Wasm: Allow to set the HTTP response status.

This commit enables WebAssembly modules to set the HTTP response status
to something other than the previously hard coded '200 OK'.

To do this they can make a call to nxt_wasm_set_resp_status() providing
the required status code.

If this function isn't called the status code defaults to '200 OK'. The
WebAssembly module can also return -1 from the request_handler function
as a short cut to signal a '500 Internal Server Error'.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

src/wasm/nxt_rt_wasmtime.c

@@ -102,6 +102,19 @@ nxt_wasm_send_headers(void *env, wasmtime_caller_t *caller,
 }
 
 
+static wasm_trap_t *
+nxt_wasm_set_resp_status(void *env, wasmtime_caller_t *caller,
+                         const wasmtime_val_t *args, size_t nargs,
+                         wasmtime_val_t *results, size_t nresults)
+{
+    nxt_wasm_ctx_t  *ctx = env;
+
+    ctx->status = args[0].of.i32;
+
+    return NULL;
+}
+
+
 static void
 nxt_wasmtime_execute_hook(const nxt_wasm_ctx_t *ctx, nxt_wasm_fh_t hook)
 {
@@ -123,8 +136,8 @@ nxt_wasmtime_execute_hook(const nxt_wasm_ctx_t *ctx, nxt_wasm_fh_t hook)
 }
 
 
-static void
+static int
-nxt_wasmtime_execute_request(const nxt_wasm_ctx_t *ctx)
+nxt_wasmtime_execute_request(nxt_wasm_ctx_t *ctx)
 {
     int                    i = 0;
     wasm_trap_t            *trap = NULL;
@@ -142,7 +155,10 @@ nxt_wasmtime_execute_request(const nxt_wasm_ctx_t *ctx)
         nxt_wasmtime_err_msg(error, trap,
                              "failed to call function [->wasm_request_handler]"
                             );
+        return -1;
     }
+
+    return results[0].of.i32;
 }
 
 
@@ -183,6 +199,11 @@ nxt_wasmtime_set_function_imports(nxt_wasm_ctx_t *ctx)
             .func      = nxt_wasm_send_headers,
             .params    = { WASM_I32 },
             .ft        = NXT_WASM_FT_1_0
+        }, {
+            .func_name = "nxt_wasm_set_resp_status",
+            .func      = nxt_wasm_set_resp_status,
+            .params    = { WASM_I32 },
+            .ft        = NXT_WASM_FT_1_0
         },
 
         { }

src/wasm/nxt_wasm.c

@@ -24,6 +24,11 @@ static nxt_wasm_ctx_t               nxt_wasm_ctx;
 
 static const nxt_wasm_operations_t  *nxt_wops;
 
+enum {
+    NXT_WASM_HTTP_OK     = 200,
+    NXT_WASM_HTTP_ERROR  = 500
+};
+
 
 void
 nxt_wasm_do_response_end(nxt_wasm_ctx_t *ctx)
@@ -48,7 +53,7 @@ nxt_wasm_do_send_headers(nxt_wasm_ctx_t *ctx, uint32_t offset)
         fields_len += rh->fields[i].name_len + rh->fields[i].value_len;
     }
 
-    nxt_unit_response_init(ctx->req, 200, rh->nfields, fields_len);
+    nxt_unit_response_init(ctx->req, ctx->status, rh->nfields, fields_len);
 
     for (i = 0; i < rh->nfields; i++) {
         const char  *name;
@@ -72,7 +77,7 @@ nxt_wasm_do_send_response(nxt_wasm_ctx_t *ctx, uint32_t offset)
     nxt_unit_request_info_t  *req = ctx->req;
 
     if (!nxt_unit_response_is_init(req)) {
-        nxt_unit_response_init(req, 200, 0, 0);
+        nxt_unit_response_init(req, ctx->status, 0, 0);
     }
 
     resp = (nxt_wasm_response_t *)(nxt_wasm_ctx.baddr + offset);
@@ -84,6 +89,7 @@ nxt_wasm_do_send_response(nxt_wasm_ctx_t *ctx, uint32_t offset)
 static void
 nxt_wasm_request_handler(nxt_unit_request_info_t *req)
 {
+    int                    err;
     size_t                 offset, read_bytes, content_sent, content_len;
     ssize_t                bytes_read;
     nxt_unit_field_t       *sf, *sf_end;
@@ -149,8 +155,12 @@ nxt_wasm_request_handler(nxt_unit_request_info_t *req)
 
     wr->request_size = offset + bytes_read;
 
+    nxt_wasm_ctx.status = NXT_WASM_HTTP_OK;
     nxt_wasm_ctx.req = req;
-    nxt_wops->exec_request(&nxt_wasm_ctx);
+    err = nxt_wops->exec_request(&nxt_wasm_ctx);
+    if (err) {
+        goto out_err_500;
+    }
 
     if (content_len == content_sent) {
         goto request_done;
@@ -168,9 +178,18 @@ nxt_wasm_request_handler(nxt_unit_request_info_t *req)
         wr->request_size = wr->content_sent = bytes_read;
         wr->total_content_sent = content_sent;
 
-        nxt_wops->exec_request(&nxt_wasm_ctx);
+        err = nxt_wops->exec_request(&nxt_wasm_ctx);
+        if (err) {
+            goto out_err_500;
+        }
     } while (content_sent < content_len);
 
+    goto request_done;
+
+out_err_500:
+    nxt_unit_response_init(req, NXT_WASM_HTTP_ERROR, 0, 0);
+    nxt_unit_request_done(req, NXT_UNIT_OK);
+
 request_done:
     NXT_WASM_DO_HOOK(NXT_WASM_FH_REQUEST_END);
 }

src/wasm/nxt_wasm.h

@@ -118,12 +118,14 @@ struct nxt_wasm_ctx_s {
     size_t                   baddr_off;
 
     size_t                   response_off;
+
+    uint16_t                 status;
 };
 
 struct nxt_wasm_operations_s {
     int   (*init)(nxt_wasm_ctx_t *ctx);
     void  (*destroy)(const nxt_wasm_ctx_t *ctx);
-    void  (*exec_request)(const nxt_wasm_ctx_t *ctx);
+    int   (*exec_request)(nxt_wasm_ctx_t *ctx);
     void  (*exec_hook)(const nxt_wasm_ctx_t *ctx, nxt_wasm_fh_t hook);
 };