shared: Introduce max_message_size_… features

lakers-python/Cargo.toml

@@ -11,7 +11,7 @@ license.workspace = true
 pyo3 = { version = "0.22", features = ["extension-module"] }
 lakers = { package = "lakers", path = "../lib", default-features = false, features = [ "log" ] }
 lakers-ead-authz = { path = "../ead/lakers-ead-authz", features = [ "log" ] }
-lakers-shared = { path = "../shared", features = ["python-bindings", "quadruple_sizes"] }
+lakers-shared = { path = "../shared", features = ["python-bindings", "large_buffers"] }
 lakers-crypto = { path = "../crypto", default-features = false, features = ["rustcrypto"] }
 log = "0.4"
 pyo3-log = "0.11.0"

shared/Cargo.toml

@@ -26,11 +26,52 @@ rstest = "0.21.0"
 default = [  ]
 python-bindings = ["pyo3", "hex"]
 
-## For all arbitrarily limited buffers, pick 4x the current default.
+## For all arbitrarily limited buffers, pick the maximum.
 ##
-## On the long run, this might be replaced with a more fine-grained feature set
-## picking the minimum size of all the items, or even an option to generalize,
-## but this provides an easy way to allow unconstrained systems to stomach
-## larger sizes (especially for experimentation) without making sizes explode
-## on embedded.
-quadruple_sizes = []
+## This provides an easy way to allow unconstrained systems to stomach larger
+## sizes (especially for experimentation).
+large_buffers = [
+    "max_message_size_len_1024",
+    "max_kdf_content_len_1024",
+    "max_buffer_len_1024",
+    "max_connid_encoded_len_24",
+]
+
+## Precise control of `MAX_MESSAGE_SIZE_LEN`.
+##
+## If any of those is set, they override the default of 192. If multiple are
+## set, the highest wins.
+
+max_message_size_len_256 = []
+max_message_size_len_320 = []
+max_message_size_len_384 = []
+max_message_size_len_448 = []
+max_message_size_len_512 = []
+max_message_size_len_1024 = []
+
+## Precise control of `MAX_KDF_CONTENT_LEN`.
+##
+## If any of those is set, they override the default of 256. If multiple are
+## set, the highest wins.
+
+max_kdf_content_len_320 = []
+max_kdf_content_len_384 = []
+max_kdf_content_len_448 = []
+max_kdf_content_len_512 = []
+max_kdf_content_len_1024 = []
+
+## Precise control of `MAX_BUFFER_LEN`.
+##
+## If any of those is set, they override the default of 320. If multiple are
+## set, the highest wins.
+
+max_buffer_len_384 = []
+max_buffer_len_448 = []
+max_buffer_len_512 = []
+max_buffer_len_1024 = []
+
+## Control of `MAX_CONNID_ENCODED_LEN`.
+##
+## If this is not set, the minimum sensible default (8 bytes) is used.
+
+max_connid_encoded_len_24 = []

shared/cbindgen.toml

@@ -12,7 +12,7 @@ include_guard = "LAKERS_SHARED_H"
 cpp_compat = true
 
 [defines]
-"feature = quadruple_sizes" = "QUADRUPLE_SIZES"
+"feature = large_buffers" = "LARGE_BUFFERS"
 
 [export]
 include = [

shared/src/lib.rs

@@ -32,19 +32,22 @@ use pyo3::prelude::*;
 #[cfg(feature = "python-bindings")]
 mod python_bindings;
 
-/// Configured upscaling applied to fixed-size buffers
-///
-/// Do not rely on this: It is only pub because cbindgen needs it.
-#[cfg(not(feature = "quadruple_sizes"))]
-#[doc(hidden)]
-pub const SCALE_FACTOR: usize = 1;
-#[cfg(feature = "quadruple_sizes")]
-#[doc(hidden)]
-pub const SCALE_FACTOR: usize = 4;
-
-// TODO: find a way to configure the buffer size
-// need 128 to handle EAD fields, and 192 for the EAD_1 voucher
-pub const MAX_MESSAGE_SIZE_LEN: usize = SCALE_FACTOR * (128 + 64);
+pub const MAX_MESSAGE_SIZE_LEN: usize = if cfg!(feature = "max_message_size_len_1024") {
+    1024
+} else if cfg!(feature = "max_message_size_len_512") {
+    512
+} else if cfg!(feature = "max_message_size_len_448") {
+    448
+} else if cfg!(feature = "max_message_size_len_384") {
+    384
+} else if cfg!(feature = "max_message_size_len_320") {
+    320
+} else if cfg!(feature = "max_message_size_len_256") {
+    256
+} else {
+    // need 128 to handle EAD fields, and 192 for the EAD_1 voucher
+    128 + 64
+};
 
 pub const ID_CRED_LEN: usize = 4;
 pub const SUITES_LEN: usize = 9;
@@ -61,9 +64,31 @@ pub const MAC_LENGTH_3: usize = MAC_LENGTH_2;
 pub const ENCODED_VOUCHER_LEN: usize = 1 + MAC_LENGTH; // 1 byte for the length of the bstr-encoded voucher
 
 // maximum supported length of connection identifier for R
-pub const MAX_KDF_CONTEXT_LEN: usize = SCALE_FACTOR * 256;
+pub const MAX_KDF_CONTEXT_LEN: usize = if cfg!(feature = "max_kdf_content_len_1024") {
+    1024
+} else if cfg!(feature = "max_kdf_content_len_512") {
+    512
+} else if cfg!(feature = "max_kdf_content_len_448") {
+    448
+} else if cfg!(feature = "max_kdf_content_len_384") {
+    384
+} else if cfg!(feature = "max_kdf_content_len_320") {
+    320
+} else {
+    256
+};
 pub const MAX_KDF_LABEL_LEN: usize = 15; // for "KEYSTREAM_2"
-pub const MAX_BUFFER_LEN: usize = SCALE_FACTOR * 256 + 64;
+pub const MAX_BUFFER_LEN: usize = if cfg!(feature = "max_buffer_len_1024") {
+    1024
+} else if cfg!(feature = "max_buffer_len_512") {
+    512
+} else if cfg!(feature = "max_buffer_len_448") {
+    448
+} else if cfg!(feature = "max_buffer_len_384") {
+    384
+} else {
+    256 + 64
+};
 pub const CBOR_BYTE_STRING: u8 = 0x58u8;
 pub const CBOR_TEXT_STRING: u8 = 0x78u8;
 pub const CBOR_UINT_1BYTE: u8 = 0x18u8;
@@ -87,13 +112,14 @@ pub const KID_LABEL: u8 = 4;
 
 pub const ENC_STRUCTURE_LEN: usize = 8 + 5 + SHA256_DIGEST_LEN; // 8 for ENCRYPT0
 
-pub const MAX_EAD_SIZE_LEN: usize = SCALE_FACTOR * 64;
+pub const MAX_EAD_SIZE_LEN: usize = 64;
 
 /// Maximum length of a [`ConnId`] (`C_x`).
 ///
 /// This length includes the leading CBOR encoding byte(s).
-// If ints had a const `.clamp()` feature, this could be (8 * SCALE_FACTOR).clamp(1, 23).
-const MAX_CONNID_ENCODED_LEN: usize = if cfg!(feature = "quadruple_sizes") {
+// Note that when implementing larger sizes than 24, the encoding will need to use actual CBOR
+// rather than masking a known short length into a byte.
+const MAX_CONNID_ENCODED_LEN: usize = if cfg!(feature = "max_connid_encoded_len_24") {
     24
 } else {
     8