Fix for too long G-code replies (#1073)

Added extra parameter to OutputBuffer::Allocate to specify if the buffer
to be allocated may be taken from the output buffer reserve. This is
always true except if appending to an existing output buffer chain or
when the request may be repeated without downsides.
Also reduced the number of reserved output buffers to 2 on Duet 2 series

src/Config/Configuration.h

@@ -180,7 +180,7 @@ constexpr size_t MinimumBuffersForObjectModel = 20;		// Minimum number of free b
 #elif SAM4E || SAM4S
 constexpr size_t OUTPUT_BUFFER_SIZE = 256;				// How many bytes does each OutputBuffer hold?
 constexpr size_t OUTPUT_BUFFER_COUNT = 26;				// How many OutputBuffer instances do we have?
-constexpr size_t RESERVED_OUTPUT_BUFFERS = 4;			// Number of reserved output buffers after long responses, enough to hold a status response
+constexpr size_t RESERVED_OUTPUT_BUFFERS = 2;			// Number of reserved output buffers after long responses, enough to hold a status response
 constexpr size_t MinimumBuffersForObjectModel = 20;		// Minimum number of free buffers we want before we start assembling a request for the object model
 #else
 # error Unsupported processor

src/GCodes/GCodes2.cpp

@@ -994,7 +994,7 @@ bool GCodes::HandleMcode(GCodeBuffer& gb, const StringRef& reply) THROWS(GCodeEx
 					}
 					else
 					{
-						if (!OutputBuffer::Allocate(outBuf))
+						if (!OutputBuffer::Allocate(outBuf, false))
 						{
 							return false;												// cannot allocate an output buffer, try again later
 						}
@@ -3276,7 +3276,7 @@ bool GCodes::HandleMcode(GCodeBuffer& gb, const StringRef& reply) THROWS(GCodeEx
 					}
 
 					// Need a valid output buffer to continue
-					if (!OutputBuffer::Allocate(outBuf))
+					if (!OutputBuffer::Allocate(outBuf, false))
 					{
 						// No buffer available, try again later
 						return false;

src/GCodes/GCodes5.cpp

@@ -287,7 +287,7 @@ GCodeResult GCodes::HandleM486(GCodeBuffer &gb, const StringRef &reply, OutputBu
 	if (!seen)
 	{
 		// List objects on build plate
-		if (!OutputBuffer::Allocate(buf))
+		if (!OutputBuffer::Allocate(buf, false))
 		{
 			return GCodeResult::notFinished;
 		}

src/Movement/Move.cpp

@@ -3071,7 +3071,7 @@ GCodeResult Move::ConfigureStallDetection(GCodeBuffer& gb, const StringRef& repl
 		drivers = LocalDriversBitmap::MakeLowestNBits(numSmartDrivers);
 	}
 
-	if (!OutputBuffer::Allocate(buf))
+	if (!OutputBuffer::Allocate(buf, false))
 	{
 		return GCodeResult::notFinished;
 	}

src/Networking/HttpResponder.cpp

@@ -1523,7 +1523,7 @@ void HttpResponder::Diagnostics(MessageType mt) const noexcept
 		OutputBuffer *_ecv_null buffer = gcodeReply.GetLastItem();
 		if (buffer == nullptr || buffer->IsReferenced())
 		{
-			if (!OutputBuffer::Allocate(buffer))
+			if (!OutputBuffer::Allocate(buffer, false))
 			{
 				// No more space available, stop here
 				return;

src/Platform/OutputMemory.cpp

@@ -177,7 +177,7 @@ size_t OutputBuffer::cat(const char c) noexcept
 	{
 		// No - allocate a new item and copy the data
 		OutputBuffer *nextBuffer;
-		if (!Allocate(nextBuffer))
+		if (!Allocate(nextBuffer, false))
 		{
 			// We cannot store any more data
 			hadOverflow = true;
@@ -218,9 +218,10 @@ size_t OutputBuffer::cat(const char *_ecv_array src, size_t len) noexcept
 	{
 		if (last->dataLength == OUTPUT_BUFFER_SIZE)
 		{
-			// The last buffer is full
+			// Save at least some output buffers in case this buffer chain has to be sent via network.
+			// If we don't do this, the network responder may be unable to allocate enough for the header
 			OutputBuffer *nextBuffer;
-			if (!Allocate(nextBuffer))
+			if (!Allocate(nextBuffer, false))
 			{
 				// We cannot store any more data, stop here
 				hadOverflow = true;
@@ -359,13 +360,13 @@ bool OutputBuffer::WriteToFile(FileData& f) const noexcept
 }
 
 // Allocates an output buffer instance which can be used for (large) string outputs. This must be thread safe. Not safe to call from interrupts!
-/*static*/ bool OutputBuffer::Allocate(OutputBuffer *_ecv_null &buf) noexcept
+/*static*/ bool OutputBuffer::Allocate(OutputBuffer *_ecv_null &buf, bool allowReserved) noexcept
 {
 	{
 		TaskCriticalSectionLocker lock;
 
 		buf = freeOutputBuffers;
-		if (buf != nullptr)
+		if (buf != nullptr && (allowReserved || OUTPUT_BUFFER_COUNT - usedOutputBuffers > RESERVED_OUTPUT_BUFFERS))
 		{
 			freeOutputBuffers = buf->next;
 			usedOutputBuffers++;

src/Platform/OutputMemory.h

@@ -72,8 +72,8 @@ class OutputBuffer
 	// Initialise the output buffers manager
 	static void Init() noexcept;
 
-	// Allocate an unused OutputBuffer instance. Returns true on success or false if no instance could be allocated.
-	static bool Allocate(OutputBuffer *_ecv_null &buf) noexcept;
+	// Allocate an unused OutputBuffer instance, optionally from the reserve. Returns true on success or false if no instance could be allocated.
+	static bool Allocate(OutputBuffer *_ecv_null &buf, bool allowReserved = true) noexcept;
 
 	// Get the number of bytes left for allocation. If writingBuffer is not NULL, this returns the number of free bytes for
 	// continuous writes, i.e. for writes that need to allocate an extra OutputBuffer instance to finish the message.

src/Platform/RepRap.cpp

@@ -2145,7 +2145,7 @@ GCodeResult RepRap::GetFileInfoResponse(c_string _ecv_null filename, OutputBuffe
 		return GCodeResult::notFinished;
 	}
 
-	if (!OutputBuffer::Allocate(response))
+	if (!OutputBuffer::Allocate(response, false))
 	{
 		return GCodeResult::notFinished;
 	}
@@ -2282,7 +2282,7 @@ void RepRap::AppendStringArray(OutputBuffer *buf, c_string _ecv_null name, size_
 OutputBuffer *RepRap::GetModelResponse(const GCodeBuffer *_ecv_null gb, c_string _ecv_null key, c_string _ecv_null flags) const THROWS(GCodeException)
 {
 	OutputBuffer *outBuf;
-	if (OutputBuffer::Allocate(outBuf))
+	if (OutputBuffer::Allocate(outBuf, false))
 	{
 		if (key == nullptr) { key = ""; }
 		if (flags == nullptr) { flags = ""; }

src/Tools/Tool.cpp

@@ -927,7 +927,7 @@ GCodeResult Tool::SetFirmwareRetraction(GCodeBuffer &gb, const StringRef &reply,
 	else
 	{
 		// Use an output buffer because M207 can report on all tools
-		if (outBuf == nullptr && !OutputBuffer::Allocate(outBuf))
+		if (outBuf == nullptr && !OutputBuffer::Allocate(outBuf, false))
 		{
 			return GCodeResult::notFinished;
 		}