feat: add external JACK test program for audio routing verification

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

Let's produce the block.test_audio_routing.c

@@ -0,0 +1,180 @@
+/*
+ * test_audio_routing.c
+ *
+ * External test program for the looper application.
+ * Connects to JACK, sends a test tone to the application's audio_in ports,
+ * captures the output from audio_out ports, and verifies that audio is flowing.
+ *
+ * Compile with:
+ *   gcc -o test_audio_routing test_audio_routing.c -ljack -lm
+ *
+ * Run after the looper application is running and JACK is active.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+#include <jack/jack.h>
+#include <unistd.h>
+
+#define TEST_DURATION_SECONDS 2
+#define SAMPLE_RATE 48000
+#define NUM_CHANNELS 2   // test first two channels
+
+static jack_client_t *client = NULL;
+static jack_port_t *test_out_ports[NUM_CHANNELS];
+static jack_port_t *test_in_ports[NUM_CHANNELS];
+static float *captured_output[NUM_CHANNELS];
+static jack_nframes_t captured_frames = 0;
+static volatile int running = 1;
+
+/* Generate a sine wave sample */
+static float sine_sample(jack_nframes_t frame, float freq, float sample_rate) {
+    return sinf(2.0f * M_PI * freq * frame / sample_rate);
+}
+
+/* Process callback: generate test tone on output ports, capture input ports */
+static int process(jack_nframes_t nframes, void *arg) {
+    (void)arg;
+
+    /* Generate test tone on each output port */
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        jack_default_audio_sample_t *out =
+            (jack_default_audio_sample_t *)jack_port_get_buffer(test_out_ports[ch], nframes);
+        for (jack_nframes_t i = 0; i < nframes; i++) {
+            /* 440 Hz sine wave, amplitude 0.5 */
+            out[i] = 0.5f * sine_sample(captured_frames + i, 440.0f, SAMPLE_RATE);
+        }
+    }
+
+    /* Capture input ports */
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        jack_default_audio_sample_t *in =
+            (jack_default_audio_sample_t *)jack_port_get_buffer(test_in_ports[ch], nframes);
+        /* Append to captured buffer */
+        if (captured_output[ch]) {
+            memcpy(captured_output[ch] + captured_frames, in, nframes * sizeof(float));
+        }
+    }
+    captured_frames += nframes;
+
+    return 0;
+}
+
+/* Shutdown callback */
+static void shutdown(void *arg) {
+    (void)arg;
+    running = 0;
+}
+
+int main(void) {
+    jack_status_t status;
+    const char *client_name = "test_audio_routing";
+
+    client = jack_client_open(client_name, JackNullOption, &status, NULL);
+    if (!client) {
+        fprintf(stderr, "Failed to open JACK client, status = 0x%2.0x\n", status);
+        return 1;
+    }
+
+    /* Register ports */
+    char port_name[64];
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        snprintf(port_name, sizeof(port_name), "test_out_%d", ch);
+        test_out_ports[ch] = jack_port_register(client, port_name,
+                                                JACK_DEFAULT_AUDIO_TYPE,
+                                                JackPortIsOutput, 0);
+        if (!test_out_ports[ch]) {
+            fprintf(stderr, "Failed to register output port %d\n", ch);
+            jack_client_close(client);
+            return 1;
+        }
+
+        snprintf(port_name, sizeof(port_name), "test_in_%d", ch);
+        test_in_ports[ch] = jack_port_register(client, port_name,
+                                               JACK_DEFAULT_AUDIO_TYPE,
+                                               JackPortIsInput, 0);
+        if (!test_in_ports[ch]) {
+            fprintf(stderr, "Failed to register input port %d\n", ch);
+            jack_client_close(client);
+            return 1;
+        }
+    }
+
+    /* Set process callback */
+    jack_set_process_callback(client, process, NULL);
+    jack_on_shutdown(client, shutdown, NULL);
+
+    /* Allocate capture buffers */
+    jack_nframes_t sample_rate = jack_get_sample_rate(client);
+    jack_nframes_t total_frames = sample_rate * TEST_DURATION_SECONDS;
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        captured_output[ch] = (float *)calloc(total_frames, sizeof(float));
+        if (!captured_output[ch]) {
+            fprintf(stderr, "Memory allocation failed\n");
+            jack_client_close(client);
+            return 1;
+        }
+    }
+
+    /* Activate client */
+    if (jack_activate(client) != 0) {
+        fprintf(stderr, "Failed to activate JACK client\n");
+        jack_client_close(client);
+        return 1;
+    }
+
+    /* Connect to the looper application's ports */
+    const char *app_client_name = "looper";  /* adjust if your app uses a different name */
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        char src_port[128], dst_port[128];
+        snprintf(src_port, sizeof(src_port), "%s:test_out_%d", client_name, ch);
+        snprintf(dst_port, sizeof(dst_port), "%s:audio_in_%d", app_client_name, ch);
+        if (jack_connect(client, src_port, dst_port) != 0) {
+            fprintf(stderr, "Warning: could not connect %s -> %s\n", src_port, dst_port);
+        }
+
+        snprintf(src_port, sizeof(src_port), "%s:audio_out_%d", app_client_name, ch);
+        snprintf(dst_port, sizeof(dst_port), "%s:test_in_%d", client_name, ch);
+        if (jack_connect(client, src_port, dst_port) != 0) {
+            fprintf(stderr, "Warning: could not connect %s -> %s\n", src_port, dst_port);
+        }
+    }
+
+    /* Run for the test duration */
+    printf("Running test for %d seconds...\n", TEST_DURATION_SECONDS);
+    sleep(TEST_DURATION_SECONDS);
+
+    /* Deactivate and close */
+    jack_deactivate(client);
+    jack_client_close(client);
+
+    /* Analyze captured output */
+    int pass = 1;
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        float max_val = 0.0f;
+        for (jack_nframes_t i = 0; i < total_frames; i++) {
+            float abs_val = fabsf(captured_output[ch][i]);
+            if (abs_val > max_val) max_val = abs_val;
+        }
+        printf("Channel %d: max output amplitude = %f\n", ch, max_val);
+        if (max_val < 0.001f) {
+            printf("FAIL: Channel %d output is near zero (no audio flowing)\n", ch);
+            pass = 0;
+        }
+    }
+
+    /* Cleanup */
+    for (int ch = 0; ch < NUM_CHANNELS; ch++) {
+        free(captured_output[ch]);
+    }
+
+    if (pass) {
+        printf("PASS: Audio routing is working correctly.\n");
+        return 0;
+    } else {
+        printf("FAIL: Audio routing test failed.\n");
+        return 1;
+    }
+}