Fix some warnings for size_t, DWORD and int conversions.

These cases are all in the sp_[non]blocking_{read,write} functions.

On MSVC, these conversions would generate warnings such as:
warning C4267: '=': conversion from 'size_t' to 'DWORD', possible loss of data

The warnings are genuine. There are some places where overflow is technically
possible, due to our use of size_t for sizes in function parameters (unsigned
64-bit on Windows x64), but an enum for return values (typically signed int
and 32-bit, but not guaranteed to be so by the standards), plus the Win32 API
usage of DWORD (unsigned 32-bit) for sizes in ReadFile/WriteFile.

However, overflow in practice would require reading/writing more than 2GB
over a serial port in a single call and is therefore unlikely to be a
real-world concern. I have therefore not tried to catch those cases - but the
places it is possible do now have explicit casts to the smaller types so that
they are more obvious.

We could document and test for a maximum read/write size of INT_MAX, but that
would still depend on the storage of 'enum sp_return' being at least a signed
int, which as I understand it the C standard does not require.

To be absolutely correct we would need a different API where sp_return
was only used for result codes, and the read/write functions took a
pointer to size_t for result sizes.

diff --git a/serialport.c b/serialport.c
index e86603bfa000fe750c924c8ec056ae53258963d4..b2e4a7984fdcf2738209bc74cacd60f66c693a9b 100644 (file)
--- a/serialport.c
+++ b/serialport.c
@@ -782,7 +782,8 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
                RETURN_INT(0);
 
 #ifdef _WIN32
-       DWORD remaining_ms, write_size, bytes_written, total_bytes_written = 0;
+       DWORD remaining_ms, write_size, bytes_written;
+       size_t remaining_bytes, total_bytes_written = 0;
        const uint8_t *write_ptr = (uint8_t *) buf;
        bool result;
        struct timeout timeout;
@@ -805,9 +806,11 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
                }
 
                /* Reduce write size if it exceeds the WriteFile limit. */
-               write_size = count - total_bytes_written;
-               if (write_size > WRITEFILE_MAX_SIZE)
+               remaining_bytes = count - total_bytes_written;
+               if (remaining_bytes > WRITEFILE_MAX_SIZE)
                        write_size = WRITEFILE_MAX_SIZE;
+               else
+                       write_size = (DWORD) remaining_bytes;
 
                /* Start write. */
 
@@ -837,7 +840,7 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
                total_bytes_written += bytes_written;
        }
 
-       RETURN_INT(total_bytes_written);
+       RETURN_INT((int) total_bytes_written);
 #else
        size_t bytes_written = 0;
        unsigned char *ptr = (unsigned char *) buf;
@@ -911,7 +914,7 @@ SP_API enum sp_return sp_nonblocking_write(struct sp_port *port,
                RETURN_INT(0);
 
 #ifdef _WIN32
-       DWORD buf_bytes;
+       size_t buf_bytes;
 
        /* Check whether previous write is complete. */
        if (port->writing) {
@@ -941,7 +944,7 @@ SP_API enum sp_return sp_nonblocking_write(struct sp_port *port,
        memcpy(port->write_buf, buf, buf_bytes);
 
        /* Start asynchronous write. */
-       if (WriteFile(port->hdl, port->write_buf, buf_bytes, NULL, &port->write_ovl) == 0) {
+       if (WriteFile(port->hdl, port->write_buf, (DWORD) buf_bytes, NULL, &port->write_ovl) == 0) {
                if (GetLastError() == ERROR_IO_PENDING) {
                        if ((port->writing = !HasOverlappedIoCompleted(&port->write_ovl)))
                                DEBUG("Asynchronous write completed immediately");
@@ -955,7 +958,7 @@ SP_API enum sp_return sp_nonblocking_write(struct sp_port *port,
 
        DEBUG("All bytes written immediately");
 
-       RETURN_INT(buf_bytes);
+       RETURN_INT((int) buf_bytes);
 #else
        /* Returns the number of bytes written, or -1 upon failure. */
        ssize_t written = write(port->fd, buf, count);
@@ -1013,7 +1016,7 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
                RETURN_INT(0);
 
 #ifdef _WIN32
-       DWORD bytes_read = 0;
+       DWORD bytes_read;
 
        /* Set timeout. */
        if (port->timeouts.ReadIntervalTimeout != 0 ||
@@ -1027,9 +1030,9 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
        }
 
        /* Start read. */
-       if (ReadFile(port->hdl, buf, count, NULL, &port->read_ovl)) {
+       if (ReadFile(port->hdl, buf, (DWORD) count, NULL, &port->read_ovl)) {
                DEBUG("Read completed immediately");
-               bytes_read = count;
+               bytes_read = (DWORD) count;
        } else if (GetLastError() == ERROR_IO_PENDING) {
                DEBUG("Waiting for read to complete");
                if (GetOverlappedResult(port->hdl, &port->read_ovl, &bytes_read, TRUE) == 0)
@@ -1041,7 +1044,7 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
 
        TRY(restart_wait_if_needed(port, bytes_read));
 
-       RETURN_INT(bytes_read);
+       RETURN_INT((int) bytes_read);
 
 #else
        size_t bytes_read = 0;
@@ -1144,7 +1147,7 @@ SP_API enum sp_return sp_blocking_read_next(struct sp_port *port, void *buf,
        /* Loop until we have at least one byte, or timeout is reached. */
        while (bytes_read == 0) {
                /* Start read. */
-               if (ReadFile(port->hdl, buf, count, &bytes_read, &port->read_ovl)) {
+               if (ReadFile(port->hdl, buf, (DWORD) count, &bytes_read, &port->read_ovl)) {
                        DEBUG("Read completed immediately");
                } else if (GetLastError() == ERROR_IO_PENDING) {
                        DEBUG("Waiting for read to complete");
@@ -1250,7 +1253,7 @@ SP_API enum sp_return sp_nonblocking_read(struct sp_port *port, void *buf,
        }
 
        /* Do read. */
-       if (ReadFile(port->hdl, buf, count, NULL, &port->read_ovl) == 0)
+       if (ReadFile(port->hdl, buf, (DWORD) count, NULL, &port->read_ovl) == 0)
                if (GetLastError() != ERROR_IO_PENDING)
                        RETURN_FAIL("ReadFile() failed");