Move the ZLIB_STANDALONE main() into its own file.

Now, instead of getting the zlib test/helper program by manually
compiling a source file with unusual options, it gets built as
standard by the ordinary Makefile.

testzlib.c

@@ -0,0 +1,114 @@
+/*
+ * Main program to compile sshzlib.c into a zlib decoding tool.
+ *
+ * This is potentially a handy tool in its own right for picking apart
+ * Zip files or PDFs or PNGs, because it accepts the bare Deflate
+ * format and the zlib wrapper format, unlike 'zcat' which accepts
+ * only the gzip wrapper format.
+ *
+ * It's also useful as a means for a fuzzer to get reasonably direct
+ * access to PuTTY's zlib decompressor.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#include "defs.h"
+#include "ssh.h"
+
+void modalfatalbox(const char *p, ...)
+{
+    va_list ap;
+    fprintf(stderr, "FATAL ERROR: ");
+    va_start(ap, p);
+    vfprintf(stderr, p, ap);
+    va_end(ap);
+    fputc('\n', stderr);
+    exit(1);
+}
+
+int main(int argc, char **argv)
+{
+    unsigned char buf[16], *outbuf;
+    int ret, outlen;
+    ssh_decompressor *handle;
+    int noheader = false, opts = true;
+    char *filename = NULL;
+    FILE *fp;
+
+    while (--argc) {
+        char *p = *++argv;
+
+        if (p[0] == '-' && opts) {
+            if (!strcmp(p, "-d")) {
+                noheader = true;
+            } else if (!strcmp(p, "--")) {
+                opts = false;          /* next thing is filename */
+            } else if (!strcmp(p, "--help")) {
+                printf("usage: testzlib          decode zlib (RFC1950) data"
+                       " from standard input\n");
+                printf("       testzlib -d       decode Deflate (RFC1951) data"
+                       " from standard input\n");
+                printf("       testzlib --help   display this text\n");
+                return 0;
+            } else {
+                fprintf(stderr, "unknown command line option '%s'\n", p);
+                return 1;
+            }
+        } else if (!filename) {
+            filename = p;
+        } else {
+            fprintf(stderr, "can only handle one filename\n");
+            return 1;
+        }
+    }
+
+    handle = ssh_decompressor_new(&ssh_zlib);
+
+    if (noheader) {
+        /*
+         * Provide missing zlib header if -d was specified.
+         */
+        static const unsigned char ersatz_zlib_header[] = { 0x78, 0x9C };
+        ssh_decompressor_decompress(
+            handle, ersatz_zlib_header, sizeof(ersatz_zlib_header),
+            &outbuf, &outlen);
+        assert(outlen == 0);
+    }
+
+    if (filename)
+        fp = fopen(filename, "rb");
+    else
+        fp = stdin;
+
+    if (!fp) {
+        assert(filename);
+        fprintf(stderr, "unable to open '%s'\n", filename);
+        return 1;
+    }
+
+    while (1) {
+	ret = fread(buf, 1, sizeof(buf), fp);
+	if (ret <= 0)
+	    break;
+	ssh_decompressor_decompress(handle, buf, ret, &outbuf, &outlen);
+        if (outbuf) {
+            if (outlen)
+                fwrite(outbuf, 1, outlen, stdout);
+            sfree(outbuf);
+        } else {
+            fprintf(stderr, "decoding error\n");
+            fclose(fp);
+            return 1;
+        }
+    }
+
+    ssh_decompressor_free(handle);
+
+    if (filename)
+        fclose(fp);
+
+    return 0;
+}