Scratch JSON parser. No unit test yet, that gets built next.

1 files changed, 131 insertions, 0 deletions

diff --git a/json.c b/json.c
new file mode 100644
index 00000000..97c5db5f
--- /dev/null
+++ b/json.c
@@ -0,0 +1,131 @@
+/* json.c - parse JSON into fixed-extent data structures */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "json.h"
+
+int parse_json(char *cp, struct json_attr_t *attrs)
+{
+    enum {init, await_attr, in_attr, await_value, 
+	  in_val_string, in_val_token, post_val} state = 0;
+    char attrbuf[JSON_ATTR_MAX+1], *pattr = NULL;
+    char valbuf[JSON_VAL_MAX+1], *pval = NULL;
+    struct json_attr_t *cursor;
+
+    /* stuff fields with defaults in case they're omitted in the JSON input */
+    for (cursor = attrs; cursor->attribute != NULL; cursor++)
+	switch(cursor->type)
+	{
+	case integer:
+	    *(cursor->addr.integer) = cursor->dflt.integer;
+	    break;
+	case real:
+	    *(cursor->addr.real) = cursor->dflt.real;
+	    break;
+	case string:
+	    *(cursor->addr.string)[0] = '\0';
+	    break;
+	case boolean:
+	    *(cursor->addr.boolean) = cursor->dflt.boolean;
+	    break;
+	}
+
+    /* parse input JSON */
+    for (; *cp; cp++) {
+	switch (state)
+	{
+	case init:
+	    if (isspace(*cp))
+		continue;
+	    else if (*cp == '{')
+		state = await_attr;
+	    else
+		return -1;	/* non-whitespace when expecting object start */
+	    break;
+	case await_attr:
+	    if (isspace(*cp))
+		continue;
+	    else if (*cp == '"') {
+		state = in_attr;
+		pattr = attrbuf;
+	    } else if (*cp == '}')
+		break;
+	    else
+		return -2;	/* non-whitespace while expecting attribute */
+	    break;
+	case in_attr:
+	    if (*cp == '"') {
+		*pattr++ = '\0';
+		for (cursor = attrs; cursor->attribute != NULL; cursor++)
+		    if (strcmp(cursor->attribute, attrbuf)==0)
+			break;
+		if (cursor->attribute == NULL)
+		    return -3;	/* unknown attribute name */
+		state = await_value;
+		pval = valbuf;
+	    } else if (pattr >= attrbuf + JSON_ATTR_MAX - 1)
+		return -4;	/* attribute name too long */
+	    else
+		*pattr = *cp;
+	    break;
+	case await_value:
+	    if (isspace(*cp) || *cp == ':')
+		continue;
+	    else if (*cp == '"') {
+		state = in_val_string;
+		pval = valbuf;
+	    } else {
+		state = in_val_token;
+		pval = valbuf;
+	    }
+	    break;
+	case in_val_string:
+	    if (*cp == '"') {
+		state = post_val;
+	    } else if (pval > valbuf + JSON_VAL_MAX - 1)
+		return -5;	/* value too long */
+	    else
+		*pval++ = *cp;
+	    break;
+	case in_val_token:
+	    if (isspace(*cp) || *cp == ',' || *cp == '}') {
+		state = post_val;
+		if (*cp == '}')
+		    --cp;
+	    } else if (pval > valbuf + JSON_VAL_MAX - 1)
+		return -5;	/* value too long */
+	    else
+		*pval++ = *cp;
+	    break;
+	case post_val:
+	    switch(cursor->type)
+	    {
+	    case integer:
+		*(cursor->addr.integer) = atoi(valbuf);
+		break;
+	    case real:
+		*(cursor->addr.real) = atof(valbuf);
+		break;
+	    case string:
+		(void)strcpy(*(cursor->addr.string), valbuf);
+		break;
+	    case boolean:
+		*(cursor->addr.boolean) = (bool)!strcmp(valbuf, "true");
+		break;
+	    }
+	    if (isspace(*cp))
+		continue;
+	    else if (*cp == ',')
+		state = await_attr;
+	    else if (*cp == '}')
+		return 0;
+	    else
+		return -6;	/* garbage while expecting comma or } */
+	    break;
+	}
+    }
+
+    return 0;
+}