Display SSH completion candidates for ambiguous prefixes

src/admin_ssh_console.c

@@ -29,6 +29,7 @@
 #define ADMIN_UART_CONSOLE_TASK_PRIORITY 3U
 #define ADMIN_SSH_CONSOLE_MAX_ARGUMENTS 10U
 #define ADMIN_SSH_CONSOLE_HISTORY_DEPTH 4U
+#define ADMIN_SSH_CONSOLE_COMPLETION_OUTPUT_CAPACITY 2048U
 #define ADMIN_SSH_CONTROL_QUEUE_LENGTH 2U
 #define ADMIN_SSH_CONTROL_TASK_STACK_SIZE 4096U
 #define ADMIN_SSH_CONTROL_TASK_PRIORITY 3U
@@ -92,6 +93,8 @@ typedef struct {
 
 static portMUX_TYPE s_lock = portMUX_INITIALIZER_UNLOCKED;
 static admin_session_t s_sessions[ADMIN_SSH_CONSOLE_MAX_SESSIONS];
+/* admin_ssh_console_feed_input() is called only by the sole SSH owner task. */
+static char s_completion_output[ADMIN_SSH_CONSOLE_COMPLETION_OUTPUT_CAPACITY];
 
 static StaticQueue_t s_request_queue_storage;
 static uint8_t s_request_queue_bytes[ADMIN_SSH_CONSOLE_REQUEST_QUEUE_LENGTH *
@@ -967,8 +970,13 @@ bool admin_ssh_console_feed_input(const admin_ssh_console_token_t *token,
             ++*consumed;
             taskEXIT_CRITICAL(&s_lock);
             char completed[ADMIN_SSH_CONSOLE_COMMAND_LINE_CAPACITY + 1U] = {0};
+            size_t candidates_length = 0U;
             bool expanded = console_completion_expand(current, completed,
                                                        sizeof(completed));
+            bool candidates_formatted = !expanded &&
+                console_completion_format_matches(current, s_completion_output,
+                                                  sizeof(s_completion_output),
+                                                  &candidates_length);
             taskENTER_CRITICAL(&s_lock);
             session = &s_sessions[token->slot_index];
             if (token_matches(session, token) && !session->command_pending &&
@@ -979,6 +987,14 @@ bool admin_ssh_console_feed_input(const admin_ssh_console_token_t *token,
                     session->input_cursor = session->input_length;
                     session->history_position = -1;
                     (void)redraw_line_locked(session);
+                } else if (candidates_formatted && candidates_length > 0U &&
+                           candidates_length + 2U + sizeof("admin@serial-tool> ") - 1U +
+                               session->input_length <=
+                               ADMIN_SSH_CONSOLE_OUTPUT_CAPACITY - session->output_length) {
+                    (void)append_output_locked(session, (const uint8_t *)"\r\n", 2U);
+                    (void)append_output_locked(session, (const uint8_t *)s_completion_output,
+                                               candidates_length);
+                    (void)redraw_line_locked(session);
                 } else {
                     (void)append_output_locked(session, (const uint8_t *)"\a", 1U);
                 }

src/console_completion.c

@@ -270,6 +270,47 @@ bool console_completion_expand(const char *line, char *completed, size_t capacit
     return true;
 }
 
+typedef struct {
+    char *output;
+    size_t capacity;
+    size_t length;
+    bool complete;
+} completion_format_context_t;
+
+static bool format_completion_candidate(const char *candidate, void *context)
+{
+    completion_format_context_t *result = context;
+    size_t candidate_length = strlen(candidate);
+    if (candidate_length + 2U > result->capacity - result->length) {
+        result->complete = false;
+        return false;
+    }
+    memcpy(result->output + result->length, candidate, candidate_length);
+    result->length += candidate_length;
+    result->output[result->length++] = '\r';
+    result->output[result->length++] = '\n';
+    return true;
+}
+
+bool console_completion_format_matches(const char *line, char *output, size_t capacity,
+                                       size_t *output_length)
+{
+    if (line == NULL || output == NULL || output_length == NULL || capacity == 0U) {
+        return false;
+    }
+    completion_format_context_t result = {
+        .output = output,
+        .capacity = capacity,
+        .complete = true,
+    };
+    console_completion_visit(line, format_completion_candidate, &result);
+    if (!result.complete) {
+        return false;
+    }
+    *output_length = result.length;
+    return true;
+}
+
 static ssize_t console_read_with_late_terminal_upgrade(int file_descriptor,
                                                        void *buffer,
                                                        size_t size)

src/console_completion.h

@@ -22,6 +22,15 @@ void console_completion_visit(const char *line,
 /* Bounded longest-prefix completion shared by the UART and admin SSH frontends. */
 bool console_completion_expand(const char *line, char *completed, size_t capacity);
 
+/*
+ * Format the matching candidates as CRLF-terminated lines for a frontend that
+ * cannot use linenoise's native completion display. A successful empty result
+ * means no candidate matched; false means the supplied output buffer was too
+ * small or an argument was invalid.
+ */
+bool console_completion_format_matches(const char *line, char *output, size_t capacity,
+                                       size_t *output_length);
+
 #ifdef __cplusplus
 }
 #endif