json: add a nice JSON parser

As preparation for OCI support in nspawn, let's add a JSON parser.

The json.h file contains an explanation why this is new code instead of
just us linking against an existing JSON library.

src/basic/json-internal.h

@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#pragma once
+
+#include "json.h"
+
+/* This header should include all prototypes only the JSON parser itself and
+ * its tests need access to. Normal code consuming the JSON parser should not
+ * interface with this. */
+
+typedef union JsonValue  {
+        /* Encodes a simple value. On x86-64 this structure is 16 bytes wide (as long double is 128bit). */
+        bool boolean;
+        long double real;
+        intmax_t integer;
+        uintmax_t unsig;
+} JsonValue;
+
+/* Let's protect us against accidental structure size changes on our most relevant arch */
+#ifdef __x86_64__
+assert_cc(sizeof(JsonValue) == 16U);
+#endif
+
+#define JSON_VALUE_NULL ((JsonValue) {})
+
+/* We use fake JsonVariant objects for some special values, in order to avoid memory allocations for them. Note that
+ * effectively this means that there are multiple ways to encode the same objects: via these magic values or as
+ * properly allocated JsonVariant. We convert between both on-the-fly as necessary. */
+#define JSON_VARIANT_MAGIC_TRUE ((JsonVariant*) 1)
+#define JSON_VARIANT_MAGIC_FALSE ((JsonVariant*) 2)
+#define JSON_VARIANT_MAGIC_NULL ((JsonVariant*) 3)
+#define JSON_VARIANT_MAGIC_ZERO_INTEGER ((JsonVariant*) 4)
+#define JSON_VARIANT_MAGIC_ZERO_UNSIGNED ((JsonVariant*) 5)
+#define JSON_VARIANT_MAGIC_ZERO_REAL ((JsonVariant*) 6)
+#define JSON_VARIANT_MAGIC_EMPTY_STRING ((JsonVariant*) 7)
+#define JSON_VARIANT_MAGIC_EMPTY_ARRAY ((JsonVariant*) 8)
+#define JSON_VARIANT_MAGIC_EMPTY_OBJECT ((JsonVariant*) 9)
+
+enum { /* JSON tokens */
+        JSON_TOKEN_END,
+        JSON_TOKEN_COLON,
+        JSON_TOKEN_COMMA,
+        JSON_TOKEN_OBJECT_OPEN,
+        JSON_TOKEN_OBJECT_CLOSE,
+        JSON_TOKEN_ARRAY_OPEN,
+        JSON_TOKEN_ARRAY_CLOSE,
+        JSON_TOKEN_STRING,
+        JSON_TOKEN_REAL,
+        JSON_TOKEN_INTEGER,
+        JSON_TOKEN_UNSIGNED,
+        JSON_TOKEN_BOOLEAN,
+        JSON_TOKEN_NULL,
+        _JSON_TOKEN_MAX,
+        _JSON_TOKEN_INVALID = -1,
+};
+
+int json_tokenize(const char **p, char **ret_string, JsonValue *ret_value, unsigned *ret_line, unsigned *ret_column, void **state, unsigned *line, unsigned *column);

src/basic/json.h

@@ -0,0 +1,274 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include "macro.h"
+#include "string-util.h"
+#include "util.h"
+
+/*
+  In case you wonder why we have our own JSON implementation, here are a couple of reasons why this implementation has
+  benefits over various other implementatins:
+
+  - We need support for 64bit signed and unsigned integers, i.e. the full 64,5bit range of -9223372036854775808…18446744073709551615
+  - All our variants are immutable after creation
+  - Special values such as true, false, zero, null, empty strings, empty array, empty objects require zero dynamic memory
+  - Progressive parsing
+  - Our integer/real type implicitly converts, but only if that's safe and loss-lessly possible
+  - There's a "builder" for putting together objects easily in varargs function calls
+  - There's a "dispatcher" for mapping objects to C data structures
+  - Every variant optionally carries parsing location information, which simplifies debugging and parse log error generation
+  - Formatter has color, line, column support
+
+  Limitations:
+  - Doesn't allow embedded NUL in strings
+  - Can't store integers outside of the -9223372036854775808…18446744073709551615 range (it will use 'long double' for
+    values outside this range, which is lossy)
+  - Can't store negative zero (will be treated identical to positive zero, and not retained across serialization)
+  - Can't store non-integer numbers that can't be stored in "long double" losslessly
+  - Allows creation and parsing of objects with duplicate keys. The "dispatcher" will refuse them however. This means
+    we can parse and pass around such objects, but will carefully refuse them when we convert them into our own data.
+
+  (These limitations should be pretty much in line with those of other JSON implementations, in fact might be less
+  limiting in most cases even.)
+*/
+
+typedef struct JsonVariant JsonVariant;
+
+typedef enum JsonVariantType {
+        JSON_VARIANT_STRING,
+        JSON_VARIANT_INTEGER,
+        JSON_VARIANT_UNSIGNED,
+        JSON_VARIANT_REAL,
+        JSON_VARIANT_NUMBER, /* This a pseudo-type: we can never create variants of this type, but we use it as wildcard check for the above three types */
+        JSON_VARIANT_BOOLEAN,
+        JSON_VARIANT_ARRAY,
+        JSON_VARIANT_OBJECT,
+        JSON_VARIANT_NULL,
+        _JSON_VARIANT_TYPE_MAX,
+        _JSON_VARIANT_TYPE_INVALID = -1
+} JsonVariantType;
+
+int json_variant_new_stringn(JsonVariant **ret, const char *s, size_t n);
+int json_variant_new_integer(JsonVariant **ret, intmax_t i);
+int json_variant_new_unsigned(JsonVariant **ret, uintmax_t u);
+int json_variant_new_real(JsonVariant **ret, long double d);
+int json_variant_new_boolean(JsonVariant **ret, bool b);
+int json_variant_new_array(JsonVariant **ret, JsonVariant **array, size_t n);
+int json_variant_new_array_bytes(JsonVariant **ret, const void *p, size_t n);
+int json_variant_new_array_strv(JsonVariant **ret, char **l);
+int json_variant_new_object(JsonVariant **ret, JsonVariant **array, size_t n);
+int json_variant_new_null(JsonVariant **ret);
+
+static inline int json_variant_new_string(JsonVariant **ret, const char *s) {
+        return json_variant_new_stringn(ret, s, strlen_ptr(s));
+}
+
+JsonVariant *json_variant_ref(JsonVariant *v);
+JsonVariant *json_variant_unref(JsonVariant *v);
+void json_variant_unref_many(JsonVariant **array, size_t n);
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(JsonVariant *, json_variant_unref);
+
+const char *json_variant_string(JsonVariant *v);
+intmax_t json_variant_integer(JsonVariant *v);
+uintmax_t json_variant_unsigned(JsonVariant *v);
+long double json_variant_real(JsonVariant *v);
+bool json_variant_boolean(JsonVariant *v);
+
+JsonVariantType json_variant_type(JsonVariant *v);
+bool json_variant_has_type(JsonVariant *v, JsonVariantType type);
+
+static inline bool json_variant_is_string(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_STRING);
+}
+
+static inline bool json_variant_is_integer(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_INTEGER);
+}
+
+static inline bool json_variant_is_unsigned(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_UNSIGNED);
+}
+
+static inline bool json_variant_is_real(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_REAL);
+}
+
+static inline bool json_variant_is_number(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_NUMBER);
+}
+
+static inline bool json_variant_is_boolean(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_BOOLEAN);
+}
+
+static inline bool json_variant_is_array(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_ARRAY);
+}
+
+static inline bool json_variant_is_object(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_OBJECT);
+}
+
+static inline bool json_variant_is_null(JsonVariant *v) {
+        return json_variant_has_type(v, JSON_VARIANT_NULL);
+}
+
+bool json_variant_is_negative(JsonVariant *v);
+
+size_t json_variant_elements(JsonVariant *v);
+JsonVariant *json_variant_by_index(JsonVariant *v, size_t index);
+JsonVariant *json_variant_by_key(JsonVariant *v, const char *key);
+JsonVariant *json_variant_by_key_full(JsonVariant *v, const char *key, JsonVariant **ret_key);
+
+bool json_variant_equal(JsonVariant *a, JsonVariant *b);
+
+struct json_variant_foreach_state {
+        JsonVariant *variant;
+        size_t idx;
+};
+
+#define JSON_VARIANT_ARRAY_FOREACH(i, v)                                \
+        for (struct json_variant_foreach_state _state = { (v), 0 };     \
+             _state.idx < json_variant_elements(_state.variant) &&      \
+                     ({ i = json_variant_by_index(_state.variant, _state.idx); \
+                             true; });                                  \
+             _state.idx++)
+
+#define JSON_VARIANT_OBJECT_FOREACH(k, e, v)                            \
+        for (struct json_variant_foreach_state _state = { (v), 0 };     \
+             _state.idx < json_variant_elements(_state.variant) &&      \
+                     ({ k = json_variant_by_index(_state.variant, _state.idx); \
+                             e = json_variant_by_index(_state.variant, _state.idx + 1); \
+                             true; });                                  \
+             _state.idx += 2)
+
+int json_variant_get_source(JsonVariant *v, const char **ret_source, unsigned *ret_line, unsigned *ret_column);
+
+enum {
+        JSON_FORMAT_NEWLINE = 1 << 0, /* suffix with newline */
+        JSON_FORMAT_PRETTY  = 1 << 1, /* add internal whitespace to appeal to human readers */
+        JSON_FORMAT_COLOR   = 1 << 2, /* insert ANSI color sequences */
+        JSON_FORMAT_SOURCE  = 1 << 3, /* prefix with source filename/line/column */
+        JSON_FORMAT_SSE     = 1 << 4, /* prefix/suffix with W3C server-sent events */
+        JSON_FORMAT_SEQ     = 1 << 5, /* prefix/suffix with RFC 7464 application/json-seq */
+};
+
+int json_variant_format(JsonVariant *v, unsigned flags, char **ret);
+void json_variant_dump(JsonVariant *v, unsigned flags, FILE *f, const char *prefix);
+
+int json_parse(const char *string, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column);
+int json_parse_continue(const char **p, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column);
+int json_parse_file(FILE *f, const char *path, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column);
+
+enum {
+        _JSON_BUILD_STRING,
+        _JSON_BUILD_INTEGER,
+        _JSON_BUILD_UNSIGNED,
+        _JSON_BUILD_REAL,
+        _JSON_BUILD_BOOLEAN,
+        _JSON_BUILD_ARRAY_BEGIN,
+        _JSON_BUILD_ARRAY_END,
+        _JSON_BUILD_OBJECT_BEGIN,
+        _JSON_BUILD_OBJECT_END,
+        _JSON_BUILD_PAIR,
+        _JSON_BUILD_NULL,
+        _JSON_BUILD_VARIANT,
+        _JSON_BUILD_LITERAL,
+        _JSON_BUILD_STRV,
+        _JSON_BUILD_MAX,
+};
+
+#define JSON_BUILD_STRING(s) _JSON_BUILD_STRING, ({ const char *_x = s; _x; })
+#define JSON_BUILD_INTEGER(i) _JSON_BUILD_INTEGER, ({ intmax_t _x = i; _x; })
+#define JSON_BUILD_UNSIGNED(u) _JSON_BUILD_UNSIGNED, ({ uintmax_t _x = u; _x; })
+#define JSON_BUILD_REAL(d) _JSON_BUILD_REAL, ({ long double _x = d; _x; })
+#define JSON_BUILD_BOOLEAN(b) _JSON_BUILD_BOOLEAN, ({ bool _x = b; _x; })
+#define JSON_BUILD_ARRAY(...) _JSON_BUILD_ARRAY_BEGIN, __VA_ARGS__, _JSON_BUILD_ARRAY_END
+#define JSON_BUILD_OBJECT(...) _JSON_BUILD_OBJECT_BEGIN, __VA_ARGS__, _JSON_BUILD_OBJECT_END
+#define JSON_BUILD_PAIR(n, ...) _JSON_BUILD_PAIR, ({ const char *_x = n; _x; }), __VA_ARGS__
+#define JSON_BUILD_NULL _JSON_BUILD_NULL
+#define JSON_BUILD_VARIANT(v) _JSON_BUILD_VARIANT, ({ JsonVariant *_x = v; _x; })
+#define JSON_BUILD_LITERAL(l) _JSON_BUILD_LITERAL, ({ const char *_x = l; _x; })
+#define JSON_BUILD_STRV(l) _JSON_BUILD_STRV, ({ char **_x = l; _x; })
+
+int json_build(JsonVariant **ret, ...);
+int json_buildv(JsonVariant **ret, va_list ap);
+
+/* A bitmask of flags used by the dispatch logic. Note that this is a combined bit mask, that is generated from the bit
+ * mask originally passed into json_dispatch(), the individual bitmask associated with the static JsonDispatch callout
+ * entry, as well the bitmask specified for json_log() calls */
+typedef enum JsonDispatchFlags {
+        /* The following three may be set in JsonDispatch's .flags field or the json_dispatch() flags parameter  */
+        JSON_PERMISSIVE = 1 << 0, /* Shall parsing errors be considered fatal for this property? */
+        JSON_MANDATORY  = 1 << 1, /* Should existance of this property be mandatory? */
+        JSON_LOG        = 1 << 2, /* Should the parser log about errors? */
+
+        /* The following two may be passed into log_json() in addition to the three above */
+        JSON_DEBUG      = 1 << 3, /* Indicates that this log message is a debug message */
+        JSON_WARNING    = 1 << 4, /* Indicates that this log message is a warning message */
+} JsonDispatchFlags;
+
+typedef int (*JsonDispatchCallback)(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+
+typedef struct JsonDispatch {
+        const char *name;
+        JsonVariantType type;
+        JsonDispatchCallback callback;
+        size_t offset;
+        JsonDispatchFlags flags;
+} JsonDispatch;
+
+int json_dispatch(JsonVariant *v, const JsonDispatch table[], JsonDispatchCallback bad, JsonDispatchFlags flags, void *userdata);
+
+int json_dispatch_string(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_strv(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_boolean(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_tristate(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_variant(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_integer(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_unsigned(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_uint32(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+int json_dispatch_int32(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata);
+
+assert_cc(sizeof(uintmax_t) == sizeof(uint64_t))
+#define json_dispatch_uint64 json_dispatch_unsigned
+
+assert_cc(sizeof(intmax_t) == sizeof(int64_t))
+#define json_dispatch_int64 json_dispatch_integer
+
+static inline int json_dispatch_level(JsonDispatchFlags flags) {
+
+        /* Did the user request no logging? If so, then never log higher than LOG_DEBUG. Also, if this is marked as
+         * debug message, then also log at debug level. */
+
+        if (!(flags & JSON_LOG) ||
+            (flags & JSON_DEBUG))
+                return LOG_DEBUG;
+
+        /* Are we invoked in permissive mode, or is this explicitly marked as warning message? Then this should be
+         * printed at LOG_WARNING */
+        if (flags & (JSON_PERMISSIVE|JSON_WARNING))
+                return LOG_WARNING;
+
+        /* Otherwise it's an error. */
+        return LOG_ERR;
+}
+
+int json_log_internal(JsonVariant *variant, int level, int error, const char *file, int line, const char *func, const char *format, ...)  _printf_(7, 8);
+
+#define json_log(variant, flags, error, ...)                       \
+        ({                                                              \
+                int _level = json_dispatch_level(flags), _e = (error);    \
+                (log_get_max_level() >= LOG_PRI(_level))                \
+                        ? json_log_internal(variant, _level, _e, __FILE__, __LINE__, __func__, __VA_ARGS__) \
+                        : -abs(_e);                                     \
+        })
+
+const char *json_variant_type_to_string(JsonVariantType t);
+JsonVariantType json_variant_type_from_string(const char *s);

src/basic/meson.build

@@ -99,6 +99,9 @@ basic_sources = files('''
         ioprio.h
         journal-importer.c
         journal-importer.h
+        json-internal.h
+        json.c
+        json.h
         khash.c
         khash.h
         label.c
@@ -313,7 +316,8 @@ libbasic = static_library(
                         libcap,
                         libblkid,
                         libmount,
-                        libselinux],
+                        libselinux,
+                        libm],
         c_args : ['-fvisibility=default'],
         install : false)