From 61636f15718edc7ea17b91f22f1d97b905eaf951 Mon Sep 17 00:00:00 2001
From: Paul Barker <paul@paulbarker.me.uk>
Date: Sat, 7 Nov 2015 10:23:52 +0000
Subject: [PATCH 4/4] opkg_download: Use short cache file name

Source URIs can be very long. The cache directory itself may already have a very
long path, especially if we're installing packages into an offline rootfs.
Therefore it's not a good idea to simply tag the source URI onto the cache
directory path to create a cache file name.

To create shorter cache file names which are deterministic and very likely to be
unique, we use the md5sum of the source URI along with the basename of the
source URI. The basename is length limited to ensure that it the resulting
filename length is always reasonable.

Signed-off-by: Paul Barker <paul@paulbarker.me.uk>
Signed-off-by: Alejandro del Castillo <alejandro.delcastillo@ni.com>

Upstream-Status: Accepted
---
 libopkg/opkg_download.c | 35 ++++++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/libopkg/opkg_download.c b/libopkg/opkg_download.c
index e9b86a5..a37b10d 100644
--- a/libopkg/opkg_download.c
+++ b/libopkg/opkg_download.c
@@ -29,10 +29,18 @@
 #include "opkg_verify.h"
 #include "opkg_utils.h"
 
+#include "md5.h"
 #include "sprintf_alloc.h"
 #include "file_util.h"
 #include "xfuncs.h"
 
+/* Limit the short file name used to generate cache file names to 90 characters
+ * so that when added to the md5sum (32 characters) and an underscore, the
+ * resulting length is below 128 characters. The maximum file name length
+ * differs between plaforms but 128 characters should be reasonable.
+ */
+#define MAX_SHORT_FILE_NAME_LENGTH 90
+
 static int opkg_download_set_env()
 {
     int r;
@@ -135,15 +143,28 @@ int opkg_download_internal(const char *src, const char *dest,
  */
 char *get_cache_location(const char *src)
 {
-    char *cache_name = xstrdup(src);
-    char *cache_location, *p;
+    unsigned char md5sum_bin[16];
+    char *md5sum_hex;
+    char *cache_location;
+    char *short_file_name;
+    char *tmp = xstrdup(src);
 
-    for (p = cache_name; *p; p++)
-        if (*p == '/')
-            *p = '_';
+    md5_buffer(src, strlen(src), md5sum_bin);
+    md5sum_hex = md5_to_string(md5sum_bin);
 
-    sprintf_alloc(&cache_location, "%s/%s", opkg_config->cache_dir, cache_name);
-    free(cache_name);
+    /* Generate a short file name which will be used along with an md5sum of the
+     * full src URI in the cache file name. This short file name is limited to
+     * MAX_SHORT_FILE_NAME_LENGTH to ensure that the total cache file name
+     * length is reasonable.
+     */
+    short_file_name = basename(tmp);
+    if (strlen(short_file_name) > MAX_SHORT_FILE_NAME_LENGTH)
+        short_file_name[MAX_SHORT_FILE_NAME_LENGTH] = '\0';
+
+    sprintf_alloc(&cache_location, "%s/%s_%s", opkg_config->cache_dir,
+                  md5sum_hex, short_file_name);
+    free(md5sum_hex);
+    free(tmp);
     return cache_location;
 }
 
-- 
1.9.1