Added support for reading from stdin.

[leoleoasd]

Added support for reading from stdin.

As described in this issue.

I only added functionality to read, didn't add an interface in HTML to specify the input. You can change the default MemFS.stdinStr to test this patch.

[leoleoasd]

Why the memfs binary is smaller than original 🤔

[binji]

A few comments, otherwise looks pretty good!

Also, can you remove memfs changes here from the PR?

[binji]

I'm not sure if this is correct behavior; I think the rest of the reads should still go through, even if the previous one fails.

[leoleoasd]

when the lenToWrite is not equivalent with the len, it means that there is nothing more to read, we reached the EOF of the stdin file. I wrote break to speed things up, but when reading from regular files as you can see here, it will return some random data when reached EOF? I'm not sure about this.

[leoleoasd]

Checked the memfs.c again, I still can't figure out how the procedure of reading from a regular file works. These lines seems will write the whole file to the buf at once even the buf is smaller than the file? Have you tested this on use cases like reading large files?

[binji]

No you're right. These functions are meant to work like linux readv. The confusion here is the difference between readv and preadv I think. ReadIovec assumes that the offset is fixed (like preadv), so it won't work properly if there are multiple buffers on a readv call.

[leoleoasd]

So should we break here? In my opinion, we should, because we reached the end of the input string, continue reading seems useless.

[binji]

Yes, I think so, at least for now. Ultimately I think we may want a separate call, so preadv and readv can be handled separately when interacting with JS. But if most applications are treating stdin as stream-like, then updating the offset and stopping when there's no more input seems like the right choice.

[leoleoasd]

Also, can you remove memfs changes here from the PR?

Should I make a git revert commit or git reset --soft and commit again to avoid the modified memfs file left in the git history?

[binji]

I just realized you will need to update memfs anyway; host_read isn't defined there, so you'll need to call out from memfs to the host in the same way host_write is implemented.

[binji]

No you're right. These functions are meant to work like linux readv. The confusion here is the difference between readv and preadv I think. ReadIovec assumes that the offset is fixed (like preadv), so it won't work properly if there are multiple buffers on a readv call.

[leoleoasd]

I just realized you will need to update memfs anyway; host_read isn't defined there, so you'll need to call out from memfs to the host in the same way host_write is implemented.

Also created a PR for your fork of llvm contains the changes of memfs.c.

[leoleoasd]

Another question is that the js file (shared.js) requires the binary mapping of the iovs, such as the first 4 bytes is the buf. So, this can only be used with a specified wasi-sdk version, (10.0 wont work on my side), should we migrate it to use some helper functions from memfs.c such as getBufOfIovs to get the pointer of buf?

[binji]

So, this can only be used with a specified wasi-sdk version, (10.0 wont work on my side), should we migrate it to use some helper functions from memfs.c such as getBufOfIovs to get the pointer of buf?

I'd guess that there would be a lot more changes required for a different WASI version, so I'm not sure it's worth abstracting it for just this one case.

[leoleoasd]

Ready for final review and merge.

[binji]

thanks, lgtm!

[kkoomen]

How can I make this work in the current version without the use of any server? Because the example C code below inside the editor component doesn't prompt xterm for some stdin:

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("The number you entered is %d\n", num);
    return 0;
}