lib: add jsmn JSON parser support

Board code may require JSON support to parse factory data or to verify
JSON web tokens in locked-down systems. Import the current master
state[1] of JSMN, a minimalistic JSON parser, with slight changes
to make it compile in barebox

[1]: https://github.com/zserge/jsmn/commit/25647e6

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20230110084930.3439001-2-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

3 files changed, 377 insertions, 0 deletions

diff --git a/lib/Kconfig b/lib/Kconfig
index a0f28b935c..5af7ea33f2 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -8,6 +8,11 @@ config UNCOMPRESS
 	bool
 	select FILETYPE
 
+config JSMN
+	bool "JSMN JSON Parser" if COMPILE_TEST
+	help
+	  A minimalistic JSON parser.
+
 config XXHASH
 	bool
 
diff --git a/lib/Makefile b/lib/Makefile
index 21afb233fa..4717b8aec3 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -19,6 +19,7 @@ obj-y			+= readkey.o
 obj-y			+= kfifo.o
 obj-y			+= libbb.o
 obj-y			+= libgen.o
+obj-$(CONFIG_JSMN)	+= jsmn.o
 obj-$(CONFIG_BLOBGEN)	+= blobgen.o
 obj-y			+= stringlist.o
 obj-y			+= cmdlinepart.o
diff --git a/lib/jsmn.c b/lib/jsmn.c
new file mode 100644
index 0000000000..3a68f89337
--- /dev/null
+++ b/lib/jsmn.c
@@ -0,0 +1,371 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright (c) 2010 Serge Zaitsev
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <jsmn.h>
+
+/**
+ * Allocates a fresh unused token from the token pool.
+ */
+static jsmntok_t *jsmn_alloc_token(jsmn_parser *parser, jsmntok_t *tokens,
+				   const size_t num_tokens) {
+	jsmntok_t *tok;
+	if (parser->toknext >= num_tokens) {
+		return NULL;
+	}
+	tok = &tokens[parser->toknext++];
+	tok->start = tok->end = -1;
+	tok->size = 0;
+#ifdef JSMN_PARENT_LINKS
+	tok->parent = -1;
+#endif
+	return tok;
+}
+
+/**
+ * Fills token type and boundaries.
+ */
+static void jsmn_fill_token(jsmntok_t *token, const jsmntype_t type,
+			    const int start, const int end) {
+	token->type = type;
+	token->start = start;
+	token->end = end;
+	token->size = 0;
+}
+
+/**
+ * Fills next available token with JSON primitive.
+ */
+static int jsmn_parse_primitive(jsmn_parser *parser, const char *js,
+				const size_t len, jsmntok_t *tokens,
+				const size_t num_tokens) {
+	jsmntok_t *token;
+	int start;
+
+	start = parser->pos;
+
+	for (; parser->pos < len && js[parser->pos] != '\0'; parser->pos++) {
+		switch (js[parser->pos]) {
+#ifndef JSMN_STRICT
+			/* In strict mode primitive must be followed by "," or "}" or "]" */
+		case ':':
+#endif
+		case '\t':
+		case '\r':
+		case '\n':
+		case ' ':
+		case ',':
+		case ']':
+		case '}':
+			goto found;
+		default:
+			/* to quiet a warning from gcc*/
+			break;
+		}
+		if (js[parser->pos] < 32 || js[parser->pos] >= 127) {
+			parser->pos = start;
+			return JSMN_ERROR_INVAL;
+		}
+	}
+#ifdef JSMN_STRICT
+	/* In strict mode primitive must be followed by a comma/object/array */
+	parser->pos = start;
+	return JSMN_ERROR_PART;
+#endif
+
+found:
+	if (tokens == NULL) {
+		parser->pos--;
+		return 0;
+	}
+	token = jsmn_alloc_token(parser, tokens, num_tokens);
+	if (token == NULL) {
+		parser->pos = start;
+		return JSMN_ERROR_NOMEM;
+	}
+	jsmn_fill_token(token, JSMN_PRIMITIVE, start, parser->pos);
+#ifdef JSMN_PARENT_LINKS
+	token->parent = parser->toksuper;
+#endif
+	parser->pos--;
+	return 0;
+}
+
+/**
+ * Fills next token with JSON string.
+ */
+static int jsmn_parse_string(jsmn_parser *parser, const char *js,
+			     const size_t len, jsmntok_t *tokens,
+			     const size_t num_tokens) {
+	jsmntok_t *token;
+
+	int start = parser->pos;
+
+	/* Skip starting quote */
+	parser->pos++;
+
+	for (; parser->pos < len && js[parser->pos] != '\0'; parser->pos++) {
+		char c = js[parser->pos];
+
+		/* Quote: end of string */
+		if (c == '\"') {
+			if (tokens == NULL) {
+				return 0;
+			}
+			token = jsmn_alloc_token(parser, tokens, num_tokens);
+			if (token == NULL) {
+				parser->pos = start;
+				return JSMN_ERROR_NOMEM;
+			}
+			jsmn_fill_token(token, JSMN_STRING, start + 1, parser->pos);
+#ifdef JSMN_PARENT_LINKS
+			token->parent = parser->toksuper;
+#endif
+			return 0;
+		}
+
+		/* Backslash: Quoted symbol expected */
+		if (c == '\\' && parser->pos + 1 < len) {
+			int i;
+			parser->pos++;
+			switch (js[parser->pos]) {
+				/* Allowed escaped symbols */
+			case '\"':
+			case '/':
+			case '\\':
+			case 'b':
+			case 'f':
+			case 'r':
+			case 'n':
+			case 't':
+				break;
+				/* Allows escaped symbol \uXXXX */
+			case 'u':
+				parser->pos++;
+				for (i = 0; i < 4 && parser->pos < len && js[parser->pos] != '\0';
+				     i++) {
+					/* If it isn't a hex character we have an error */
+					if (!((js[parser->pos] >= 48 && js[parser->pos] <= 57) ||   /* 0-9 */
+					      (js[parser->pos] >= 65 && js[parser->pos] <= 70) ||   /* A-F */
+					      (js[parser->pos] >= 97 && js[parser->pos] <= 102))) { /* a-f */
+						parser->pos = start;
+						return JSMN_ERROR_INVAL;
+					}
+					parser->pos++;
+				}
+				parser->pos--;
+				break;
+				/* Unexpected symbol */
+			default:
+				parser->pos = start;
+				return JSMN_ERROR_INVAL;
+			}
+		}
+	}
+	parser->pos = start;
+	return JSMN_ERROR_PART;
+}
+
+/**
+ * Parse JSON string and fill tokens.
+ */
+JSMN_API int jsmn_parse(jsmn_parser *parser, const char *js, const size_t len,
+			jsmntok_t *tokens, const unsigned int num_tokens) {
+	int r;
+	int i;
+	jsmntok_t *token;
+	int count = parser->toknext;
+
+	for (; parser->pos < len && js[parser->pos] != '\0'; parser->pos++) {
+		char c;
+		jsmntype_t type;
+
+		c = js[parser->pos];
+		switch (c) {
+		case '{':
+		case '[':
+			count++;
+			if (tokens == NULL) {
+				break;
+			}
+			token = jsmn_alloc_token(parser, tokens, num_tokens);
+			if (token == NULL) {
+				return JSMN_ERROR_NOMEM;
+			}
+			if (parser->toksuper != -1) {
+				jsmntok_t *t = &tokens[parser->toksuper];
+#ifdef JSMN_STRICT
+				/* In strict mode an object or array can't become a key */
+				if (t->type == JSMN_OBJECT) {
+					return JSMN_ERROR_INVAL;
+				}
+#endif
+				t->size++;
+#ifdef JSMN_PARENT_LINKS
+				token->parent = parser->toksuper;
+#endif
+			}
+			token->type = (c == '{' ? JSMN_OBJECT : JSMN_ARRAY);
+			token->start = parser->pos;
+			parser->toksuper = parser->toknext - 1;
+			break;
+		case '}':
+		case ']':
+			if (tokens == NULL) {
+				break;
+			}
+			type = (c == '}' ? JSMN_OBJECT : JSMN_ARRAY);
+#ifdef JSMN_PARENT_LINKS
+			if (parser->toknext < 1) {
+				return JSMN_ERROR_INVAL;
+			}
+			token = &tokens[parser->toknext - 1];
+			for (;;) {
+				if (token->start != -1 && token->end == -1) {
+					if (token->type != type) {
+						return JSMN_ERROR_INVAL;
+					}
+					token->end = parser->pos + 1;
+					parser->toksuper = token->parent;
+					break;
+				}
+				if (token->parent == -1) {
+					if (token->type != type || parser->toksuper == -1) {
+						return JSMN_ERROR_INVAL;
+					}
+					break;
+				}
+				token = &tokens[token->parent];
+			}
+#else
+			for (i = parser->toknext - 1; i >= 0; i--) {
+				token = &tokens[i];
+				if (token->start != -1 && token->end == -1) {
+					if (token->type != type) {
+						return JSMN_ERROR_INVAL;
+					}
+					parser->toksuper = -1;
+					token->end = parser->pos + 1;
+					break;
+				}
+			}
+			/* Error if unmatched closing bracket */
+			if (i == -1) {
+				return JSMN_ERROR_INVAL;
+			}
+			for (; i >= 0; i--) {
+				token = &tokens[i];
+				if (token->start != -1 && token->end == -1) {
+					parser->toksuper = i;
+					break;
+				}
+			}
+#endif
+			break;
+		case '\"':
+			r = jsmn_parse_string(parser, js, len, tokens, num_tokens);
+			if (r < 0) {
+				return r;
+			}
+			count++;
+			if (parser->toksuper != -1 && tokens != NULL) {
+				tokens[parser->toksuper].size++;
+			}
+			break;
+		case '\t':
+		case '\r':
+		case '\n':
+		case ' ':
+			break;
+		case ':':
+			parser->toksuper = parser->toknext - 1;
+			break;
+		case ',':
+			if (tokens != NULL && parser->toksuper != -1 &&
+			    tokens[parser->toksuper].type != JSMN_ARRAY &&
+			    tokens[parser->toksuper].type != JSMN_OBJECT) {
+#ifdef JSMN_PARENT_LINKS
+				parser->toksuper = tokens[parser->toksuper].parent;
+#else
+				for (i = parser->toknext - 1; i >= 0; i--) {
+					if (tokens[i].type == JSMN_ARRAY || tokens[i].type == JSMN_OBJECT) {
+						if (tokens[i].start != -1 && tokens[i].end == -1) {
+							parser->toksuper = i;
+							break;
+						}
+					}
+				}
+#endif
+			}
+			break;
+#ifdef JSMN_STRICT
+			/* In strict mode primitives are: numbers and booleans */
+		case '-':
+		case '0':
+		case '1':
+		case '2':
+		case '3':
+		case '4':
+		case '5':
+		case '6':
+		case '7':
+		case '8':
+		case '9':
+		case 't':
+		case 'f':
+		case 'n':
+			/* And they must not be keys of the object */
+			if (tokens != NULL && parser->toksuper != -1) {
+				const jsmntok_t *t = &tokens[parser->toksuper];
+				if (t->type == JSMN_OBJECT ||
+				    (t->type == JSMN_STRING && t->size != 0)) {
+					return JSMN_ERROR_INVAL;
+				}
+			}
+#else
+			/* In non-strict mode every unquoted value is a primitive */
+		default:
+#endif
+			r = jsmn_parse_primitive(parser, js, len, tokens, num_tokens);
+			if (r < 0) {
+				return r;
+			}
+			count++;
+			if (parser->toksuper != -1 && tokens != NULL) {
+				tokens[parser->toksuper].size++;
+			}
+			break;
+
+#ifdef JSMN_STRICT
+			/* Unexpected char in strict mode */
+		default:
+			return JSMN_ERROR_INVAL;
+#endif
+		}
+	}
+
+	if (tokens != NULL) {
+		for (i = parser->toknext - 1; i >= 0; i--) {
+			/* Unmatched opened object or array */
+			if (tokens[i].start != -1 && tokens[i].end == -1) {
+				return JSMN_ERROR_PART;
+			}
+		}
+	}
+
+	return count;
+}
+
+/**
+ * Creates a new parser based over a given buffer with an array of tokens
+ * available.
+ */
+JSMN_API void jsmn_init(jsmn_parser *parser) {
+	parser->pos = 0;
+	parser->toknext = 0;
+	parser->toksuper = -1;
+}