Merge branch 'main' into Xe/anubis-custom-logger

Signed-off-by: Xe Iaso <xe.iaso@techaro.lol>

.github/workflows/zizmor.yml

@@ -21,7 +21,7 @@ jobs:
           persist-credentials: false
 
       - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@7edac99f961f18b581bbd960d59d049f04c0002f # v6.4.1
+        uses: astral-sh/setup-uv@e92bafb6253dcd438e0484186d7669ea7a8ca1cc # v6.4.3
 
       - name: Run zizmor 🌈
         run: uvx zizmor --format sarif . > results.sarif 
@@ -29,7 +29,7 @@ jobs:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }} 
 
       - name: Upload SARIF file
-        uses: github/codeql-action/upload-sarif@181d5eefc20863364f96762470ba6f862bdef56b # v3.29.2
+        uses: github/codeql-action/upload-sarif@4e828ff8d448a8a6e532957b1811f387a63867e8 # v3.29.4
         with:
           sarif_file: results.sarif
           category: zizmor

data/bots/_deny-pathological.yaml

@@ -1,3 +1,4 @@
 - import: (data)/bots/cloudflare-workers.yaml
 - import: (data)/bots/headless-browsers.yaml
 - import: (data)/bots/us-ai-scraper.yaml
+- import: (data)/bots/custom-async-http-client.yaml

data/bots/custom-async-http-client.yaml

@@ -0,0 +1,5 @@
+- name: "custom-async-http-client"
+  user_agent_regex: "Custom-AsyncHttpClient"
+  action: WEIGH
+  weight:
+    adjust: 10

docs/docs/CHANGELOG.md

@@ -15,6 +15,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Downstream consumers can change the default [log/slog#Logger](https://pkg.go.dev/log/slog#Logger) instance that Anubis uses by setting `opts.Logger` to your slog instance of choice ([#864](https://github.com/TecharoHQ/anubis/issues/864)).
 - The [Thoth client](https://anubis.techaro.lol/docs/admin/thoth) is now public in the repo instead of being an internal package.
+- [Custom-AsyncHttpClient](https://github.com/AsyncHttpClient/async-http-client)'s default User-Agent has an increased weight by default ([#852](https://github.com/TecharoHQ/anubis/issues/852)).
+- The [`segments`](./admin/configuration/expressions.mdx#segments) function was added for splitting a path into its slash-separated segments.
+- When issuing a challenge, Anubis stores information about that challenge into the store. That stored information is later used to validate challenge responses. This works around nondeterminism in bot rules. ([#917](https://github.com/TecharoHQ/anubis/issues/917))
 
 ## v1.21.3: Minfilia Warde - Echo 3
 

docs/docs/admin/configuration/expressions.mdx

@@ -232,6 +232,39 @@ This is best applied when doing explicit block rules, eg:
 
 It seems counter-intuitive to allow known bad clients through sometimes, but this allows you to confuse attackers by making Anubis' behavior random. Adjust the thresholds and numbers as facts and circumstances demand.
 
+### `segments`
+
+Available in `bot` expressions.
+
+```ts
+function segments(path: string): string[];
+```
+
+`segments` returns the number of slash-separated path segments, ignoring the leading slash. Here is what it will return with some common paths:
+
+| Input                    | Output                 |
+| :----------------------- | :--------------------- |
+| `segments("/")`          | `[""]`                 |
+| `segments("/foo/bar")`   | `["foo", "bar"] `      |
+| `segments("/users/xe/")` | `["users", "xe", ""] ` |
+
+:::note
+
+If the path ends with a `/`, then the last element of the result will be an empty string. This is because `/users/xe` and `/users/xe/` are semantically different paths.
+
+:::
+
+This is useful if you want to write rules that allow requests that have no query parameters only if they have less than two path segments:
+
+```yaml
+- name: two-path-segments-no-query
+  action: ALLOW
+  expression:
+    all:
+      - size(query) == 0
+      - size(segments(path)) < 2
+```
+
 ## Life advice
 
 Expressions are very powerful. This is a benefit and a burden. If you are not careful with your expression targeting, you will be liable to get yourself into trouble. If you are at all in doubt, throw a `CHALLENGE` over a `DENY`. Legitimate users can easily work around a `CHALLENGE` result with a [proof of work challenge](../../design/why-proof-of-work.mdx). Bots are less likely to be able to do this.

internal/log.go

@@ -28,6 +28,9 @@ func InitSlog(level string) {
 
 func GetRequestLogger(base *slog.Logger, r *http.Request) *slog.Logger {
 	return base.With(
+		"host", r.Host,
+		"method", r.Method,
+		"path", r.URL.Path,
 		"user_agent", r.UserAgent(),
 		"accept_language", r.Header.Get("Accept-Language"),
 		"priority", r.Header.Get("Priority"),

lib/anubis.go

@@ -91,41 +91,39 @@ func (s *Server) getTokenKeyfunc() jwt.Keyfunc {
 	}
 }
 
-func (s *Server) challengeFor(r *http.Request) (*challenge.Challenge, error) {
+func (s *Server) getChallenge(r *http.Request) (*challenge.Challenge, error) {
 	ckies := r.CookiesNamed(anubis.TestCookieName)
-
 	if len(ckies) == 0 {
-		return s.issueChallenge(r.Context(), r)
+		return nil, store.ErrNotFound
 	}
 
 	j := store.JSON[challenge.Challenge]{Underlying: s.store}
 
 	ckie := ckies[0]
 	chall, err := j.Get(r.Context(), "challenge:"+ckie.Value)
-	if err != nil {
-		if errors.Is(err, store.ErrNotFound) {
-			return s.issueChallenge(r.Context(), r)
-		}
 
-		return nil, err
-	}
-
-	return &chall, nil
+	return &chall, err
 }
 
-func (s *Server) issueChallenge(ctx context.Context, r *http.Request) (*challenge.Challenge, error) {
+func (s *Server) issueChallenge(ctx context.Context, r *http.Request, lg *slog.Logger, cr policy.CheckResult, rule *policy.Bot) (*challenge.Challenge, error) {
+	if cr.Rule != config.RuleChallenge {
+		slog.Error("this should be impossible, asked to issue a challenge but the rule is not a challenge rule", "cr", cr, "rule", rule)
+		//return nil, errors.New("[unexpected] this codepath should be impossible, asked to issue a challenge for a non-challenge rule")
+	}
+
 	id, err := uuid.NewV7()
 	if err != nil {
 		return nil, err
 	}
 
-	var randomData = make([]byte, 256)
+	var randomData = make([]byte, 64)
 	if _, err := rand.Read(randomData); err != nil {
 		return nil, err
 	}
 
 	chall := challenge.Challenge{
 		ID:         id.String(),
+		Method:     rule.Challenge.Algorithm,
 		RandomData: fmt.Sprintf("%x", randomData),
 		IssuedAt:   time.Now(),
 		Metadata: map[string]string{
@@ -139,6 +137,8 @@ func (s *Server) issueChallenge(ctx context.Context, r *http.Request) (*challeng
 		return nil, err
 	}
 
+	lg.Info("new challenge issued", "challenge", id.String())
+
 	return &chall, err
 }
 
@@ -186,21 +186,21 @@ func (s *Server) maybeReverseProxy(w http.ResponseWriter, r *http.Request, httpS
 	if err != nil {
 		lg.Debug("cookie not found", "path", r.URL.Path)
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
 	if err := ckie.Valid(); err != nil {
 		lg.Debug("cookie is invalid", "err", err)
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
 	if time.Now().After(ckie.Expires) && !ckie.Expires.IsZero() {
 		lg.Debug("cookie expired", "path", r.URL.Path)
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
@@ -209,7 +209,7 @@ func (s *Server) maybeReverseProxy(w http.ResponseWriter, r *http.Request, httpS
 	if err != nil || !token.Valid {
 		lg.Debug("invalid token", "path", r.URL.Path, "err", err)
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
@@ -217,7 +217,7 @@ func (s *Server) maybeReverseProxy(w http.ResponseWriter, r *http.Request, httpS
 	if !ok {
 		lg.Debug("invalid token claims type", "path", r.URL.Path)
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
@@ -225,14 +225,14 @@ func (s *Server) maybeReverseProxy(w http.ResponseWriter, r *http.Request, httpS
 	if !ok {
 		lg.Debug("policyRule claim is not a string")
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
 	if policyRule != rule.Hash() {
 		lg.Debug("user originally passed with a different rule, issuing new challenge", "old", policyRule, "new", rule.Name)
 		s.ClearCookie(w, CookieOpts{Path: cookiePath, Host: r.Host})
-		s.RenderIndex(w, r, rule, httpStatusOnly)
+		s.RenderIndex(w, r, cr, rule, httpStatusOnly)
 		return
 	}
 
@@ -347,7 +347,7 @@ func (s *Server) MakeChallenge(w http.ResponseWriter, r *http.Request) {
 	}
 	lg = lg.With("check_result", cr)
 
-	chall, err := s.challengeFor(r)
+	chall, err := s.issueChallenge(r.Context(), r, lg, cr, rule)
 	if err != nil {
 		lg.Error("failed to fetch or issue challenge", "err", err)
 		w.WriteHeader(http.StatusInternalServerError)
@@ -437,19 +437,21 @@ func (s *Server) PassChallenge(w http.ResponseWriter, r *http.Request) {
 	}
 	lg = lg.With("check_result", cr)
 
-	impl, ok := challenge.Get(rule.Challenge.Algorithm)
+	chall, err := s.getChallenge(r)
+	if err != nil {
+		lg.Error("getChallenge failed", "err", err)
+		s.respondWithError(w, r, fmt.Sprintf("%s: %s", localizer.T("internal_server_error"), rule.Challenge.Algorithm))
+		return
+	}
+
+	impl, ok := challenge.Get(chall.Method)
 	if !ok {
 		lg.Error("check failed", "err", err)
 		s.respondWithError(w, r, fmt.Sprintf("%s: %s", localizer.T("internal_server_error"), rule.Challenge.Algorithm))
 		return
 	}
 
-	chall, err := s.challengeFor(r)
-	if err != nil {
-		lg.Error("check failed", "err", err)
-		s.respondWithError(w, r, fmt.Sprintf("%s: %s", localizer.T("internal_server_error"), rule.Challenge.Algorithm))
-		return
-	}
+	lg = lg.With("challenge", chall.ID)
 
 	in := &challenge.ValidateInput{
 		Challenge: chall,
@@ -467,9 +469,13 @@ func (s *Server) PassChallenge(w http.ResponseWriter, r *http.Request) {
 		case errors.As(err, &cerr):
 			switch {
 			case errors.Is(err, challenge.ErrFailed):
+				lg.Error("challenge failed", "err", err)
 				s.respondWithStatus(w, r, cerr.PublicReason, cerr.StatusCode)
+				return
 			case errors.Is(err, challenge.ErrInvalidFormat), errors.Is(err, challenge.ErrMissingField):
+				lg.Error("invalid challenge format", "err", err)
 				s.respondWithError(w, r, cerr.PublicReason)
+				return
 			}
 		}
 	}

lib/challenge/challenge.go

@@ -5,6 +5,7 @@ import "time"
 // Challenge is the metadata about a single challenge issuance.
 type Challenge struct {
 	ID         string            `json:"id"`         // UUID identifying the challenge
+	Method     string            `json:"method"`     // Challenge method
 	RandomData string            `json:"randomData"` // The random data the client processes
 	IssuedAt   time.Time         `json:"issuedAt"`   // When the challenge was issued
 	Metadata   map[string]string `json:"metadata"`   // Challenge metadata such as IP address and user agent

lib/http.go

@@ -111,7 +111,7 @@ func randomChance(n int) bool {
 	return rand.Intn(n) == 0
 }
 
-func (s *Server) RenderIndex(w http.ResponseWriter, r *http.Request, rule *policy.Bot, returnHTTPStatusOnly bool) {
+func (s *Server) RenderIndex(w http.ResponseWriter, r *http.Request, cr policy.CheckResult, rule *policy.Bot, returnHTTPStatusOnly bool) {
 	localizer := localization.GetLocalizer(r)
 
 	if returnHTTPStatusOnly {
@@ -129,14 +129,16 @@ func (s *Server) RenderIndex(w http.ResponseWriter, r *http.Request, rule *polic
 	}
 
 	challengesIssued.WithLabelValues("embedded").Add(1)
-	chall, err := s.challengeFor(r)
+	chall, err := s.issueChallenge(r.Context(), r, lg, cr, rule)
 	if err != nil {
-		lg.Error("can't get challenge", "err", "err")
+		lg.Error("can't get challenge", "err", err)
 		s.ClearCookie(w, CookieOpts{Name: anubis.TestCookieName, Host: r.Host})
 		s.respondWithError(w, r, fmt.Sprintf("%s: %s", localizer.T("internal_server_error"), rule.Challenge.Algorithm))
 		return
 	}
 
+	lg = lg.With("challenge", chall.ID)
+
 	var ogTags map[string]string = nil
 	if s.opts.OpenGraph.Enabled {
 		var err error
@@ -154,7 +156,7 @@ func (s *Server) RenderIndex(w http.ResponseWriter, r *http.Request, rule *polic
 		Expiry: 30 * time.Minute,
 	})
 
-	impl, ok := challenge.Get(rule.Challenge.Algorithm)
+	impl, ok := challenge.Get(chall.Method)
 	if !ok {
 		lg.Error("check failed", "err", "can't get algorithm", "algorithm", rule.Challenge.Algorithm)
 		s.ClearCookie(w, CookieOpts{Name: anubis.TestCookieName, Host: r.Host})

lib/policy/expressions/environment.go

@@ -2,6 +2,7 @@ package expressions
 
 import (
 	"math/rand/v2"
+	"strings"
 
 	"github.com/google/cel-go/cel"
 	"github.com/google/cel-go/common/types"
@@ -54,6 +55,28 @@ func BotEnvironment() (*cel.Env, error) {
 				}),
 			),
 		),
+
+		cel.Function("segments",
+			cel.Overload("segments_string_list_string",
+				[]*cel.Type{cel.StringType},
+				cel.ListType(cel.StringType),
+				cel.UnaryBinding(func(path ref.Val) ref.Val {
+					pathStrType, ok := path.(types.String)
+					if !ok {
+						return types.ValOrErr(path, "path is not a string, but is %T", path)
+					}
+
+					pathStr := string(pathStrType)
+					if !strings.HasPrefix(pathStr, "/") {
+						return types.ValOrErr(path, "path does not start with /")
+					}
+
+					pathList := strings.Split(string(pathStr), "/")[1:]
+
+					return types.NewStringList(types.DefaultTypeAdapter, pathList)
+				}),
+			),
+		),
 	)
 }
 

lib/policy/expressions/environment_test.go

@@ -12,99 +12,228 @@ func TestBotEnvironment(t *testing.T) {
 		t.Fatalf("failed to create bot environment: %v", err)
 	}
 
-	tests := []struct {
-		name        string
-		expression  string
-		headers     map[string]string
-		expected    types.Bool
-		description string
-	}{
-		{
-			name:       "missing-header",
-			expression: `missingHeader(headers, "Missing-Header")`,
-			headers: map[string]string{
-				"User-Agent":   "test-agent",
-				"Content-Type": "application/json",
+	t.Run("missingHeader", func(t *testing.T) {
+		tests := []struct {
+			name        string
+			expression  string
+			headers     map[string]string
+			expected    types.Bool
+			description string
+		}{
+			{
+				name:       "missing-header",
+				expression: `missingHeader(headers, "Missing-Header")`,
+				headers: map[string]string{
+					"User-Agent":   "test-agent",
+					"Content-Type": "application/json",
+				},
+				expected:    types.Bool(true),
+				description: "should return true when header is missing",
 			},
-			expected:    types.Bool(true),
-			description: "should return true when header is missing",
-		},
-		{
-			name:       "existing-header",
-			expression: `missingHeader(headers, "User-Agent")`,
-			headers: map[string]string{
-				"User-Agent":   "test-agent",
-				"Content-Type": "application/json",
+			{
+				name:       "existing-header",
+				expression: `missingHeader(headers, "User-Agent")`,
+				headers: map[string]string{
+					"User-Agent":   "test-agent",
+					"Content-Type": "application/json",
+				},
+				expected:    types.Bool(false),
+				description: "should return false when header exists",
 			},
-			expected:    types.Bool(false),
-			description: "should return false when header exists",
-		},
-		{
-			name:       "case-sensitive",
-			expression: `missingHeader(headers, "user-agent")`,
-			headers: map[string]string{
-				"User-Agent": "test-agent",
+			{
+				name:       "case-sensitive",
+				expression: `missingHeader(headers, "user-agent")`,
+				headers: map[string]string{
+					"User-Agent": "test-agent",
+				},
+				expected:    types.Bool(true),
+				description: "should be case-sensitive (user-agent != User-Agent)",
 			},
-			expected:    types.Bool(true),
-			description: "should be case-sensitive (user-agent != User-Agent)",
-		},
-		{
-			name:        "empty-headers",
-			expression:  `missingHeader(headers, "Any-Header")`,
-			headers:     map[string]string{},
-			expected:    types.Bool(true),
-			description: "should return true for any header when map is empty",
-		},
-		{
-			name:       "real-world-sec-ch-ua",
-			expression: `missingHeader(headers, "Sec-Ch-Ua")`,
-			headers: map[string]string{
-				"User-Agent": "curl/7.68.0",
-				"Accept":     "*/*",
-				"Host":       "example.com",
+			{
+				name:        "empty-headers",
+				expression:  `missingHeader(headers, "Any-Header")`,
+				headers:     map[string]string{},
+				expected:    types.Bool(true),
+				description: "should return true for any header when map is empty",
 			},
-			expected:    types.Bool(true),
-			description: "should detect missing browser-specific headers from bots",
-		},
-		{
-			name:       "browser-with-sec-ch-ua",
-			expression: `missingHeader(headers, "Sec-Ch-Ua")`,
-			headers: map[string]string{
-				"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36",
-				"Sec-Ch-Ua":  `"Chrome"; v="91", "Not A Brand"; v="99"`,
-				"Accept":     "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
+			{
+				name:       "real-world-sec-ch-ua",
+				expression: `missingHeader(headers, "Sec-Ch-Ua")`,
+				headers: map[string]string{
+					"User-Agent": "curl/7.68.0",
+					"Accept":     "*/*",
+					"Host":       "example.com",
+				},
+				expected:    types.Bool(true),
+				description: "should detect missing browser-specific headers from bots",
 			},
-			expected:    types.Bool(false),
-			description: "should return false when browser sends Sec-Ch-Ua header",
-		},
-	}
+			{
+				name:       "browser-with-sec-ch-ua",
+				expression: `missingHeader(headers, "Sec-Ch-Ua")`,
+				headers: map[string]string{
+					"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36",
+					"Sec-Ch-Ua":  `"Chrome"; v="91", "Not A Brand"; v="99"`,
+					"Accept":     "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
+				},
+				expected:    types.Bool(false),
+				description: "should return false when browser sends Sec-Ch-Ua header",
+			},
+		}
 
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			prog, err := Compile(env, tt.expression)
-			if err != nil {
-				t.Fatalf("failed to compile expression %q: %v", tt.expression, err)
-			}
+		for _, tt := range tests {
+			t.Run(tt.name, func(t *testing.T) {
+				prog, err := Compile(env, tt.expression)
+				if err != nil {
+					t.Fatalf("failed to compile expression %q: %v", tt.expression, err)
+				}
 
-			result, _, err := prog.Eval(map[string]interface{}{
-				"headers": tt.headers,
+				result, _, err := prog.Eval(map[string]interface{}{
+					"headers": tt.headers,
+				})
+				if err != nil {
+					t.Fatalf("failed to evaluate expression %q: %v", tt.expression, err)
+				}
+
+				if result != tt.expected {
+					t.Errorf("%s: expected %v, got %v", tt.description, tt.expected, result)
+				}
 			})
-			if err != nil {
-				t.Fatalf("failed to evaluate expression %q: %v", tt.expression, err)
-			}
+		}
 
-			if result != tt.expected {
-				t.Errorf("%s: expected %v, got %v", tt.description, tt.expected, result)
+		t.Run("function-compilation", func(t *testing.T) {
+			src := `missingHeader(headers, "Test-Header")`
+			_, err := Compile(env, src)
+			if err != nil {
+				t.Fatalf("failed to compile missingHeader expression: %v", err)
 			}
 		})
-	}
+	})
 
-	t.Run("function-compilation", func(t *testing.T) {
-		src := `missingHeader(headers, "Test-Header")`
-		_, err := Compile(env, src)
-		if err != nil {
-			t.Fatalf("failed to compile missingHeader expression: %v", err)
+	t.Run("segments", func(t *testing.T) {
+		for _, tt := range []struct {
+			name        string
+			description string
+			expression  string
+			path        string
+			expected    types.Bool
+		}{
+			{
+				name:        "simple",
+				description: "/ should have one path segment",
+				expression:  `size(segments(path)) == 1`,
+				path:        "/",
+				expected:    types.Bool(true),
+			},
+			{
+				name:        "two segments without trailing slash",
+				description: "/user/foo should have two segments",
+				expression:  `size(segments(path)) == 2`,
+				path:        "/user/foo",
+				expected:    types.Bool(true),
+			},
+			{
+				name:        "at least two segments",
+				description: "/foo/bar/ should have at least two path segments",
+				expression:  `size(segments(path)) >= 2`,
+				path:        "/foo/bar/",
+				expected:    types.Bool(true),
+			},
+			{
+				name:        "at most two segments",
+				description: "/foo/bar/ does not have less than two path segments",
+				expression:  `size(segments(path)) < 2`,
+				path:        "/foo/bar/",
+				expected:    types.Bool(false),
+			},
+		} {
+			t.Run(tt.name, func(t *testing.T) {
+				prog, err := Compile(env, tt.expression)
+				if err != nil {
+					t.Fatalf("failed to compile expression %q: %v", tt.expression, err)
+				}
+
+				result, _, err := prog.Eval(map[string]interface{}{
+					"path": tt.path,
+				})
+				if err != nil {
+					t.Fatalf("failed to evaluate expression %q: %v", tt.expression, err)
+				}
+
+				if result != tt.expected {
+					t.Errorf("%s: expected %v, got %v", tt.description, tt.expected, result)
+				}
+			})
 		}
+
+		t.Run("invalid", func(t *testing.T) {
+			for _, tt := range []struct {
+				name            string
+				description     string
+				expression      string
+				env             any
+				wantFailCompile bool
+				wantFailEval    bool
+			}{
+				{
+					name:        "segments of headers",
+					description: "headers are not a path list",
+					expression:  `segments(headers)`,
+					env: map[string]any{
+						"headers": map[string]string{
+							"foo": "bar",
+						},
+					},
+					wantFailCompile: true,
+				},
+				{
+					name:        "invalid path type",
+					description: "a path should be a sting",
+					expression:  `size(segments(path)) != 0`,
+					env: map[string]any{
+						"path": 4,
+					},
+					wantFailEval: true,
+				},
+				{
+					name:        "invalid path",
+					description: "a path should start with a leading slash",
+					expression:  `size(segments(path)) != 0`,
+					env: map[string]any{
+						"path": "foo",
+					},
+					wantFailEval: true,
+				},
+			} {
+				t.Run(tt.name, func(t *testing.T) {
+					prog, err := Compile(env, tt.expression)
+					if err != nil {
+						if !tt.wantFailCompile {
+							t.Log(tt.description)
+							t.Fatalf("failed to compile expression %q: %v", tt.expression, err)
+						} else {
+							return
+						}
+					}
+
+					_, _, err = prog.Eval(tt.env)
+
+					if err == nil {
+						t.Log(tt.description)
+						t.Fatal("wanted an error but got none")
+					}
+
+					t.Log(err)
+				})
+			}
+		})
+
+		t.Run("function-compilation", func(t *testing.T) {
+			src := `size(segments(path)) <= 2`
+			_, err := Compile(env, src)
+			if err != nil {
+				t.Fatalf("failed to compile missingHeader expression: %v", err)
+			}
+		})
 	})
 }