Add client support, use it to dump json to stdout first.

client.c

@@ -0,0 +1,98 @@
+#include <stdbool.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <strings.h>
+#include <stdio.h>
+
+#include "json.h"
+#include "client.h"
+
+struct client {
+	char id[UUID_LEN];
+	int fd;
+	struct client *next;
+};
+
+typedef size_t (*serializer)(struct packet *, char *);
+struct serializer {
+	char *name;
+	serializer serialize;
+	struct client *client_head;
+} serializers[] = {
+	{
+		.name = "json",
+		.serialize = json_serialize,
+		.client_head = NULL,
+	},
+};
+#define NUM_SERIALIZERS (sizeof(serializers) / sizeof(*serializers))
+
+
+struct serializer *client_get_serializer(char *name) {
+	for (int i = 0; i < NUM_SERIALIZERS; i++) {
+		if (strcasecmp(serializers[i].name, name) == 0) {
+			return &serializers[i];
+		}
+	}
+	return NULL;
+}
+
+static bool client_hello(int fd, struct serializer *serializer) {
+	char buf[SERIALIZE_LEN];
+	size_t len = serializer->serialize(NULL, buf);
+	if (len == 0) {
+		return true;
+	}
+	if (write(fd, buf, len) != len) {
+		fprintf(stderr, "Failed to write hello to client\n");
+		return false;
+	}
+	return true;
+}
+
+void client_add(int fd, struct serializer *serializer) {
+	if (!client_hello(fd, serializer)) {
+		return;
+	}
+
+	struct client *client = malloc(sizeof(*client));
+	assert(client);
+
+	uuid_gen(client->id);
+	client->fd = fd;
+	client->next = serializer->client_head;
+	serializer->client_head = client;
+
+	fprintf(stderr, "%s (%s): New client\n", client->id, serializer->name);
+}
+
+void client_write(struct packet *packet) {
+	for (int i = 0; i < NUM_SERIALIZERS; i++) {
+		struct serializer *serializer = &serializers[i];
+		if (serializer->client_head == NULL) {
+			continue;
+		}
+		char buf[SERIALIZE_LEN];
+		size_t len = serializer->serialize(packet, buf);
+		if (len == 0) {
+			continue;
+		}
+		struct client *client = serializer->client_head, *prev_client = NULL;
+		while (client) {
+			if (write(client->fd, buf, len) == len) {
+				prev_client = client;
+				client = client->next;
+			} else {
+				fprintf(stderr, "%s (%s): Client disconnected\n", client->id, serializer->name);
+				if (prev_client) {
+					prev_client->next = client->next;
+				} else {
+					serializer->client_head = client->next;
+				}
+				struct client *del = client;
+				client = client->next;
+				free(del);
+			}
+		}
+	}
+}