lib: implement render(), an include variant capturing output in a string

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

2 files changed, 56 insertions, 2 deletions

diff --git a/README.md b/README.md
index 549459e..83bfc07 100644
--- a/README.md
+++ b/README.md
@@ -998,7 +998,7 @@ json('{"a":true, "b":123}')   // { "a": true, "b": 123 }
 json('[1,2,')                 // Throws exception
 ```
 
-#### 6.50. `include(path, scope)`
+#### 6.50. `include(path[, scope])`
 
 Evaluate and include the file at the given path and optionally override the
 execution scope with the given scope object.
@@ -1113,3 +1113,9 @@ an invalid value was passed, otherwise `true`.
 
 Raise an exception with the given `message` parameter if the value in `cond`
 is not truish. When `message` is omitted, the default value is `Assertion failed`.
+
+#### 6.57. `render(path[, scope])`
+
+Like `include()` but capture output of included file as string and return it.
+
+See `include()` for details on scoping.
diff --git a/lib.c b/lib.c
index 9d8241b..453f976 100644
--- a/lib.c
+++ b/lib.c
@@ -2199,6 +2199,53 @@ uc_include(uc_vm *vm, size_t nargs)
 }
 
 static uc_value_t *
+uc_render(uc_vm *vm, size_t nargs)
+{
+	uc_string_t *ustr = NULL;
+	FILE *mem, *prev;
+	size_t len = 0;
+
+	mem = open_memstream((char **)&ustr, &len);
+
+	if (!mem)
+		goto out;
+
+	/* reserve space for uc_string_t header... */
+	if (fseek(mem, sizeof(*ustr), SEEK_SET))
+		goto out;
+
+	/* divert VM output to memory fd */
+	prev = vm->output;
+	vm->output = mem;
+
+	/* execute include */
+	(void) uc_include(vm, nargs);
+
+	/* restore previous VM output */
+	vm->output = prev;
+	fclose(mem);
+
+	/* update uc_string_t length */
+	ustr->header.type = UC_STRING;
+	ustr->header.refcount = 1;
+	ustr->length = len - sizeof(*ustr);
+
+	return &ustr->header;
+
+out:
+	uc_vm_raise_exception(vm, EXCEPTION_RUNTIME,
+	                      "Unable to initialize output memory: %s",
+	                      strerror(errno));
+
+	if (mem)
+		fclose(mem);
+
+	free(ustr);
+
+	return NULL;
+}
+
+static uc_value_t *
 uc_warn(uc_vm *vm, size_t nargs)
 {
 	return uc_print_common(vm, nargs, stderr);
@@ -2473,7 +2520,8 @@ static const uc_cfunction_list functions[] = {
 	{ "trace",		uc_trace },
 	{ "proto",		uc_proto },
 	{ "sleep",		uc_sleep },
-	{ "assert",		uc_assert }
+	{ "assert",		uc_assert },
+	{ "render",		uc_render }
 };