Add a "fork" of musl as //fusl.

fusl/src/stdio/fmemopen.c

Index: fusl/src/stdio/fmemopen.c
diff --git a/fusl/src/stdio/fmemopen.c b/fusl/src/stdio/fmemopen.c
new file mode 100644
index 0000000000000000000000000000000000000000..7c193a579ba4b5e5d780a63c2cce0e526276f8d3
--- /dev/null
+++ b/fusl/src/stdio/fmemopen.c
@@ -0,0 +1,114 @@
+#include "stdio_impl.h"
+#include <errno.h>
+#include <string.h>
+#include <inttypes.h>
+
+struct cookie {
+	size_t pos, len, size;
+	unsigned char *buf;
+	int mode;
+};
+
+static off_t mseek(FILE *f, off_t off, int whence)
+{
+	ssize_t base;
+	struct cookie *c = f->cookie;
+	if (whence>2U) {
+fail:
+		errno = EINVAL;
+		return -1;
+	}
+	base = (size_t [3]){0, c->pos, c->len}[whence];
+	if (off < -base || off > (ssize_t)c->size-base) goto fail;
+	return c->pos = base+off;
+}
+
+static size_t mread(FILE *f, unsigned char *buf, size_t len)
+{
+	struct cookie *c = f->cookie;
+	size_t rem = c->len - c->pos;
+	if (c->pos > c->len) rem = 0;
+	if (len > rem) {
+		len = rem;
+		f->flags |= F_EOF;
+	}
+	memcpy(buf, c->buf+c->pos, len);
+	c->pos += len;
+	rem -= len;
+	if (rem > f->buf_size) rem = f->buf_size;
+	f->rpos = f->buf;
+	f->rend = f->buf + rem;
+	memcpy(f->rpos, c->buf+c->pos, rem);
+	c->pos += rem;
+	return len;
+}
+
+static size_t mwrite(FILE *f, const unsigned char *buf, size_t len)
+{
+	struct cookie *c = f->cookie;
+	size_t rem;
+	size_t len2 = f->wpos - f->wbase;
+	if (len2) {
+		f->wpos = f->wbase;
+		if (mwrite(f, f->wpos, len2) < len2) return 0;
+	}
+	if (c->mode == 'a') c->pos = c->len;
+	rem = c->size - c->pos;
+	if (len > rem) len = rem;
+	memcpy(c->buf+c->pos, buf, len);
+	c->pos += len;
+	if (c->pos > c->len) {
+		c->len = c->pos;
+		if (c->len < c->size) c->buf[c->len] = 0;
+		else if ((f->flags&F_NORD) && c->size) c->buf[c->size-1] = 0;
+	}
+	return len;
+}
+
+static int mclose(FILE *m)
+{
+	return 0;
+}
+
+FILE *fmemopen(void *restrict buf, size_t size, const char *restrict mode)
+{
+	FILE *f;
+	struct cookie *c;
+	int plus = !!strchr(mode, '+');
+	
+	if (!size || !strchr("rwa", *mode)) {
+		errno = EINVAL;
+		return 0;
+	}
+
+	if (!buf && size > SIZE_MAX-sizeof(FILE)-BUFSIZ-UNGET) {
+		errno = ENOMEM;
+		return 0;
+	}
+
+	f = calloc(sizeof *f + sizeof *c + UNGET + BUFSIZ + (buf?0:size), 1);
+	if (!f) return 0;
+	f->cookie = c = (void *)(f+1);
+	f->fd = -1;
+	f->lbf = EOF;
+	f->buf = (unsigned char *)(c+1) + UNGET;
+	f->buf_size = BUFSIZ;
+	if (!buf) buf = f->buf + BUFSIZ;
+
+	c->buf = buf;
+	c->size = size;
+	c->mode = *mode;
+	
+	if (!plus) f->flags = (*mode == 'r') ? F_NOWR : F_NORD;
+	if (*mode == 'r') c->len = size;
+	else if (*mode == 'a') c->len = c->pos = strnlen(buf, size);
+
+	f->read = mread;
+	f->write = mwrite;
+	f->seek = mseek;
+	f->close = mclose;
+
+	if (!libc.threaded) f->lock = -1;
+
+	return __ofl_add(f);
+}