Support matching JSON body with CEL expressions

CONFIGURATION.md

@@ -89,6 +89,12 @@ modules:
   # Probe fails if SSL is not present.
   [ fail_if_not_ssl: <boolean> | default = false ]
 
+  # Probe fails if response body JSON matches CEL:
+  fail_if_body_json_matches_cel: <cel expression, root field is called body>
+
+  # Probe fails if response body JSON does not match CEL:
+  fail_if_body_json_not_matches_cel: <cel expression, root field is called body>
+
   # Probe fails if response body matches regex.
   fail_if_body_matches_regexp:
     [ - <regex>, ... ]

config/config.go

@@ -28,6 +28,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/checker/decls"
 	yaml "gopkg.in/yaml.v3"
 
 	"github.com/alecthomas/units"
@@ -144,6 +146,74 @@ func (sc *SafeConfig) ReloadConfig(confFile string, logger *slog.Logger) (err er
 	return nil
 }
 
+// CelProgram encapsulates a cel.Program and makes it YAML marshalable.
+type CelProgram struct {
+	cel.Program
+	Expression string
+}
+
+// NewCelProgram creates a new CEL Program and returns an error if the
+// passed-in CEL expression does not compile.
+func NewCelProgram(s string) (CelProgram, error) {
+	program := CelProgram{
+		Expression: s,
+	}
+
+	env, err := cel.NewEnv(
+		cel.Declarations(
+			decls.NewVar("body", decls.NewMapType(decls.String, decls.Dyn)),
+		),
+	)
+	if err != nil {
+		return program, fmt.Errorf("error creating CEL environment: %s", err)
+	}
+
+	ast, issues := env.Compile(s)
+	if issues != nil && issues.Err() != nil {
+		return program, fmt.Errorf("error compiling CEL program: %s", issues.Err())
+	}
+
+	celProg, err := env.Program(ast, cel.InterruptCheckFrequency(100))
+	if err != nil {
+		return program, fmt.Errorf("error creating CEL program: %s", err)
+	}
+
+	program.Program = celProg
+
+	return program, nil
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface.
+func (c *CelProgram) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var expr string
+	if err := unmarshal(&expr); err != nil {
+		return err
+	}
+	celProg, err := NewCelProgram(expr)
+	if err != nil {
+		return fmt.Errorf("\"Could not compile CEL program\" expression=\"%s\"", expr)
+	}
+	*c = celProg
+	return nil
+}
+
+// MarshalYAML implements the yaml.Marshaler interface.
+func (c CelProgram) MarshalYAML() (interface{}, error) {
+	if c.Expression != "" {
+		return c.Expression, nil
+	}
+	return nil, nil
+}
+
+// MustNewCelProgram works like NewCelProgram, but panics if the CEL expression does not compile.
+func MustNewCelProgram(s string) CelProgram {
+	c, err := NewCelProgram(s)
+	if err != nil {
+		panic(err)
+	}
+	return c
+}
+
 // Regexp encapsulates a regexp.Regexp and makes it YAML marshalable.
 type Regexp struct {
 	*regexp.Regexp
@@ -215,6 +285,8 @@ type HTTPProbe struct {
 	Headers                      map[string]string       `yaml:"headers,omitempty"`
 	FailIfBodyMatchesRegexp      []Regexp                `yaml:"fail_if_body_matches_regexp,omitempty"`
 	FailIfBodyNotMatchesRegexp   []Regexp                `yaml:"fail_if_body_not_matches_regexp,omitempty"`
+	FailIfBodyJSONMatchesCel     *CelProgram             `yaml:"fail_if_body_json_matches_cel,omitempty"`
+	FailIfBodyJSONNotMatchesCel  *CelProgram             `yaml:"fail_if_body_json_not_matches_cel,omitempty"`
 	FailIfHeaderMatchesRegexp    []HeaderMatch           `yaml:"fail_if_header_matches,omitempty"`
 	FailIfHeaderNotMatchesRegexp []HeaderMatch           `yaml:"fail_if_header_not_matches,omitempty"`
 	Body                         string                  `yaml:"body,omitempty"`

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/alecthomas/kingpin/v2 v2.4.0
 	github.com/alecthomas/units v0.0.0-20231202071711-9a357b53e9c9
 	github.com/andybalholm/brotli v1.1.0
+	github.com/google/cel-go v0.20.1
 	github.com/miekg/dns v1.1.62
 	github.com/prometheus/client_golang v1.20.5
 	github.com/prometheus/client_model v0.6.1
@@ -18,6 +19,7 @@ require (
 )
 
 require (
+	github.com/antlr4-go/antlr/v4 v4.13.1 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/coreos/go-systemd/v22 v22.5.0 // indirect
@@ -28,14 +30,17 @@ require (
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
+	github.com/stoewer/go-strcase v1.2.0 // indirect
 	github.com/xhit/go-str2duration/v2 v2.1.0 // indirect
 	golang.org/x/crypto v0.28.0 // indirect
+	golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842 // indirect
 	golang.org/x/mod v0.18.0 // indirect
 	golang.org/x/oauth2 v0.23.0 // indirect
 	golang.org/x/sync v0.8.0 // indirect
 	golang.org/x/sys v0.26.0 // indirect
 	golang.org/x/text v0.19.0 // indirect
 	golang.org/x/tools v0.22.0 // indirect
+	google.golang.org/genproto/googleapis/api v0.0.0-20240814211410-ddb44dafa142 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 // indirect
 	google.golang.org/protobuf v1.34.2 // indirect
 )

go.sum

@@ -4,6 +4,8 @@ github.com/alecthomas/units v0.0.0-20231202071711-9a357b53e9c9 h1:ez/4by2iGztzR4
 github.com/alecthomas/units v0.0.0-20231202071711-9a357b53e9c9/go.mod h1:OMCwj8VM1Kc9e19TLln2VL61YJF0x1XFtfdL4JdbSyE=
 github.com/andybalholm/brotli v1.1.0 h1:eLKJA0d02Lf0mVpIDgYnqXcUn0GqVmEFny3VuID1U3M=
 github.com/andybalholm/brotli v1.1.0/go.mod h1:sms7XGricyQI9K10gOSf56VKKWS4oLer58Q+mhRPtnY=
+github.com/antlr4-go/antlr/v4 v4.13.1 h1:SqQKkuVZ+zWkMMNkjy5FZe5mr5WURWnlpmOuzYWrPrQ=
+github.com/antlr4-go/antlr/v4 v4.13.1/go.mod h1:GKmUxMtwp6ZgGwZSva4eWPC5mS6vUAmOABFgjdkM7Nw=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
@@ -14,6 +16,8 @@ github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/google/cel-go v0.20.1 h1:nDx9r8S3L4pE61eDdt8igGj8rf5kjYR3ILxWIpWNi84=
+github.com/google/cel-go v0.20.1/go.mod h1:kWcIzTsPX0zmQ+H3TirHstLLf9ep5QTsZBN9u4dOYLg=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/jpillora/backoff v1.0.0 h1:uvFg412JmmHBHw7iwprIxkPMI+sGQ4kzOWsMeHnm2EA=
@@ -50,14 +54,19 @@ github.com/prometheus/procfs v0.15.1 h1:YagwOFzUgYfKKHX6Dr+sHT7km/hxC76UB0leargg
 github.com/prometheus/procfs v0.15.1/go.mod h1:fB45yRUv8NstnjriLhBQLuOUt+WW4BsoGhij/e3PBqk=
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
+github.com/stoewer/go-strcase v1.2.0 h1:Z2iHWqGXH00XYgqDmNgQbIBxf3wrNq0F3feEy0ainaU=
+github.com/stoewer/go-strcase v1.2.0/go.mod h1:IBiWB2sKIp3wVVQ3Y035++gc+knqhUQag1KpM8ahLw8=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.5.1/go.mod h1:5W2xD1RspED5o8YsWQXVCued0rvSQ+mT+I5cxcmMvtA=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 github.com/xhit/go-str2duration/v2 v2.1.0 h1:lxklc02Drh6ynqX+DdPyp5pCKLUQpRT8bp8Ydu2Bstc=
 github.com/xhit/go-str2duration/v2 v2.1.0/go.mod h1:ohY8p+0f07DiV6Em5LKB0s2YpLtXVyJfNt1+BlmyAsU=
 golang.org/x/crypto v0.28.0 h1:GBDwsMXVQi34v5CCYUm2jkJvu4cbtru2U4TN2PSyQnw=
 golang.org/x/crypto v0.28.0/go.mod h1:rmgy+3RHxRZMyY0jjAJShp2zgEdOqj2AO7U0pYmeQ7U=
+golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842 h1:vr/HnozRka3pE4EsMEg1lgkXJkTFJCVUX+S/ZT6wYzM=
+golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842/go.mod h1:XtvwrStGgqGPLc4cjQfWqZHG1YFdYs6swckp8vpsjnc=
 golang.org/x/mod v0.18.0 h1:5+9lSbEzPSdWkH32vYPBwEpX8KwDbM52Ud9xBUvNlb0=
 golang.org/x/mod v0.18.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/net v0.29.0 h1:5ORfpBpCs4HzDYoodCDBbwHzdR5UrLBZ3sOnUJmFoHo=
@@ -72,6 +81,8 @@ golang.org/x/text v0.19.0 h1:kTxAhCbGbxhK0IwgSKiMO5awPoDQ0RpfiVYBfK860YM=
 golang.org/x/text v0.19.0/go.mod h1:BuEKDfySbSR4drPmRPG/7iBdf8hvFMuRexcpahXilzY=
 golang.org/x/tools v0.22.0 h1:gqSGLZqv+AI9lIQzniJ0nZDRG5GBPsSi+DRNHWNz6yA=
 golang.org/x/tools v0.22.0/go.mod h1:aCwcsjqvq7Yqt6TNyX7QMU2enbQ/Gt0bo6krSeEri+c=
+google.golang.org/genproto/googleapis/api v0.0.0-20240814211410-ddb44dafa142 h1:wKguEg1hsxI2/L3hUYrpo1RVi48K+uTyzKqprwLXsb8=
+google.golang.org/genproto/googleapis/api v0.0.0-20240814211410-ddb44dafa142/go.mod h1:d6be+8HhtEtucleCbxpPW9PA9XwISACu8nvpPqF0BVo=
 google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 h1:e7S5W7MGGLaSu8j3YjdezkZ+m1/Nm0uRVRMEMGk26Xs=
 google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142/go.mod h1:UqMtugtsSgubUsoxbuAoiCXvqvErP7Gf0so0mK9tHxU=
 google.golang.org/grpc v1.67.0 h1:IdH9y6PF5MPSdAntIcpjQ+tXO41pcQsfZV2RxtQgVcw=

prober/http.go

@@ -18,6 +18,7 @@ import (
 	"compress/gzip"
 	"context"
 	"crypto/tls"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -35,6 +36,7 @@ import (
 	"time"
 
 	"github.com/andybalholm/brotli"
+	"github.com/google/cel-go/cel"
 	"github.com/prometheus/client_golang/prometheus"
 	pconfig "github.com/prometheus/common/config"
 	"github.com/prometheus/common/version"
@@ -64,6 +66,58 @@ func matchRegularExpressions(reader io.Reader, httpConfig config.HTTPProbe, logg
 	return true
 }
 
+func matchCelExpressions(ctx context.Context, reader io.Reader, httpConfig config.HTTPProbe, logger *slog.Logger) bool {
+	body, err := io.ReadAll(reader)
+	if err != nil {
+		logger.Error("Error reading HTTP body", "err", err)
+		return false
+	}
+
+	bodyJSON := make(map[string]interface{})
+	if err := json.Unmarshal(body, &bodyJSON); err != nil {
+		logger.Error("Error unmarshalling HTTP body", "err", err)
+		return false
+	}
+
+	evalPayload := map[string]interface{}{
+		"body": bodyJSON,
+	}
+
+	if httpConfig.FailIfBodyJSONMatchesCel != nil {
+		result, details, err := httpConfig.FailIfBodyJSONMatchesCel.ContextEval(ctx, evalPayload)
+		if err != nil {
+			logger.Error("Error evaluating CEL expression", "err", err)
+			return false
+		}
+		if result.Type() != cel.BoolType {
+			logger.Error("CEL evaluation result is not a boolean", "details", details)
+			return false
+		}
+		if result.Type() == cel.BoolType && result.Value().(bool) {
+			logger.Error("Body matched CEL expression", "expression", httpConfig.FailIfBodyJSONMatchesCel.Expression)
+			return false
+		}
+	}
+
+	if httpConfig.FailIfBodyJSONNotMatchesCel != nil {
+		result, details, err := httpConfig.FailIfBodyJSONNotMatchesCel.ContextEval(ctx, evalPayload)
+		if err != nil {
+			logger.Error("Error evaluating CEL expression", "err", err)
+			return false
+		}
+		if result.Type() != cel.BoolType {
+			logger.Error("CEL evaluation result is not a boolean", "details", details)
+			return false
+		}
+		if result.Type() == cel.BoolType && !result.Value().(bool) {
+			logger.Error("Body did not match CEL expression", "expression", httpConfig.FailIfBodyJSONNotMatchesCel.Expression)
+			return false
+		}
+	}
+
+	return true
+}
+
 func matchRegularExpressionsOnHeaders(header http.Header, httpConfig config.HTTPProbe, logger *slog.Logger) bool {
 	for _, headerMatchSpec := range httpConfig.FailIfHeaderMatchesRegexp {
 		values := header[textproto.CanonicalMIMEHeaderKey(headerMatchSpec.Header)]
@@ -296,6 +350,11 @@ func ProbeHTTP(ctx context.Context, target string, module config.Module, registr
 			Help: "Indicates if probe failed due to regex",
 		})
 
+		probeFailedDueToCel = prometheus.NewGauge(prometheus.GaugeOpts{
+			Name: "probe_failed_due_to_cel",
+			Help: "Indicates if probe failed due to CEL",
+		})
+
 		probeHTTPLastModified = prometheus.NewGauge(prometheus.GaugeOpts{
 			Name: "probe_http_last_modified_timestamp_seconds",
 			Help: "Returns the Last-Modified HTTP response header in unixtime",
@@ -310,6 +369,7 @@ func ProbeHTTP(ctx context.Context, target string, module config.Module, registr
 	registry.MustRegister(statusCodeGauge)
 	registry.MustRegister(probeHTTPVersionGauge)
 	registry.MustRegister(probeFailedDueToRegex)
+	registry.MustRegister(probeFailedDueToCel)
 
 	httpConfig := module.HTTP
 
@@ -547,6 +607,15 @@ func ProbeHTTP(ctx context.Context, target string, module config.Module, registr
 			}
 		}
 
+		if success && (httpConfig.FailIfBodyJSONMatchesCel != nil || httpConfig.FailIfBodyJSONNotMatchesCel != nil) {
+			success = matchCelExpressions(ctx, byteCounter, httpConfig, logger)
+			if success {
+				probeFailedDueToCel.Set(0)
+			} else {
+				probeFailedDueToCel.Set(1)
+			}
+		}
+
 		if !requestErrored {
 			_, err = io.Copy(io.Discard, byteCounter)
 			if err != nil {