feat(usb_cdc): Update vfs read() to comply with POSIX standards

components/esp_vfs_console/test_apps/usb_cdc_vfs/main/test_app_main.c

@@ -40,6 +40,63 @@ static bool wait_for_read_ready(FILE *stream)
     }
 }
 
+static void test_usb_cdc_select(void)
+{
+    test_setup(__func__, sizeof(__func__));
+
+    struct timeval tv;
+    tv.tv_sec = 1;
+    tv.tv_usec = 0;
+    char out_buffer[32];
+    memset(out_buffer, 0, sizeof(out_buffer));
+    size_t out_buffer_len = sizeof(out_buffer);
+
+    // stdin needs to be non blocking to properly call read after select returns
+    // with read ready on stdin.
+    int fd = fileno(stdin);
+    int flags = fcntl(fd, F_GETFL);
+    flags |= O_NONBLOCK;
+    int res = fcntl(fd, F_SETFL, flags);
+    TEST_ASSERT(res == 0);
+
+    // init driver
+    // ESP_ERROR_CHECK(esp_usb_console_init());
+    // esp_vfs_dev_cdcacm_register();
+
+    // send the message from pytest environment and make sure it can be read
+    bool message_received = false;
+    size_t char_read = 0;
+    while (!message_received && out_buffer_len > char_read) {
+        int nread = read_bytes_with_select(stdin, out_buffer + char_read, out_buffer_len - char_read, &tv);
+        if (nread > 0) {
+            char_read += nread;
+            if (out_buffer[char_read - 1] == '\n') {
+                message_received = true;
+            }
+        } else if (nread == -2) {
+            // time out occurred, send the expected message back to the testing
+            // environment to trigger the testing environment into sending the
+            // test message. don't update this message without updating the pytest
+            // function since the string is expected as is by the test environment
+            char timeout_msg[] = "select timed out\n";
+            write(fileno(stdout), timeout_msg, sizeof(timeout_msg));
+            flush_write();
+        } else {
+            break;
+        }
+    }
+
+    // write the received message back to the test environment. The test
+    // environment will check that the message received matches the one sent
+    write(fileno(stdout), out_buffer, char_read);
+    flush_write();
+
+    vTaskDelay(10); // wait for the string to send
+}
+
+/**
+ * @brief Test that the non blocking read is compliant with POSIX standards
+ */
 static void test_usb_cdc_read_non_blocking(void)
 {
     test_setup(__func__, sizeof(__func__));
@@ -86,6 +143,44 @@ static void test_usb_cdc_read_non_blocking(void)
     TEST_ASSERT(errno != EWOULDBLOCK);
 }
 
+/**
+ * @brief Test that the blocking read will return with the available
+ * data even if the size is less than the requested size.
+ */
+static void test_usb_cdc_read_blocking(void)
+{
+    test_setup(__func__, sizeof(__func__));
+
+    const size_t out_buffer_len = 32;
+    char out_buffer[out_buffer_len] = {};
+
+    ESP_ERROR_CHECK(esp_vfs_dev_cdcacm_register());
+
+    esp_vfs_dev_cdcacm_set_rx_line_endings(ESP_LINE_ENDINGS_LF);
+    esp_vfs_dev_cdcacm_set_tx_line_endings(ESP_LINE_ENDINGS_LF);
+
+    /* make sure blocking mode is enabled */
+    int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
+    fcntl(STDIN_FILENO, F_SETFL, flags & (~O_NONBLOCK));
+
+    // trigger the test environment to send the test message
+    char ready_msg[] = "ready to receive\n";
+    write(fileno(stdout), ready_msg, sizeof(ready_msg));
+
+    const int nread = read(STDIN_FILENO, out_buffer, out_buffer_len);
+    TEST_ASSERT(nread > 0);
+    TEST_ASSERT(nread < out_buffer_len);
+
+    fcntl(STDIN_FILENO, F_SETFL, flags);
+    esp_vfs_dev_cdcacm_set_rx_line_endings(ESP_LINE_ENDINGS_CRLF);
+    esp_vfs_dev_cdcacm_set_tx_line_endings(ESP_LINE_ENDINGS_CRLF);
+    vTaskDelay(2);  // wait for tasks to exit
+}
+
+/**
+ * @brief Test that the read function does not prematurely return
+ * on reception of new line character.
+ */
 static void test_usb_cdc_read_no_exit_on_newline_reception(void)
 {
     test_setup(__func__, sizeof(__func__));
@@ -133,8 +228,12 @@ static void test_usb_cdc_read_no_exit_on_newline_reception(void)
     vTaskDelay(2);  // wait for tasks to exit
 }
 
+/* Always make sure that the function calling sequence in the main
+ * function matches the expected order in the pytest function.
+ */
 void app_main(void)
 {
     test_usb_cdc_read_non_blocking();
+    test_usb_cdc_read_blocking();
     test_usb_cdc_read_no_exit_on_newline_reception();
 }

components/esp_vfs_console/test_apps/usb_cdc_vfs/pytest_usb_cdc_vfs.py

@@ -19,6 +19,11 @@ def test_usb_cdc_vfs_default(dut: Dut, test_message: str) -> None:
     dut.expect_exact('send_bytes', timeout=2)
     dut.write('abcdefgh')
 
+    # test run: test_usb_cdc_read_blocking
+    dut.expect_exact('test_usb_cdc_read_blocking', timeout=2)
+    dut.expect_exact('ready to receive', timeout=2)
+    dut.write('testdata')
+
     # test run: test_usb_cdc_read_no_exit_on_newline_reception
     dut.expect_exact('test_usb_cdc_read_no_exit_on_newline_reception', timeout=2)
     dut.expect_exact('ready to receive', timeout=2)

components/esp_vfs_console/vfs_cdcacm.c

@@ -146,13 +146,16 @@ static void cdcacm_return_char(int c)
 
 static ssize_t cdcacm_read(int fd, void *data, size_t size)
 {
-    assert(fd == 0);
+    assert(fd == USB_CDC_LOCAL_FD);
     char *data_c = (char *) data;
     ssize_t received = 0;
     _lock_acquire_recursive(&s_read_lock);
 
     if (s_blocking) {
-        while (cdcacm_data_length_in_buffer() < size) {
+        /* in blocking mode, wait for data. by the POSIX standards,
+         * the amount of available bytes does not need to match the
+         * requested size to return */
+        while (cdcacm_data_length_in_buffer() <= 0) {
             xSemaphoreTake(s_rx_semaphore, portMAX_DELAY);
         }
     } else {
@@ -161,21 +164,12 @@ static ssize_t cdcacm_read(int fd, void *data, size_t size)
         size = MIN(size, cdcacm_data_length_in_buffer());
     }
 
-    if (s_rx_mode == ESP_LINE_ENDINGS_CR || s_rx_mode == ESP_LINE_ENDINGS_LF) {
-        /* This is easy. Just receive, and if needed replace \r by \n. */
-        received = esp_usb_console_read_buf(data_c, size);
-        if (s_rx_mode == ESP_LINE_ENDINGS_CR) {
-            /* Change CRs to newlines */
-            for (ssize_t i = 0; i < received; i++) {
-                if (data_c[i] == '\r') {
-                    data_c[i] = '\n';
-                }
-            }
-        }
-    } else {
-        while (received < size) {
-            int c = cdcacm_read_char();
-            if (c == '\r') {
+    while (received < size) {
+        int c = cdcacm_read_char();
+        if (c == '\r') {
+            if (s_rx_mode == ESP_LINE_ENDINGS_CR) {
+                c = '\n';
+            } else if (s_rx_mode == ESP_LINE_ENDINGS_CRLF) {
                 /* look ahead */
                 int c2 = cdcacm_read_char();
                 if (c2 == NONE) {
@@ -192,11 +186,12 @@ static ssize_t cdcacm_read(int fd, void *data, size_t size)
                      */
                     cdcacm_return_char(c2);
                 }
-            } else if (c == NONE) {
-                break;
             }
-            data_c[received++] = (char) c;
+
+        } else if (c == NONE) {
+            break;
         }
+        data_c[received++] = (char) c;
     }
     _lock_release_recursive(&s_read_lock);
     if (received > 0) {