WASI Target Support

[milas]

Originally posted by @milas in #9 :

I am happy to open a new issue for this, but is there interest in accepting PRs for / supporting WASI as a target as part of this? (More generally, WASM but not on the web. I made a POC repo and am using cargo build --target wasm32-wasip1 for reference.)

Besides some dependencies, it's mostly local timezone that causes trouble, but I think there's reasonably minimally invasive #[cfg(not(target_arch = "wasm32"))] options here. I believe the Cargo changes are also safe, it's more about different features/etc.

Originally posted by @milas in #1616 (comment):

Hi! I'm interested in this PR from the perspective of WASI compatibility: #9 (comment)

I attached a diff from a POC -- I successfully compiled/used (mainline) VRL via WASI (Go/wazero) but was focused on getting something compiling just to understand how far off we are currently.

vrl-wasi.patch

commit 50ccec7c2207b0f6e1bc593585dd9e7c9e302502
Author: Milas Bowman <milas@realm.security>
Date:   Wed Jan 21 19:50:45 2026 -0500

    feat: add wasm32-wasi support
    
    This commit enables VRL to compile for the wasm32-wasip1 target by:
    - Gating OS-specific dependencies (iana-time-zone, hostname) to non-WASM targets.
    - Removing the 'wasmbind' feature from chrono.
    - Adding a fallback to UTC for 'TimeZone::Local' on WASM, since WASI lacks system local time.

diff --git a/Cargo.lock b/Cargo.lock
index 40d21b0e8..1db2e4e34 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -450,10 +450,8 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "145052bdd345b87320e369255277e3fb5152762ad123a901ef5c262dd38fe8d2"
 dependencies = [
  "iana-time-zone",
- "js-sys",
  "num-traits",
  "serde",
- "wasm-bindgen",
  "windows-link 0.2.0",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index ee2b101b8..4793ceadc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -134,7 +134,7 @@ base64-simd = { version = "0.8", optional = true }
 bytes = { version = "1", default-features = false, optional = true }
 charset = { version = "0.1", optional = true }
 encoding_rs = { version = "0.8.35", optional = true }
-chrono = { version = "0.4", default-features = false, features = ["clock", "serde", "wasmbind"], optional = true }
+chrono = { version = "0.4", default-features = false, features = ["serde"], optional = true }
 chrono-tz = { version = "0.10", default-features = false, optional = true }
 ciborium = { version = "0.2.2", default-features = false, optional = true }
 cidr = { version = "0.3", optional = true }
@@ -149,7 +149,6 @@ exitcode = { version = "1", optional = true }
 flate2 = { version = "1.1.2", default-features = false, features = ["zlib-rs"], optional = true }
 hex = { version = "0.4", optional = true }
 hmac = { version = "0.12", optional = true }
-iana-time-zone = { version = "0.1", optional = true }
 idna = { version = "1.0", optional = true }
 indexmap = { version = "2", default-features = false, features = ["std"], optional = true }
 influxdb-line-protocol = { version = "2.0.0", optional = true }
@@ -206,7 +205,7 @@ xxhash-rust = { version = "0.8", optional = true, features = [
 ] }
 community-id = { version = "0.2", optional = true }
 
-zstd = { version = "0.13", default-features = false, features = ["wasm"], optional = true }
+zstd = { version = "0.13", default-features = false, features = ["wasm", "thin"], optional = true }
 
 # Cryptography
 aes = { version = "0.8", optional = true }
@@ -235,9 +234,11 @@ reqwest-retry = { version = "0.7", default-features = false }
 
 # Dependencies used for non-WASM
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
+chrono = { version = "0.4", default-features = false, features = ["clock"] }
+iana-time-zone = { version = "0.1", optional = true }
+hostname = { version = "0.4", optional = true }
 dns-lookup = { version = "2", optional = true }
 domain = { version = "0.11.0", optional = true, features = ["resolv-sync", "serde"] }
-hostname = { version = "0.4", optional = true }
 grok = { version = "2.4", optional = true }
 onig = { version = "6", default-features = false, optional = true }
 tokio = { version = "1.45", optional = true, features = ["io-util", "macros", "net", "time", "sync", "rt", "rt-multi-thread"] }
diff --git a/src/compiler/datetime.rs b/src/compiler/datetime.rs
index 2d3ab280c..080c68f59 100644
--- a/src/compiler/datetime.rs
+++ b/src/compiler/datetime.rs
@@ -1,7 +1,9 @@
 use std::fmt::Debug;
 
 use chrono::format::{Parsed, StrftimeItems, parse};
-use chrono::{DateTime, FixedOffset, Local, Offset, ParseError, TimeZone as _, Utc};
+use chrono::{DateTime, FixedOffset, Offset, ParseError, TimeZone as _, Utc};
+#[cfg(not(target_arch = "wasm32"))]
+use chrono::Local;
 use chrono_tz::Tz;
 use serde::{Deserialize, Serialize};
 
@@ -39,8 +41,16 @@ impl TimeZone {
 
         match self {
             Self::Local => {
-                let local_datetime = parsed.to_datetime_with_timezone(&Local)?;
-                Ok(datetime_to_utc(&local_datetime))
+                #[cfg(not(target_arch = "wasm32"))]
+                {
+                    let local_datetime = parsed.to_datetime_with_timezone(&Local)?;
+                    Ok(datetime_to_utc(&local_datetime))
+                }
+                #[cfg(target_arch = "wasm32")]
+                {
+                    let utc_datetime = parsed.to_datetime_with_timezone(&Utc)?;
+                    Ok(utc_datetime)
+                }
             }
             Self::Named(tz) => {
                 let tz_datetime = parsed.to_datetime_with_timezone(tz)?;
@@ -88,7 +98,16 @@ impl TryFrom<String> for TimeZone {
 impl From<TimeZone> for FixedOffset {
     fn from(tz: TimeZone) -> Self {
         match tz {
-            TimeZone::Local => *Utc::now().with_timezone(&Local).offset(),
+            TimeZone::Local => {
+                #[cfg(not(target_arch = "wasm32"))]
+                {
+                    *Utc::now().with_timezone(&Local).offset()
+                }
+                #[cfg(target_arch = "wasm32")]
+                {
+                    chrono::FixedOffset::east_opt(0).unwrap()
+                }
+            }
             TimeZone::Named(tz) => Utc::now().with_timezone(&tz).offset().fix(),
         }
     }
diff --git a/src/stdlib/get_timezone_name.rs b/src/stdlib/get_timezone_name.rs
index 150edc962..5d9d2cf00 100644
--- a/src/stdlib/get_timezone_name.rs
+++ b/src/stdlib/get_timezone_name.rs
@@ -1,4 +1,5 @@
 use crate::compiler::prelude::*;
+#[cfg(not(target_arch = "wasm32"))]
 use chrono::Local;
 use std::borrow::Cow;
 
@@ -6,9 +7,18 @@ use std::borrow::Cow;
 pub fn get_name_for_timezone(tz: &TimeZone) -> Cow<'_, str> {
     match tz {
         TimeZone::Named(tz) => tz.name().into(),
-        TimeZone::Local => iana_time_zone::get_timezone()
-            .unwrap_or_else(|_| Local::now().offset().to_string())
-            .into(),
+        TimeZone::Local => {
+            #[cfg(not(target_arch = "wasm32"))]
+            {
+                iana_time_zone::get_timezone()
+                    .unwrap_or_else(|_| Local::now().offset().to_string())
+                    .into()
+            }
+            #[cfg(target_arch = "wasm32")]
+            {
+                "UTC".into()
+            }
+        }
     }
 }

From a features standpoint, I do think the no system/no env make sense, especially for a pure wasm32 target, but I am wondering if there's a mix of target conditionals + features that would be helpful?

---

Copy-pasting these to a new discussion: I'm happy to contribute PRs and testing here, but I'm trying to gauge if there's any interest/appetite from maintainers first.

If this is not of interest for the project, that's fine! Just hoping to get direction one way or another.

[thomasqueirozb]

Hi @milas,

we already have a WASM VRL build here, we can maybe build on top of that. AFAICT these changes are not necessary to build for a WASM target. Could you provide a set of commands so I can try to build this myself on the latest changes to main?

A WASI build is a nice to have, but this is not something we're actively looking to implement at the moment because there are a quite few higher priority projects pending. However, we absolutely welcome community contributions and do our best to provide guidance and timely reviews for those. This would be a nice addition to the project.

[milas]

Awesome, thanks! I will open a draft PR with instructions on how to build / use when I have a little more time.

Thankfully wasm32-wasip1 support in rustc is pretty good these days - the collapsible diff in my post shows minimal changes for a POC that works, which are mostly around dependency features & timezone handling.

RE: Dependency features, I need to do a deeper-dive on the potential impact of each of these, e.g. need these to be conditional on the wasip1 target at the very least and need to understand how they actually impact behavior.

RE: Timezone, there's no concept of system local for WASI, but I think a reasonable alternative would be to allow setting the 'local' TZ as part of the runtime. Non-WASI builds could then still default to using chrono::Local while for WASI you'd need to specify a value (my POC just used Etc/UTC).

If that seems like reasonable behavior (allow defining "local" TZ as part of runtime instead of enforcing chrono::LOcal), I'm happy to start with a PR there.