THRIFT-4914: Make TClient.Call to return the response meta

Client: go

Make a breaking change so that TClient.Call returns the response
meta, currently only contains headers but could be expanded in the
future, and make a compiler change to compiler generated clients to take
advantage of that and provide access to response metadata to users.

7 files changed, 60 insertions, 34 deletions

diff --git a/CHANGES.md b/CHANGES.md
index 8e4d08edd..c6c08f29f 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -18,6 +18,7 @@
 - [THRIFT-5152](https://issues.apache.org/jira/browse/THRIFT-5152) - go: TSocket and TSSLSocket now have separated connect timeout and socket timeout
 - c++: dropped support for Windows XP
 - [THRIFT-5326](https://issues.apache.org/jira/browse/THRIFT-5326) - go: TException interface now has a new function: TExceptionType
+- [THRIFT-4914](https://issues.apache.org/jira/browse/THRIFT-4914) - go: TClient.Call now returns ResponseMeta in addition to error
 
 ### Java
 
@@ -31,6 +32,7 @@
 - [THRIFT-5233](https://issues.apache.org/jira/browse/THRIFT-5233) - Add context deadline check to ReadMessageBegin in TBinaryProtocol, TCompactProtocol, and THeaderProtocol.
 - [THRIFT-5240](https://issues.apache.org/jira/browse/THRIFT-5240) - The context passed into server handler implementations will be canceled when we detected that the client closed the connection.
 - [THRIFT-5322](https://issues.apache.org/jira/browse/THRIFT-5322) - Add support to TConfiguration, and also fix a bug that could cause excessive memory usage when reading malformed messages from TCompactProtocol.
+- [THRIFT-4914](https://issues.apache.org/jira/browse/THRIFT-4914) - Compiler generated service clients now provide a new function, LastResponseMeta_(), to get the response metadata (e.g. headers from THeader) from the last client call.
 
 ## 0.13.0
 
diff --git a/compiler/cpp/src/thrift/generate/t_go_generator.cc b/compiler/cpp/src/thrift/generate/t_go_generator.cc
index 49d8bc119..33cd12d46 100644
--- a/compiler/cpp/src/thrift/generate/t_go_generator.cc
+++ b/compiler/cpp/src/thrift/generate/t_go_generator.cc
@@ -1493,11 +1493,15 @@ void t_go_generator::generate_go_struct_definition(ostream& out,
 
   if (is_exception) {
     out << indent() << "func (p *" << tstruct_name << ") Error() string {" << endl;
-    out << indent() << indent() << "return p.String()" << endl;
+    indent_up();
+    out << indent() << "return p.String()" << endl;
+    indent_down();
     out << indent() << "}" << endl << endl;
 
     out << indent() << "func (" << tstruct_name << ") TExceptionType() thrift.TExceptionType {" << endl;
-    out << indent() << indent() << "return thrift.TExceptionTypeCompiled" << endl;
+    indent_up();
+    out << indent() << "return thrift.TExceptionTypeCompiled" << endl;
+    indent_down();
     out << indent() << "}" << endl << endl;
 
     out << indent() << "var _ thrift.TException = (*" << tstruct_name << ")(nil)"
@@ -1990,6 +1994,7 @@ void t_go_generator::generate_service_client(t_service* tservice) {
     f_types_ << indent() << "*" << extends_client << endl;
   } else {
     f_types_ << indent() << "c thrift.TClient" << endl;
+    f_types_ << indent() << "meta thrift.ResponseMeta" << endl;
   }
 
   indent_down();
@@ -2059,7 +2064,19 @@ void t_go_generator::generate_service_client(t_service* tservice) {
     indent_up();
     f_types_ << indent() << "return p.c" << endl;
     indent_down();
-    f_types_ << indent() << "}" << endl;
+    f_types_ << indent() << "}" << endl << endl;
+
+    f_types_ << indent() << "func (p *" << serviceName << "Client) LastResponseMeta_() thrift.ResponseMeta {" << endl;
+    indent_up();
+    f_types_ << indent() << "return p.meta" << endl;
+    indent_down();
+    f_types_ << indent() << "}" << endl << endl;
+
+    f_types_ << indent() << "func (p *" << serviceName << "Client) SetLastResponseMeta_(meta thrift.ResponseMeta) {" << endl;
+    indent_up();
+    f_types_ << indent() << "p.meta = meta" << endl;
+    indent_down();
+    f_types_ << indent() << "}" << endl << endl;
   }
 
   // Generate client method implementations
@@ -2091,8 +2108,11 @@ void t_go_generator::generate_service_client(t_service* tservice) {
       std::string resultName = tmp("_result");
       std::string resultType = publicize(method + "_result", true);
       f_types_ << indent() << "var " << resultName << " " << resultType << endl;
-      f_types_ << indent() << "if err = p.Client_().Call(ctx, \""
-        << method << "\", &" << argsName << ", &" << resultName << "); err != nil {" << endl;
+      f_types_ << indent() << "var meta thrift.ResponseMeta" << endl;
+      f_types_ << indent() << "meta, err = p.Client_().Call(ctx, \""
+        << method << "\", &" << argsName << ", &" << resultName << ")" << endl;
+      f_types_ << indent() << "p.SetLastResponseMeta_(meta)" << endl;
+      f_types_ << indent() << "if err != nil {" << endl;
 
       indent_up();
       f_types_ << indent() << "return" << endl;
@@ -2131,9 +2151,13 @@ void t_go_generator::generate_service_client(t_service* tservice) {
         f_types_ << indent() << "return nil" << endl;
       }
     } else {
+      // Since we don't have response meta for oneway calls, overwrite it with
+      // an empty one to avoid users getting the meta from last call and
+      // mistaken it as from the oneway call.
+      f_types_ << indent() << "p.SetLastResponseMeta_(thrift.ResponseMeta{})" << endl;
       // TODO: would be nice to not to duplicate the call generation
-      f_types_ << indent() << "if err := p.Client_().Call(ctx, \""
-      << method << "\", &"<< argsName << ", nil); err != nil {" << endl;
+      f_types_ << indent() << "if _, err := p.Client_().Call(ctx, \""
+        << method << "\", &"<< argsName << ", nil); err != nil {" << endl;
 
       indent_up();
       f_types_ << indent() << "return err" << endl;
diff --git a/lib/go/thrift/client.go b/lib/go/thrift/client.go
index 1c5705d55..ea2c01fda 100644
--- a/lib/go/thrift/client.go
+++ b/lib/go/thrift/client.go
@@ -5,8 +5,15 @@ import (
 	"fmt"
 )
 
+// ResponseMeta represents the metadata attached to the response.
+type ResponseMeta struct {
+	// The headers in the response, if any.
+	// If the underlying transport/protocol is not THeader, this will always be nil.
+	Headers THeaderMap
+}
+
 type TClient interface {
-	Call(ctx context.Context, method string, args, result TStruct) error
+	Call(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error)
 }
 
 type TStandardClient struct {
@@ -78,18 +85,25 @@ func (p *TStandardClient) Recv(ctx context.Context, iprot TProtocol, seqId int32
 	return iprot.ReadMessageEnd(ctx)
 }
 
-func (p *TStandardClient) Call(ctx context.Context, method string, args, result TStruct) error {
+func (p *TStandardClient) Call(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error) {
 	p.seqId++
 	seqId := p.seqId
 
 	if err := p.Send(ctx, p.oprot, seqId, method, args); err != nil {
-		return err
+		return ResponseMeta{}, err
 	}
 
 	// method is oneway
 	if result == nil {
-		return nil
+		return ResponseMeta{}, nil
 	}
 
-	return p.Recv(ctx, p.iprot, seqId, method, result)
+	err := p.Recv(ctx, p.iprot, seqId, method, result)
+	var headers THeaderMap
+	if hp, ok := p.iprot.(*THeaderProtocol); ok {
+		headers = hp.transport.readHeaders
+	}
+	return ResponseMeta{
+		Headers: headers,
+	}, err
 }
diff --git a/lib/go/thrift/example_client_middleware_test.go b/lib/go/thrift/example_client_middleware_test.go
index 8a29083c0..a68cdbc34 100644
--- a/lib/go/thrift/example_client_middleware_test.go
+++ b/lib/go/thrift/example_client_middleware_test.go
@@ -45,16 +45,16 @@ func NewMyServiceClient(_ TClient) MyService {
 
 func simpleClientLoggingMiddleware(next TClient) TClient {
 	return WrappedTClient{
-		Wrapped: func(ctx context.Context, method string, args, result TStruct) error {
+		Wrapped: func(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error) {
 			log.Printf("Before: %q", method)
 			log.Printf("Args: %#v", args)
-			err := next.Call(ctx, method, args, result)
+			headers, err := next.Call(ctx, method, args, result)
 			log.Printf("After: %q", method)
 			log.Printf("Result: %#v", result)
 			if err != nil {
 				log.Printf("Error: %v", err)
 			}
-			return err
+			return headers, err
 		},
 	}
 }
diff --git a/lib/go/thrift/header_protocol.go b/lib/go/thrift/header_protocol.go
index 35e045805..878041f8d 100644
--- a/lib/go/thrift/header_protocol.go
+++ b/lib/go/thrift/header_protocol.go
@@ -345,20 +345,6 @@ func (p *THeaderProtocol) SetTConfiguration(cfg *TConfiguration) {
 	p.cfg = cfg
 }
 
-// GetResponseHeadersFromClient is a helper function to get the read THeaderMap
-// from the last response received from the given client.
-//
-// If the last response was not sent over THeader protocol,
-// a nil map will be returned.
-func GetResponseHeadersFromClient(c TClient) THeaderMap {
-	if sc, ok := c.(*TStandardClient); ok {
-		if hp, ok := sc.iprot.(*THeaderProtocol); ok {
-			return hp.transport.readHeaders
-		}
-	}
-	return nil
-}
-
 var (
 	_ TConfigurationSetter = (*tHeaderProtocolFactory)(nil)
 	_ TConfigurationSetter = (*THeaderProtocol)(nil)
diff --git a/lib/go/thrift/middleware.go b/lib/go/thrift/middleware.go
index b575e16c4..8a788df02 100644
--- a/lib/go/thrift/middleware.go
+++ b/lib/go/thrift/middleware.go
@@ -78,11 +78,11 @@ type ClientMiddleware func(TClient) TClient
 //
 // This is provided to aid in developing ClientMiddleware.
 type WrappedTClient struct {
-	Wrapped func(ctx context.Context, method string, args, result TStruct) error
+	Wrapped func(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error)
 }
 
 // Call implements the TClient interface by calling and returning c.Wrapped.
-func (c WrappedTClient) Call(ctx context.Context, method string, args, result TStruct) error {
+func (c WrappedTClient) Call(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error) {
 	return c.Wrapped(ctx, method, args, result)
 }
 
diff --git a/lib/go/thrift/middleware_test.go b/lib/go/thrift/middleware_test.go
index 2a4d1f957..6c4058fe1 100644
--- a/lib/go/thrift/middleware_test.go
+++ b/lib/go/thrift/middleware_test.go
@@ -54,7 +54,7 @@ func testProcessorMiddleware(c *counter) ProcessorMiddleware {
 func testClientMiddleware(c *counter) ClientMiddleware {
 	return func(next TClient) TClient {
 		return WrappedTClient{
-			Wrapped: func(ctx context.Context, method string, args, result TStruct) error {
+			Wrapped: func(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error) {
 				c.incr()
 				return next.Call(ctx, method, args, result)
 			},
@@ -122,8 +122,8 @@ func TestWrapTMultiplexedProcessor(t *testing.T) {
 
 func TestWrapClient(t *testing.T) {
 	client := WrappedTClient{
-		Wrapped: func(ctx context.Context, method string, args, result TStruct) error {
-			return nil
+		Wrapped: func(ctx context.Context, method string, args, result TStruct) (ResponseMeta, error) {
+			return ResponseMeta{}, nil
 		},
 	}
 	c := newCounter(t)