr) > 0 && (expr[0] == '!' || expr[0] == '>' || expr[0] == '<') {
+		return "status" + expr
+	}
+	return "status=" + expr
+}
+
+// quoteMaybe wraps s in double quotes when it contains spaces or quote characters.
+func quoteMaybe(s string) string {
+	if strings.ContainsAny(s, " \t\"'") {
+		return `"` + strings.ReplaceAll(s, `"`, `\"`) + `"`
+	}
+	return s
+}