fix(rust-client): restore bare-metal no_std builds

.github/workflows/build.yml

@@ -67,6 +67,28 @@ jobs:
       - name: make - build-wasm
         run: make build-wasm
 
+  build-no-std:
+    name: Build bare metal (no_std)
+    runs-on: warp-ubuntu-latest-x64-8x
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+        with:
+          persist-credentials: false
+      - name: Cleanup large tools for build space
+        uses: ./.github/actions/cleanup-runner
+      - name: Install Rust toolchain
+        run: |
+          rustup update --no-self-update
+          rustup target add thumbv7em-none-eabihf
+      - name: Add Rust Cache
+        uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          shared-key: rust-release
+          prefix-key: ${{ env.RUST_CACHE_KEY }}
+          save-if: false
+      - name: make - build-no-std
+        run: make build-no-std
+
   install:
     name: Install ${{ matrix.target }}
     runs-on: ubuntu-latest

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Fixes
 
+* [FIX][rust] `miden-client` no longer pulls the `tonic` runtime into builds without the `tonic` or `std` features, restoring support for bare-metal `no_std` targets.
 * [FIX][rust] Added validation of cached transaction encryption keys during deserialization. Unsupported encryption schemes and empty or oversized key IDs are rejected before reading the key ID bytes ([#2411](https://github.com/0xMiden/rust-sdk/pull/2411)).
 * [FIX][cli] `miden-client import` now rejects invocations without a file path instead of silently succeeding ([#2450](https://github.com/0xMiden/rust-sdk/pull/2450)).
 * [FIX][rust] `TransactionRequestBuilder::build_swap` and `build_pswap_create` now reject a zero-amount asset on either side of the exchange. A zero requested asset produced a payback P2ID note carrying nothing, and a zero offered asset produced a note whose consumer pays and receives nothing ([#2459](https://github.com/0xMiden/rust-sdk/pull/2459)).

Makefile

@@ -182,6 +182,10 @@ build: ## Build the CLI binary, client library and tests binary in release mode
 build-wasm: ## Build the client library for wasm32 with no_std (no default features)
 	cargo build --package miden-client --target wasm32-unknown-unknown --no-default-features --locked
 
+.PHONY: build-no-std
+build-no-std: ## Build the client library for a bare-metal no_std target
+	cargo build --package miden-client --target thumbv7em-none-eabihf --no-default-features --locked
+
 # --- Check ---------------------------------------------------------------------------------------
 
 .PHONY: check

crates/rust-client/Cargo.toml

@@ -52,16 +52,24 @@ dap = ["dep:miden-debug", "std"]
 default = ["std"]
 std = [
   "concurrent",
+  "dep:chrono",
   "dep:tempfile",
   "dep:tokio",
+  "dep:tonic-prost",
+  "futures/std",
+  "hex/std",
   "miden-agglayer/std",
   "miden-assembly-syntax/std",
   "miden-processor/std",
   "miden-protocol/std",
   "miden-tx/std",
+  "rand/std",
+  "rand/thread_rng",
+  "serde/std",
   "tonic/tls-native-roots",
   "tonic/tls-ring",
   "tonic/transport",
+  "tracing/std",
 ]
 testing = [
   "dep:miden-testing",
@@ -71,7 +79,12 @@ testing = [
   "miden-standards/testing",
   "miden-tx/testing",
 ]
-tonic = []
+tonic = [
+  "dep:tonic",
+  "dep:tonic-health",
+  "dep:tonic-prost",
+  "dep:tonic-web-wasm-client",
+]
 
 [dependencies]
 # Miden dependencies
@@ -88,28 +101,27 @@ miden-tx-batch        = { workspace = true }
 # External dependencies
 anyhow       = { workspace = true }
 async-trait  = { workspace = true }
-chrono       = { workspace = true }
-futures      = { version = "0.3" }
-hex          = { workspace = true }
+chrono       = { optional = true, workspace = true }
+futures      = { default-features = false, features = ["alloc", "async-await"], version = "0.3" }
+hex          = { default-features = false, features = ["alloc"], workspace = true }
 prost        = { features = ["derive"], workspace = true }
 prost-types  = { version = "0.14" }
-rand         = { workspace = true }
-serde        = { workspace = true }
-serde_json   = { workspace = true }
+rand         = { default-features = false, workspace = true }
+serde        = { default-features = false, features = ["derive"], workspace = true }
 tempfile     = { optional = true, workspace = true }
 thiserror    = { workspace = true }
 tokio        = { features = ["sync", "time"], optional = true, workspace = true }
-tonic        = { features = ["codegen"], workspace = true }
-tonic-health = { version = "0.14" }
-tonic-prost  = { version = "0.14" }
-tracing      = { workspace = true }
+tonic        = { features = ["codegen"], optional = true, workspace = true }
+tonic-health = { optional = true, version = "0.14" }
+tonic-prost  = { optional = true, version = "0.14" }
+tracing      = { default-features = false, workspace = true }
 uuid         = { features = ["js", "serde", "v4"], optional = true, workspace = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 getrandom             = { features = ["wasm_js"], version = "0.3" }
 gloo-timers           = { features = ["futures"], version = "0.3" }
 tokio                 = { default-features = false, features = ["sync"], version = "1.48" }
-tonic-web-wasm-client = { default-features = false, version = "0.9" }
+tonic-web-wasm-client = { default-features = false, optional = true, version = "0.9" }
 
 [build-dependencies]
 miden-node-proto-build           = { workspace = true }

crates/rust-client/build.rs

@@ -46,6 +46,11 @@ fn main() -> miette::Result<()> {
     Ok(())
 }
 
+/// Whether transport-capable client bindings are needed for a no-std build.
+fn tonic_feature_enabled() -> bool {
+    std::env::var_os("CARGO_FEATURE_TONIC").is_some()
+}
+
 // REMOTE PROVER CLIENT PROTO CODEGEN
 // ===============================================================================================
 
@@ -61,6 +66,7 @@ fn compile_tonic_remote_prover_proto(out_dir: &Path) -> miette::Result<()> {
     // The `nostd` bindings target `wasm32`, where the transport is provided by
     // `tonic-web-wasm-client`, so tonic's own transport codegen must be disabled.
     tonic_prost_build::configure()
+        .build_client(tonic_feature_enabled())
         .build_transport(false)
         .build_server(false)
         .out_dir(&nostd_out)
@@ -98,6 +104,7 @@ fn compile_tonic_note_transport_proto(out_dir: &Path) -> miette::Result<()> {
 
     // Generate the header of the user facing server from its proto file
     tonic_prost_build::configure()
+        .build_client(tonic_feature_enabled())
         .build_transport(false)
         .build_server(false)
         .out_dir(&nostd_out)
@@ -136,6 +143,7 @@ fn compile_tonic_client_proto(out_dir: &Path) -> miette::Result<()> {
 
     // Generate the header of the user facing server from its proto file
     tonic_prost_build::configure()
+        .build_client(tonic_feature_enabled())
         .build_transport(false)
         .build_server(false)
         .out_dir(&nostd_out)

crates/rust-client/src/builder.rs

@@ -474,9 +474,17 @@ where
         let rng = if let Some(user_rng) = self.rng {
             user_rng
         } else {
-            let mut seed_rng = rand::rng();
-            let coin_seed: [u64; 4] = seed_rng.random();
-            Box::new(RandomCoin::new(coin_seed.map(Felt::new_unchecked).into()))
+            #[cfg(not(feature = "std"))]
+            return Err(ClientError::ClientInitializationError(
+                "RNG is required in no_std builds. Call `.rng(...)`.".into(),
+            ));
+
+            #[cfg(feature = "std")]
+            {
+                let mut seed_rng = rand::rng();
+                let coin_seed: [u64; 4] = seed_rng.random();
+                Box::new(RandomCoin::new(coin_seed.map(Felt::new_unchecked).into()))
+            }
         };
 
         let tx_prover: Arc<dyn TransactionProver + Send + Sync> =

crates/rust-client/src/store/note_record/input_note_record/states/mod.rs

@@ -1,6 +1,7 @@
-use alloc::string::ToString;
+use alloc::string::{String, ToString};
 use core::fmt::{self, Display};
 
+#[cfg(feature = "std")]
 use chrono::{Local, TimeZone};
 use miden_protocol::account::AccountId;
 use miden_protocol::block::{BlockHeader, BlockNumber};
@@ -308,17 +309,7 @@ impl Display for InputNoteState {
                 write!(
                     f,
                     "Processing (submitted at {} by account {})",
-                    submission_data.submitted_at.map_or("?".to_string(), |submitted_at| {
-                        Local
-                            .timestamp_opt(
-                                i64::try_from(submitted_at)
-                                    .expect("i64::MAX as timestamp is year 2262"),
-                                0,
-                            )
-                            .single()
-                            .expect("timestamp should be valid")
-                            .to_string()
-                    }),
+                    submission_data.submitted_at.map_or("?".to_string(), format_timestamp),
                     submission_data.consumer_account
                 )
             },
@@ -355,6 +346,23 @@ impl Display for InputNoteState {
     }
 }
 
+#[cfg(feature = "std")]
+fn format_timestamp(timestamp: u64) -> String {
+    Local
+        .timestamp_opt(
+            i64::try_from(timestamp).expect("i64::MAX as timestamp is year 2262"),
+            0,
+        )
+        .single()
+        .expect("timestamp should be valid")
+        .to_string()
+}
+
+#[cfg(not(feature = "std"))]
+fn format_timestamp(timestamp: u64) -> String {
+    timestamp.to_string()
+}
+
 pub trait NoteStateHandler {
     fn metadata(&self) -> Option<&NoteMetadata>;