first commit

internal/sieve/interp.go

@@ -0,0 +1,105 @@
+package sieve
+
+import "strings"
+
+// Result is the outcome of running a script against one message.
+type Result struct {
+	Action string // "fileinto" | "discard" | "keep" (default if nothing else fired)
+	Folder string // set only when Action == "fileinto"
+}
+
+// Execute runs script against the given headers (case-insensitive header
+// names, matching real email header semantics) and returns the first
+// decisive action encountered. "stop" halts execution immediately with
+// whatever result has accumulated so far. If no action fires, the default
+// result is "keep" (deliver to INBOX), matching RFC 5228 §2.10's implicit
+// keep behavior.
+//
+// Simplification: real Sieve treats keep/fileinto/discard as an
+// accumulating SET of actions (a message can be filed into a folder AND
+// kept in INBOX, for instance) — this implementation tracks only the single
+// most recent action instead, last-one-wins. This still matches RFC 5228's
+// core rule that "discard cancels the implicit keep, but an explicit keep
+// after it still delivers" (§4.4) — a discard followed by an unconditional
+// keep with no stop in between DOES deliver the message, correctly. What's
+// NOT supported is a script that intends both fileinto AND keep to fire
+// simultaneously (message copied to a folder AND left in INBOX) — write
+// "stop;" after the decisive action if that's not the intended behavior,
+// same as real Sieve authors are advised to do to avoid ambiguity.
+func Execute(script *Script, headers map[string]string) Result {
+	result := Result{Action: "keep"}
+	execStatements(script.Statements, headers, &result)
+	return result
+}
+
+// execStatements returns true if execution should stop (a "stop" action fired).
+func execStatements(stmts []Statement, headers map[string]string, result *Result) bool {
+	for _, stmt := range stmts {
+		switch s := stmt.(type) {
+		case Action:
+			switch s.Name {
+			case "fileinto":
+				result.Action = "fileinto"
+				result.Folder = s.Arg
+			case "discard":
+				result.Action = "discard"
+			case "keep":
+				result.Action = "keep"
+			case "stop":
+				return true
+			}
+		case IfStatement:
+			if evalTest(s.Test, headers) {
+				if execStatements(s.Then, headers, result) {
+					return true
+				}
+				continue
+			}
+			matched := false
+			for _, ei := range s.ElseIfs {
+				if evalTest(ei.Test, headers) {
+					matched = true
+					if execStatements(ei.Then, headers, result) {
+						return true
+					}
+					break
+				}
+			}
+			if !matched && s.HasElse {
+				if execStatements(s.Else, headers, result) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func evalTest(t Test, headers map[string]string) bool {
+	switch t.Kind {
+	case "true":
+		return true
+	case "header":
+		actual, ok := lookupHeader(headers, t.Header)
+		if !ok {
+			return false
+		}
+		switch t.MatchType {
+		case "contains":
+			return strings.Contains(strings.ToLower(actual), strings.ToLower(t.Value))
+		case "is":
+			return strings.EqualFold(strings.TrimSpace(actual), strings.TrimSpace(t.Value))
+		}
+	}
+	return false
+}
+
+func lookupHeader(headers map[string]string, name string) (string, bool) {
+	// Case-insensitive lookup — email headers are case-insensitive per RFC 5322.
+	for k, v := range headers {
+		if strings.EqualFold(k, name) {
+			return v, true
+		}
+	}
+	return "", false
+}