Implement task 1.2 myunzip0

myunzip0.c

+#include <stdio.h> 
+#include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+struct file_record {
+    uint32_t signature;
+    uint16_t version;
+    uint16_t flag;
+    uint16_t compression;
+    uint16_t mod_time;
+    uint16_t mod_date;
+    uint32_t crc32;
+    uint32_t compressed_size;
+    uint32_t uncompressed_size;
+    uint16_t file_name_len;
+    uint16_t extra_len; 
+} 
+/* Don't pad this struct, i.e. guaranteed that sizeof(struct file_record) = 
+ * sum of the sizes of its elements. This makes the code a bit nicer;  
+ * we can just fread() the first sizeof(struct file_record) bytes in the 
+ * file directly into the struct.
+ */
+__attribute__((packed));
+
+typedef struct file_record file_record_t; 
+
+const int UNCOMPRESSED = 0;
+const int DEFLATE = 8; 
+
+void unzip(FILE *fp) { 
+    file_record_t *record = (file_record_t *) malloc(sizeof(file_record_t));
+    if (!record) {
+        fprintf(stderr, "error: memory error\n");
+        exit(1);
+    }
+
+    /* Read metadata */ 
+    fread(record, 1, sizeof(file_record_t), fp); 
+
+    char *fname = (char *) malloc(record->file_name_len); 
+    fread(fname, 1, record->file_name_len, fp);
+
+    /* Move pointer to start of file data */
+    fseek(fp, record->extra_len, SEEK_CUR);
+
+    int size;
+    if (record->compression == UNCOMPRESSED) {
+        size = record->uncompressed_size;
+    } else if (record->compression == DEFLATE) {
+        size = record->compressed_size;
+        strcat(fname, ".deflate"); 
+    } else {
+        fprintf(stderr, "error: invalid compression\n");
+        exit(1); 
+    }
+    
+    FILE *out = fopen(fname, "wb");
+
+    /* TODO is there a better way to do this? 
+     * worried about storing a huge buffer for large files... */
+    char *buf = (char *) malloc(size * sizeof(char));
+    fread(buf, 1, size, fp);
+    fwrite(buf, 1, size, out); 
+    fclose(out);
+    
+    free(record); 
+}
+
+int main(int argc, char *argv[]) {
+    FILE *fp;
+
+    if (argc != 2) {
+        fprintf(stderr, "usage: myunzip0 [filename]\n");
+        return 1;
+    }   
+    
+    fp = fopen(argv[1], "rb");
+
+    if (!fp) {
+        fprintf(stderr, "error: no such file\n");
+        return 1;
+    }    
+    
+    unzip(fp);
+    fclose(fp);
+
+    return 0; 
+}