read() on a pipe returns -1 instead of 0 after the write end is closed

[Ryan2026R]

Version of emscripten/emsdk:

5.0.6

After closing the write end of a pipe(), read() on the read end should return 0 to signal EOF. Under Emscripten it returns -1 with errno=EAGAIN, potentially breaking pipe-based producer/consumer loop that waits for EOF.

Failing command line in full:

$ emcc -O0 -Wall pipe_eof.c -o a.out.js
$ node a.out.js
read(pipe_read after close_write): ret=-1 errno=6

The same program on native Linux prints read(pipe_read after close_write): ret=0 errno=0.

Example code snippet:

#include <unistd.h>
#include <stdio.h>
#include <errno.h>

int main(void) {
    int pipefd[2];
    char buf[16];
    pipe(pipefd);
    close(pipefd[1]);                          // close write end

    errno = 0;
    ssize_t r = read(pipefd[0], buf, sizeof(buf));
    printf("read(pipe_read after close_write): ret=%zd errno=%d\n", r, errno);
    close(pipefd[0]);
    return (r == 0) ? 0 : 1;
}