Wasm: Add the core of initial WebAssembly language module support.

This adds the core of runtime WebAssembly[0] support. Future commits
will enable this in the Unit core and expose the configuration.

This introduces a new src/wasm directory for storing this source.

We are initially using Wasmtime[0] as the WebAssembly runtime, however
this has been designed with the ability to use different runtimes in
mind.

src/wasm/nxt_wasm.[ch] is the main interface to Unit.

src/wasm/nxt_rt_wasmtime.c is the Wasmtime runtime support. This is
nicely insulated from any knowledge of internal Unit workings.

Wasmtime is what loads and runs the Wasm modules.

The Wasm modules can export functions Wasmtime can call and Wasmtime can
export functions that the module can call.

We make use of both. The terminology used is that function exports are
what the Wasm module exports and function imports are what the Wasm
runtime exports to the module.

We currently have four function imports (functions exported by the
runtime to be called by the Wasm module).

1) nxt_wasm_get_init_mem_size

This allows Wasm modules to get the size of the initially allocated
shared memory. This is the size allocated at Unit startup and what the
Wasm modules can assume they have access to (in reality this shared
memory will likely be larger).

The amount of memory allocated at startup is NXT_WASM_MEM_SIZE which as
of this commit is 32MiB.

We do actually allocate NXT_WASM_MEM_SIZE + NXT_WASM_PAGE_SIZE at
startup which is an extra 64KiB (the smallest allocation unit), this is
to allow room for the response structure and so module developers can
just assume they have the full 32MiB for their actual response.

2) nxt_wasm_send_headers

This allows WASM modules to send their headers.

3) nxt_wasm_send_response

This allows WASM modules to send their response.

4) nxt_wasm_response_end

This allows WASM modules to inform Unit they have finished sending their
response. This calls nxt_unit_request_done()

Then there are currently up to eight functions that a module can export.
Three of which are required. These function can be named anything. I'll
use the Unit configuration names to refer to them

1) request_handler

The main driving function. This may be called multiple times for a
single HTTP request if the request is larger than the shared memory.

2) malloc_handler

Used to allocate a chunk of memory at language module startup. This
memory is allocated from the WASM modules address space and is what is
sued for communicating between the WASM module (the guest) and Unit (the
host).

3) free_handler

Used to free the memory from above at language module shutdown.

Then there are the following optional handlers

1) module_init_handler

If set, called at language module startup.

2) module_end_handler

If set, called at language module shutdown.

3) request_init_handler

If set, called at the start of request. Called only once per HTTP
request.

4) request_end_handler

If set, called once all of a request has been sent to the WASM module.

5) response_end_handler

If set, called at the end of a request, once the WASM module has sent
all its headers and data.

32bits

We currently support 32bit WASM modules, I.e wasm32-wasi. Newer version
of clang, 13+[2], do seem to have support for wasm64 as a target (which
uses a LP64 model). However it's not entirely clear if the WASI SDK
fully supports[3] this and by extension WASI libc/wasi-sysroot.

64bit support is something than can be explored more thoroughly in the
future.

As such in structures that are used to communicate between the host and
guest we use 32bit ints. Even when a single byte might be enough. This
is to avoid issues with structure layout differences between a 64bit
host and 32bit guest (I.e WASM module) and the need for various bits of
structure padding depending on host architecture. Instead everything is
4-byte aligned.

[0]: <https://webassembly.org/>
[1]: <https://wasmtime.dev/>
[2]: <https://reviews.llvm.org/rG670944fb20b226fc22fa993ab521125f9adbd30a>
[3]: <https://github.com/WebAssembly/wasi-sdk/issues/185>

Reviewed-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

3 files changed, 801 insertions, 0 deletions

diff --git a/src/wasm/nxt_rt_wasmtime.c b/src/wasm/nxt_rt_wasmtime.c
new file mode 100644
index 00000000..07a6165a
--- /dev/null
+++ b/src/wasm/nxt_rt_wasmtime.c
@@ -0,0 +1,407 @@
+/*
+ * Copyright (C) Andrew Clayton
+ * Copyright (C) F5, Inc.
+ */
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdarg.h>
+
+#include <wasm.h>
+#include <wasi.h>
+#include <wasmtime.h>
+
+#include "nxt_wasm.h"
+
+
+typedef struct nxt_wasmtime_ctx_s  nxt_wasmtime_ctx_t;
+
+struct nxt_wasmtime_ctx_s {
+    wasm_engine_t       *engine;
+    wasmtime_store_t    *store;
+    wasmtime_memory_t   memory;
+    wasmtime_module_t   *module;
+    wasmtime_linker_t   *linker;
+    wasmtime_context_t  *ctx;
+};
+
+static nxt_wasmtime_ctx_t  nxt_wasmtime_ctx;
+
+
+static void
+nxt_wasmtime_err_msg(wasmtime_error_t *error, wasm_trap_t *trap,
+                     const char *fmt, ...)
+{
+    va_list          args;
+    wasm_byte_vec_t  error_message;
+
+    fprintf(stderr, "WASMTIME ERROR: ");
+    va_start(args, fmt);
+    vfprintf(stderr, fmt, args);
+    va_end(args);
+    fprintf(stderr, "\n");
+
+    if (error == NULL && trap == NULL) {
+        return;
+    }
+
+    if (error != NULL) {
+        wasmtime_error_message(error, &error_message);
+        wasmtime_error_delete(error);
+    } else {
+        wasm_trap_message(trap, &error_message);
+        wasm_trap_delete(trap);
+    }
+    fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data);
+
+    wasm_byte_vec_delete(&error_message);
+}
+
+
+static wasm_trap_t *
+nxt_wasm_get_init_mem_size(void *env, wasmtime_caller_t *caller,
+                           const wasmtime_val_t *args, size_t nargs,
+                           wasmtime_val_t *results, size_t nresults)
+{
+    results[0].of.i32 = NXT_WASM_MEM_SIZE;
+
+    return NULL;
+}
+
+
+static wasm_trap_t *
+nxt_wasm_response_end(void *env, wasmtime_caller_t *caller,
+                      const wasmtime_val_t *args, size_t nargs,
+                      wasmtime_val_t *results, size_t nresults)
+{
+    nxt_wasm_do_response_end(env);
+
+    return NULL;
+}
+
+
+static wasm_trap_t *
+nxt_wasm_send_response(void *env, wasmtime_caller_t *caller,
+                       const wasmtime_val_t *args, size_t nargs,
+                       wasmtime_val_t *results, size_t nresults)
+{
+    nxt_wasm_do_send_response(env, args[0].of.i32);
+
+    return NULL;
+}
+
+
+static wasm_trap_t *
+nxt_wasm_send_headers(void *env, wasmtime_caller_t *caller,
+                      const wasmtime_val_t *args, size_t nargs,
+                      wasmtime_val_t *results, size_t nresults)
+{
+    nxt_wasm_do_send_headers(env, args[0].of.i32);
+
+    return NULL;
+}
+
+
+static void
+nxt_wasmtime_execute_hook(const nxt_wasm_ctx_t *ctx, nxt_wasm_fh_t hook)
+{
+    const char             *name = ctx->fh[hook].func_name;
+    wasm_trap_t            *trap = NULL;
+    wasmtime_error_t       *error;
+    nxt_wasmtime_ctx_t     *rt_ctx = &nxt_wasmtime_ctx;
+    const nxt_wasm_func_t  *func = &ctx->fh[hook].func;
+
+    if (name == NULL) {
+        return;
+    }
+
+    error = wasmtime_func_call(rt_ctx->ctx, func, NULL, 0, NULL, 0, &trap);
+    if (error != NULL || trap != NULL) {
+        nxt_wasmtime_err_msg(error, trap, "failed to call hook function [%s]",
+                             name);
+    }
+}
+
+
+static void
+nxt_wasmtime_execute_request(const nxt_wasm_ctx_t *ctx)
+{
+    int                    i = 0;
+    wasm_trap_t            *trap = NULL;
+    wasmtime_val_t         args[1] = { };
+    wasmtime_val_t         results[1] = { };
+    wasmtime_error_t       *error;
+    nxt_wasmtime_ctx_t     *rt_ctx = &nxt_wasmtime_ctx;
+    const nxt_wasm_func_t  *func = &ctx->fh[NXT_WASM_FH_REQUEST].func;
+
+    args[i].kind = WASMTIME_I32;
+    args[i++].of.i32 = ctx->baddr_off;
+
+    error = wasmtime_func_call(rt_ctx->ctx, func, args, i, results, 1, &trap);
+    if (error != NULL || trap != NULL) {
+        nxt_wasmtime_err_msg(error, trap,
+                             "failed to call function [->wasm_request_handler]"
+                            );
+    }
+}
+
+
+static void
+nxt_wasmtime_set_function_imports(nxt_wasm_ctx_t *ctx)
+{
+    nxt_wasmtime_ctx_t  *rt_ctx = &nxt_wasmtime_ctx;
+
+    static const struct {
+        const char                *func_name;
+
+        wasmtime_func_callback_t  func;
+        wasm_valkind_t            params[1];
+        wasm_valkind_t            results[1];
+
+        enum {
+            NXT_WASM_FT_0_0,
+            NXT_WASM_FT_1_0,
+            NXT_WASM_FT_0_1,
+        }                         ft;
+    } import_functions[] = {
+        {
+            .func_name = "nxt_wasm_get_init_mem_size",
+            .func      = nxt_wasm_get_init_mem_size,
+            .results   = { WASM_I32 },
+            .ft        = NXT_WASM_FT_0_1
+        }, {
+            .func_name = "nxt_wasm_response_end",
+            .func      = nxt_wasm_response_end,
+            .ft        = NXT_WASM_FT_0_0
+        }, {
+            .func_name = "nxt_wasm_send_response",
+            .func      = nxt_wasm_send_response,
+            .params    = { WASM_I32 },
+            .ft        = NXT_WASM_FT_1_0
+        }, {
+            .func_name = "nxt_wasm_send_headers",
+            .func      = nxt_wasm_send_headers,
+            .params    = { WASM_I32 },
+            .ft        = NXT_WASM_FT_1_0
+        },
+
+        { }
+    }, *imf;
+
+    for (imf = import_functions; imf->func_name != NULL; imf++) {
+        wasm_functype_t  *func_ty;
+
+        switch (imf->ft) {
+        case NXT_WASM_FT_0_0:
+            func_ty = wasm_functype_new_0_0();
+            break;
+        case NXT_WASM_FT_1_0:
+            func_ty = wasm_functype_new_1_0(wasm_valtype_new(imf->params[0]));
+            break;
+        case NXT_WASM_FT_0_1:
+            func_ty = wasm_functype_new_0_1(wasm_valtype_new(imf->results[0]));
+            break;
+        default:
+            /* Stop GCC complaining about func_ty being used uninitialised */
+            func_ty = NULL;
+        }
+
+        wasmtime_linker_define_func(rt_ctx->linker, "env", 3,
+                                    imf->func_name, strlen(imf->func_name),
+                                    func_ty,  imf->func, ctx, NULL);
+        wasm_functype_delete(func_ty);
+    }
+}
+
+
+static int
+nxt_wasmtime_get_function_exports(nxt_wasm_ctx_t *ctx)
+{
+    int                 i;
+    nxt_wasmtime_ctx_t  *rt_ctx = &nxt_wasmtime_ctx;
+
+    for (i = 0; i < NXT_WASM_FH_NR; i++) {
+        bool               ok;
+        wasmtime_extern_t  item;
+
+        if (ctx->fh[i].func_name == NULL) {
+            continue;
+        }
+
+        ok = wasmtime_linker_get(rt_ctx->linker, rt_ctx->ctx, "", 0,
+                                 ctx->fh[i].func_name,
+                                 strlen(ctx->fh[i].func_name), &item);
+        if (!ok) {
+            nxt_wasmtime_err_msg(NULL, NULL,
+                                 "couldn't get (%s) export from module",
+                                 ctx->fh[i].func_name);
+            return -1;
+        }
+        ctx->fh[i].func = item.of.func;
+    }
+
+    return 0;
+}
+
+
+static int
+nxt_wasmtime_wasi_init(const nxt_wasm_ctx_t *ctx)
+{
+    wasi_config_t       *wasi_config;
+    wasmtime_error_t    *error;
+    nxt_wasmtime_ctx_t  *rt_ctx = &nxt_wasmtime_ctx;
+
+    wasi_config = wasi_config_new();
+
+    wasi_config_inherit_env(wasi_config);
+    wasi_config_inherit_stdin(wasi_config);
+    wasi_config_inherit_stdout(wasi_config);
+    wasi_config_inherit_stderr(wasi_config);
+
+    error = wasmtime_context_set_wasi(rt_ctx->ctx, wasi_config);
+    if (error != NULL) {
+        nxt_wasmtime_err_msg(error, NULL, "failed to instantiate WASI");
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
+nxt_wasmtime_init_memory(nxt_wasm_ctx_t *ctx)
+{
+    int                    i = 0;
+    bool                   ok;
+    wasm_trap_t            *trap = NULL;
+    wasmtime_val_t         args[1] = { };
+    wasmtime_val_t         results[1] = { };
+    wasmtime_error_t       *error;
+    wasmtime_extern_t      item;
+    nxt_wasmtime_ctx_t     *rt_ctx = &nxt_wasmtime_ctx;
+    const nxt_wasm_func_t  *func = &ctx->fh[NXT_WASM_FH_MALLOC].func;
+
+    args[i].kind = WASMTIME_I32;
+    args[i++].of.i32 = NXT_WASM_MEM_SIZE + NXT_WASM_PAGE_SIZE;
+
+    error = wasmtime_func_call(rt_ctx->ctx, func, args, i, results, 1, &trap);
+    if (error != NULL || trap != NULL) {
+        nxt_wasmtime_err_msg(error, trap,
+                             "failed to call function [->wasm_malloc_handler]"
+                            );
+        return -1;
+    }
+
+    ok = wasmtime_linker_get(rt_ctx->linker, rt_ctx->ctx, "", 0, "memory",
+                             strlen("memory"), &item);
+    if (!ok) {
+        nxt_wasmtime_err_msg(NULL, NULL, "couldn't get 'memory' from module\n");
+        return -1;
+    }
+    rt_ctx->memory = item.of.memory;
+
+    ctx->baddr_off = results[0].of.i32;
+    ctx->baddr = wasmtime_memory_data(rt_ctx->ctx, &rt_ctx->memory);
+
+    ctx->baddr += ctx->baddr_off;
+
+    return 0;
+}
+
+
+static int
+nxt_wasmtime_init(nxt_wasm_ctx_t *ctx)
+{
+    int                 err;
+    FILE                *fp;
+    size_t              file_size;
+    wasm_byte_vec_t     wasm;
+    wasmtime_error_t    *error;
+    nxt_wasmtime_ctx_t  *rt_ctx = &nxt_wasmtime_ctx;
+
+    rt_ctx->engine = wasm_engine_new();
+    rt_ctx->store = wasmtime_store_new(rt_ctx->engine, NULL, NULL);
+    rt_ctx->ctx = wasmtime_store_context(rt_ctx->store);
+
+    rt_ctx->linker = wasmtime_linker_new(rt_ctx->engine);
+    error = wasmtime_linker_define_wasi(rt_ctx->linker);
+    if (error != NULL) {
+        nxt_wasmtime_err_msg(error, NULL, "failed to link wasi");
+        return -1;
+    }
+
+    fp = fopen(ctx->module_path, "r");
+    if (!fp) {
+        nxt_wasmtime_err_msg(NULL, NULL,
+                             "error opening file (%s)", ctx->module_path);
+        return -1;
+    }
+    fseek(fp, 0L, SEEK_END);
+    file_size = ftell(fp);
+    wasm_byte_vec_new_uninitialized(&wasm, file_size);
+    fseek(fp, 0L, SEEK_SET);
+    if (fread(wasm.data, file_size, 1, fp) != 1) {
+        nxt_wasmtime_err_msg(NULL, NULL, "error loading module");
+        fclose(fp);
+        return -1;
+    }
+    fclose(fp);
+
+    error = wasmtime_module_new(rt_ctx->engine, (uint8_t *)wasm.data, wasm.size,
+                                &rt_ctx->module);
+    if (!rt_ctx->module) {
+        nxt_wasmtime_err_msg(error, NULL, "failed to compile module");
+        return -1;
+    }
+    wasm_byte_vec_delete(&wasm);
+
+    nxt_wasmtime_set_function_imports(ctx);
+
+    nxt_wasmtime_wasi_init(ctx);
+
+    error = wasmtime_linker_module(rt_ctx->linker, rt_ctx->ctx, "", 0,
+                                   rt_ctx->module);
+    if (error != NULL) {
+         nxt_wasmtime_err_msg(error, NULL, "failed to instantiate");
+         return -1;
+    }
+
+    err = nxt_wasmtime_get_function_exports(ctx);
+    if (err) {
+        return -1;
+    }
+
+    err = nxt_wasmtime_init_memory(ctx);
+    if (err) {
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static void
+nxt_wasmtime_destroy(const nxt_wasm_ctx_t *ctx)
+{
+    int                    i = 0;
+    wasmtime_val_t         args[1] = { };
+    nxt_wasmtime_ctx_t     *rt_ctx = &nxt_wasmtime_ctx;
+    const nxt_wasm_func_t  *func = &ctx->fh[NXT_WASM_FH_FREE].func;
+
+    args[i].kind = WASMTIME_I32;
+    args[i++].of.i32 = ctx->baddr_off;
+
+    wasmtime_func_call(rt_ctx->ctx, func, args, i, NULL, 0, NULL);
+
+    wasmtime_module_delete(rt_ctx->module);
+    wasmtime_store_delete(rt_ctx->store);
+    wasm_engine_delete(rt_ctx->engine);
+}
+
+
+const nxt_wasm_operations_t  nxt_wasm_ops = {
+    .init               = nxt_wasmtime_init,
+    .destroy            = nxt_wasmtime_destroy,
+    .exec_request       = nxt_wasmtime_execute_request,
+    .exec_hook          = nxt_wasmtime_execute_hook,
+};
diff --git a/src/wasm/nxt_wasm.c b/src/wasm/nxt_wasm.c
new file mode 100644
index 00000000..d96668ad
--- /dev/null
+++ b/src/wasm/nxt_wasm.c
@@ -0,0 +1,258 @@
+/*
+ * Copyright (C) Andrew Clayton
+ * Copyright (C) F5, Inc.
+ */
+
+#include <nxt_main.h>
+#include <nxt_application.h>
+#include <nxt_unit.h>
+#include <nxt_unit_request.h>
+
+#include "nxt_wasm.h"
+
+
+#define NXT_WASM_VERSION        "0.1"
+
+#define NXT_WASM_DO_HOOK(hook)  nxt_wops->exec_hook(&nxt_wasm_ctx, hook);
+
+
+static uint32_t  compat[] = {
+    NXT_VERNUM, NXT_DEBUG,
+};
+
+static nxt_wasm_ctx_t               nxt_wasm_ctx;
+
+static const nxt_wasm_operations_t  *nxt_wops;
+
+
+void
+nxt_wasm_do_response_end(nxt_wasm_ctx_t *ctx)
+{
+    nxt_unit_request_done(ctx->req, NXT_UNIT_OK);
+
+    NXT_WASM_DO_HOOK(NXT_WASM_FH_RESPONSE_END);
+}
+
+
+void
+nxt_wasm_do_send_headers(nxt_wasm_ctx_t *ctx, uint32_t offset)
+{
+    size_t                      fields_len;
+    unsigned int                i;
+    nxt_wasm_response_fields_t  *rh;
+
+    rh = (nxt_wasm_response_fields_t *)(ctx->baddr + offset);
+
+    fields_len = 0;
+    for (i = 0; i < rh->nfields; i++) {
+        fields_len += rh->fields[i].name_len + rh->fields[i].value_len;
+    }
+
+    nxt_unit_response_init(ctx->req, 200, rh->nfields, fields_len);
+
+    for (i = 0; i < rh->nfields; i++) {
+        const char  *name;
+        const char  *val;
+
+        name = (const char *)rh + rh->fields[i].name_off;
+        val = (const char *)rh + rh->fields[i].value_off;
+
+        nxt_unit_response_add_field(ctx->req, name, rh->fields[i].name_len,
+                                    val, rh->fields[i].value_len);
+    }
+
+    nxt_unit_response_send(ctx->req);
+}
+
+
+void
+nxt_wasm_do_send_response(nxt_wasm_ctx_t *ctx, uint32_t offset)
+{
+    nxt_wasm_response_t      *resp;
+    nxt_unit_request_info_t  *req = ctx->req;
+
+    if (!nxt_unit_response_is_init(req)) {
+        nxt_unit_response_init(req, 200, 0, 0);
+    }
+
+    resp = (nxt_wasm_response_t *)(nxt_wasm_ctx.baddr + offset);
+
+    nxt_unit_response_write(req, (const char *)resp->data, resp->size);
+}
+
+
+static void
+nxt_wasm_request_handler(nxt_unit_request_info_t *req)
+{
+    size_t                 offset, read_bytes, content_sent, content_len;
+    ssize_t                bytes_read;
+    nxt_unit_field_t       *sf, *sf_end;
+    nxt_unit_request_t     *r;
+    nxt_wasm_request_t     *wr;
+    nxt_wasm_http_field_t  *df;
+
+    NXT_WASM_DO_HOOK(NXT_WASM_FH_REQUEST_INIT);
+
+    wr = (nxt_wasm_request_t *)nxt_wasm_ctx.baddr;
+
+#define SET_REQ_MEMBER(dmember, smember) \
+    do { \
+        const char *str = nxt_unit_sptr_get(&r->smember); \
+        wr->dmember##_off = offset; \
+        wr->dmember##_len = strlen(str); \
+        memcpy((uint8_t *)wr + offset, str, wr->dmember##_len + 1); \
+        offset += wr->dmember##_len + 1; \
+    } while (0)
+
+    r = req->request;
+    offset = sizeof(nxt_wasm_request_t)
+             + (r->fields_count * sizeof(nxt_wasm_http_field_t));
+
+    SET_REQ_MEMBER(path, path);
+    SET_REQ_MEMBER(method, method);
+    SET_REQ_MEMBER(version, version);
+    SET_REQ_MEMBER(query, query);
+    SET_REQ_MEMBER(remote, remote);
+    SET_REQ_MEMBER(local_addr, local_addr);
+    SET_REQ_MEMBER(local_port, local_port);
+    SET_REQ_MEMBER(server_name, server_name);
+#undef SET_REQ_MEMBER
+
+    df = wr->fields;
+    sf_end = r->fields + r->fields_count;
+    for (sf = r->fields; sf < sf_end; sf++) {
+        const char  *name = nxt_unit_sptr_get(&sf->name);
+        const char  *value = nxt_unit_sptr_get(&sf->value);
+
+        df->name_off = offset;
+        df->name_len = strlen(name);
+        memcpy((uint8_t *)wr + offset, name, df->name_len + 1);
+        offset += df->name_len + 1;
+
+        df->value_off = offset;
+        df->value_len = strlen(value);
+        memcpy((uint8_t *)wr + offset, value, df->value_len + 1);
+        offset += df->value_len + 1;
+
+        df++;
+    }
+
+    wr->tls = r->tls;
+    wr->nfields = r->fields_count;
+    wr->content_off = offset;
+    wr->content_len = content_len = r->content_length;
+
+    read_bytes = nxt_min(wr->content_len, NXT_WASM_MEM_SIZE - offset);
+
+    bytes_read = nxt_unit_request_read(req, (uint8_t *)wr + offset, read_bytes);
+    wr->content_sent = wr->total_content_sent = content_sent = bytes_read;
+
+    wr->request_size = offset + bytes_read;
+
+    nxt_wasm_ctx.req = req;
+    nxt_wops->exec_request(&nxt_wasm_ctx);
+
+    if (content_len == content_sent) {
+        goto request_done;
+    }
+
+    wr->nfields = 0;
+    wr->content_off = offset = sizeof(nxt_wasm_request_t);
+    do {
+        read_bytes = nxt_min(content_len - content_sent,
+                             NXT_WASM_MEM_SIZE - offset);
+        bytes_read = nxt_unit_request_read(req, (uint8_t *)wr + offset,
+                                           read_bytes);
+
+        content_sent += bytes_read;
+        wr->request_size = wr->content_sent = bytes_read;
+        wr->total_content_sent = content_sent;
+
+        nxt_wops->exec_request(&nxt_wasm_ctx);
+    } while (content_sent < content_len);
+
+request_done:
+    NXT_WASM_DO_HOOK(NXT_WASM_FH_REQUEST_END);
+}
+
+
+static nxt_int_t
+nxt_wasm_start(nxt_task_t *task, nxt_process_data_t *data)
+{
+    nxt_int_t              ret;
+    nxt_unit_ctx_t         *unit_ctx;
+    nxt_unit_init_t        wasm_init;
+    nxt_common_app_conf_t  *conf;
+
+    conf = data->app;
+
+    ret = nxt_unit_default_init(task, &wasm_init, conf);
+    if (nxt_slow_path(ret != NXT_OK)) {
+        nxt_alert(task, "nxt_unit_default_init() failed");
+        return ret;
+    }
+
+    wasm_init.callbacks.request_handler = nxt_wasm_request_handler;
+
+    unit_ctx = nxt_unit_init(&wasm_init);
+    if (nxt_slow_path(unit_ctx == NULL)) {
+        return NXT_ERROR;
+    }
+
+    NXT_WASM_DO_HOOK(NXT_WASM_FH_MODULE_INIT);
+    nxt_unit_run(unit_ctx);
+    nxt_unit_done(unit_ctx);
+    NXT_WASM_DO_HOOK(NXT_WASM_FH_MODULE_END);
+
+    nxt_wops->destroy(&nxt_wasm_ctx);
+
+    exit(EXIT_SUCCESS);
+}
+
+
+static nxt_int_t
+nxt_wasm_setup(nxt_task_t *task, nxt_process_t *process,
+               nxt_common_app_conf_t *conf)
+{
+    int                      err;
+    nxt_wasm_app_conf_t      *c;
+    nxt_wasm_func_handler_t  *fh;
+
+    c = &conf->u.wasm;
+
+    nxt_wops = &nxt_wasm_ops;
+
+    nxt_wasm_ctx.module_path = c->module;
+
+    fh = nxt_wasm_ctx.fh;
+
+    fh[NXT_WASM_FH_REQUEST].func_name = c->request_handler;
+    fh[NXT_WASM_FH_MALLOC].func_name = c->malloc_handler;
+    fh[NXT_WASM_FH_FREE].func_name = c->free_handler;
+
+    /* Optional function handlers (hooks) */
+    fh[NXT_WASM_FH_MODULE_INIT].func_name = c->module_init_handler;
+    fh[NXT_WASM_FH_MODULE_END].func_name = c->module_end_handler;
+    fh[NXT_WASM_FH_REQUEST_INIT].func_name = c->request_init_handler;
+    fh[NXT_WASM_FH_REQUEST_END].func_name = c->request_end_handler;
+    fh[NXT_WASM_FH_RESPONSE_END].func_name = c->response_end_handler;
+
+    err = nxt_wops->init(&nxt_wasm_ctx);
+    if (err) {
+        exit(EXIT_FAILURE);
+    }
+
+    return NXT_OK;
+}
+
+
+NXT_EXPORT nxt_app_module_t  nxt_app_module = {
+    .compat_length  = sizeof(compat),
+    .compat         = compat,
+    .type           = nxt_string("wasm"),
+    .version        = NXT_WASM_VERSION,
+    .mounts         = NULL,
+    .nmounts        = 0,
+    .setup          = nxt_wasm_setup,
+    .start          = nxt_wasm_start,
+};
diff --git a/src/wasm/nxt_wasm.h b/src/wasm/nxt_wasm.h
new file mode 100644
index 00000000..9e18f931
--- /dev/null
+++ b/src/wasm/nxt_wasm.h
@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) Andrew Clayton
+ * Copyright (C) F5, Inc.
+ */
+
+#ifndef _NXT_WASM_H_INCLUDED_
+#define _NXT_WASM_H_INCLUDED_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <nxt_unit.h>
+
+#include <wasm.h>
+#if defined(NXT_HAVE_WASM_WASMTIME)
+#include <wasmtime.h>
+#endif
+
+
+#define NXT_WASM_PAGE_SIZE          (64 * 1024)
+#define NXT_WASM_MEM_SIZE           (32UL * 1024 * 1024)
+
+#if defined(NXT_HAVE_WASM_WASMTIME)
+typedef wasmtime_func_t  nxt_wasm_func_t;
+#endif
+
+
+typedef struct nxt_wasm_http_field_s       nxt_wasm_http_field_t;
+typedef struct nxt_wasm_request_s          nxt_wasm_request_t;
+typedef struct nxt_wasm_response_s         nxt_wasm_response_t;
+typedef struct nxt_wasm_response_fields_s  nxt_wasm_response_fields_t;
+typedef enum nxt_wasm_fh_e                 nxt_wasm_fh_t;
+typedef struct nxt_wasm_func_handler_s     nxt_wasm_func_handler_t;
+typedef struct nxt_wasm_ctx_s              nxt_wasm_ctx_t;
+typedef struct nxt_wasm_operations_s       nxt_wasm_operations_t;
+
+struct nxt_wasm_http_field_s {
+    uint32_t  name_off;
+    uint32_t  name_len;
+    uint32_t  value_off;
+    uint32_t  value_len;
+};
+
+struct nxt_wasm_request_s {
+    uint32_t               method_off;
+    uint32_t               method_len;
+    uint32_t               version_off;
+    uint32_t               version_len;
+    uint32_t               path_off;
+    uint32_t               path_len;
+    uint32_t               query_off;
+    uint32_t               query_len;
+    uint32_t               remote_off;
+    uint32_t               remote_len;
+    uint32_t               local_addr_off;
+    uint32_t               local_addr_len;
+    uint32_t               local_port_off;
+    uint32_t               local_port_len;
+    uint32_t               server_name_off;
+    uint32_t               server_name_len;
+
+    uint32_t               content_off;
+    uint32_t               content_len;
+    uint32_t               content_sent;
+    uint32_t               total_content_sent;
+
+    uint32_t               request_size;
+
+    uint32_t               nfields;
+
+    uint32_t               tls;
+
+    nxt_wasm_http_field_t  fields[];
+};
+
+struct nxt_wasm_response_s {
+    uint32_t  size;
+
+    uint8_t   data[];
+};
+
+struct nxt_wasm_response_fields_s {
+    uint32_t               nfields;
+
+    nxt_wasm_http_field_t  fields[];
+};
+
+enum nxt_wasm_fh_e {
+    NXT_WASM_FH_REQUEST = 0,
+    NXT_WASM_FH_MALLOC,
+    NXT_WASM_FH_FREE,
+
+    /* Optional handlers */
+    NXT_WASM_FH_MODULE_INIT,
+    NXT_WASM_FH_MODULE_END,
+    NXT_WASM_FH_REQUEST_INIT,
+    NXT_WASM_FH_REQUEST_END,
+    NXT_WASM_FH_RESPONSE_END,
+
+    NXT_WASM_FH_NR
+};
+
+struct nxt_wasm_func_handler_s {
+    const char       *func_name;
+    nxt_wasm_func_t  func;
+};
+
+struct nxt_wasm_ctx_s {
+    const char               *module_path;
+
+    nxt_wasm_func_handler_t  fh[NXT_WASM_FH_NR];
+
+    nxt_unit_request_info_t  *req;
+
+    uint8_t                  *baddr;
+    size_t                   baddr_off;
+
+    size_t                   response_off;
+};
+
+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);
+    void  (*exec_hook)(const nxt_wasm_ctx_t *ctx, nxt_wasm_fh_t hook);
+};
+
+extern const nxt_wasm_operations_t  nxt_wasm_ops;
+
+
+/* Exported to the WASM module */
+extern void nxt_wasm_do_response_end(nxt_wasm_ctx_t *ctx);
+extern void nxt_wasm_do_send_response(nxt_wasm_ctx_t *ctx, uint32_t offset);
+extern void nxt_wasm_do_send_headers(nxt_wasm_ctx_t *ctx, uint32_t offset);
+
+#endif  /* _NXT_WASM_H_INCLUDED_ */