stream: Make capability device IDs an JSON object

Also change the encoding of the byte array to use hexadecimal encoding,
i.e. the byte array [100, 200] in becomes "64c8".

doc/dox/internals/dma-buf.dox

@@ -365,10 +365,13 @@ with. This can be used to reduce the amount of devices that are queried for form
 metadata, which can be a time consuming task, if devices needs to be woken up.
 
 To achieve this, the consumer adds another \ref SPA_PARAM_PeerCapability item with the key
-\ref PW_CAPABILITY_DEVICE_IDS set to a string of base 64 encoded `dev_t` device IDs.
+\ref PW_CAPABILITY_DEVICE_IDS set to a JSON object describing what device IDs are supported.
+
+This JSON object as of version 1 contains a single key "available-devices" that contain
+a list of hexadecimal encoded `dev_t` device IDs.
 
 ```
-	char *device_ids = ...; /* Base 64 encoding of a dev_t. */.
+	char *device_ids = "{\"available-devices\": [\"6464000000000000\",\"c8c8000000000000\"]}";
 	&SPA_DICT_ITEMS(
 		SPA_DICT_ITEM(PW_CAPABILITY_DEVICE_ID_NEGOTIATION, "1"),
 		SPA_DICT_ITEM(PW_CAPABILITY_DEVICE_IDS, device_ids)));

src/examples/base64.h

@@ -1,46 +0,0 @@
-/* PipeWire */
-/* SPDX-FileCopyrightText: Copyright © 2021 Wim Taymans */
-/* SPDX-License-Identifier: MIT */
-
-static inline void base64_encode(const uint8_t *data, size_t len, char *enc, char pad)
-{
-	static const char tab[] =
-	    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-	size_t i;
-	for (i = 0; i < len; i += 3) {
-		uint32_t v;
-		v  =              data[i+0]      << 16;
-		v |= (i+1 < len ? data[i+1] : 0) << 8;
-		v |= (i+2 < len ? data[i+2] : 0);
-		*enc++ =             tab[(v >> (3*6)) & 0x3f];
-		*enc++ =             tab[(v >> (2*6)) & 0x3f];
-		*enc++ = i+1 < len ? tab[(v >> (1*6)) & 0x3f] : pad;
-		*enc++ = i+2 < len ? tab[(v >> (0*6)) & 0x3f] : pad;
-	}
-	*enc = '\0';
-}
-
-static inline size_t base64_decode(const char *data, size_t len, uint8_t *dec)
-{
-	uint8_t tab[] = {
-		62, -1, -1, -1, 63, 52, 53, 54, 55, 56,
-		57, 58, 59, 60, 61, -1, -1, -1, -1, -1,
-		-1, -1,  0,  1,  2,  3,  4,  5,  6,  7,
-		 8,  9, 10, 11, 12, 13, 14, 15, 16, 17,
-		18, 19, 20, 21, 22, 23, 24, 25, -1, -1,
-		-1, -1, -1, -1, 26, 27, 28, 29, 30, 31,
-		32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
-		42, 43, 44, 45, 46, 47, 48, 49, 50, 51 };
-	size_t i, j;
-	for (i = 0, j = 0; i < len; i += 4) {
-		uint32_t v;
-		v =                          tab[data[i+0]-43]  << (3*6);
-		v |=                         tab[data[i+1]-43]  << (2*6);
-		v |= (data[i+2] == '=' ? 0 : tab[data[i+2]-43]) << (1*6);
-		v |= (data[i+3] == '=' ? 0 : tab[data[i+3]-43]);
-		                      dec[j++] = (v >> 16) & 0xff;
-		if (data[i+2] != '=') dec[j++] = (v >> 8)  & 0xff;
-		if (data[i+3] != '=') dec[j++] =  v        & 0xff;
-	}
-	return j;
-}

src/examples/utils.h

@@ -0,0 +1,60 @@
+/* PipeWire */
+/* SPDX-FileCopyrightText: Copyright © 2026 Red Hat */
+/* SPDX-License-Identifier: MIT */
+
+static inline char *
+encode_hex(const uint8_t *data, size_t size)
+{
+	FILE *ms;
+	char *encoded = NULL;
+	size_t encoded_size = 0;
+	size_t i;
+
+	ms = open_memstream(&encoded, &encoded_size);
+	for (i = 0; i < size; i++) {
+		fprintf(ms, "%02x", data[i]);
+	}
+	fclose(ms);
+
+	return encoded;
+}
+
+static inline int8_t
+ascii_hex_to_hex(uint8_t ascii_hex)
+{
+	if (ascii_hex >= '0' && ascii_hex <= '9')
+		return ascii_hex - '0';
+	else if (ascii_hex >= 'a' && ascii_hex <= 'f')
+		return ascii_hex - 'a' + 10;
+	else if (ascii_hex >= 'A' && ascii_hex <= 'F')
+		return ascii_hex - 'A' + 10;
+	else
+		return -1;
+}
+
+static inline int
+decode_hex(const char *encoded, uint8_t *data, size_t size)
+{
+	size_t length;
+	size_t i;
+
+	length = strlen(encoded);
+
+	if (size < (length / 2) * sizeof(uint8_t))
+		return -1;
+
+	i = 0;
+	while (i < length) {
+		int8_t top = ascii_hex_to_hex(encoded[i]);
+		int8_t bottom = ascii_hex_to_hex(encoded[i + 1]);
+
+		if (top == -1 || bottom == -1)
+			return -1;
+
+		uint8_t el = top << 4 | bottom;
+		data[i / 2] = el;
+		i += 2;
+	}
+
+	return 1;
+}

src/examples/video-play-fixate.c

@@ -29,7 +29,7 @@
 #include <pipewire/pipewire.h>
 #include <pipewire/capabilities.h>
 
-#include "base64.h"
+#include "utils.h"
 
 /* Comment out to test device ID negotation backward compatibility. */
 #define SUPPORT_DEVICE_ID_NEGOTIATION 1
@@ -372,46 +372,56 @@ collect_device_ids(struct data *data, const char *json)
 	int len;
 	const char *value;
 	struct spa_json sub;
+	char key[1024];
 
 	if ((len = spa_json_begin(&it, json, strlen(json), &value)) <= 0) {
 		fprintf(stderr, "invalid device IDs value\n");
 		return;
 	}
-	if (!spa_json_is_array(value, len)) {
-		fprintf(stderr, "device IDs not array\n");
+	if (!spa_json_is_object(value, len)) {
+		fprintf(stderr, "device IDs not object\n");
 		return;
 	}
 
 	spa_json_enter(&it, &sub);
-	while ((len = spa_json_next(&sub, &value)) > 0) {
-		char *string;
-		union {
-			dev_t device_id;
-			uint8_t buffer[1024];
-		} dec;
+	while ((len = spa_json_object_next(&sub, key, sizeof(key), &value)) > 0) {
+		struct spa_json devices_sub;
 
-		string = alloca(len + 1);
-
-		if (!spa_json_is_string(value, len)) {
-			fprintf(stderr, "device ID not string\n");
+		if (!spa_json_is_array(value, len)) {
+			fprintf(stderr, "available-devices not array\n");
 			return;
 		}
 
-		if (spa_json_parse_string(value, len, string) <= 0) {
-			fprintf(stderr, "invalid device ID string\n");
-			return;
+		spa_json_enter(&sub, &devices_sub);
+		while ((len = spa_json_next(&devices_sub, &value)) > 0) {
+			char *string;
+			union {
+				dev_t device_id;
+				uint8_t buffer[1024];
+			} dec;
+
+			string = alloca(len + 1);
+
+			if (!spa_json_is_string(value, len)) {
+				fprintf(stderr, "device ID not string\n");
+				return;
+			}
+
+			if (spa_json_parse_string(value, len, string) <= 0) {
+				fprintf(stderr, "invalid device ID string\n");
+				return;
+			}
+
+			if (decode_hex(string, dec.buffer, sizeof (dec.buffer)) < 0) {
+				fprintf(stderr, "invalid device ID string\n");
+				return;
+			}
+
+			fprintf(stderr, "discovered device ID %u:%u\n",
+				major(dec.device_id), minor(dec.device_id));
+
+			data->device_ids[data->n_device_ids++] = dec.device_id;
 		}
-
-		if (base64_decode(string, strlen(string),
-				  (uint8_t *)&dec.device_id) < sizeof(dev_t)) {
-			fprintf(stderr, "invalid device ID\n");
-			return;
-		}
-
-		fprintf(stderr, "discovered device ID %u:%u\n",
-			major(dec.device_id), minor(dec.device_id));
-
-		data->device_ids[data->n_device_ids++] = dec.device_id;
 	}
 }
 

src/examples/video-src-fixate.c

@@ -30,7 +30,7 @@
 #include <pipewire/pipewire.h>
 #include <pipewire/capabilities.h>
 
-#include "base64.h"
+#include "utils.h"
 
 /* Comment out to test device ID negotation backward compatibility. */
 #define SUPPORT_DEVICE_ID_NEGOTIATION 1
@@ -784,17 +784,20 @@ int main(int argc, char *argv[])
 	size_t i;
 
 	ms = open_memstream(&device_ids, &device_ids_size);
-	fprintf(ms, "[");
+	fprintf(ms, "{\"available-devices\": [");
 	for (i = 0; i < SPA_N_ELEMENTS(devices); i++) {
 		dev_t device_id = makedev(devices[i].major, devices[i].minor);
-		char device_id_encoded[256];
+		char *device_id_encoded;
+
+		device_id_encoded = encode_hex((const uint8_t *) &device_id, sizeof (device_id));
 
-		base64_encode((const uint8_t *) &device_id, sizeof (device_id), device_id_encoded, '\0');
 		if (i > 0)
 			fprintf(ms, ",");
 		fprintf(ms, "\"%s\"", device_id_encoded);
+
+		free(device_id_encoded);
 	}
-	fprintf(ms, "]");
+	fprintf(ms, "]}");
 	fclose(ms);
 #endif /* SUPPORT_DEVICE_IDS_LIST */