From 72c64c76262fef08cc09b25b3ec3ed80ad6136e7 Mon Sep 17 00:00:00 2001
From: Juan RP <xtraeme@gmail.com>
Date: Wed, 17 Sep 2014 06:50:46 +0200
Subject: [PATCH] xbps_file_hash: reduce memory footprint and process file in
 small chunks.

With xbps-rindex(8) -c/-r being multithreaded, the memory usage was
insanely high in the build server, with peaks of almost 4GB (this depends
on the file size being processed and number of threads).

Process the file in small chunks instead to compute the SHA256 hash.
---
 NEWS            |  4 ++++
 lib/util_hash.c | 33 +++++++++++++++------------------
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/NEWS b/NEWS
index e2a6d9ee..e68acf37 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,9 @@
 xbps-0.40 (???):
 
+ * Reduced considerably memory requirement when checking SHA256 hashes on
+   files. Previous way of allocating heap memory as big as the file being
+   processed wasn't a great idea.
+
  * xbps-{install,remove}: the post-install/pre-remove messages are now
    printed with some guards, i.e:
 
diff --git a/lib/util_hash.c b/lib/util_hash.c
index 4663ea11..990e31a8 100644
--- a/lib/util_hash.c
+++ b/lib/util_hash.c
@@ -61,17 +61,16 @@ char *
 xbps_file_hash(const char *file)
 {
 	struct stat st;
+	SHA256_CTX ctx;
 	char hash[SHA256_DIGEST_LENGTH * 2 + 1];
-	unsigned char *buf = NULL, digest[SHA256_DIGEST_LENGTH];
+	unsigned char digest[SHA256_DIGEST_LENGTH];
+	ssize_t ret;
+	unsigned char buf[256];
 	int fd;
 
-	assert(file != NULL);
-
-	if ((fd = open(file, O_RDONLY|O_CLOEXEC)) == -1) {
-		free(buf);
+	if ((fd = open(file, O_RDONLY)) == -1)
 		return NULL;
-	}
-	memset(&st, 0, sizeof(st));
+
 	if (fstat(fd, &st) == -1) {
 		(void)close(fd);
 		return NULL;
@@ -81,20 +80,18 @@ xbps_file_hash(const char *file)
 		return NULL;
 	}
 
-	buf = malloc(st.st_size);
-	assert(buf);
+	SHA256_Init(&ctx);
+	while ((ret = read(fd, buf, sizeof(buf))) > 0)
+		SHA256_Update(&ctx, buf, ret);
 
-	if (read(fd, buf, st.st_size) != st.st_size) {
-	       free(buf);
-	       (void)close(fd);
-	       return NULL;
-	}
-	(void)close(fd);
-	if (SHA256(buf, st.st_size, digest) == NULL) {
-		free(buf);
+	if (ret == -1) {
+		/* read error */
+		(void)close(fd);
 		return NULL;
 	}
-	free(buf);
+
+	SHA256_Final(digest, &ctx);
+	(void)close(fd);
 	digest2string(digest, hash, SHA256_DIGEST_LENGTH);
 
 	return strdup(hash);