Wire protocol improvement: prefetch blob info and some data when open blob (#8307)

* Group op_open_blob2, op_info_blob and op_get_segment into single physical packet.
It allows to prefetch and cache blob info and some blob data in single network roundtrip.
Return cached blob info, if present, without remote access.

* No need to reserve space for segment length.
Fixed typo.
Thanks to @dyemanov for comments.

* Add 'const' for parameter declaration, as @AlexPeshkoff suggested

* Use 'if constexpr' as @TreeHunter9 suggested.
Also, avoid hardcoded constants when possible.

Author: hvlad

src/common/utils_proto.h

@@ -31,10 +31,13 @@
 
 #include <cctype>
 #include <string.h>
+#include <type_traits>
+
 #include "../common/classes/fb_string.h"
 #include "../common/classes/array.h"
 #include "iberror.h"
 #include "firebird/Interface.h"
+#include "memory_routines.h"
 
 #ifdef SFIO
 #include <stdio.h>
@@ -271,6 +274,47 @@ namespace fb_utils
 	// Frequently used actions with clumplets
 	bool isBpbSegmented(unsigned parLength, const unsigned char* par);
 
+
+	// Put integer value into info buffer
+	template<typename T>
+	inline unsigned char* putInfoItemInt(const unsigned char item, T value,
+		unsigned char* ptr, const unsigned char* end)
+	{
+		static_assert(std::is_integral_v<T>, "Integral type expected");
+
+		constexpr auto len = sizeof(T);
+
+		if (ptr + len + 1 + 2 > end)
+		{
+			if (ptr < end)
+			{
+				*ptr++ = isc_info_truncated;
+				if (ptr < end)
+					*ptr++ = isc_info_end;
+			}
+			return nullptr;
+		}
+
+		*ptr++ = item;
+		*ptr++ = len;
+		*ptr++ = 0;
+
+		if constexpr (len == sizeof(SINT64))
+			put_vax_int64(ptr, value);
+		else if constexpr (len == sizeof(SLONG))
+			put_vax_long(ptr, value);
+		else if constexpr (len == sizeof(SSHORT))
+			put_vax_short(ptr, value);
+		else if constexpr (len == sizeof(char))
+			*ptr = value;
+		else
+			static_assert(always_false<T>::value, "unknown data type");
+
+		ptr += len;
+		return ptr;
+	}
+
+
 	// RAII to call fb_shutdown() in utilities
 	class FbShutdown
 	{

src/remote/client/interface.cpp

@@ -1303,6 +1303,10 @@ void Blob::getInfo(CheckStatusWrapper* status,
 
 		Rdb* rdb = blob->rbl_rdb;
 		CHECK_HANDLE(rdb, isc_bad_db_handle);
+
+		if (blob->rbl_info.getLocalInfo(itemsLength, items, bufferLength, buffer))
+			return;
+
 		rem_port* port = rdb->rdb_port;
 		RefMutexGuard portGuard(*port->port_sync, FB_FUNCTION);
 
@@ -5611,7 +5615,79 @@ IBlob* Attachment::openBlob(CheckStatusWrapper* status, ITransaction* apiTra, IS
 		// would try to write to the application's provided R/O buffer.
 		p_blob->p_blob_bpb.cstr_address = bpb;
 
-		send_and_receive(status, rdb, packet);
+		UCHAR infoBuffer[128];
+
+		if (port->port_flags & PORT_lazy)
+		{
+			send_partial_packet(port, packet);
+
+			// prefetch blob info
+			const UCHAR items[] = {
+				isc_info_blob_num_segments,
+				isc_info_blob_max_segment,
+				isc_info_blob_total_length,
+				isc_info_blob_type,
+				isc_info_end
+			};
+
+			packet->p_operation = op_info_blob;
+			P_INFO* information = &packet->p_info;
+			information->p_info_object = INVALID_OBJECT;
+			information->p_info_incarnation = 0;
+			information->p_info_items.cstr_length = sizeof(items);
+			information->p_info_items.cstr_address = items;
+			information->p_info_buffer_length = sizeof(infoBuffer);
+
+			send_partial_packet(port, packet);
+
+			// prefetch some data
+			packet->p_operation = op_get_segment;
+			P_SGMT* segment = &packet->p_sgmt;
+			segment->p_sgmt_length = BLOB_LENGTH;
+			segment->p_sgmt_blob = INVALID_OBJECT;
+			segment->p_sgmt_segment.cstr_length = 0;
+
+			send_packet(port, packet);
+
+			try
+			{
+				receive_response(status, rdb, packet);
+			}
+			catch (const Exception& ex)
+			{
+				// re-throw network error immediately, for other errors receive two more packets first
+				if (port->port_state != rem_port::PENDING)
+					throw;
+
+				FbLocalStatus local;
+				ex.stuffException(&local);
+
+				auto errs = local->getErrors();
+
+				if (fb_utils::containsErrorCode(errs, isc_network_error) ||
+					fb_utils::containsErrorCode(errs, isc_net_read_err) ||
+					port->port_state != rem_port::PENDING)
+				{
+					throw;
+				}
+
+				for (int i = 0; i < 2; i++)
+				{
+					try
+					{
+						UseStandardBuffer temp(packet->p_resp.p_resp_data);
+						receive_response(status, rdb, packet);
+					}
+					catch (const Exception&) {}
+				}
+
+				throw;
+			}
+		}
+		else
+		{
+			send_and_receive(status, rdb, packet);
+		}
 
 		// CVC: It's not evident to me why these two lines that I've copied
 		// here as comments are only found in create_blob calls.
@@ -5627,9 +5703,46 @@ IBlob* Attachment::openBlob(CheckStatusWrapper* status, ITransaction* apiTra, IS
 		blob->rbl_next = transaction->rtr_blobs;
 		transaction->rtr_blobs = blob;
 
-		Firebird::IBlob* b = FB_NEW Blob(blob);
-		b->addRef();
-		return b;
+		Blob* iBlob = FB_NEW Blob(blob);
+		iBlob->addRef();
+
+		if (port->port_flags & PORT_lazy)
+		{
+			// Receive two more responses. Ignore errors here, let client to receive
+			// and handle it later, when/if it runs corresponding action by itself.
+
+			P_RESP* response = &packet->p_resp;
+			// receive blob info
+			try
+			{
+				UsePreallocatedBuffer temp(response->p_resp_data, sizeof(infoBuffer), infoBuffer);
+
+				receive_response(status, rdb, packet);
+				blob->rbl_info.parseInfo(sizeof(infoBuffer), infoBuffer);
+			}
+			catch (const Exception&)
+			{ }
+
+			// receive blob data
+			try
+			{
+				UsePreallocatedBuffer temp(response->p_resp_data, blob->rbl_buffer_length, blob->rbl_buffer);
+
+				receive_response(status, rdb, packet);
+
+				blob->rbl_length = (USHORT) response->p_resp_data.cstr_length;
+				blob->rbl_ptr = blob->rbl_buffer;
+
+				if (response->p_resp_object == 1)
+					blob->rbl_flags |= Rbl::SEGMENT;
+				else if (response->p_resp_object == 2)
+					blob->rbl_flags |= Rbl::EOF_PENDING;
+			}
+			catch (const Exception&)
+			{ }
+		}
+
+		return iBlob;
 	}
 	catch (const Exception& ex)
 	{

src/remote/remote.cpp

@@ -38,6 +38,7 @@
 #include "../common/os/mod_loader.h"
 #include "../jrd/license.h"
 #include "../common/classes/ImplementHelper.h"
+#include "../common/utils_proto.h"
 
 #ifdef DEV_BUILD
 Firebird::AtomicCounter rem_port::portCounter;
@@ -855,6 +856,87 @@ ISC_STATUS* Rdb::get_status_vector() noexcept
 }
 */
 
+
+bool RBlobInfo::getLocalInfo(unsigned int itemsLength, const unsigned char* items,
+	unsigned int bufferLength, unsigned char* buffer)
+{
+	if (!valid)
+		return false;
+
+	unsigned char* p = buffer;
+	const unsigned char* const end = buffer + bufferLength;
+
+	for (auto item = items; p && (item < items + itemsLength); item++)
+	{
+		switch (*item)
+		{
+		case isc_info_blob_num_segments:
+			p = fb_utils::putInfoItemInt(*item, num_segments, p, end);
+			break;
+
+		case isc_info_blob_max_segment:
+			p = fb_utils::putInfoItemInt(*item, max_segment, p, end);
+			break;
+
+		case isc_info_blob_total_length:
+			p = fb_utils::putInfoItemInt(*item, total_length, p, end);
+			break;
+
+		case isc_info_blob_type:
+			p = fb_utils::putInfoItemInt(*item, blob_type, p, end);
+			break;
+
+		case isc_info_end:
+			if (p < end)
+				*p++ = isc_info_end;
+			break;
+
+		default:
+			// unknown info item, let remote server handle it
+			return false;
+		}
+	}
+
+	return true;
+}
+
+
+void RBlobInfo::parseInfo(unsigned int bufferLength, const unsigned char* buffer)
+{
+	int c = 0;
+	valid = false;
+
+	Firebird::ClumpletReader p(Firebird::ClumpletReader::InfoResponse, buffer, bufferLength);
+	for (; !p.isEof(); p.moveNext())
+	{
+		switch (p.getClumpTag())
+		{
+		case isc_info_blob_num_segments:
+			num_segments = p.getInt();
+			c++;
+			break;
+		case isc_info_blob_max_segment:
+			max_segment = p.getInt();
+			c++;
+			break;
+		case isc_info_blob_total_length:
+			total_length = p.getInt();
+			c++;
+			break;
+		case isc_info_blob_type:
+			blob_type = p.getInt();
+			c++;
+			break;
+		case isc_info_end:
+			break;
+		default:
+			fb_assert(false);
+			break;
+		}
+	}
+	valid = (c == 4);
+}
+
 void Rrq::saveStatus(const Firebird::Exception& ex) noexcept
 {
 	if (rrqStatus.isSuccess())

src/remote/remote.h

@@ -221,6 +221,27 @@ struct Rtr : public Firebird::GlobalStorage, public TypedHandle<rem_type_rtr>
 };
 
 
+struct RBlobInfo
+{
+	bool	valid;
+	UCHAR	blob_type;
+	ULONG	num_segments;
+	ULONG	max_segment;
+	ULONG	total_length;
+
+	RBlobInfo()
+	{
+		memset(this, 0, sizeof(*this));
+	}
+
+	// parse into response into m_info, assume buffer contains all known info items
+	void parseInfo(unsigned int bufferLength, const unsigned char* buffer);
+
+	// returns false if there is no valid local info or if unknown item encountered
+	bool getLocalInfo(unsigned int itemsLength, const unsigned char* items,
+		unsigned int bufferLength, unsigned char* buffer);
+};
+
 struct Rbl : public Firebird::GlobalStorage, public TypedHandle<rem_type_rbl>
 {
 	Firebird::HalfStaticArray<UCHAR, BLOB_LENGTH> rbl_data;
@@ -239,6 +260,7 @@ struct Rbl : public Firebird::GlobalStorage, public TypedHandle<rem_type_rbl>
 	USHORT		rbl_source_interp;	// source interp (for writing)
 	USHORT		rbl_target_interp;	// destination interp (for reading)
 	Rbl**		rbl_self;
+	RBlobInfo	rbl_info;
 
 public:
 	// Values for rbl_flags