add ability to read gzipped zdab files

1 files changed, 21 insertions, 12 deletions

diff --git a/src/zebra.c b/src/zebra.c
index 690294b..1289318 100644
--- a/src/zebra.c
+++ b/src/zebra.c
@@ -21,16 +21,25 @@
 #include <string.h> /* for memmove() */
 #include <stdint.h> /* for uint8_t, etc. */
 #include <errno.h> /* for strerror(), etc. */
+#include <zlib.h>
 
 char zebra_err[256];
 
+/* Returns a pointer to a new zebra file object.
+ *
+ * Returns the pointer to the zebraFile object on success, or NULL on error. */
 zebraFile *zebra_open(const char *filename)
 {
-    /* Returns a pointer to a new zebra file object.
+    /* We use gzopen() here even though the file may not be gzipped. According
+     * to the docs:
+     *
+     *      gzopen can be used to read a file which is not in gzip format; in
+     *      this case gzread will directly read from the file without
+     *      decompression.  When reading, this will be detected automatically
+     *      by looking for the magic two-byte gzip header.
      *
-     * Returns the pointer to the zebraFile object on success, or NULL on
-     * error. */
-    FILE *f = fopen(filename, "r");
+     * See https://zlib.net/manual.html. */
+    gzFile f = gzopen(filename, "r");
 
     if (!f) {
         sprintf(zebra_err, "failed to open '%s': %s", filename, strerror(errno));
@@ -41,7 +50,7 @@ zebraFile *zebra_open(const char *filename)
 
     if (!z) {
         sprintf(zebra_err, "failed to allocate space for zebraFile struct: %s", strerror(errno));
-        fclose(f);
+        gzclose(f);
         return NULL;
     }
 
@@ -64,12 +73,12 @@ static int read_next_physical_record(zebraFile *z)
     size_t nbytes;
     uint32_t s0, s1, s2, s3, nwphr, nfast;
 
-    nbytes = fread(buf,4,8,z->f);
+    nbytes = gzread(z->f,buf,4*8);
 
     if (nbytes == 0) return 1;
 
-    if (nbytes != 8) {
-        sprintf(zebra_err, "expected %i words but only read %zu", 8, nbytes);
+    if (nbytes != 8*4) {
+        sprintf(zebra_err, "expected %i bytes but only read %zu", 8*4, nbytes);
         return -1;
     }
 
@@ -109,12 +118,12 @@ static int read_next_physical_record(zebraFile *z)
 
     z->buf = realloc(z->buf, z->buf_size+words*4);
 
-    nbytes = fread(z->buf+z->buf_size, 4, words, z->f);
+    nbytes = gzread(z->f, z->buf+z->buf_size, 4*words);
 
     z->buf_size += words*4;
 
-    if (nbytes != words) {
-        sprintf(zebra_err, "expected %i words but only read %zu", words, nbytes);
+    if (nbytes != words*4) {
+        sprintf(zebra_err, "expected %i bytes but only read %zu", words*4, nbytes);
         return -1;
     }
 
@@ -383,7 +392,7 @@ int zebra_get_bank(zebraFile *z, zebraBank *b, uint32_t link)
 
 void zebra_close(zebraFile *z)
 {
-    fclose(z->f);
+    gzclose(z->f);
     if (z->tab) free(z->tab);
     if (z->buf) free(z->buf);
     free(z);