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stdio/file: fix numerous issues in the fread/fwrite functions #376

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stdio/file: fix numerous issues in the fread/fwrite functions #376

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36da264
unistd/file: add a non-blocking safe read function
ziemleszcz Aug 21, 2024
7058c9c
stdio/file: fix numerous issues in the fread/fwrite functions
ziemleszcz Aug 21, 2024
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88 changes: 60 additions & 28 deletions stdio/file.c
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Original file line number Diff line number Diff line change
Expand Up @@ -290,16 +290,25 @@ FILE *freopen(const char *pathname, const char *mode, FILE *stream)
}


static int full_read(int fd, void *ptr, size_t size)
static int full_read(int fd, void *ptr, size_t size, int *eof)
{
int err;
int total = 0;

*eof = 0;

while (size) {
if ((err = __safe_read(fd, ptr, size)) < 0) {
return -1;
err = __safe_read_nb(fd, ptr, size);
if (err < 0) {
if (errno == EAGAIN) {
return total;
}
else {
return -1;
}
}
else if (!err) {
*eof = 1;
return total;
}
ptr += err;
Expand Down Expand Up @@ -328,21 +337,34 @@ static int full_write(int fd, const void *ptr, size_t size)

size_t fread_unlocked(void *ptr, size_t size, size_t nmemb, FILE *stream)
{
int err;
int err, eof;
size_t readsz = nmemb * size;
size_t bytes;

if (!readsz) {
if (readsz == 0) {
return 0;
}

if (stream->buffer == NULL) {
/* unbuffered read */
if ((err = full_read(stream->fd, ptr, readsz)) < 0) {
err = full_read(stream->fd, ptr, readsz, &eof);
if (err >= 0) {
if (err < readsz) {
if (eof == 1) {
stream->flags |= F_EOF;
}
else {
/* received EAGAIN */
stream->flags |= F_ERROR;
}
}

return err / size;
}
else {
stream->flags |= F_ERROR;
return 0;
}

return err / size;
}

/* flush write buffer if writing */
Expand All @@ -363,43 +385,49 @@ size_t fread_unlocked(void *ptr, size_t size, size_t nmemb, FILE *stream)

/* refill read buffer */
if (stream->bufpos == stream->bufeof) {
if ((err = __safe_read(stream->fd, stream->buffer, stream->bufsz)) == -1) {
err = __safe_read_nb(stream->fd, stream->buffer, stream->bufsz);
if (err < 0) {
stream->flags |= F_ERROR;
return 0;
}

stream->bufpos = 0;
stream->bufeof = err;

if (!err) {
else if (err == 0) {
stream->flags |= F_EOF;
return 0;
}
else {
stream->bufpos = 0;
stream->bufeof = err;
}
}

if ((bytes = stream->bufeof - stream->bufpos)) {
bytes = min(bytes, readsz);
memcpy(ptr, stream->buffer + stream->bufpos, bytes);
bytes = min(stream->bufeof - stream->bufpos, readsz);
memcpy(ptr, stream->buffer + stream->bufpos, bytes);

ptr += bytes;
stream->bufpos += bytes;
readsz -= bytes;
ptr += bytes;
stream->bufpos += bytes;
readsz -= bytes;

if (!readsz) {
return nmemb;
}
if (readsz == 0) {
return nmemb;
}

/* read remainder directly into ptr */
if ((err = full_read(stream->fd, ptr, readsz)) != -1) {
/* read the remaining bytes directly into the user buffer */
err = full_read(stream->fd, ptr, readsz, &eof);
if (err >= 0) {
bytes += err;

if (err < readsz) {
stream->flags |= F_EOF;
if (eof == 1) {
stream->flags |= F_EOF;
}
else {
/* received EAGAIN */
stream->flags |= F_ERROR;
}
}
}
else {
stream->flags |= F_ERROR;
return 0;
}

return bytes / size;
Expand Down Expand Up @@ -437,7 +465,11 @@ size_t fwrite_unlocked(const void *ptr, size_t size, size_t nmemb, FILE *stream)

/* discard reading buffer */
if (!(stream->flags & F_WRITING)) {
fflush_unlocked(stream);
if (stream->bufpos != stream->bufeof) {
if (fflush_unlocked(stream) < 0) {
return 0;
}
}
stream->flags |= F_WRITING;
stream->bufpos = 0;
}
Expand Down
4 changes: 4 additions & 0 deletions unistd/file-internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,10 @@ ssize_t __safe_write(int fd, const void *buff, size_t size);
ssize_t __safe_read(int fd, void *buf, size_t size);


/* non-blocking variant - returns on EAGAIN */
ssize_t __safe_read_nb(int fd, void *buf, size_t size);


int __safe_open(const char *path, int oflag, mode_t mode);


Expand Down
18 changes: 13 additions & 5 deletions unistd/file.c
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Original file line number Diff line number Diff line change
Expand Up @@ -101,18 +101,26 @@ ssize_t __safe_read(int fd, void *buf, size_t size)
continue;
}
else {
break;
return -1;
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Also fixed error handling in blocking safe read to always return -1 on error.

How is this different? The else branch is taken when rlen < 0, so if (rlen < 0) below is still executed.

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You're right - disregard this comment.

}
}

if (rlen < 0) {
return -1;
}

return size - todo;
}


ssize_t __safe_read_nb(int fd, void *buf, size_t size)
{
ssize_t rlen;

do {
rlen = read(fd, buf, size);
} while (rlen < 0 && errno == EINTR);

return rlen;
}


int __safe_open(const char *path, int oflag, mode_t mode)
{
int err;
Expand Down
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