adds some basic json parsing stuff

src/include/json.h

@@ -0,0 +1,10 @@
+#include <cjson/cJSON.h>
+#include "curl.h"
+
+#ifndef JSON_H
+#define JSON_H
+
+void json_out(cJSON** json);
+void get_json_book(get_response* resp, cJSON** query);
+
+#endif

src/json.c

@@ -0,0 +1,42 @@
+#include <cjson/cJSON.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#include "include/curl.h"
+#include "include/json.h"
+
+static bool check_valid_query(cJSON* query) {return (query->valueint != 0);}
+
+#define FILE_OUT "book.json"
+void json_out(cJSON** json)
+{
+	FILE* f = fopen(FILE_OUT, "w");
+	fprintf(f, "%s", cJSON_Print(*json));
+	fclose(f);
+}
+#undef FILE_OUT
+
+void get_json_book(get_response* resp, cJSON** query)
+{
+	bool err;
+	cJSON* json;
+	
+	json = cJSON_Parse(resp->buf);
+	if (!json) {
+		const char* err_ptr = cJSON_GetErrorPtr();
+		if (err_ptr)
+			fprintf(stderr, "cJSON_Parse: %s\n", err_ptr);
+		cJSON_Delete(json);
+		exit(EXIT_FAILURE);
+	}
+
+	err = check_valid_query(cJSON_GetObjectItemCaseSensitive(json, "numFound"));
+	if (!err) {
+		fprintf(stderr, "ISBN not found!\n");
+		exit(EXIT_SUCCESS);
+	}
+
+	// first entry of the "docs" json entry, which is the search result	
+	(*query) = cJSON_GetObjectItemCaseSensitive(json, "docs")->child;
+}
+