index: add sensible error message if metadata is too long

fixes #1476

Instead of:
ERROR: Index generation failed: Success

The following is now printed:
ERROR: Metadata for package timo-1.0-r0 is too long.
ERROR: Index generation failed: No buffer space available

3 files changed, 34 insertions, 26 deletions

diff --git a/src/database.c b/src/database.c
index 61e719d..0b40273 100644
--- a/src/database.c
+++ b/src/database.c
@@ -874,11 +874,11 @@ static int apk_db_write_fdb(struct apk_database *db, struct apk_ostream *os)
 				apk_blob_push_blob(&bbuf, APK_BLOB_STR("\n"));
 
 				if (os->write(os, buf, bbuf.ptr - buf) != bbuf.ptr - buf)
-					return -1;
+					return -EIO;
 				bbuf = APK_BLOB_BUF(buf);
 			}
 			if (os->write(os, buf, bbuf.ptr - buf) != bbuf.ptr - buf)
-				return -1;
+				return -EIO;
 			bbuf = APK_BLOB_BUF(buf);
 		}
 		os->write(os, "\n", 1);
@@ -1101,7 +1101,7 @@ static int write_index_entry(apk_hash_item item, void *ctx)
 		return r;
 
 	if (iwctx->os->write(iwctx->os, "\n", 1) != 1)
-		return -1;
+		return -EIO;
 
 	iwctx->count++;
 	return 0;
@@ -1124,7 +1124,7 @@ static int apk_db_index_write_nr_cache(struct apk_database *db)
 				 "installed.new",
 				 0644);
 	if (os == NULL)
-		return -1;
+		return -EIO;
 
 	ctx.os = os;
 	list_for_each_entry(ipkg, &db->installed.packages, installed_pkgs_list) {
diff --git a/src/index.c b/src/index.c
index 8d62252..a862d2a 100644
--- a/src/index.c
+++ b/src/index.c
@@ -9,6 +9,7 @@
  * by the Free Software Foundation. See http://www.gnu.org/ for details.
  */
 
+#include <errno.h>
 #include <stdio.h>
 #include <fcntl.h>
 #include <unistd.h>
@@ -61,7 +62,7 @@ static int index_read_file(struct apk_database *db, struct index_ctx *ictx)
 	if (ictx->index == NULL)
 		return 0;
 	if (apk_file_get_info(AT_FDCWD, ictx->index, APK_CHECKSUM_NONE, &fi) < 0)
-		return -1;
+		return -EIO;
 	ictx->index_mtime = fi.mtime;
 
 	return apk_db_index_read_file(db, ictx->index, 0);
@@ -185,37 +186,41 @@ static int index_main(void *ctx, struct apk_database *db, int argc, char **argv)
 	if (ictx->method == APK_SIGN_GENERATE) {
 		struct apk_ostream *counter;
 
-		os = apk_ostream_gzip(os);
-
-		if (ictx->description != NULL) {
-			memset(&fi, 0, sizeof(fi));
-			fi.mode = 0644 | S_IFREG;
-			fi.name = "DESCRIPTION";
-			fi.size = strlen(ictx->description);
-			apk_tar_write_entry(os, &fi, ictx->description);
-		}
-
 		memset(&fi, 0, sizeof(fi));
 		fi.mode = 0644 | S_IFREG;
 		fi.name = "APKINDEX";
 		counter = apk_ostream_counter(&fi.size);
-		apk_db_index_write(db, counter);
+		r = apk_db_index_write(db, counter);
 		counter->close(counter);
-		apk_tar_write_entry(os, &fi, NULL);
-		total = apk_db_index_write(db, os);
-		apk_tar_write_padding(os, &fi);
 
-		apk_tar_write_entry(os, NULL, NULL);
+		if (r >= 0) {
+			os = apk_ostream_gzip(os);
+			if (ictx->description != NULL) {
+				struct apk_file_info fi_desc;
+				memset(&fi_desc, 0, sizeof(fi));
+				fi_desc.mode = 0644 | S_IFREG;
+				fi_desc.name = "DESCRIPTION";
+				fi_desc.size = strlen(ictx->description);
+				apk_tar_write_entry(os, &fi_desc, ictx->description);
+			}
+
+			apk_tar_write_entry(os, &fi, NULL);
+			r = apk_db_index_write(db, os);
+			apk_tar_write_padding(os, &fi);
+
+			apk_tar_write_entry(os, NULL, NULL);
+		}
 	} else {
-		total = apk_db_index_write(db, os);
+		r = apk_db_index_write(db, os);
 	}
 	os->close(os);
 
-	if (total < 0) {
+	if (r < 0) {
 		apk_error("Index generation failed: %s", apk_error_str(r));
-		return total;
+		return r;
 	}
 
+	total = r;
 	apk_hash_foreach(&db->available.names, warn_if_no_providers, &counts);
 
 	if (counts.unsatisfied != 0)
diff --git a/src/package.c b/src/package.c
index 9ad17e9..ecf88c2 100644
--- a/src/package.c
+++ b/src/package.c
@@ -1156,15 +1156,18 @@ int apk_pkg_write_index_entry(struct apk_package *info,
 	}
 	apk_blob_push_blob(&bbuf, APK_BLOB_STR("\n"));
 
-	if (APK_BLOB_IS_NULL(bbuf))
-		return -1;
+	if (APK_BLOB_IS_NULL(bbuf)) {
+		apk_error("Metadata for package " PKG_VER_FMT " is too long.",
+			  PKG_VER_PRINTF(info));
+		return -ENOBUFS;
+	}
 
 	bbuf = apk_blob_pushed(APK_BLOB_BUF(buf), bbuf);
 	if (os->write(os, bbuf.ptr, bbuf.len) != bbuf.len ||
 	    write_depends(os, "D:", info->depends) ||
 	    write_depends(os, "p:", info->provides) ||
 	    write_depends(os, "i:", info->install_if))
-		return -1;
+		return -EIO;
 
 	return 0;
 }