Add httpassert header validation (#286)

## What

- Add httpassert header validation

## References

<!-- Add identifier for issue tickets, links to other PRs, etc. -->

## Checklist

<!-- Remove this section if not applicable to your changes -->

- [ ] Tests

Author: stefanTolksdorf

pkg/httpassert/extracter.go

@@ -7,6 +7,7 @@ package httpassert
 import (
 	"fmt"
 	"reflect"
+	"regexp"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -21,68 +22,127 @@ type Extractor func(t *testing.T, actual any) any
 //	request.Expect().JsonPath("$.data.id", httpassert.ExtractTo(&id))
 func ExtractTo(ptr any) Extractor {
 	return func(t *testing.T, actual any) any {
-		targetVal := reflect.ValueOf(ptr)
-		if targetVal.Kind() != reflect.Ptr || targetVal.IsNil() {
-			assert.Fail(t, "ExtractTo requires a non-nil pointer")
+		return extractInto(t, ptr, actual, nil)
+	}
+}
+
+func ExtractRegexTo(value string, ptr any) Extractor {
+	return func(t *testing.T, actual any) any {
+		return extractInto(t, ptr, actual, func(t *testing.T, v any, dstType reflect.Type) (any, bool) {
+			s, ok := v.(string)
+			if !ok {
+				assert.Fail(t, fmt.Sprintf("ExtractRegexTo expects actual to be string, got %T", v))
+				return nil, false
+			}
+
+			re := regexp.MustCompile(value)
+
+			m := re.FindStringSubmatch(s)
+			if m == nil {
+				assert.Fail(t, fmt.Sprintf("ExtractRegexTo no match for %q in %q", re.String(), s))
+				return nil, false
+			}
+
+			// m[0] full match, m[1:] groups
+			groups := m[1:]
+			if len(groups) == 0 {
+				groups = []string{m[0]}
+			}
+
+			if dstType.Kind() == reflect.Slice {
+				return groups, true
+			}
+			return groups[0], true
+		})
+	}
+}
+
+func extractInto(
+	t *testing.T,
+	ptr any,
+	actual any,
+	preprocess func(t *testing.T, actual any, dstType reflect.Type) (any, bool),
+) any {
+	target := reflect.ValueOf(ptr)
+	if target.Kind() != reflect.Ptr || target.IsNil() {
+		assert.Fail(t, "ExtractTo requires a non-nil pointer")
+		return nil
+	}
+	if actual == nil {
+		assert.Fail(t, "ExtractTo actual value is nil")
+		return nil
+	}
+
+	dst := target.Elem()
+	dstType := dst.Type()
+
+	if preprocess != nil {
+		var ok bool
+		actual, ok = preprocess(t, actual, dstType)
+		if !ok {
 			return nil
 		}
-
 		if actual == nil {
 			assert.Fail(t, "ExtractTo actual value is nil")
 			return nil
 		}
+	}
 
-		outVal := reflect.ValueOf(actual)
-		targetType := targetVal.Elem().Type()
+	src := reflect.ValueOf(actual)
 
-		// Direct assign / convert for simple values (string, int, etc.)
-		if outVal.Type().AssignableTo(targetType) {
-			targetVal.Elem().Set(outVal)
-			return ptr
-		}
+	// unwrap interface{}
+	if src.IsValid() && src.Kind() == reflect.Interface && !src.IsNil() {
+		src = reflect.ValueOf(src.Interface())
+	}
 
-		if outVal.Type().ConvertibleTo(targetType) {
-			targetVal.Elem().Set(outVal.Convert(targetType))
-			return ptr
-		}
+	// direct assign / convert
+	if src.IsValid() && src.Type().AssignableTo(dstType) {
+		dst.Set(src)
+		return ptr
+	}
+	if src.IsValid() && src.Type().ConvertibleTo(dstType) {
+		dst.Set(src.Convert(dstType))
+		return ptr
+	}
 
-		// Special handling for slices, e.g. []interface{} -> []string
-		if outVal.Kind() == reflect.Slice && targetType.Kind() == reflect.Slice {
-			elemType := targetType.Elem()
-			n := outVal.Len()
-			dst := reflect.MakeSlice(targetType, n, n)
-
-			for i := 0; i < n; i++ {
-				src := outVal.Index(i)
-
-				// If it's interface{}, unwrap to the underlying concrete value.
-				if src.Kind() == reflect.Interface && !src.IsNil() {
-					src = reflect.ValueOf(src.Interface())
-				}
-
-				if src.Type().AssignableTo(elemType) {
-					dst.Index(i).Set(src)
-					continue
-				}
-
-				if src.Type().ConvertibleTo(elemType) {
-					dst.Index(i).Set(src.Convert(elemType))
-					continue
-				}
-
-				assert.Fail(t,
-					fmt.Sprintf("ExtractTo slice element type mismatch at index %d: cannot assign %v to %v",
-						i, src.Type(), elemType))
-				return nil
+	// slice handling: e.g. []interface{} -> []string
+	if src.IsValid() && src.Kind() == reflect.Slice && dstType.Kind() == reflect.Slice {
+		elemType := dstType.Elem()
+		n := src.Len()
+		out := reflect.MakeSlice(dstType, n, n)
+
+		for i := 0; i < n; i++ {
+			s := src.Index(i)
+
+			// unwrap interface{} elements
+			if s.Kind() == reflect.Interface && !s.IsNil() {
+				s = reflect.ValueOf(s.Interface())
+			}
+
+			if s.Type().AssignableTo(elemType) {
+				out.Index(i).Set(s)
+				continue
+			}
+			if s.Type().ConvertibleTo(elemType) {
+				out.Index(i).Set(s.Convert(elemType))
+				continue
 			}
 
-			targetVal.Elem().Set(dst)
-			return ptr
+			assert.Fail(t, fmt.Sprintf(
+				"ExtractTo slice element type mismatch at index %d: cannot assign %v to %v",
+				i, s.Type(), elemType,
+			))
+			return nil
 		}
 
-		assert.Fail(t,
-			fmt.Sprintf("ExtractTo type mismatch: cannot assign %v to %v",
-				outVal.Type(), targetType))
-		return nil
+		dst.Set(out)
+		return ptr
+	}
+
+	srcType := any("<invalid>")
+	if src.IsValid() {
+		srcType = src.Type()
 	}
+	assert.Fail(t, fmt.Sprintf("ExtractTo type mismatch: cannot assign %v to %v", srcType, dstType))
+	return nil
 }

pkg/httpassert/matcher.go

@@ -6,6 +6,7 @@ package httpassert
 
 import (
 	"fmt"
+	"regexp"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -45,3 +46,13 @@ func Contains(v string) Matcher {
 		return valid
 	}
 }
+
+// Regex checks if a string matches the given regular expression
+// Example: ExpectJsonPath("$.data.name", httpassert.Regex("^foo.*bar$"))
+func Regex(expr string) Matcher {
+	re := regexp.MustCompile(expr)
+
+	return func(t *testing.T, value any) bool {
+		return assert.Regexp(t, re, value)
+	}
+}

pkg/httpassert/response.go

@@ -36,13 +36,32 @@ type Response interface {
 	JsonTemplateFile(path string, values map[string]any) Response
 	JsonFile(path string) Response
 
+	Header(name string, value any) Response
+
 	Body(body string) Response
 	GetJsonBodyObject(target any) Response
 	GetBody() string
 
 	Log() Response
 }
 
+func (r *responseImpl) Header(name string, value any) Response {
+	out := r.response.Header().Get(name)
+
+	switch v := value.(type) {
+	case Extractor:
+		v(r.t, out)
+		return r
+	case Matcher:
+		v(r.t, out)
+		return r
+
+	default:
+		assert.Equal(r.t, value, out)
+		return r
+	}
+}
+
 func (r *responseImpl) StatusCode(expected int) Response {
 	require.Equal(r.t, expected, r.response.Code)
 	return r

pkg/httpassert/response_test.go

@@ -143,6 +143,40 @@ func TestResponse(t *testing.T) {
 		})
 	})
 
+	t.Run("Header", func(t *testing.T) {
+		router := http.NewServeMux()
+		router.HandleFunc("/api", func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(http.StatusOK)
+		})
+
+		t.Run("compare string", func(t *testing.T) {
+			m := New(t, router)
+
+			m.Get("/api").
+				Expect().
+				Header("Content-Type", "application/json")
+		})
+
+		t.Run("extract value to variable", func(t *testing.T) {
+			m := New(t, router)
+
+			var value string
+			m.Get("/api").
+				Expect().
+				Header("Content-Type", ExtractRegexTo(`application/(.*)`, &value))
+			assert.Equal(t, "json", value)
+		})
+
+		t.Run("use matcher", func(t *testing.T) {
+			m := New(t, router)
+
+			m.Get("/api").
+				Expect().
+				Header("Content-Type", Regex("application/[json]"))
+		})
+	})
+
 	t.Run("POST basic JSON", func(t *testing.T) {
 		request.Post("/json").
 			ContentType("application/json").