Compress short files with a pre-defined zlib dictionary from command line

zlibdict.c

#include <stdio.h>
#include <string.h>
#include <zlib.h>

#include <inttypes.h>
#include <assert.h>

uint8_t dict[4096];
size_t dict_size;

uint8_t input[65536];
size_t input_size;

uint8_t output[65536];


int main(int argc, char* argv[])
{
    assert(!strcmp(zlibVersion(),ZLIB_VERSION));
    if (argc < 3 || !strcmp(argv[1], "--help")) {
        printf("Compress short files with a pre-defined zlib dictionary from command line.\n");
        printf("Try using some input file as a basis for the dictionary.\n");
        printf("Usage:\n");
        printf("  zlibdict compress   dictfile < input > output\n");
        printf("  zlibdict decompress dictfile < input > output\n");
        return 1;
    }
    
    {
        FILE* d;
        
        d = fopen(argv[2], "r");
        if (!d) { perror("fopen"); return 1; }
        dict_size = fread(dict, 1, sizeof dict, d);
        if (!dict_size) {
            fprintf(stderr, "Warning: empty dictionary\n");
        }
        fclose(d);
    }
    
    {
        input_size = fread(input, 1, sizeof input, stdin);
        if (input_size == sizeof input) {
            fprintf(stderr, "Warning: input size may be too large\n");
        }
    }
    
    z_stream s;
    memset(&s, 0, sizeof s);
    
    s.zalloc = Z_NULL;
    s.zfree = Z_NULL;
    s.opaque = Z_NULL;
    
    s.next_in = input;
    s.avail_in = input_size;
    
    s.next_out = output;
    s.avail_out = sizeof output;
    
    if (!strcmp(argv[1], "compress")) {
        if (Z_OK != deflateInit2(&s, 8, Z_DEFLATED, -12, 8, Z_DEFAULT_STRATEGY)) {
            fprintf(stderr, "deflateInit2 error\n");
            fprintf(stderr, "%s\n", s.msg);
            return 2;
        }
        
        if (Z_OK != deflateSetDictionary(&s, dict, dict_size)) {
            fprintf(stderr, "deflateSetDictionary error\n");
            return 3;
        }
        
        if (Z_STREAM_END != deflate(&s, Z_FINISH)) {
            fprintf(stderr, "deflate error or too large output\n");
            return 4;
        };
        
    } else
    if (!strcmp(argv[1], "decompress")) {
        
        if (Z_OK != inflateInit2(&s, -12)) {
            fprintf(stderr, "inflateInit2 error\n");
            fprintf(stderr, "%s\n", s.msg);
            return 2;
        }
        
        if (Z_OK != inflateSetDictionary(&s, dict, dict_size)) {
            fprintf(stderr, "inflateSetDictionary error\n");
            return 3;
        }
        
        if (Z_STREAM_END != inflate(&s, Z_FINISH)) {
            fprintf(stderr, "inflate error or too large output\n");
            return 4;
        };
        
        
    } else {
        fprintf(stderr, "zlibdict: Unknown command %s\n", argv[1]);
        return 1;
    }
    
    fwrite(output, 1, s.total_out, stdout);
    
    return 0;
}