feat: support http_headers host function (#64)

* feat: support http_headers host function

* cleanup: free http_headers memory, add example

Makefile

@@ -2,7 +2,9 @@ plugins:
 	mkdir -p test
 	cargo build --release --example count_vowels
 	cargo build --release --example http
+	cargo build --release --example http_headers
 	cargo build --release --example host_function
 	cp target/wasm32-unknown-unknown/release/examples/count_vowels.wasm test/code.wasm
 	cp target/wasm32-unknown-unknown/release/examples/http.wasm test/http.wasm
-	cp target/wasm32-unknown-unknown/release/examples/host_function.wasm test/host_function.wasm
+	cp target/wasm32-unknown-unknown/release/examples/http_headers.wasm test/http_headers.wasm
+	cp target/wasm32-unknown-unknown/release/examples/host_function.wasm test/host_function.wasm

examples/http_headers.rs

@@ -0,0 +1,12 @@
+#![no_main]
+
+use std::collections::HashMap;
+
+use extism_pdk::*;
+
+#[plugin_fn]
+pub fn http_get(Json(req): Json<HttpRequest>) -> FnResult<Json<HashMap<String, String>>> {
+    info!("Request to: {}", req.url);
+    let res = http::request::<()>(&req, None)?;
+    Ok(Json(res.headers().clone()))
+}

src/extism.rs

@@ -18,6 +18,7 @@ extern "C" {
     pub fn var_set(offs: u64, offs1: u64);
     pub fn http_request(req: u64, body: u64) -> u64;
     pub fn http_status_code() -> i32;
+    pub fn http_headers() -> u64;
     pub fn log_info(offs: u64);
     pub fn log_debug(offs: u64);
     pub fn log_warn(offs: u64);

src/http.rs

@@ -1,10 +1,13 @@
+use std::collections::HashMap;
+
 use crate::*;
 
 /// A HttpResponse is used to wrap the memory returned by
 /// `extism_pdk::http::request`
 pub struct HttpResponse {
     memory: Memory,
     status: u16,
+    headers: HashMap<String, String>,
 }
 
 impl HttpResponse {
@@ -28,6 +31,14 @@ impl HttpResponse {
         let x = serde_json::from_slice(&self.body())?;
         Ok(x)
     }
+
+    pub fn headers(&self) -> &HashMap<String, String> {
+        &self.headers
+    }
+
+    pub fn header(&self, s: impl AsRef<str>) -> Option<&str> {
+        self.headers.get(s.as_ref()).map(|x| x.as_ref())
+    }
 }
 
 /// Execute `HttpRequest`, if `body` is not `None` then it will be sent as the
@@ -46,11 +57,26 @@ pub fn request<T: ToMemory>(
     let offs = unsafe { extism::http_request(req.offset(), data) };
     let status = unsafe { extism::http_status_code() };
     let len = unsafe { extism::length_unsafe(offs) };
+
+    let headers = unsafe { extism::http_headers() };
+    let headers = if headers == 0 {
+        HashMap::new()
+    } else {
+        if let Some(h) = Memory::find(headers) {
+            let Json(j) = h.to()?;
+            h.free();
+            j
+        } else {
+            HashMap::new()
+        }
+    };
+
     Ok(HttpResponse {
         memory: Memory(MemoryHandle {
             offset: offs,
             length: len,
         }),
         status: status as u16,
+        headers,
     })
 }