Impl serialized_length() without LengthCalculatingWriter

With the new `serialized_length()` method potentially being
significantly more efficient than `LengthCalculatingWriter`, this
commit ensures we call `serialized_length()` when calculating
length of a larger struct.

Specifically, prior to this commit a call to
`serialized_length()` on a large object serialized with
`impl_writeable`, `impl_writeable_len_match`, or
`encode_varint_length_prefixed_tlv` (and
`impl_writeable_tlv_based`) would always serialize all inner fields
of that object using `LengthCalculatingWriter`. This would ignore
any `serialized_length()` overrides by inner fields. Instead, we
override `serialized_length()` on all of the above by calculating
the serialized size using calls to `serialized_length()` on inner
fields.

Further, writes to `LengthCalculatingWriter` should never fail as
its `write` method never returns an error. Thus, any write failures
indicate a bug in an object's write method or in our
object-creation sanity checking. We `.expect()` such write calls
here.

As of this commit, on an Intel 2687W v3, the serialization
benchmarks take:

test routing::network_graph::benches::read_network_graph  ... bench: 2,039,451,296 ns/iter (+/- 4,329,821)
test routing::network_graph::benches::write_network_graph ... bench: 166,685,412 ns/iter (+/- 352,537)

Author: TheBlueMatt

lightning/src/util/ser_macros.rs

@@ -47,29 +47,36 @@ macro_rules! encode_tlv {
 	} }
 }
 
-macro_rules! encode_varint_length_prefixed_tlv {
-	($stream: expr, {$(($type: expr, $field: expr)),*}, {$(($optional_type: expr, $optional_field: expr)),*}) => { {
-		use util::ser::{BigSize, LengthCalculatingWriter};
+macro_rules! get_varint_length_prefixed_tlv_length {
+	({$(($type: expr, $field: expr)),*}, {$(($optional_type: expr, $optional_field: expr)),* $(,)*}) => { {
+		use util::ser::LengthCalculatingWriter;
 		#[allow(unused_mut)]
 		let mut len = LengthCalculatingWriter(0);
 		{
 			$(
-				BigSize($type).write(&mut len)?;
+				BigSize($type).write(&mut len).expect("No in-memory data may fail to serialize");
 				let field_len = $field.serialized_length();
-				BigSize(field_len as u64).write(&mut len)?;
+				BigSize(field_len as u64).write(&mut len).expect("No in-memory data may fail to serialize");
 				len.0 += field_len;
 			)*
 			$(
 				if let Some(ref field) = $optional_field {
-					BigSize($optional_type).write(&mut len)?;
+					BigSize($optional_type).write(&mut len).expect("No in-memory data may fail to serialize");
 					let field_len = field.serialized_length();
-					BigSize(field_len as u64).write(&mut len)?;
+					BigSize(field_len as u64).write(&mut len).expect("No in-memory data may fail to serialize");
 					len.0 += field_len;
 				}
 			)*
 		}
+		len.0
+	} }
+}
 
-		BigSize(len.0 as u64).write($stream)?;
+macro_rules! encode_varint_length_prefixed_tlv {
+	($stream: expr, {$(($type: expr, $field: expr)),*}, {$(($optional_type: expr, $optional_field: expr)),*}) => { {
+		use util::ser::BigSize;
+		let len = get_varint_length_prefixed_tlv_length!({ $(($type, $field)),* }, { $(($optional_type, $optional_field)),* });
+		BigSize(len as u64).write($stream)?;
 		encode_tlv!($stream, { $(($type, $field)),* }, { $(($optional_type, $optional_field)),* });
 	} }
 }
@@ -167,13 +174,28 @@ macro_rules! impl_writeable {
 					if $len != 0 {
 						use util::ser::LengthCalculatingWriter;
 						let mut len_calc = LengthCalculatingWriter(0);
-						$( self.$field.write(&mut len_calc)?; )*
+						$( self.$field.write(&mut len_calc).expect("No in-memory data may fail to serialize"); )*
 						assert_eq!(len_calc.0, $len);
 					}
 				}
 				$( self.$field.write(w)?; )*
 				Ok(())
 			}
+
+			#[inline]
+			fn serialized_length(&self) -> usize {
+				if $len == 0 || cfg!(any(test, feature = "fuzztarget")) {
+					let mut len_calc = 0;
+					$( len_calc += self.$field.serialized_length(); )*
+					if $len != 0 {
+						// In tests, assert that the hard-coded length matches the actual one
+						assert_eq!(len_calc, $len);
+					} else {
+						return len_calc;
+					}
+				}
+				$len
+			}
 		}
 
 		impl ::util::ser::Readable for $st {
@@ -186,7 +208,7 @@ macro_rules! impl_writeable {
 	}
 }
 macro_rules! impl_writeable_len_match {
-	($struct: ident, $cmp: tt, {$({$match: pat, $length: expr}),*}, {$($field:ident),*}) => {
+	($struct: ident, $cmp: tt, ($calc_len: expr), {$({$match: pat, $length: expr}),*}, {$($field:ident),*}) => {
 		impl Writeable for $struct {
 			fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
 				let len = match *self {
@@ -198,12 +220,29 @@ macro_rules! impl_writeable_len_match {
 					// In tests, assert that the hard-coded length matches the actual one
 					use util::ser::LengthCalculatingWriter;
 					let mut len_calc = LengthCalculatingWriter(0);
-					$( self.$field.write(&mut len_calc)?; )*
+					$( self.$field.write(&mut len_calc).expect("No in-memory data may fail to serialize"); )*
 					assert!(len_calc.0 $cmp len);
 				}
 				$( self.$field.write(w)?; )*
 				Ok(())
 			}
+
+			#[inline]
+			fn serialized_length(&self) -> usize {
+				if $calc_len || cfg!(any(test, feature = "fuzztarget")) {
+					let mut len_calc = 0;
+					$( len_calc += self.$field.serialized_length(); )*
+					if !$calc_len {
+						assert_eq!(len_calc, match *self {
+							$($match => $length,)*
+						});
+					}
+					return len_calc
+				}
+				match *self {
+					$($match => $length,)*
+				}
+			}
 		}
 
 		impl ::util::ser::Readable for $struct {
@@ -214,8 +253,11 @@ macro_rules! impl_writeable_len_match {
 			}
 		}
 	};
+	($struct: ident, $cmp: tt, {$({$match: pat, $length: expr}),*}, {$($field:ident),*}) => {
+		impl_writeable_len_match!($struct, $cmp, (true), { $({ $match, $length }),* }, { $($field),* });
+	};
 	($struct: ident, {$({$match: pat, $length: expr}),*}, {$($field:ident),*}) => {
-		impl_writeable_len_match!($struct, ==, { $({ $match, $length }),* }, { $($field),* });
+		impl_writeable_len_match!($struct, ==, (false), { $({ $match, $length }),* }, { $($field),* });
 	}
 }
 
@@ -319,6 +361,14 @@ macro_rules! _write_tlv_fields {
 		write_tlv_fields!($stream, {$(($type, $field)),*} , {$(($optional_type, $optional_field)),*, $(($optional_type_2, $optional_field_2)),*});
 	}
 }
+macro_rules! _get_tlv_len {
+	({$(($type: expr, $field: expr)),* $(,)*}, {}, {$(($optional_type: expr, $optional_field: expr)),* $(,)*}) => {
+		get_varint_length_prefixed_tlv_length!({$(($type, $field)),*} , {$(($optional_type, $optional_field)),*})
+	};
+	({$(($type: expr, $field: expr)),* $(,)*}, {$(($optional_type: expr, $optional_field: expr)),* $(,)*}, {$(($optional_type_2: expr, $optional_field_2: expr)),* $(,)*}) => {
+		get_varint_length_prefixed_tlv_length!({$(($type, $field)),*} , {$(($optional_type, $optional_field)),*, $(($optional_type_2, $optional_field_2)),*})
+	}
+}
 macro_rules! _read_tlv_fields {
 	($stream: expr, {$(($reqtype: expr, $reqfield: ident)),* $(,)*}, {}, {$(($type: expr, $field: ident)),* $(,)*}) => {
 		read_tlv_fields!($stream, {$(($reqtype, $reqfield)),*}, {$(($type, $field)),*});
@@ -346,6 +396,21 @@ macro_rules! impl_writeable_tlv_based {
 				});
 				Ok(())
 			}
+
+			#[inline]
+			fn serialized_length(&self) -> usize {
+				let len = _get_tlv_len!({
+					$(($reqtype, self.$reqfield)),*
+				}, {
+					$(($type, self.$field)),*
+				}, {
+					$(($vectype, Some(::util::ser::VecWriteWrapper(&self.$vecfield)))),*
+				});
+				use util::ser::{BigSize, LengthCalculatingWriter};
+				let mut len_calc = LengthCalculatingWriter(0);
+				BigSize(len as u64).write(&mut len_calc).expect("No in-memory data may fail to serialize");
+				len + len_calc.0
+			}
 		}
 
 		impl ::util::ser::Readable for $st {