Default

By default stdin is ignored by lws, although user code can adopt it.

Stdin bulk RX handling

If you:

1) define info.system_ops at context creation time 2) set the member .stdio_rx to a callback that gets stdin RX fragments 3) call lws_system_adopt_stdin(context, 0); after creating the context

then you will receive any stdin content in the callback. This is useful for cases where you are receiving bulk data into the app, eg, a PNG file for a PNG decoder.

When whatever is driving stdin closes it, you will receive a callback with a NULL buffer and length 0.

Stdin commandline handling

As an alternative, you can have lws treat stdin as additional, invisible commandline content. This is very useful for situations where you are passing secrets to the app, which must not leak eg by ps seeing what is on the normal commandline.

To enable this, call lws_system_adopt_stdin(context, LWS_SAS_FLAG__APPEND_COMMANDLINE) There is no need to implement any lws_system callbacks in this case, lws will deal with the stdin data.

Commandline access apis

There are four apis available for commandline querying:

LWS_VISIBLE LWS_EXTERN const char *
lws_cmdline_option(int argc, const char **argv, const char *val);
LWS_VISIBLE LWS_EXTERN const char *
lws_cmdline_options(int argc, const char * const *argv, const char *val, const char *last);
LWS_VISIBLE LWS_EXTERN const char *
lws_cmdline_options_cx(const struct lws_context *cx, const char *val, const char *last);
LWS_VISIBLE LWS_EXTERN const char *
lws_cmdline_option_cx(const struct lws_context *cx, const char *val);

api	context	argc/argv	stdin	iterative
`lws_cmdline_option()`	n	y	n	n
`lws_cmdline_options()`	n	y	n	y
`lws_cmdline_options_cx()`	y	y	y	y
`lws_cmdline_option_cx()`	y	y	y	n

Selecting non-switch args

All four apis can be called with NULL val, in order to return a non-switch argument. You can use the lws_cmdline_options[_cx]() variant to interate through the non-switch arguments for NULL val case too.

For example, the commandline --switch1=abc def would return a pointer to def if the api lws_cmdline_options() was called with NULL val and last.

Although switches with args like -d 1039 are supported, users will have to use the form -d=1039 to allow non-switch args to be correctly distinguished.

Timing of stdin commandline access

The normal argc / argv commandline is available from main() starting. But the part of the commandline contributed via stdin is only available after the event loop starts, which happens after the lws_context exists.

To help synchronize this, lws_system follows what state the system is in, and waits to process stdin traffic before reaching the OPERATIONAL state where user code normally runs. See

minimal-examples-lowlevel/http-client/minimal-http-client-post/minimal-http-client-post.c

for examples of how to deal with this.