test_json_parser_incremental.c

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/*-------------------------------------------------------------------------
 *
 * test_json_parser_incremental.c
 *    Test program for incremental JSON parser
 *
 * Copyright (c) 2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/test/modules/test_json_parser/test_json_parser_incremental.c
 *
 * This program tests incremental parsing of json. The input is fed into
 * the parser in very small chunks. In practice you would normally use
 * much larger chunks, but doing this makes it more likely that the
 * full range of increment handling, especially in the lexer, is exercised.
 * If the "-c SIZE" option is provided, that chunk size is used instead
 * of the default of 60.
 *
 * If the -s flag is given, the program does semantic processing. This should
 * just mirror back the json, albeit with white space changes.
 *
 * The argument specifies the file containing the JSON input.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
 
#include "common/jsonapi.h"
#include "common/logging.h"
#include "lib/stringinfo.h"
#include "mb/pg_wchar.h"
#include "pg_getopt.h"
 
#define BUFSIZE 6000
#define DEFAULT_CHUNK_SIZE 60
 
typedef struct DoState
{
    JsonLexContext *lex;
    bool        elem_is_first;
    StringInfo  buf;
} DoState;
 
static void usage(const char *progname);
static void escape_json(StringInfo buf, const char *str);
 
/* semantic action functions for parser */
static JsonParseErrorType do_object_start(void *state);
static JsonParseErrorType do_object_end(void *state);
static JsonParseErrorType do_object_field_start(void *state, char *fname, bool isnull);
static JsonParseErrorType do_object_field_end(void *state, char *fname, bool isnull);
static JsonParseErrorType do_array_start(void *state);
static JsonParseErrorType do_array_end(void *state);
static JsonParseErrorType do_array_element_start(void *state, bool isnull);
static JsonParseErrorType do_array_element_end(void *state, bool isnull);
static JsonParseErrorType do_scalar(void *state, char *token, JsonTokenType tokentype);
 
static JsonSemAction sem = {
    .object_start = do_object_start,
    .object_end = do_object_end,
    .object_field_start = do_object_field_start,
    .object_field_end = do_object_field_end,
    .array_start = do_array_start,
    .array_end = do_array_end,
    .array_element_start = do_array_element_start,
    .array_element_end = do_array_element_end,
    .scalar = do_scalar
};
 
int
main(int argc, char **argv)
{
    char        buff[BUFSIZE];
    FILE       *json_file;
    JsonParseErrorType result;
    JsonLexContext lex;
    StringInfoData json;
    int         n_read;
    size_t      chunk_size = DEFAULT_CHUNK_SIZE;
    struct stat statbuf;
    off_t       bytes_left;
    const JsonSemAction *testsem = &nullSemAction;
    char       *testfile;
    int         c;
    bool        need_strings = false;
 
    pg_logging_init(argv[0]);
 
    while ((c = getopt(argc, argv, "c:s")) != -1)
    {
        switch (c)
        {
            case 'c':           /* chunksize */
                chunk_size = strtou64(optarg, NULL, 10);
                if (chunk_size > BUFSIZE)
                    pg_fatal("chunk size cannot exceed %d", BUFSIZE);
                break;
            case 's':           /* do semantic processing */
                testsem = &sem;
                sem.semstate = palloc(sizeof(struct DoState));
                ((struct DoState *) sem.semstate)->lex = &lex;
                ((struct DoState *) sem.semstate)->buf = makeStringInfo();
                need_strings = true;
                break;
        }
    }
 
    if (optind < argc)
    {
        testfile = pg_strdup(argv[optind]);
        optind++;
    }
    else
    {
        usage(argv[0]);
        exit(1);
    }
 
    makeJsonLexContextIncremental(&lex, PG_UTF8, need_strings);
    initStringInfo(&json);
 
    if ((json_file = fopen(testfile, PG_BINARY_R)) == NULL)
        pg_fatal("error opening input: %m");
 
    if (fstat(fileno(json_file), &statbuf) != 0)
        pg_fatal("error statting input: %m");
 
    bytes_left = statbuf.st_size;
 
    for (;;)
    {
        /* We will break when there's nothing left to read */
 
        if (bytes_left < chunk_size)
            chunk_size = bytes_left;
 
        n_read = fread(buff, 1, chunk_size, json_file);
        if (n_read < chunk_size)
            pg_fatal("error reading input file: %d", ferror(json_file));
 
        appendBinaryStringInfo(&json, buff, n_read);
 
        /*
         * Append some trailing junk to the buffer passed to the parser. This
         * helps us ensure that the parser does the right thing even if the
         * chunk isn't terminated with a '\0'.
         */
        appendStringInfoString(&json, "1+23 trailing junk");
        bytes_left -= n_read;
        if (bytes_left > 0)
        {
            result = pg_parse_json_incremental(&lex, testsem,
                                               json.data, n_read,
                                               false);
            if (result != JSON_INCOMPLETE)
            {
                fprintf(stderr, "%s\n", json_errdetail(result, &lex));
                exit(1);
            }
            resetStringInfo(&json);
        }
        else
        {
            result = pg_parse_json_incremental(&lex, testsem,
                                               json.data, n_read,
                                               true);
            if (result != JSON_SUCCESS)
            {
                fprintf(stderr, "%s\n", json_errdetail(result, &lex));
                exit(1);
            }
            if (!need_strings)
                printf("SUCCESS!\n");
            break;
        }
    }
    fclose(json_file);
    exit(0);
}
 
/*
 * The semantic routines here essentially just output the same json, except
 * for white space. We could pretty print it but there's no need for our
 * purposes. The result should be able to be fed to any JSON processor
 * such as jq for validation.
 */
 
static JsonParseErrorType
do_object_start(void *state)
{
    DoState    *_state = (DoState *) state;
 
    printf("{\n");
    _state->elem_is_first = true;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_object_end(void *state)
{
    DoState    *_state = (DoState *) state;
 
    printf("\n}\n");
    _state->elem_is_first = false;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_object_field_start(void *state, char *fname, bool isnull)
{
    DoState    *_state = (DoState *) state;
 
    if (!_state->elem_is_first)
        printf(",\n");
    resetStringInfo(_state->buf);
    escape_json(_state->buf, fname);
    printf("%s: ", _state->buf->data);
    _state->elem_is_first = false;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_object_field_end(void *state, char *fname, bool isnull)
{
    /* nothing to do really */
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_array_start(void *state)
{
    DoState    *_state = (DoState *) state;
 
    printf("[\n");
    _state->elem_is_first = true;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_array_end(void *state)
{
    DoState    *_state = (DoState *) state;
 
    printf("\n]\n");
    _state->elem_is_first = false;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_array_element_start(void *state, bool isnull)
{
    DoState    *_state = (DoState *) state;
 
    if (!_state->elem_is_first)
        printf(",\n");
    _state->elem_is_first = false;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_array_element_end(void *state, bool isnull)
{
    /* nothing to do */
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
do_scalar(void *state, char *token, JsonTokenType tokentype)
{
    DoState    *_state = (DoState *) state;
 
    if (tokentype == JSON_TOKEN_STRING)
    {
        resetStringInfo(_state->buf);
        escape_json(_state->buf, token);
        printf("%s", _state->buf->data);
    }
    else
        printf("%s", token);
 
    return JSON_SUCCESS;
}
 
 
/*  copied from backend code */
static void
escape_json(StringInfo buf, const char *str)
{
    const char *p;
 
    appendStringInfoCharMacro(buf, '"');
    for (p = str; *p; p++)
    {
        switch (*p)
        {
            case '\b':
                appendStringInfoString(buf, "\\b");
                break;
            case '\f':
                appendStringInfoString(buf, "\\f");
                break;
            case '\n':
                appendStringInfoString(buf, "\\n");
                break;
            case '\r':
                appendStringInfoString(buf, "\\r");
                break;
            case '\t':
                appendStringInfoString(buf, "\\t");
                break;
            case '"':
                appendStringInfoString(buf, "\\\"");
                break;
            case '\\':
                appendStringInfoString(buf, "\\\\");
                break;
            default:
                if ((unsigned char) *p < ' ')
                    appendStringInfo(buf, "\\u%04x", (int) *p);
                else
                    appendStringInfoCharMacro(buf, *p);
                break;
        }
    }
    appendStringInfoCharMacro(buf, '"');
}
 
static void
usage(const char *progname)
{
    fprintf(stderr, "Usage: %s [OPTION ...] testfile\n", progname);
    fprintf(stderr, "Options:\n");
    fprintf(stderr, "  -c chunksize      size of piece fed to parser (default 64)n");
    fprintf(stderr, "  -s                do semantic processing\n");
 
}