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authorWilliam Pitcock <nenolod@dereferenced.org>2017-12-05 16:04:43 -0500
committerRich Felker <dalias@aerifal.cx>2017-12-06 13:11:48 -0500
commit061843340fbf2493bb615e20e66f60c5d1ef0455 (patch)
tree0613a9ef9b70c5bd3653617b56cf7ca1a615325a /src
parent4000b0107ddd7fe733fa31d4f078c6fcd35851d6 (diff)
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implement the fopencookie extension to stdio
notes added by maintainer: this function is a GNU extension. it was chosen over the similar BSD function funopen because the latter depends on fpos_t being an arithmetic type as part of its public API, conflicting with our definition of fpos_t and with the intent that it be an opaque type. it was accepted for inclusion because, despite not being widely used, it is usually very difficult to extricate software using it from the dependency on it. calling pattern for the read and write callbacks is not likely to match glibc or other implementations, but should work with any reasonable callbacks. in particular the read function is never called without at least one byte being needed to satisfy its caller, so that spurious blocking is not introduced. contracts for what callbacks called from inside libc/stdio can do are always complicated, and at some point still need to be specified explicitly. at the very least, the callbacks must return or block indefinitely (they cannot perform nonlocal exits) and they should not make calls to stdio using their own FILE as an argument.
Diffstat (limited to 'src')
-rw-r--r--src/stdio/fopencookie.c138
1 files changed, 138 insertions, 0 deletions
diff --git a/src/stdio/fopencookie.c b/src/stdio/fopencookie.c
new file mode 100644
index 00000000..2f46dd53
--- /dev/null
+++ b/src/stdio/fopencookie.c
@@ -0,0 +1,138 @@
+#define _GNU_SOURCE
+#include "stdio_impl.h"
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+
+struct fcookie {
+ void *cookie;
+ cookie_io_functions_t iofuncs;
+};
+
+struct cookie_FILE {
+ FILE f;
+ struct fcookie fc;
+ unsigned char buf[UNGET+BUFSIZ];
+};
+
+static size_t cookieread(FILE *f, unsigned char *buf, size_t len)
+{
+ struct fcookie *fc = f->cookie;
+ ssize_t ret = -1;
+ size_t remain = len, readlen = 0;
+ size_t len2 = len - !!f->buf_size;
+
+ if (!fc->iofuncs.read) goto bail;
+
+ if (len2) {
+ ret = fc->iofuncs.read(fc->cookie, (char *) buf, len2);
+ if (ret <= 0) goto bail;
+
+ readlen += ret;
+ remain -= ret;
+ }
+
+ if (!f->buf_size || remain > !!f->buf_size) return readlen;
+
+ f->rpos = f->buf;
+ ret = fc->iofuncs.read(fc->cookie, (char *) f->rpos, f->buf_size);
+ if (ret <= 0) goto bail;
+ f->rend = f->rpos + ret;
+
+ buf[readlen++] = *f->rpos++;
+
+ return readlen;
+
+bail:
+ f->flags |= ret == 0 ? F_EOF : F_ERR;
+ f->rpos = f->rend = f->buf;
+ return readlen;
+}
+
+static size_t cookiewrite(FILE *f, const unsigned char *buf, size_t len)
+{
+ struct fcookie *fc = f->cookie;
+ ssize_t ret;
+ size_t len2 = f->wpos - f->wbase;
+ if (!fc->iofuncs.write) return len;
+ if (len2) {
+ f->wpos = f->wbase;
+ if (cookiewrite(f, f->wpos, len2) < len2) return 0;
+ }
+ ret = fc->iofuncs.write(fc->cookie, (const char *) buf, len);
+ if (ret < 0) {
+ f->wpos = f->wbase = f->wend = 0;
+ f->flags |= F_ERR;
+ return 0;
+ }
+ return ret;
+}
+
+static off_t cookieseek(FILE *f, off_t off, int whence)
+{
+ struct fcookie *fc = f->cookie;
+ int res;
+ if (whence > 2U) {
+ errno = EINVAL;
+ return -1;
+ }
+ if (!fc->iofuncs.seek) {
+ errno = ENOTSUP;
+ return -1;
+ }
+ res = fc->iofuncs.seek(fc->cookie, &off, whence);
+ if (res < 0)
+ return res;
+ return off;
+}
+
+static int cookieclose(FILE *f)
+{
+ struct fcookie *fc = f->cookie;
+ if (fc->iofuncs.close) return fc->iofuncs.close(fc->cookie);
+ return 0;
+}
+
+FILE *fopencookie(void *cookie, const char *mode, cookie_io_functions_t iofuncs)
+{
+ struct cookie_FILE *f;
+
+ /* Check for valid initial mode character */
+ if (!strchr("rwa", *mode)) {
+ errno = EINVAL;
+ return 0;
+ }
+
+ /* Allocate FILE+fcookie+buffer or fail */
+ if (!(f=malloc(sizeof *f))) return 0;
+
+ /* Zero-fill only the struct, not the buffer */
+ memset(&f->f, 0, sizeof f->f);
+
+ /* Impose mode restrictions */
+ if (!strchr(mode, '+')) f->f.flags = (*mode == 'r') ? F_NOWR : F_NORD;
+
+ /* Set up our fcookie */
+ f->fc.cookie = cookie;
+ f->fc.iofuncs.read = iofuncs.read;
+ f->fc.iofuncs.write = iofuncs.write;
+ f->fc.iofuncs.seek = iofuncs.seek;
+ f->fc.iofuncs.close = iofuncs.close;
+
+ f->f.fd = -1;
+ f->f.cookie = &f->fc;
+ f->f.buf = f->buf + UNGET;
+ f->f.buf_size = BUFSIZ;
+ f->f.lbf = EOF;
+
+ /* Initialize op ptrs. No problem if some are unneeded. */
+ f->f.read = cookieread;
+ f->f.write = cookiewrite;
+ f->f.seek = cookieseek;
+ f->f.close = cookieclose;
+
+ /* Add new FILE to open file list */
+ return __ofl_add(&f->f);
+}