duk_console.c

/*
 *  Minimal 'console' binding.
 *
 *  https://github.com/DeveloperToolsWG/console-object/blob/master/api.md
 *  https://developers.google.com/web/tools/chrome-devtools/debug/console/console-reference
 *  https://developer.mozilla.org/en/docs/Web/API/console
 */

#include <stdio.h>
#include <stdarg.h>
#include "duktape.h"
#include "duk_console.h"

/* XXX: Add some form of log level filtering. */

/* XXX: Should all output be written via e.g. console.write(formattedMsg)?
 * This would make it easier for user code to redirect all console output
 * to a custom backend.
 */

/* XXX: Init console object using duk_def_prop() when that call is available. */

static duk_ret_t duk__console_log_helper(duk_context *ctx, const char *error_name) {
	duk_uint_t flags = (duk_uint_t) duk_get_current_magic(ctx);
	FILE *output = (flags & DUK_CONSOLE_STDOUT_ONLY) ? stdout : stderr;
	duk_idx_t n = duk_get_top(ctx);
	duk_idx_t i;

	duk_get_global_string(ctx, "console");
	duk_get_prop_string(ctx, -1, "format");

	for (i = 0; i < n; i++) {
		if (duk_check_type_mask(ctx, i, DUK_TYPE_MASK_OBJECT)) {
			/* Slow path formatting. */
			duk_dup(ctx, -1);  /* console.format */
			duk_dup(ctx, i);
			duk_call(ctx, 1);
			duk_replace(ctx, i);  /* arg[i] = console.format(arg[i]); */
		}
	}

	duk_pop_2(ctx);

	duk_push_string(ctx, " ");
	duk_insert(ctx, 0);
	duk_join(ctx, n);

	if (error_name) {
		duk_push_error_object(ctx, DUK_ERR_ERROR, "%s", duk_require_string(ctx, -1));
		duk_push_string(ctx, "name");
		duk_push_string(ctx, error_name);
		duk_def_prop(ctx, -3, DUK_DEFPROP_FORCE | DUK_DEFPROP_HAVE_VALUE);  /* to get e.g. 'Trace: 1 2 3' */
		duk_get_prop_string(ctx, -1, "stack");
	}

	fprintf(output, "%s\n", duk_to_string(ctx, -1));
	if (flags & DUK_CONSOLE_FLUSH) {
		fflush(output);
	}
	return 0;
}

static duk_ret_t duk__console_assert(duk_context *ctx) {
	if (duk_to_boolean(ctx, 0)) {
		return 0;
	}
	duk_remove(ctx, 0);

	return duk__console_log_helper(ctx, "AssertionError");
}

static duk_ret_t duk__console_log(duk_context *ctx) {
	return duk__console_log_helper(ctx, NULL);
}

static duk_ret_t duk__console_trace(duk_context *ctx) {
	return duk__console_log_helper(ctx, "Trace");
}

static duk_ret_t duk__console_info(duk_context *ctx) {
	return duk__console_log_helper(ctx, NULL);
}

static duk_ret_t duk__console_warn(duk_context *ctx) {
	return duk__console_log_helper(ctx, NULL);
}

static duk_ret_t duk__console_error(duk_context *ctx) {
	return duk__console_log_helper(ctx, "Error");
}

static duk_ret_t duk__console_dir(duk_context *ctx) {
	/* For now, just share the formatting of .log() */
	return duk__console_log_helper(ctx, 0);
}

static void duk__console_reg_vararg_func(duk_context *ctx, duk_c_function func, const char *name, duk_uint_t flags) {
	duk_push_c_function(ctx, func, DUK_VARARGS);
	duk_push_string(ctx, "name");
	duk_push_string(ctx, name);
	duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE | DUK_DEFPROP_FORCE);  /* Improve stacktraces by displaying function name */
	duk_set_magic(ctx, -1, (duk_int_t) flags);
	duk_put_prop_string(ctx, -2, name);
}

void duk_console_init(duk_context *ctx, duk_uint_t flags) {
	duk_uint_t flags_orig;

	/* If both DUK_CONSOLE_STDOUT_ONLY and DUK_CONSOLE_STDERR_ONLY where specified,
	 * just turn off DUK_CONSOLE_STDOUT_ONLY and keep DUK_CONSOLE_STDERR_ONLY.
	 */
	if ((flags & DUK_CONSOLE_STDOUT_ONLY) && (flags & DUK_CONSOLE_STDERR_ONLY)) {
	    flags &= ~DUK_CONSOLE_STDOUT_ONLY;
	}
	/* Remember the (possibly corrected) flags we received. */
	flags_orig = flags;

	duk_push_object(ctx);

	/* Custom function to format objects; user can replace.
	 * For now, try JX-formatting and if that fails, fall back
	 * to ToString(v).
	 */
	duk_eval_string(ctx,
		"(function (E) {"
		    "return function format(v){"
		        "try{"
		            "return E('jx',v);"
		        "}catch(e){"
		            "return String(v);"  /* String() allows symbols, ToString() internal algorithm doesn't. */
		        "}"
		    "};"
		"})(Duktape.enc)");
	duk_put_prop_string(ctx, -2, "format");

	flags = flags_orig;
	if (!(flags & DUK_CONSOLE_STDOUT_ONLY) && !(flags & DUK_CONSOLE_STDERR_ONLY)) {
	    /* No output indicators were specified; these levels go to stdout. */
	    flags |= DUK_CONSOLE_STDOUT_ONLY;
	}
	duk__console_reg_vararg_func(ctx, duk__console_assert, "assert", flags);
	duk__console_reg_vararg_func(ctx, duk__console_log, "log", flags);
	duk__console_reg_vararg_func(ctx, duk__console_log, "debug", flags);  /* alias to console.log */
	duk__console_reg_vararg_func(ctx, duk__console_trace, "trace", flags);
	duk__console_reg_vararg_func(ctx, duk__console_info, "info", flags);

	flags = flags_orig;
	if (!(flags & DUK_CONSOLE_STDOUT_ONLY) && !(flags & DUK_CONSOLE_STDERR_ONLY)) {
	    /* No output indicators were specified; these levels go to stderr. */
	    flags |= DUK_CONSOLE_STDERR_ONLY;
	}
	duk__console_reg_vararg_func(ctx, duk__console_warn, "warn", flags);
	duk__console_reg_vararg_func(ctx, duk__console_error, "error", flags);
	duk__console_reg_vararg_func(ctx, duk__console_error, "exception", flags);  /* alias to console.error */
	duk__console_reg_vararg_func(ctx, duk__console_dir, "dir", flags);

	duk_put_global_string(ctx, "console");

	/* Proxy wrapping: ensures any undefined console method calls are
	 * ignored silently.  This was required specifically by the
	 * DeveloperToolsWG proposal (and was implemented also by Firefox:
	 * https://bugzilla.mozilla.org/show_bug.cgi?id=629607).  This is
	 * apparently no longer the preferred way of implementing console.
	 * When Proxy is enabled, whitelist at least .toJSON() to avoid
	 * confusing JX serialization of the console object.
	 */

	if (flags & DUK_CONSOLE_PROXY_WRAPPER) {
		/* Tolerate failure to initialize Proxy wrapper in case
		 * Proxy support is disabled.
		 */
		(void) duk_peval_string_noresult(ctx,
			"(function(){"
			    "var D=function(){};"
			    "var W={toJSON:true};"  /* whitelisted */
			    "console=new Proxy(console,{"
			        "get:function(t,k){"
			            "var v=t[k];"
			            "return typeof v==='function'||W[k]?v:D;"
			        "}"
			    "});"
			"})();"
		);
	}
}