common: implement simple JSON writer

Slightly modified by Jan Hák <jan.hak@nic.cz>

Knot.files

@@ -23,6 +23,8 @@ src/contrib/files.c
 src/contrib/files.h
 src/contrib/getline.c
 src/contrib/getline.h
+src/contrib/json.c
+src/contrib/json.h
 src/contrib/libbpf/bpf/bpf.c
 src/contrib/libbpf/bpf/bpf.h
 src/contrib/libbpf/bpf/bpf_core_read.h

src/contrib/Makefile.inc

@@ -37,6 +37,8 @@ libcontrib_la_SOURCES = \
 	contrib/files.h				\
 	contrib/getline.c			\
 	contrib/getline.h			\
+	contrib/json.c				\
+	contrib/json.h				\
 	contrib/macros.h			\
 	contrib/mempattern.c			\
 	contrib/mempattern.h			\

src/contrib/json.c

+/*  Copyright (C) 2022 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "contrib/json.h"
+
+#define MAX_DEPTH 8
+
+enum {
+	BLOCK_INVALID = 0,
+	BLOCK_OBJECT,
+	BLOCK_LIST,
+};
+
+/*! One indented block of JSON. */
+struct block {
+	/*! Block type. */
+	int type;
+	/*! Number of elements written. */
+	int count;
+};
+
+struct jsonw {
+	/*! Output file stream. */
+	FILE *out;
+	/*! Indentaiton string. */
+	const char *indent;
+	/*! List to be used as a stack of blocks in progress. */
+	struct block stack[MAX_DEPTH];
+	/*! Index pointing to the top of the stack. */
+	int top;
+};
+
+static const char *DEFAULT_INDENT = "\t";
+
+static void start_block(jsonw_t *w, int type)
+{
+	assert(w->top > 0);
+
+	struct block b = {
+		.type = type,
+		.count = 0,
+	};
+
+	w->top -= 1;
+	w->stack[w->top] = b;
+}
+
+static struct block *cur_block(jsonw_t *w)
+{
+	if (w && w->top < MAX_DEPTH) {
+		return &w->stack[w->top];
+	}
+	return NULL;
+}
+
+/*! Insert new line and indent for the next write. */
+static void wrap(jsonw_t *w)
+{
+	fputc('\n', w->out);
+	int level = MAX_DEPTH - w->top;
+	for (int i = 0; i < level; i++) {
+		fprintf(w->out, "%s", w->indent);
+	}
+}
+
+static void end_block(jsonw_t *w)
+{
+	assert(w->top < MAX_DEPTH);
+
+	w->top += 1;
+}
+
+static void escaped_print(jsonw_t *w, const char *str)
+{
+	fputc('"', w->out);
+	for (const char *pos = str; *pos != '\0'; pos++) {
+		char c = *pos;
+		if (c == '\\' || c == '\"') {
+			fputc('\\', w->out);
+		}
+		fputc(c, w->out);
+	}
+	fputc('"', w->out);
+}
+
+static void align_key(jsonw_t *w, const char *key)
+{
+	struct block *top = cur_block(w);
+	if (top && top->count++) {
+		fputc(',', w->out);
+	}
+
+	wrap(w);
+
+	if (key && key[0]) {
+		escaped_print(w, key);
+		fprintf(w->out, ": ");
+	}
+}
+
+jsonw_t *jsonw_new(FILE *out, const char *indent)
+{
+	assert(out);
+
+	jsonw_t *w = calloc(1, sizeof(*w));
+	if (w == NULL) {
+		return w;
+	}
+
+	w->out = out;
+	w->indent = indent ? indent : DEFAULT_INDENT;
+	w->top = MAX_DEPTH;
+
+	return w;
+}
+
+void jsonw_free(jsonw_t **w)
+{
+	if (w == NULL) {
+		return;
+	}
+
+	free(*w);
+	*w = NULL;
+}
+
+void jsonw_object(jsonw_t *w, const char *key)
+{
+	assert(w);
+
+	align_key(w, key);
+	fprintf(w->out, "{");
+	start_block(w, BLOCK_OBJECT);
+}
+
+void jsonw_list(jsonw_t *w, const char *key)
+{
+	assert(w);
+
+	align_key(w, key);
+	fprintf(w->out, "[");
+	start_block(w, BLOCK_LIST);
+}
+
+void jsonw_str(jsonw_t *w, const char *key, const char *value)
+{
+	assert(w);
+
+	align_key(w, key);
+	escaped_print(w, value);
+}
+
+void jsonw_ulong(jsonw_t *w, const char *key, unsigned long value)
+{
+	assert(w);
+
+	align_key(w, key);
+	fprintf(w->out, "%lu", value);
+}
+
+void jsonw_int(jsonw_t *w, const char *key, int value)
+{
+	assert(w);
+
+	align_key(w, key);
+	fprintf(w->out, "%d", value);
+}
+
+
+void jsonw_bool(jsonw_t *w, const char *key, bool value)
+{
+	assert(w);
+
+	align_key(w, key);
+	fprintf(w->out, "%s", value ? "true" : "false");
+}
+
+void jsonw_end(jsonw_t *w)
+{
+	assert(w);
+
+	struct block *top = cur_block(w);
+	if (top == NULL) {
+		return;
+	}
+
+	end_block(w);
+	wrap(w);
+
+	switch (top->type) {
+	case BLOCK_OBJECT:
+		fprintf(w->out, "}");
+		break;
+	case BLOCK_LIST:
+		fprintf(w->out, "]");
+		break;
+	}
+}

src/contrib/json.h

+/*  Copyright (C) 2022 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include <stdio.h>
+#include <stdbool.h>
+
+/*!
+ * Simple pretty JSON writer.
+ */
+struct jsonw;
+typedef struct jsonw jsonw_t;
+
+/*!
+ * Create new JSON writer.
+ *
+ * @param out     Output file stream.
+ * @param indent  Indentation string.
+ *
+ * @return JSON writer or NULL for allocation error.
+ */
+jsonw_t *jsonw_new(FILE *out, const char *indent);
+
+/*!
+ * Free JSON writer created with jsonw_new.
+ */
+void jsonw_free(jsonw_t **w);
+
+/*!
+ * Start writing a new object.
+ *
+ * The following writes will represent key and value pairs respectively until
+ * jsonw_end is called.
+ */
+void jsonw_object(jsonw_t *w, const char *key);
+
+/*!
+ * Start writing a new list.
+ *
+ * The following writes will represent values until jsonw_end is called.
+ */
+void jsonw_list(jsonw_t *w, const char *key);
+
+/*!
+ * Write string as JSON. The string will be escaped properly.
+ */
+void jsonw_str(jsonw_t *w, const char *key, const char *value);
+
+/*!
+ * Write unsigned long value as JSON.
+ */
+void jsonw_ulong(jsonw_t *w, const char *key, unsigned long value);
+
+/*!
+ * Write integer as JSON.
+ */
+void jsonw_int(jsonw_t *w, const char *key, int value);
+
+/*!
+ * Write boolean value as JSON.
+ */
+void jsonw_bool(jsonw_t *w, const char *key, bool value);
+
+/*!
+ * Terminate in-progress object or list.
+ */
+void jsonw_end(jsonw_t *w);