apps/buffer-test.cpp

@@ -4,7 +4,7 @@
 
 int main()
 {
-    fprintf(stderr, "Writing incomplete line to stdout (_IOLBF=%d)...\n", stdout->_mode);
+    fprintf(stderr, "Writing incomplete line to stdout (_IOLBF=%d)...\n", stdout->_buf.mode);
     fputs("hi!", stdout);
     sleep(3);
     putchar('\n');
@@ -14,7 +14,7 @@ int main()
     assert(f);
     assert(setvbuf(f, NULL, _IOFBF, 0) == 0);
 
-    fprintf(stderr, "Writing long text to file (_IOFBF=%d)...\n", f->_mode);
+    fprintf(stderr, "Writing long text to file (_IOFBF=%d)...\n", f->_buf.mode);
 
     fputs("Hello world!\nHow are you doing!\nThis is a test for many lines of buffering.\n", f);
 

libc/src/stdio.cpp

@@ -69,9 +69,27 @@ static int flush_write_buffer(FILE* stream)
     stream->_buf.index = 0;
     stream->_buf.size = 0;
 
+    stream->_buf.status &= ~FileStatusFlags::LastWrite;
+
     return result < 0 ? EOF : 0;
 }
 
+static int flush_read_buffer(FILE* stream)
+{
+    if (stream->_buf.mode == _IONBF) return 0;
+
+    // Reset the stream to its expected position.
+    ssize_t unread_bytes = stream->_buf.size - stream->_buf.index;
+    lseek(stream->_fd, -unread_bytes, SEEK_CUR);
+
+    stream->_buf.index = 0;
+    stream->_buf.size = 0;
+
+    stream->_buf.status &= ~FileStatusFlags::LastRead;
+
+    return 0;
+}
+
 static ssize_t write_into_buffer(FILE* stream, const u8* data, ssize_t size)
 {
     ssize_t total_written = 0;
@@ -81,6 +99,8 @@ static ssize_t write_into_buffer(FILE* stream, const u8* data, ssize_t size)
         ssize_t nwritten;
         if (stream->_buf.mode != _IONBF)
         {
+            if (stream->_buf.status & FileStatusFlags::LastRead) flush_read_buffer(stream);
+
             if ((stream->_buf.size + size) > stream->_buf.capacity)
             {
                 if (flush_write_buffer(stream) < 0) return -1;
@@ -90,6 +110,8 @@ static ssize_t write_into_buffer(FILE* stream, const u8* data, ssize_t size)
             nwritten = size > size_remaining ? size_remaining : size;
             memcpy(stream->_buf.buffer + stream->_buf.size, data, nwritten);
 
+            stream->_buf.status |= FileStatusFlags::LastWrite;
+
             stream->_buf.size += nwritten;
 
             if (stream->_buf.mode == _IOLBF && memchr(data, '\n', nwritten))
@@ -108,6 +130,51 @@ static ssize_t write_into_buffer(FILE* stream, const u8* data, ssize_t size)
     return total_written;
 }
 
+static ssize_t read_data_into_buffer(FILE* stream)
+{
+    stream->_buf.index = 0;
+    ssize_t nread = read(stream->_fd, stream->_buf.buffer, stream->_buf.capacity);
+    if (nread >= 0) stream->_buf.size = nread;
+    stream->_buf.status |= FileStatusFlags::LastRead;
+    return nread;
+}
+
+static ssize_t read_from_buffer(FILE* stream, u8* data, ssize_t size)
+{
+    ssize_t total_read = 0;
+
+    while (size > 0)
+    {
+        ssize_t nread;
+        if (stream->_buf.mode != _IONBF)
+        {
+            if (stream->_buf.status & FileStatusFlags::LastWrite) flush_write_buffer(stream);
+
+            if (stream->_buf.size == stream->_buf.index)
+            {
+                ssize_t rc;
+                if ((rc = read_data_into_buffer(stream)) < 0) return -1;
+                if (rc == 0) return total_read;
+            }
+
+            ssize_t size_remaining = stream->_buf.size - stream->_buf.index;
+            nread = size > size_remaining ? size_remaining : size;
+            memcpy(data, stream->_buf.buffer + stream->_buf.index, nread);
+
+            stream->_buf.index += nread;
+        }
+        else
+            nread = read(stream->_fd, data, size > BUFSIZ ? BUFSIZ : size);
+        if (nread < 0) return nread;
+        if (nread == 0) return total_read;
+        size -= nread;
+        data += nread;
+        total_read += nread;
+    }
+
+    return total_read;
+}
+
 extern "C"
 {
     void _init_stdio()
@@ -117,7 +184,12 @@ extern "C"
 
     int fflush(FILE* stream)
     {
-        if (stream && stream->_buf.mode != _IONBF) flush_write_buffer(stream);
+        if (stream && stream->_buf.mode != _IONBF)
+        {
+            if (stream->_buf.status & FileStatusFlags::LastWrite) flush_write_buffer(stream);
+            else if (stream->_buf.status & FileStatusFlags::LastRead)
+                flush_read_buffer(stream);
+        }
         else if (!stream)
         {
             for (int i = 0; i < FOPEN_MAX; i++)
@@ -246,7 +318,7 @@ extern "C"
     {
         if (size * nmemb == 0) return 0;
 
-        ssize_t nread = read(stream->_fd, buf, size * nmemb);
+        ssize_t nread = read_from_buffer(stream, (u8*)buf, size * nmemb);
 
         if (nread < 0)
         {
@@ -351,7 +423,7 @@ extern "C"
     int fgetc(FILE* stream)
     {
         u8 value;
-        ssize_t rc = read(stream->_fd, &value, 1);
+        ssize_t rc = read_from_buffer(stream, &value, 1);
         if (rc <= 0) return EOF;
         return value;
     }