ports: Fix sys.stdout.buffer.write() return value.

MicroPython code may rely on the return value of sys.stdout.buffer.write()
to reflect the number of bytes actually written. While in most scenarios a
write() operation is successful, there are cases where it fails, leading to
data loss. This problem arises because, currently, write() merely returns
the number of bytes it was supposed to write, without indication of
failure.

One scenario where write() might fail, is where USB is used and the
receiving end doesn't read quickly enough to empty the receive buffer. In
that case, write() on the MicroPython side can timeout, resulting in the
loss of data without any indication, a behavior observed notably in
communication between a Pi Pico as a client and a Linux host using the ACM
driver.

A complex issue arises with mp_hal_stdout_tx_strn() when it involves
multiple outputs, such as USB, dupterm and hardware UART. The challenge is
in handling cases where writing to one output is successful, but another
fails, either fully or partially. This patch implements the following
solution:

mp_hal_stdout_tx_strn() attempts to write len bytes to all of the possible
destinations for that data, and returns the minimum successful write
length.

The implementation of this is complicated by several factors:
- multiple outputs may be enabled or disabled at compiled time
- multiple outputs may be enabled or disabled at runtime
- mp_os_dupterm_tx_strn() is one such output, optionally containing
  multiple additional outputs
- each of these outputs may or may not be able to report success
- each of these outputs may or may not be able to report partial writes

As a result, there's no single strategy that fits all ports, necessitating
unique logic for each instance of mp_hal_stdout_tx_strn().

Note that addressing sys.stdout.write() is more complex due to its data
modification process ("cooked" output), and it remains unchanged in this
patch. Developers who are concerned about accurate return values from
write operations should use sys.stdout.buffer.write().

This patch might disrupt some existing code, but it's also expected to
resolve issues, considering that the peculiar return value behavior of
sys.stdout.buffer.write() is not well-documented and likely not widely
known. Therefore, it's improbable that much existing code relies on the
previous behavior.

Signed-off-by: Maarten van der Schrieck <maarten@thingsconnected.nl>

ports/cc3200/hal/cc3200_hal.c

@@ -140,10 +140,15 @@ void mp_hal_delay_ms(mp_uint_t delay) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
-    mp_os_dupterm_tx_strn(str, len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    mp_uint_t ret = len;
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        ret = dupterm_res;
+    }
     // and also to telnet
     telnet_tx_strn(str, len);
+    return ret;
 }
 
 int mp_hal_stdin_rx_chr(void) {

ports/esp32/mphalport.c

@@ -125,24 +125,34 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     // Only release the GIL if many characters are being sent
+    mp_uint_t ret = len;
+    bool did_write = false;
     bool release_gil = len > 20;
     if (release_gil) {
         MP_THREAD_GIL_EXIT();
     }
     #if CONFIG_ESP_CONSOLE_USB_SERIAL_JTAG
     usb_serial_jtag_tx_strn(str, len);
+    did_write = true;
     #elif CONFIG_USB_OTG_SUPPORTED
     usb_tx_strn(str, len);
+    did_write = true;
     #endif
     #if MICROPY_HW_ENABLE_UART_REPL
     uart_stdout_tx_strn(str, len);
+    did_write = true;
     #endif
     if (release_gil) {
         MP_THREAD_GIL_ENTER();
     }
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
+    return did_write ? ret : 0;
 }
 
 uint32_t mp_hal_ticks_ms(void) {

ports/esp8266/esp_mphal.c

@@ -94,8 +94,14 @@ void mp_hal_debug_str(const char *str) {
 }
 #endif
 
-void mp_hal_stdout_tx_strn(const char *str, uint32_t len) {
-    mp_os_dupterm_tx_strn(str, len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, uint32_t len) {
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res < 0) {
+        // no outputs, nothing was written
+        return 0;
+    } else {
+        return dupterm_res;
+    }
 }
 
 void mp_hal_debug_tx_strn_cooked(void *env, const char *str, uint32_t len) {

ports/mimxrt/mphalport.c

@@ -112,9 +112,12 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -125,6 +128,7 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
                 MICROPY_EVENT_POLL_HOOK
             }
             if (ticks_us64() >= timeout) {
+                ret = i;
                 break;
             }
 
@@ -132,10 +136,17 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
             tud_cdc_write_flush();
             i += n2;
         }
+        did_write = true;
+        ret = MIN(i, ret);
     }
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+    return did_write ? ret : 0;
 }
 
 uint64_t mp_hal_time_ns(void) {

ports/minimal/uart_core.c

@@ -29,10 +29,14 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
     #if MICROPY_MIN_USE_STDOUT
     int r = write(STDOUT_FILENO, str, len);
-    (void)r;
+    if (r >= 0) {
+        // in case of an error in the syscall, report no bytes written
+        ret = 0;
+    }
     #elif MICROPY_MIN_USE_STM32_MCU
     while (len--) {
         // wait for TXE
@@ -41,4 +45,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         USART1->DR = *str++;
     }
     #endif
+    return ret;
 }

ports/nrf/drivers/bluetooth/ble_uart.c

@@ -110,10 +110,11 @@ int mp_hal_stdin_rx_chr(void) {
     return (int)byte;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     // Not connected: drop output
-    if (!ble_uart_enabled()) return;
+    if (!ble_uart_enabled()) return 0;
 
+    mp_uint_t ret = len;
     uint8_t *buf = (uint8_t *)str;
     size_t send_len;
 
@@ -134,6 +135,7 @@ void mp_hal_stdout_tx_strn(const char *str, size_t len) {
         len -= send_len;
         buf += send_len;
     }
+    return ret;
 }
 
 void ble_uart_tx_char(char c) {

ports/nrf/drivers/usb/usb_cdc.c

@@ -231,12 +231,12 @@ int mp_hal_stdin_rx_chr(void) {
     return 0;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
-
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     for (const char *top = str + len; str < top; str++) {
         ringbuf_put((ringbuf_t*)&tx_ringbuf, *str);
         usb_cdc_loop();
     }
+    return len;
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, mp_uint_t len) {

ports/nrf/mphalport.c

@@ -196,10 +196,12 @@ int mp_hal_stdin_rx_chr(void) {
     return 0;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     if (MP_STATE_VM(dupterm_objs[0]) != MP_OBJ_NULL) {
         uart_tx_strn(MP_STATE_VM(dupterm_objs[0]), str, len);
+        return len;
     }
+    return 0;
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, mp_uint_t len) {

ports/pic16bit/pic16bit_mphal.c

@@ -75,10 +75,12 @@ void mp_hal_stdout_tx_str(const char *str) {
     mp_hal_stdout_tx_strn(str, strlen(str));
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    mp_uint_t ret = len;
     for (; len > 0; --len) {
         uart_tx_char(*str++);
     }
+    return ret;
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {

ports/powerpc/uart_lpc_serial.c

@@ -108,7 +108,7 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     int i;
     for (i = 0; i < len; i++) {
         while (lpc_uart_tx_full()) {
@@ -116,4 +116,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         }
         lpc_uart_reg_write(REG_RBR, str[i]);
     }
+    return len;
 }

ports/powerpc/uart_potato.c

@@ -118,7 +118,7 @@ int mp_hal_stdin_rx_chr(void) {
     return (char)(val & 0x000000ff);
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     int i;
 
     for (i = 0; i < len; i++) {
@@ -129,4 +129,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         }
         potato_uart_reg_write(POTATO_CONSOLE_TX, val);
     }
+    return len;
 }

ports/renesas-ra/mphalport.c

@@ -154,16 +154,20 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     #if MICROPY_HW_ENABLE_UART_REPL
     if (MP_STATE_PORT(pyb_stdio_uart) != NULL) {
         uart_tx_strn(MP_STATE_PORT(pyb_stdio_uart), str, len);
+        did_write = true;
     }
     #endif
 
     #if MICROPY_HW_USB_CDC
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -180,12 +184,20 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
             tud_cdc_write_flush();
             i += n2;
         }
+        ret = MIN(i, ret);
+        did_write = true;
     }
     #endif
 
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+
+    return did_write ? ret : 0;
 }
 
 void mp_hal_ticks_cpu_enable(void) {

ports/rp2/mphalport.c

@@ -151,14 +151,18 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     #if MICROPY_HW_ENABLE_UART_REPL
     mp_uart_write_strn(str, len);
+    did_write = true;
     #endif
 
     #if MICROPY_HW_USB_CDC
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -173,18 +177,26 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
                 mp_usbd_task();
             }
             if (timeout >= MICROPY_HW_USB_CDC_TX_TIMEOUT) {
+                ret = i;
                 break;
             }
             uint32_t n2 = tud_cdc_write(str + i, n);
             tud_cdc_write_flush();
             i += n2;
         }
+        ret = MIN(i, ret);
+        did_write = true;
     }
     #endif
 
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+    return did_write ? ret : 0;
 }
 
 void mp_hal_delay_ms(mp_uint_t ms) {

ports/samd/mphalport.c

@@ -200,9 +200,12 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     if (tud_cdc_connected()) {
-        for (size_t i = 0; i < len;) {
+        size_t i = 0;
+        while (i < len) {
             uint32_t n = len - i;
             if (n > CFG_TUD_CDC_EP_BUFSIZE) {
                 n = CFG_TUD_CDC_EP_BUFSIZE;
@@ -213,14 +216,22 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
                 MICROPY_EVENT_POLL_HOOK_WITH_USB;
             }
             if (timeout >= MICROPY_HW_USB_CDC_TX_TIMEOUT) {
+                ret = i;
                 break;
             }
             uint32_t n2 = tud_cdc_write(str + i, n);
             tud_cdc_write_flush();
             i += n2;
         }
+        ret = MIN(i, ret);
+        did_write = true;
     }
     #if MICROPY_PY_OS_DUPTERM
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
     #endif
+    return did_write ? ret : 0;
 }

ports/stm32/mphalport.c

@@ -57,14 +57,22 @@ MP_WEAK int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-MP_WEAK void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+MP_WEAK mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    mp_uint_t ret = len;
+    bool did_write = false;
     if (MP_STATE_PORT(pyb_stdio_uart) != NULL) {
         uart_tx_strn(MP_STATE_PORT(pyb_stdio_uart), str, len);
+        did_write = true;
     }
     #if 0 && defined(USE_HOST_MODE) && MICROPY_HW_HAS_LCD
     lcd_print_strn(str, len);
     #endif
-    mp_os_dupterm_tx_strn(str, len);
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        did_write = true;
+        ret = MIN((mp_uint_t)dupterm_res, ret);
+    }
+    return did_write ? ret : 0;
 }
 
 #if __CORTEX_M >= 0x03

ports/unix/unix_mphal.c

@@ -184,10 +184,15 @@ main_term:;
     return c;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     ssize_t ret;
     MP_HAL_RETRY_SYSCALL(ret, write(STDOUT_FILENO, str, len), {});
-    mp_os_dupterm_tx_strn(str, len);
+    mp_uint_t written = ret < 0 ? 0 : ret;
+    int dupterm_res = mp_os_dupterm_tx_strn(str, len);
+    if (dupterm_res >= 0) {
+        written = MIN((mp_uint_t)dupterm_res, written);
+    }
+    return written;
 }
 
 // cooked is same as uncooked because the terminal does some postprocessing

ports/webassembly/mphalport.c

@@ -27,8 +27,9 @@
 #include "library.h"
 #include "mphalport.h"
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     mp_js_write(str, len);
+    return len;
 }
 
 void mp_hal_delay_ms(mp_uint_t ms) {

ports/webassembly/mphalport.h

@@ -28,7 +28,7 @@
 #include "shared/runtime/interrupt_char.h"
 
 #define mp_hal_stdin_rx_chr() (0)
-void mp_hal_stdout_tx_strn(const char *str, size_t len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len);
 
 void mp_hal_delay_ms(mp_uint_t ms);
 void mp_hal_delay_us(mp_uint_t us);

ports/windows/windows_mphal.c

@@ -221,10 +221,11 @@ int mp_hal_stdin_rx_chr(void) {
     }
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     MP_THREAD_GIL_EXIT();
-    write(STDOUT_FILENO, str, len);
+    int ret = write(STDOUT_FILENO, str, len);
     MP_THREAD_GIL_ENTER();
+    return ret < 0 ? 0 : ret; // return the number of bytes written, so in case of an error in the syscall, return 0
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {

ports/zephyr/uart_core.c

@@ -44,7 +44,8 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    mp_uint_t ret = len;
     #ifdef CONFIG_CONSOLE_SUBSYS
     while (len--) {
         char c = *str++;
@@ -60,4 +61,5 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         uart_poll_out(uart_console_dev, *str++);
     }
     #endif
+    return ret;
 }

py/mphal.h

@@ -56,7 +56,7 @@ void mp_hal_stdout_tx_str(const char *str);
 #endif
 
 #ifndef mp_hal_stdout_tx_strn
-void mp_hal_stdout_tx_strn(const char *str, size_t len);
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len);
 #endif
 
 #ifndef mp_hal_stdout_tx_strn_cooked

shared/runtime/sys_stdio_mphal.c

@@ -142,8 +142,7 @@ STATIC mp_uint_t stdio_buffer_read(mp_obj_t self_in, void *buf, mp_uint_t size,
 }
 
 STATIC mp_uint_t stdio_buffer_write(mp_obj_t self_in, const void *buf, mp_uint_t size, int *errcode) {
-    mp_hal_stdout_tx_strn(buf, size);
-    return size;
+    return mp_hal_stdout_tx_strn(buf, size);
 }
 
 STATIC const mp_stream_p_t stdio_buffer_obj_stream_p = {