Add tracing setup support in C API

lib/c-api/Cargo.toml

@@ -43,6 +43,11 @@ thiserror = "1"
 typetag = { version = "0.1", optional = true }
 paste = "1.0"
 tokio = { version = "1", features = [ "rt", "rt-multi-thread", "io-util", "sync", "macros"], default_features = false }
+tracing = { version = "0.1" }
+tracing-subscriber = { version = "0.3", features = [
+	"env-filter",
+	"fmt",
+] }
 
 [dev-dependencies]
 field-offset = "0.3.3"

lib/c-api/src/lib.rs

@@ -29,4 +29,5 @@
 #![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]
 
 pub mod error;
+pub mod tracing;
 pub mod wasm_c_api;

lib/c-api/src/tracing.rs

@@ -0,0 +1,87 @@
+//! Utilities to set up tracing and logging.
+//!
+//! By default, wasmer does not generate any tracing output. To
+//! enable tracing, one must call the `wasmer_setup_tracing()`
+//! function during the initialization stage of their program.
+//!
+//! Tracing levels can be enabled/disabled using the [RUST_LOG
+//! env var](https://docs.rs/env_logger/latest/env_logger/#enabling-logging).
+//!
+//! # Example
+//!
+//! ```rust
+//! # use wasmer_inline_c::assert_c;
+//! # fn main() {
+//! #    (assert_c! {
+//! # #include "tests/wasmer.h"
+//! #
+//! int main() {
+//!     // This can go up to 4, which is the most verbose
+//!     int verbosity_level = 0;
+//!     // Whether to use colors when logging information
+//!     int use_colors = 1;
+//!     wasmer_setup_tracing(verbosity_level, use_colors);
+//!
+//!     return 0;
+//! }
+//! #    })
+//! #    .success();
+//! # }
+
+use std::ffi::c_int;
+
+use tracing::level_filters::LevelFilter;
+use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt, EnvFilter};
+
+const WHITELISTED_LOG_TARGETS: &[&str] = &["wasmer", "wasmer_wasix", "virtual_fs"];
+
+#[no_mangle]
+pub extern "C" fn wasmer_setup_tracing(verbosity_level: c_int, use_color: c_int) {
+    let fmt_layer = fmt::layer()
+        .with_target(true)
+        .with_span_events(fmt::format::FmtSpan::CLOSE)
+        .with_ansi(use_color > 0)
+        .with_thread_ids(true)
+        .with_writer(std::io::stderr);
+
+    let filter_layer = {
+        let default_filters = [
+            LevelFilter::OFF,
+            LevelFilter::WARN,
+            LevelFilter::INFO,
+            LevelFilter::DEBUG,
+        ];
+
+        // First, we set up the default log level.
+        let default_level = default_filters
+            .get(verbosity_level as usize)
+            .copied()
+            .unwrap_or(LevelFilter::TRACE);
+        let mut filter = EnvFilter::builder()
+            .with_default_directive(default_level.into())
+            .from_env_lossy();
+
+        // Next we add level-specific directives, where verbosity=0 means don't
+        // override anything. Note that these are shifted one level up so we'll
+        // get something like RUST_LOG="warn,wasmer_wasix=info"
+        let specific_filters = [LevelFilter::WARN, LevelFilter::INFO, LevelFilter::DEBUG];
+        if verbosity_level > 0 {
+            let level = specific_filters
+                .get(verbosity_level as usize)
+                .copied()
+                .unwrap_or(LevelFilter::TRACE);
+
+            for target in WHITELISTED_LOG_TARGETS {
+                let directive = format!("{target}={level}").parse().unwrap();
+                filter = filter.add_directive(directive);
+            }
+        }
+
+        filter
+    };
+
+    tracing_subscriber::registry()
+        .with(filter_layer)
+        .with(fmt_layer.compact().with_target(true))
+        .init();
+}