file_utils.c

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/* Related header */
#include "file_utils.h"
 
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
 
/* System headers */
#include <errno.h>
#include <fcntl.h>  /* open() */
#include <stdio.h>  /* rename() */
#include <string.h> /* strerror() */
#include <unistd.h> /* fdatasync() */
 
/* Own headers */
#include "xpon_trace.h"
 
#define LINE_LEN 256
 
static bool rename_file(const char* const oldpath, const char* const newpath) {
    int fd = 0;
    if(rename(oldpath, newpath) == -1) {
        SAH_TRACEZ_ERROR(ME, "Failed to rename %s to %s: %s", oldpath, newpath,
                         strerror(errno));
        return false;
    }
    if((fd = open(newpath, O_RDWR)) == -1) {
        SAH_TRACEZ_ERROR(ME, "Failed to open %s: %s", newpath, strerror(errno));
        return false;
    }
    if(fdatasync(fd) == -1) {
        SAH_TRACEZ_ERROR(ME, "Failed to sync %s: %s", newpath, strerror(errno));
    }
    close(fd);
    return true;
}
 
static bool check_file_has_value(const char* const path, const char* const value,
                                 bool* has_value) {
 
    char line[LINE_LEN] = { 0 };
    if(!read_first_line_from_file(path, line, LINE_LEN)) {
        return false;
    }
    SAH_TRACEZ_DEBUG2(ME, "line='%s' (%zd) value='%s' (%zd)", line, strlen(line),
                      value, strlen(value));
 
    const size_t line_len = strlen(line);
    const size_t value_len = strlen(value);
    if(line_len != value_len) {
        *has_value = false;
        return true;
    }
 
    if(strncmp(line, value, strlen(value)) == 0) {
        SAH_TRACEZ_DEBUG2(ME, "file already has %s", value);
        *has_value = true;
    } else {
        SAH_TRACEZ_DEBUG2(ME, "line='%s' != value='%s'", line, value);
    }
    return true;
}
 
bool write_file(const char* const path, const char* const value) {
 
    SAH_TRACEZ_DEBUG2(ME, "path='%s' value='%s'", path, value);
 
    const size_t value_len = strlen(value);
    if(value_len >= LINE_LEN) {
        SAH_TRACEZ_ERROR(ME, "strlen(value) = %zd >= %d", value_len, LINE_LEN);
        return false;
    }
    if(access(path, F_OK) == 0) {
        SAH_TRACEZ_DEBUG2(ME, "%s already exists", path);
        bool has_value = false;
        if((check_file_has_value(path, value, &has_value) == true) && has_value) {
            return true;
        }
    }
 
    char tmpfile[256];
    if(snprintf(tmpfile, 256, "%s.tmp", path) < 0) {
        SAH_TRACEZ_ERROR(ME, "%s: failed to create path with .tmp", path);
        return false;
    }
 
    FILE* f = fopen(tmpfile, "w");
    if(!f) {
        SAH_TRACEZ_ERROR(ME, "Failed to open %s: %s", tmpfile, strerror(errno));
        return false;
    }
 
    bool rv = true;
    if(fputs(value, f) == EOF) {
        SAH_TRACEZ_ERROR(ME, "Failed to write to %s", tmpfile);
        rv = false;
    }
 
    if(fclose(f) == EOF) {
        SAH_TRACEZ_ERROR(ME, "Failed to close %s: %s", tmpfile, strerror(errno));
    }
    if(!rv) {
        return false;
    }
    return rename_file(tmpfile, path);
}
 
bool read_first_line_from_file(const char* const path, char* line, size_t len) {
    FILE* f = fopen(path, "r");
    if(!f) {
        SAH_TRACEZ_ERROR(ME, "Failed to open %s: %s", path, strerror(errno));
        return false;
    }
    bool rv = true;
    if(!fgets(line, (int) len, f)) {
        SAH_TRACEZ_ERROR(ME, "Failed to read from %s", path);
        rv = false;
    }
    if(fclose(f) == EOF) {
        SAH_TRACEZ_ERROR(ME, "Failed to close %s: %s", path, strerror(errno));
    }
    return rv;
}