Fix gzeof() to behave just like feof() when read is not past end of file.

Before, gzeof() would return true (accurately) when the last read request
went just up to the end of the uncompressed data.  In the analogous case,
feof() would return false, only returning true when a read request goes
past the end of the file.  This patch corrects gzeof() to behave in the
same way as feof(), as noted in the zlib.h documentation.

gzguts.h

@@ -155,9 +155,10 @@ typedef struct {
     unsigned char *out;     /* output buffer (double-sized when reading) */
     int direct;             /* 0 if processing gzip, 1 if transparent */
         /* just for reading */
-    int eof;                /* true if end of input file reached */
-    z_off64_t start;        /* where the gzip data started, for rewinding */
     int how;                /* 0: get header, 1: copy, 2: decompress */
+    z_off64_t start;        /* where the gzip data started, for rewinding */
+    int eof;                /* true if end of input file reached */
+    int past;               /* true if read requested past end */
         /* just for writing */
     int level;              /* compression level */
     int strategy;           /* compression strategy */

gzlib.c

@@ -78,6 +78,7 @@ local void gz_reset(state)
     state->x.have = 0;              /* no output data available */
     if (state->mode == GZ_READ) {   /* for reading ... */
         state->eof = 0;             /* not at end of file */
+        state->past = 0;            /* have not read past end yet */
         state->how = LOOK;          /* look for gzip header */
     }
     state->seek = 0;                /* no seek request pending */
@@ -331,6 +332,7 @@ z_off64_t ZEXPORT gzseek64(file, offset, whence)
             return -1;
         state->x.have = 0;
         state->eof = 0;
+        state->past = 0;
         state->seek = 0;
         gz_error(state, Z_OK, NULL);
         state->strm.avail_in = 0;
@@ -453,8 +455,7 @@ int ZEXPORT gzeof(file)
         return 0;
 
     /* return end-of-file state */
-    return state->mode == GZ_READ ?
-        (state->eof && state->strm.avail_in == 0 && state->x.have == 0) : 0;
+    return state->mode == GZ_READ ? state->past : 0;
 }
 
 /* -- see zlib.h -- */
@@ -491,8 +492,10 @@ void ZEXPORT gzclearerr(file)
         return;
 
     /* clear error and end-of-file */
-    if (state->mode == GZ_READ)
+    if (state->mode == GZ_READ) {
         state->eof = 0;
+        state->past = 0;
+    }
     gz_error(state, Z_OK, NULL);
 }
 

gzread.c

@@ -329,8 +329,10 @@ int ZEXPORT gzread(file, buf, len)
         }
 
         /* output buffer empty -- return if we're at the end of the input */
-        else if (state->eof && strm->avail_in == 0)
+        else if (state->eof && strm->avail_in == 0) {
+            state->past = 1;        /* tried to read past end */
             break;
+        }
 
         /* need output data -- for small len or new stream load up our output
            buffer */
@@ -437,6 +439,7 @@ int ZEXPORT gzungetc(c, file)
         state->x.next = state->out + (state->size << 1) - 1;
         state->x.next[0] = c;
         state->x.pos--;
+        state->past = 0;
         return c;
     }
 
@@ -458,6 +461,7 @@ int ZEXPORT gzungetc(c, file)
     state->x.next--;
     state->x.next[0] = c;
     state->x.pos--;
+    state->past = 0;
     return c;
 }
 
@@ -499,9 +503,8 @@ char * ZEXPORT gzgets(file, buf, len)
         if (state->x.have == 0 && gz_fetch(state) == -1)
             return NULL;                /* error */
         if (state->x.have == 0) {       /* end of file */
-            if (buf == str)             /* got bupkus */
-                return NULL;
-            break;                      /* got something -- return it */
+            state->past = 1;            /* read past end */
+            break;                      /* return what we have */
         }
 
         /* look for end-of-line in current output buffer */
@@ -519,7 +522,9 @@ char * ZEXPORT gzgets(file, buf, len)
         buf += n;
     } while (left && eol == NULL);
 
-    /* found end-of-line or out of space -- terminate string and return it */
+    /* return terminated string, or if nothing, end of file */
+    if (buf == str)
+        return NULL;
     buf[0] = 0;
     return str;
 }