3 files changed, 49 insertions, 32 deletions

diff --git a/gzlib.c b/gzlib.c
index 79a7e97..1c5c7be 100644
--- a/gzlib.c
+++ b/gzlib.c
@@ -104,6 +104,7 @@ local gzFile gz_open(const void *path, int fd, const char *mode) {
         return NULL;
     state->size = 0;            /* no buffers allocated yet */
     state->want = GZBUFSIZE;    /* requested buffer size */
+    state->err = Z_OK;          /* no error yet */
     state->msg = NULL;          /* no error message yet */
 
     /* interpret mode */
diff --git a/gzread.c b/gzread.c
index b9075da..2c70054 100644
--- a/gzread.c
+++ b/gzread.c
@@ -166,8 +166,10 @@ local int gz_decomp(gz_statep state) {
     had = strm->avail_out;
     do {
         /* get more input for inflate() */
-        if (strm->avail_in == 0 && gz_avail(state) == -1)
-            return -1;
+        if (strm->avail_in == 0 && gz_avail(state) == -1) {
+            ret = state->err;
+            break;
+        }
         if (strm->avail_in == 0) {
             gz_error(state, Z_BUF_ERROR, "unexpected end of file");
             break;
@@ -181,22 +183,23 @@ local int gz_decomp(gz_statep state) {
         if (ret == Z_STREAM_ERROR || ret == Z_NEED_DICT) {
             gz_error(state, Z_STREAM_ERROR,
                      "internal error: inflate stream corrupt");
-            return -1;
+            break;
         }
         if (ret == Z_MEM_ERROR) {
             gz_error(state, Z_MEM_ERROR, "out of memory");
-            return -1;
+            break;
         }
         if (ret == Z_DATA_ERROR) {              /* deflate stream invalid */
             if (state->junk == 1) {             /* trailing garbage is ok */
                 strm->avail_in = 0;
                 state->eof = 1;
                 state->how = LOOK;
+                ret = Z_OK;
                 break;
             }
             gz_error(state, Z_DATA_ERROR,
                      strm->msg == NULL ? "compressed data error" : strm->msg);
-            return -1;
+            break;
         }
     } while (strm->avail_out && ret != Z_STREAM_END);
 
@@ -208,10 +211,11 @@ local int gz_decomp(gz_statep state) {
     if (ret == Z_STREAM_END) {
         state->junk = 0;
         state->how = LOOK;
+        return 0;
     }
 
-    /* good decompression */
-    return 0;
+    /* return decompression status */
+    return ret != Z_OK ? -1 : 0;
 }
 
 /* Fetch data and put it in the output buffer.  Assumes state->x.have is 0.
@@ -280,12 +284,15 @@ local int gz_skip(gz_statep state) {
 }
 
 /* Read len bytes into buf from file, or less than len up to the end of the
-   input.  Return the number of bytes read.  If zero is returned, either the
-   end of file was reached, or there was an error.  state->err must be
-   consulted in that case to determine which. */
+   input. Return the number of bytes read. If zero is returned, either the end
+   of file was reached, or there was an error. state->err must be consulted in
+   that case to determine which. If there was an error, but some uncompressed
+   bytes were read before the error, then that count is returned. The error is
+   still recorded, and so is deferred until the next call. */
 local z_size_t gz_read(gz_statep state, voidp buf, z_size_t len) {
     z_size_t got;
     unsigned n;
+    int err;
 
     /* if len is zero, avoid unnecessary operations */
     if (len == 0)
@@ -297,6 +304,7 @@ local z_size_t gz_read(gz_statep state, voidp buf, z_size_t len) {
 
     /* get len bytes to buf, or less than len if at the end */
     got = 0;
+    err = 0;
     do {
         /* set n to the maximum amount of len that fits in an unsigned int */
         n = (unsigned)-1;
@@ -310,37 +318,36 @@ local z_size_t gz_read(gz_statep state, voidp buf, z_size_t len) {
             memcpy(buf, state->x.next, n);
             state->x.next += n;
             state->x.have -= n;
+            if (state->err != Z_OK)
+                /* caught deferred error from gz_fetch() */
+                err = -1;
         }
 
         /* output buffer empty -- return if we're at the end of the input */
-        else if (state->eof && state->strm.avail_in == 0) {
-            state->past = 1;        /* tried to read past end */
+        else if (state->eof && state->strm.avail_in == 0)
             break;
-        }
 
         /* need output data -- for small len or new stream load up our output
-           buffer */
+           buffer, so that gzgetc() can be fast */
         else if (state->how == LOOK || n < (state->size << 1)) {
             /* get more output, looking for header if required */
-            if (gz_fetch(state) == -1)
-                return 0;
+            if (gz_fetch(state) == -1 && state->x.have == 0)
+                /* if state->x.have != 0, error will be caught after copy */
+                err = -1;
             continue;       /* no progress yet -- go back to copy above */
             /* the copy above assures that we will leave with space in the
                output buffer, allowing at least one gzungetc() to succeed */
         }
 
         /* large len -- read directly into user buffer */
-        else if (state->how == COPY) {      /* read directly */
-            if (gz_load(state, (unsigned char *)buf, n, &n) == -1)
-                return 0;
-        }
+        else if (state->how == COPY)        /* read directly */
+            err = gz_load(state, (unsigned char *)buf, n, &n);
 
         /* large len -- decompress directly into user buffer */
         else {  /* state->how == GZIP */
             state->strm.avail_out = n;
             state->strm.next_out = (unsigned char *)buf;
-            if (gz_decomp(state) == -1)
-                return 0;
+            err = gz_decomp(state);
             n = state->x.have;
             state->x.have = 0;
         }
@@ -350,7 +357,11 @@ local z_size_t gz_read(gz_statep state, voidp buf, z_size_t len) {
         buf = (char *)buf + n;
         got += n;
         state->x.pos += n;
-    } while (len);
+    } while (len && !err);
+
+    /* note read past eof */
+    if (len && state->eof)
+        state->past = 1;
 
     /* return number of bytes read into user buffer */
     return got;
@@ -537,7 +548,7 @@ char * ZEXPORT gzgets(gzFile file, char *buf, int len) {
     if (left) do {
         /* assure that something is in the output buffer */
         if (state->x.have == 0 && gz_fetch(state) == -1)
-            return NULL;                /* error */
+            break;                      /* error */
         if (state->x.have == 0) {       /* end of file */
             state->past = 1;            /* read past end */
             break;                      /* return what we have */
diff --git a/zlib.h b/zlib.h
index 9ec7bc1..fa8b3d4 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1454,7 +1454,8 @@ ZEXTERN int ZEXPORT gzread(gzFile file, voidp buf, unsigned len);
      gzread returns the number of uncompressed bytes actually read, less than
    len for end of file, or -1 for error.  If len is too large to fit in an int,
    then nothing is read, -1 is returned, and the error state is set to
-   Z_STREAM_ERROR.
+   Z_STREAM_ERROR. If some data was read before an error, then that data is
+   returned until exhausted, after which the next call will signal the error.
 */
 
 ZEXTERN z_size_t ZEXPORT gzfread(voidp buf, z_size_t size, z_size_t nitems,
@@ -1536,8 +1537,9 @@ ZEXTERN char * ZEXPORT gzgets(gzFile file, char *buf, int len);
    left untouched.
 
      gzgets returns buf which is a null-terminated string, or it returns NULL
-   for end-of-file or in case of error.  If there was an error, the contents at
-   buf are indeterminate.
+   for end-of-file or in case of error. If some data was read before an error,
+   then that data is returned until exhausted, after which the next call will
+   return NULL to signal the error.
 */
 
 ZEXTERN int ZEXPORT gzputc(gzFile file, int c);
@@ -1548,11 +1550,14 @@ ZEXTERN int ZEXPORT gzputc(gzFile file, int c);
 
 ZEXTERN int ZEXPORT gzgetc(gzFile file);
 /*
-     Read and decompress one byte from file.  gzgetc returns this byte or -1
-   in case of end of file or error.  This is implemented as a macro for speed.
-   As such, it does not do all of the checking the other functions do.  I.e.
-   it does not check to see if file is NULL, nor whether the structure file
-   points to has been clobbered or not.
+      Read and decompress one byte from file. gzgetc returns this byte or -1 in
+   case of end of file or error. If some data was read before an error, then
+   that data is returned until exhausted, after which the next call will return
+   -1 to signal the error.
+
+      This is implemented as a macro for speed. As such, it does not do all of
+   the checking the other functions do. I.e. it does not check to see if file
+   is NULL, nor whether the structure file points to has been clobbered or not.
 */
 
 ZEXTERN int ZEXPORT gzungetc(int c, gzFile file);