feat(bigquery): make maximum rows returned from queries configurable

docs/en/resources/sources/bigquery.md

@@ -134,6 +134,7 @@ sources:
     # scopes: # Optional: List of OAuth scopes to request.
     #   - "https://www.googleapis.com/auth/bigquery"
     #   - "https://www.googleapis.com/auth/drive.readonly"
+    # maxQueryResultRows: 50 # Optional: Limits the number of rows returned by queries. Defaults to 50.
 ```
 
 Initialize a BigQuery source that uses the client's access token:
@@ -153,6 +154,7 @@ sources:
     # scopes: # Optional: List of OAuth scopes to request.
     #   - "https://www.googleapis.com/auth/bigquery"
     #   - "https://www.googleapis.com/auth/drive.readonly"
+    # maxQueryResultRows: 50 # Optional: Limits the number of rows returned by queries. Defaults to 50.
 ```
 
 ## Reference
@@ -167,3 +169,4 @@ sources:
 | useClientOAuth            |   bool   |    false     | If true, forwards the client's OAuth access token from the "Authorization" header to downstream queries. **Note:** This cannot be used with `writeMode: protected`.                                                                                                                                                                                                                                                                                                                                                |
 | scopes                    | []string |    false     | A list of OAuth 2.0 scopes to use for the credentials. If not provided, default scopes are used.                                                                                                                                                                                                                                                                                                                                                                                                                     |
 | impersonateServiceAccount |  string  |    false     | Service account email to impersonate when making BigQuery and Dataplex API calls. The authenticated principal must have the `roles/iam.serviceAccountTokenCreator` role on the target service account. [Learn More](https://cloud.google.com/iam/docs/service-account-impersonation)                                                                                                                                                                                                                                |
+| maxQueryResultRows             |   int    |    false     | The maximum number of rows to return from a query. Defaults to 50. |

internal/prebuiltconfigs/tools/bigquery.yaml

@@ -19,6 +19,7 @@ sources:
     location: ${BIGQUERY_LOCATION:}
     useClientOAuth: ${BIGQUERY_USE_CLIENT_OAUTH:false}
     scopes: ${BIGQUERY_SCOPES:}
+    maxQueryResultRows: ${BIGQUERY_MAX_QUERY_RESULT_ROWS:50}
 
 tools:
   analyze_contribution:

internal/sources/bigquery/bigquery.go

@@ -89,6 +89,7 @@ type Config struct {
 	UseClientOAuth            bool                `yaml:"useClientOAuth"`
 	ImpersonateServiceAccount string              `yaml:"impersonateServiceAccount"`
 	Scopes                    StringOrStringSlice `yaml:"scopes"`
+	MaxQueryResultRows        int                 `yaml:"maxQueryResultRows"`
 }
 
 // StringOrStringSlice is a custom type that can unmarshal both a single string
@@ -127,6 +128,10 @@ func (r Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.So
 		r.WriteMode = WriteModeAllowed
 	}
 
+	if r.MaxQueryResultRows == 0 {
+		r.MaxQueryResultRows = 50
+	}
+
 	if r.WriteMode == WriteModeProtected && r.UseClientOAuth {
 		// The protected mode only allows write operations to the session's temporary datasets.
 		// when using client OAuth, a new session is created every
@@ -150,7 +155,7 @@ func (r Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.So
 		Client:             client,
 		RestService:        restService,
 		TokenSource:        tokenSource,
-		MaxQueryResultRows: 50,
+		MaxQueryResultRows: r.MaxQueryResultRows,
 		ClientCreator:      clientCreator,
 	}
 
@@ -567,7 +572,7 @@ func (s *Source) RunSQL(ctx context.Context, bqClient *bigqueryapi.Client, state
 	}
 
 	var out []any
-	for {
+	for s.MaxQueryResultRows <= 0 || len(out) < s.MaxQueryResultRows {
 		var val []bigqueryapi.Value
 		err = it.Next(&val)
 		if err == iterator.Done {

internal/sources/bigquery/bigquery_test.go

@@ -21,9 +21,12 @@ import (
 
 	yaml "github.com/goccy/go-yaml"
 	"github.com/google/go-cmp/cmp"
+	"go.opentelemetry.io/otel/trace/noop"
+
 	"github.com/googleapis/genai-toolbox/internal/server"
 	"github.com/googleapis/genai-toolbox/internal/sources/bigquery"
 	"github.com/googleapis/genai-toolbox/internal/testutils"
+	"github.com/googleapis/genai-toolbox/internal/util"
 )
 
 func TestParseFromYamlBigQuery(t *testing.T) {
@@ -154,6 +157,26 @@ func TestParseFromYamlBigQuery(t *testing.T) {
 				},
 			},
 		},
+		{
+			desc: "with max query result rows example",
+			in: `
+			sources:
+				my-instance:
+					kind: bigquery
+					project: my-project
+					location: us
+					maxQueryResultRows: 10
+			`,
+			want: server.SourceConfigs{
+				"my-instance": bigquery.Config{
+					Name:               "my-instance",
+					Kind:               bigquery.SourceKind,
+					Project:            "my-project",
+					Location:           "us",
+					MaxQueryResultRows: 10,
+				},
+			},
+		},
 	}
 	for _, tc := range tcs {
 		t.Run(tc.desc, func(t *testing.T) {
@@ -220,6 +243,59 @@ func TestFailParseFromYaml(t *testing.T) {
 	}
 }
 
+func TestInitialize_MaxQueryResultRows(t *testing.T) {
+	ctx, err := testutils.ContextWithNewLogger()
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	ctx = util.WithUserAgent(ctx, "test-agent")
+	tracer := noop.NewTracerProvider().Tracer("")
+
+	tcs := []struct {
+		desc string
+		cfg  bigquery.Config
+		want int
+	}{
+		{
+			desc: "default value",
+			cfg: bigquery.Config{
+				Name:           "test-default",
+				Kind:           bigquery.SourceKind,
+				Project:        "test-project",
+				UseClientOAuth: true,
+			},
+			want: 50,
+		},
+		{
+			desc: "configured value",
+			cfg: bigquery.Config{
+				Name:               "test-configured",
+				Kind:               bigquery.SourceKind,
+				Project:            "test-project",
+				UseClientOAuth:     true,
+				MaxQueryResultRows: 100,
+			},
+			want: 100,
+		},
+	}
+
+	for _, tc := range tcs {
+		t.Run(tc.desc, func(t *testing.T) {
+			src, err := tc.cfg.Initialize(ctx, tracer)
+			if err != nil {
+				t.Fatalf("Initialize failed: %v", err)
+			}
+			bqSrc, ok := src.(*bigquery.Source)
+			if !ok {
+				t.Fatalf("Expected *bigquery.Source, got %T", src)
+			}
+			if bqSrc.MaxQueryResultRows != tc.want {
+				t.Errorf("MaxQueryResultRows = %d, want %d", bqSrc.MaxQueryResultRows, tc.want)
+			}
+		})
+	}
+}
+
 func TestNormalizeValue(t *testing.T) {
 	tests := []struct {
 		name     string