[PATCH v2 2/6] json: Implement wrapping interface

[Patrick Steinhardt <ps@pks.im>]

While the newly added jsmn library provides the parsing interface, it
does not provide any kind of interface to act on parsed tokens. Instead,
the caller is expected to handle pointer arithmetics inside of the token
array in order to extract required information. While simple, this
requires users to know some of the inner workings of the library and is
thus quite an unintuitive interface.

This commit adds a new interface on top of the jsmn parser that provides
convenience functions to retrieve values from the parsed json type,
`grub_json_t`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 grub-core/lib/json/json.c | 218 ++++++++++++++++++++++++++++++++++++++
 include/grub/json.h       |  69 ++++++++++++
 2 files changed, 287 insertions(+)
 create mode 100644 include/grub/json.h

diff --git a/grub-core/lib/json/json.c b/grub-core/lib/json/json.c
index 2bddd8c46..6a6da8fd8 100644
--- a/grub-core/lib/json/json.c
+++ b/grub-core/lib/json/json.c
@@ -17,7 +17,225 @@
  */
 
 #include <grub/dl.h>
+#include <grub/json.h>
+#include <grub/mm.h>
 
+#define JSMN_STATIC
 #include "jsmn.h"
 
 GRUB_MOD_LICENSE ("GPLv3");
+
+grub_err_t
+grub_json_parse (grub_json_t **out, const char *string, grub_size_t string_len)
+{
+  grub_size_t ntokens = 128;
+  grub_json_t *json = NULL;
+  jsmn_parser parser;
+  grub_err_t err;
+  int jsmn_err;
+
+  json = grub_zalloc (sizeof (*json));
+  if (!json)
+    return GRUB_ERR_OUT_OF_MEMORY;
+  json->idx = 0;
+  json->string = grub_strndup (string, string_len);
+  if (!json->string)
+    {
+      err = GRUB_ERR_OUT_OF_MEMORY;
+      goto out;
+    }
+
+  jsmn_init(&parser);
+
+  while (1)
+    {
+      json->tokens = grub_realloc (json->tokens, sizeof (jsmntok_t) * ntokens);
+      if (!json->tokens)
+	{
+	  err = GRUB_ERR_OUT_OF_MEMORY;
+	  goto out;
+	}
+
+      jsmn_err = jsmn_parse (&parser, string, string_len, json->tokens, ntokens);
+      if (jsmn_err >= 0)
+	break;
+      if (jsmn_err != JSMN_ERROR_NOMEM)
+	{
+	  err = GRUB_ERR_BAD_ARGUMENT;
+	  goto out;
+	}
+
+      ntokens <<= 1;
+    }
+
+  err = GRUB_ERR_NONE;
+  *out = json;
+out:
+  if (err && json)
+    {
+      grub_free (json->string);
+      grub_free (json->tokens);
+      grub_free (json);
+    }
+  return err;
+}
+
+void
+grub_json_free (grub_json_t *json)
+{
+  if (json)
+    {
+      grub_free (json->string);
+      grub_free (json->tokens);
+      grub_free (json);
+    }
+}
+
+grub_size_t
+grub_json_getsize (const grub_json_t *json)
+{
+  jsmntok_t *p = &((jsmntok_t *)json->tokens)[json->idx];
+  return p->size;
+}
+
+grub_json_type_t
+grub_json_gettype (const grub_json_t *json)
+{
+  jsmntok_t *p = &((jsmntok_t *)json->tokens)[json->idx];
+  switch (p->type)
+    {
+    case JSMN_OBJECT:
+      return GRUB_JSON_OBJECT;
+    case JSMN_ARRAY:
+      return GRUB_JSON_ARRAY;
+    case JSMN_STRING:
+      return GRUB_JSON_STRING;
+    case JSMN_PRIMITIVE:
+      return GRUB_JSON_PRIMITIVE;
+    default:
+      break;
+    }
+  return GRUB_JSON_UNDEFINED;
+}
+
+grub_err_t
+grub_json_getchild(grub_json_t *out, const grub_json_t *parent, grub_size_t n)
+{
+  jsmntok_t *p = &((jsmntok_t *)parent->tokens)[parent->idx];
+  grub_size_t offset = 1;
+
+  if (n >= (unsigned) p->size)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  while (n--)
+    n += p[offset++].size;
+
+  out->string = parent->string;
+  out->tokens = parent->tokens;
+  out->idx = parent->idx + offset;
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_json_getvalue(grub_json_t *out, const grub_json_t *parent, const char *key)
+{
+  grub_size_t i;
+
+  if (grub_json_gettype (parent) != GRUB_JSON_OBJECT)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  for (i = 0; i < grub_json_getsize (parent); i++)
+    {
+      grub_json_t child;
+      const char *s;
+
+      if (grub_json_getchild (&child, parent, i) ||
+	  grub_json_getstring (&s, &child, NULL) ||
+          grub_strcmp (s, key) != 0)
+	continue;
+
+      out->string = child.string;
+      out->tokens = child.tokens;
+      out->idx = child.idx + 1;
+
+      return GRUB_ERR_NONE;
+    }
+
+  return GRUB_ERR_FILE_NOT_FOUND;
+}
+
+static grub_err_t
+get_value (grub_json_type_t *out_type, const char **out_string, const grub_json_t *parent, const char *key)
+{
+  const grub_json_t *p = parent;
+  grub_json_t child;
+  jsmntok_t *tok;
+
+  if (key)
+    {
+      grub_err_t err = grub_json_getvalue (&child, parent, key);
+      if (err)
+	return err;
+      p = &child;
+    }
+
+  tok = &((jsmntok_t *) p->tokens)[p->idx];
+  p->string[tok->end] = '\0';
+
+  *out_string = p->string + tok->start;
+  *out_type = grub_json_gettype (p);
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_json_getstring (const char **out, const grub_json_t *parent, const char *key)
+{
+  grub_json_type_t type;
+  const char *value;
+  grub_err_t err;
+
+  err = get_value(&type, &value, parent, key);
+  if (err)
+    return err;
+  if (type != GRUB_JSON_STRING)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  *out = value;
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_json_getuint64(grub_uint64_t *out, const grub_json_t *parent, const char *key)
+{
+  grub_json_type_t type;
+  const char *value;
+  grub_err_t err;
+
+  err = get_value(&type, &value, parent, key);
+  if (err)
+    return err;
+  if (type != GRUB_JSON_STRING && type != GRUB_JSON_PRIMITIVE)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  *out = grub_strtoul (value, NULL, 10);
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_json_getint64(grub_int64_t *out, const grub_json_t *parent, const char *key)
+{
+  grub_json_type_t type;
+  const char *value;
+  grub_err_t err;
+
+  err = get_value(&type, &value, parent, key);
+  if (err)
+    return err;
+  if (type != GRUB_JSON_STRING && type != GRUB_JSON_PRIMITIVE)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  *out = grub_strtol (value, NULL, 10);
+  return GRUB_ERR_NONE;
+}
diff --git a/include/grub/json.h b/include/grub/json.h
new file mode 100644
index 000000000..a59f0393d
--- /dev/null
+++ b/include/grub/json.h
@@ -0,0 +1,69 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2019  Free Software Foundation, Inc.
+ *
+ *  GRUB 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.
+ *
+ *  GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GRUB_JSON_JSON_H
+#define GRUB_JSON_JSON_H	1
+
+#include <grub/types.h>
+
+enum grub_json_type
+{
+  GRUB_JSON_OBJECT,
+  GRUB_JSON_ARRAY,
+  GRUB_JSON_STRING,
+  GRUB_JSON_PRIMITIVE,
+  GRUB_JSON_UNDEFINED,
+};
+typedef enum grub_json_type grub_json_type_t;
+
+struct grub_json
+{
+  void *tokens;
+  char *string;
+  grub_size_t idx;
+};
+typedef struct grub_json grub_json_t;
+
+grub_err_t
+grub_json_parse (grub_json_t **out, const char *string, grub_size_t string_len);
+
+void
+grub_json_free (grub_json_t *json);
+
+grub_size_t
+grub_json_getsize (const grub_json_t *json);
+
+grub_json_type_t
+grub_json_gettype (const grub_json_t *json);
+
+grub_err_t
+grub_json_getchild (grub_json_t *out, const grub_json_t *parent, grub_size_t n);
+
+grub_err_t
+grub_json_getvalue (grub_json_t *out, const grub_json_t *parent, const char *key);
+
+grub_err_t
+grub_json_getstring (const char **out, const grub_json_t *parent, const char *key);
+
+grub_err_t
+grub_json_getuint64 (grub_uint64_t *out, const grub_json_t *parent, const char *key);
+
+grub_err_t
+grub_json_getint64 (grub_int64_t *out, const grub_json_t *parent, const char *key);
+
+#endif
-- 
2.23.0