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read_form_fields.c
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read_form_fields.c
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// A program for extracting the form fields from a XFA/AcroForm PDF form.
// Maël Valais, 2018
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h> // for exit()
#include <string.h>
#include <poppler.h>
#define DEBUG 0
// A small helper function for handling arguments of the form '--arg=value'.
char *dashdashequal(const char *expected, char *argv)
{
// Var. name: Example:
// argv --beginning=ending
// argv_beginning --beginning
// argv_ending ending
char *argv_ending = strchr(argv, '=') + 1;
if (argv_ending == NULL)
{
// if argv_ending is NULL, it means that strchr did not find '=',
// then the parameter is wrong
fprintf(stderr, "error: '%s' should be of the form '%s=ARG'\n", argv, argv);
exit(1);
}
char argv_beginning[100];
stpncpy(argv_beginning, argv, strlen(expected));
if (0 != strcmp(argv_beginning, expected))
{
return NULL;
}
return argv_ending;
}
bool is_in(char *str, char **str_array, int N)
{
for (int i = 0; i < N; i++)
{
if (strcmp(str, str_array[i]) == 0)
return true;
}
return false;
}
// If you want to mutate str in-place, you can put str and str_stripped with
// the same pointer. I wrote this function because I needed a way to remove
// the \uFEFF (Byte Order Mark) which was pollutin the field names.
void strip(char *str, char *str_stripped, char *token)
{
int i = 0, i_stripped = 0;
// printf("'%s'\n", str);
while (i < strlen(str))
{
// printf("'%c'\n", str[i]);
int j = 0;
while (i + j < strlen(str) && j < strlen(token) && str[i + j] == token[j])
j++;
if (j == strlen(token))
{
i += strlen(token);
}
str_stripped[i_stripped] = str[i];
i++;
i_stripped++;
}
str_stripped[i_stripped] = '\0'; // terminate the string properly
}
int main(int argc, char **argv)
{
char help[] =
"Get the form field contents from a PDF. It uses poppler. The output looks\n"
"like PDFtk's dump_data_fields_utf8. Supports AcroForm & XfaForm PDF forms.\n"
"\n"
"Usage:\n"
" read_form_fields (<file> | -)\n"
" read_form_fields --help\n"
"\n"
"Options:\n"
" <file> is the name of the file\n"
" -h --help Show this screen.\n"
"\n"
"Details on output:\n"
" The output resembles PDFtk's. Each line consists of one of:\n"
" - A separator '---' that separate two fields\n"
" - FieldType: Choice | Button | Text | Signature | Unknown \n"
" - FieldName: <text> (only with Text, Choice, Button)\n"
" - FieldMaxLength: <integer> (only with Text)\n"
" - FieldStateOption: <text> (for Text & Choice) | Off | Yes (Button)\n"
"\n"
"Notes:\n"
" 1) The order of appearance is different from PDFtk's. This program will\n"
" show the fields by order of appearance in each page.\n"
" 2) Some field labels aren't supported: FieldValueDefault, FieldNameAlt,\n"
" FieldFlags, FieldJustification. They aren't in the Poppler Glib API.\n"
" 3) Sometimes the unicode point 'U+FEFF which corresponds to the BOM was\n"
" showing in the field values and names. So I strip 'U+FEFF' from\n"
" values/names before printing.\n";
char f_name[256] = "";
GFile *f_fd;
char *arg;
for (int i = 1; i < argc; i++)
{
if (0 == strcmp("--help", argv[i]) || 0 == strcmp("-h", argv[i]))
{
fprintf(stdout, "%s", help);
exit(0);
}
else if (0 == strcmp("-", argv[i]))
{
strcpy(f_name, "/dev/stdin");
}
else
{
strcpy(f_name, argv[i]);
}
}
if (strlen(f_name) == 0)
{
fprintf(stderr, "usage: you must give a file name (or - for stdin)\n");
return 124;
}
GError *error = NULL;
PopplerDocument *document;
document = poppler_document_new_from_gfile(g_file_new_for_commandline_arg(f_name), NULL, NULL, &error);
if (document == NULL)
{
printf("error: poppler could not open '%s': %s\n", f_name, error->message);
return 2;
}
int count = 0;
PopplerPage *page = NULL;
for (int id_page = 0; id_page < poppler_document_get_n_pages(document); id_page++)
{
GList *list = poppler_page_get_form_field_mapping(poppler_document_get_page(document, id_page));
for (int i = 0; i < g_list_length(list); i++)
{
if (i > 0)
printf("---\n");
PopplerFormFieldMapping *f = g_list_nth_data(list, i);
// printf("field found, id: %d, name: %s\n",poppler_form_field_get_id(f->field),poppler_form_field_get_name(f->field));
PopplerFormFieldType type = poppler_form_field_get_field_type(f->field);
printf("FieldType: ");
switch (type)
{
case POPPLER_FORM_FIELD_UNKNOWN:
printf("Unkonwn");
break;
case POPPLER_FORM_FIELD_BUTTON:
printf("Button");
break;
case POPPLER_FORM_FIELD_TEXT:
printf("Text");
break;
case POPPLER_FORM_FIELD_CHOICE:
printf("Choice");
break;
case POPPLER_FORM_FIELD_SIGNATURE:
printf("Signature");
break;
}
printf("\n");
if (strlen(poppler_form_field_get_name(f->field)) > 0)
{
char *txt = poppler_form_field_get_name(f->field);
if (txt != NULL)
{
strip(txt, txt, "\uFEFF");
printf("FieldName: %s\n", txt);
}
else
{
printf("FieldName:\n");
}
}
if (type == POPPLER_FORM_FIELD_TEXT)
{
gchar *txt = poppler_form_field_text_get_text(f->field);
if (txt != NULL)
{
strip(txt, txt, "\uFEFF");
printf("FieldValue: %s\n", txt);
}
else
{
printf("FieldValue:\n");
}
printf("FieldMaxLength: %d\n", poppler_form_field_text_get_max_len(f->field));
}
if (type == POPPLER_FORM_FIELD_CHOICE)
{
for (int i = 0; i < poppler_form_field_choice_get_n_items(f->field); i++)
{
char *txt = poppler_form_field_choice_get_item(f->field, i);
if (txt)
{
strip(txt, txt, "\uFEFF");
printf("FieldStateOption: %s\n", txt);
}
}
}
if (type == POPPLER_FORM_FIELD_BUTTON)
{
printf("FieldValue: %s\n", poppler_form_field_button_get_state(f->field) ? "Yes" : "Off");
printf("FieldStateOption: Off\nFieldStateOption: Yes\n");
}
count++;
}
}
if (DEBUG)
printf("number of fields: %d\n", count);
return 0;
}