fix: empty patterns in pricing are rejected (#12995)

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#### Description
Empty patterns were not rejected because of which corrupt config was
created, rejecting them at the handler layer.

<!--Reference issues using `Closes #issue-number` to enable automatic
closure on merge. -->
#### Issues closed by this PR
Part of https://github.com/SigNoz/nerve-pod/issues/282

pkg/types/llmpricingruletypes/pricing.go

@@ -208,6 +208,35 @@ func NewGettableUnmappedModels(items []*UnmappedModel) *GettableUnmappedModels {
 	}
 }
 
+func (u *UpdatableLLMPricingRule) UnmarshalJSON(data []byte) error {
+	type Alias UpdatableLLMPricingRule
+
+	var temp Alias
+	if err := json.Unmarshal(data, &temp); err != nil {
+		return err
+	}
+
+	*u = UpdatableLLMPricingRule(temp)
+	return u.Validate()
+}
+
+// Validate mirrors the collector's pattern check: at least one pattern, none
+// empty, all valid path.Match globs.
+func (u *UpdatableLLMPricingRule) Validate() error {
+	if len(u.ModelPattern) == 0 {
+		return errors.Newf(errors.TypeInvalidInput, ErrCodePricingRuleInvalidInput, "model %q: modelPattern must contain at least one pattern", u.Model)
+	}
+	for _, p := range u.ModelPattern {
+		if p == "" {
+			return errors.Newf(errors.TypeInvalidInput, ErrCodePricingRuleInvalidInput, "model %q: modelPattern must not contain an empty pattern", u.Model)
+		}
+		if _, err := path.Match(p, ""); err != nil {
+			return errors.Newf(errors.TypeInvalidInput, ErrCodePricingRuleInvalidInput, "model %q: modelPattern %q is not a valid glob", u.Model, p)
+		}
+	}
+	return nil
+}
+
 func NewLLMPricingRuleFromUpdatable(u *UpdatableLLMPricingRule, orgID valuer.UUID, userEmail string, now time.Time) *LLMPricingRule {
 	id := valuer.GenerateUUID()
 	if u.ID != nil {

pkg/types/llmpricingruletypes/processorconfig_test.go

@@ -1,6 +1,7 @@
 package llmpricingruletypes
 
 import (
+	"encoding/json"
 	"os"
 	"path/filepath"
 	"testing"
@@ -126,3 +127,34 @@ func TestGenerateCollectorConfig_EmptyInputPassthrough(t *testing.T) {
 		assert.Equal(t, in, out)
 	}
 }
+
+func TestUpdatableLLMPricingRuleUnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		pattern string
+		wantErr bool
+	}{
+		{name: "valid", pattern: `["gpt-4o*", "gpt-4o"]`},
+		{name: "missing", pattern: ``, wantErr: true},
+		{name: "null", pattern: `null`, wantErr: true},
+		{name: "empty_list", pattern: `[]`, wantErr: true},
+		{name: "empty_entry", pattern: `["gpt-4o*", ""]`, wantErr: true},
+		{name: "bad_glob", pattern: `["gpt-["]`, wantErr: true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			body := `{"modelName": "gpt-4o"}`
+			if tc.pattern != "" {
+				body = `{"modelName": "gpt-4o", "modelPattern": ` + tc.pattern + `}`
+			}
+			var req UpdatableLLMPricingRules
+			err := json.Unmarshal([]byte(`{"rules": [`+body+`]}`), &req)
+			if tc.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}

tests/integration/tests/llmpricingrules/01_upsert.py

@@ -130,3 +130,17 @@ def test_bulk_sync(
     assert all(r["pricing"]["input"] == 5 for r in stored)
 
     delete_all_llm_pricing_rules(signoz, token)
+
+
+def test_rejects_rule_without_pattern(
+    signoz: types.SigNoz,
+    create_user_admin: types.Operation,  # pylint: disable=unused-argument
+    get_token: Callable[[str, str], str],
+):
+    token = get_token(USER_ADMIN_EMAIL, USER_ADMIN_PASSWORD)
+    delete_all_llm_pricing_rules(signoz, token)
+
+    rules = zeus_rules(10)
+    rules[1]["modelPattern"] = []
+    assert upsert_llm_pricing_rules(signoz, token, rules).status_code == HTTPStatus.BAD_REQUEST
+    assert list_llm_pricing_rules(signoz, token) == []