grpc: Improve documentation of read/write buffer size server and dial…

… options (grpc#5800)

Fixes grpc#5798

dialoptions.go

@@ -116,8 +116,9 @@ func newFuncDialOption(f func(*dialOptions)) *funcDialOption {
 // be twice the size to keep syscalls low. The default value for this buffer is
 // 32KB.
 //
-// Zero will disable the write buffer such that each write will be on underlying
-// connection. Note: A Send call may not directly translate to a write.
+// Zero or negative values will disable the write buffer such that each write
+// will be on underlying connection. Note: A Send call may not directly
+// translate to a write.
 func WithWriteBufferSize(s int) DialOption {
 	return newFuncDialOption(func(o *dialOptions) {
 		o.copts.WriteBufferSize = s
@@ -127,8 +128,9 @@ func WithWriteBufferSize(s int) DialOption {
 // WithReadBufferSize lets you set the size of read buffer, this determines how
 // much data can be read at most for each read syscall.
 //
-// The default value for this buffer is 32KB. Zero will disable read buffer for
-// a connection so data framer can access the underlying conn directly.
+// The default value for this buffer is 32KB. Zero or negative values will
+// disable read buffer for a connection so data framer can access the
+// underlying conn directly.
 func WithReadBufferSize(s int) DialOption {
 	return newFuncDialOption(func(o *dialOptions) {
 		o.copts.ReadBufferSize = s

server.go

@@ -233,22 +233,22 @@ func newJoinServerOption(opts ...ServerOption) ServerOption {
 	return &joinServerOption{opts: opts}
 }
 
-// WriteBufferSize determines how much data can be batched before doing a write on the wire.
-// The corresponding memory allocation for this buffer will be twice the size to keep syscalls low.
-// The default value for this buffer is 32KB.
-// Zero will disable the write buffer such that each write will be on underlying connection.
+// WriteBufferSize determines how much data can be batched before doing a write
+// on the wire. The corresponding memory allocation for this buffer will be
+// twice the size to keep syscalls low. The default value for this buffer is
+// 32KB. Zero or negative values will disable the write buffer such that each
+// write will be on underlying connection.
 // Note: A Send call may not directly translate to a write.
 func WriteBufferSize(s int) ServerOption {
 	return newFuncServerOption(func(o *serverOptions) {
 		o.writeBufferSize = s
 	})
 }
 
-// ReadBufferSize lets you set the size of read buffer, this determines how much data can be read at most
-// for one read syscall.
-// The default value for this buffer is 32KB.
-// Zero will disable read buffer for a connection so data framer can access the underlying
-// conn directly.
+// ReadBufferSize lets you set the size of read buffer, this determines how much
+// data can be read at most for one read syscall. The default value for this
+// buffer is 32KB. Zero or negative values will disable read buffer for a
+// connection so data framer can access the underlying conn directly.
 func ReadBufferSize(s int) ServerOption {
 	return newFuncServerOption(func(o *serverOptions) {
 		o.readBufferSize = s