shared: Introduce max_message_size_… features

shared/Cargo.toml

@@ -34,3 +34,33 @@ python-bindings = ["pyo3", "hex"]
 ## larger sizes (especially for experimentation) without making sizes explode
 ## on embedded.
 quadruple_sizes = []
+
+## Precise control of `MAX_MESSAGE_SIZE_LEN`.
+##
+## If any of those is set, they override the default of 192 (as well as
+## `quadruple_sizes`). 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 = []
+
+## Precise control of `MAX_KDF_CONTENT_LEN`.
+##
+## If any of those is set, they override the default of 256 (as well as
+## `quadruple_sizes`). 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 = []
+
+## Precise control of `MAX_BUFFER_LEN`.
+##
+## If any of those is set, they override the default of 320 (as well as
+## `quadruple_sizes`). If multiple are set, the highest wins.
+
+max_buffer_len_384 = []
+max_buffer_len_448 = []
+max_buffer_len_512 = []

shared/src/lib.rs

@@ -42,9 +42,20 @@ pub const SCALE_FACTOR: usize = 1;
 #[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_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
+    SCALE_FACTOR * (128 + 64)
+};
 
 pub const ID_CRED_LEN: usize = 4;
 pub const SUITES_LEN: usize = 9;
@@ -61,9 +72,27 @@ 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_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 {
+    SCALE_FACTOR * 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_512") {
+    512
+} else if cfg!(feature = "max_buffer_len_448") {
+    448
+} else if cfg!(feature = "max_buffer_len_384") {
+    384
+} else {
+    SCALE_FACTOR * 256 + 64
+};
 pub const CBOR_BYTE_STRING: u8 = 0x58u8;
 pub const CBOR_TEXT_STRING: u8 = 0x78u8;
 pub const CBOR_UINT_1BYTE: u8 = 0x18u8;