[PATCH] Split external diff command interface to a separate file.

With this patch, the non-core'ish part of show-diff command that
invokes an external "diff" comand to obtain patches is split
into a separate file.  The next patch will introduce a new
command, diff-tree-helper, which uses this common diff interface
to format diff-tree and diff-cache output into a patch form.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 106 insertions, 0 deletions

diff --git a/diff.c b/diff.c
new file mode 100644
index 0000000000..dcefe983af
--- /dev/null
+++ b/diff.c
@@ -0,0 +1,106 @@
+#include "cache.h"
+#include "diff.h"
+
+static char *diff_cmd = "diff -L 'k/%s' -L 'l/%s' ";
+static char *diff_opts = "-p -u";
+static char *diff_arg_forward  = " - '%s'";
+static char *diff_arg_reverse  = " '%s' -";
+
+void prepare_diff_cmd(void)
+{
+	/*
+	 * Default values above are meant to match the
+	 * Linux kernel development style.  Examples of
+	 * alternative styles you can specify via environment
+	 * variables are:
+	 *
+	 * GIT_DIFF_CMD="diff -L '%s' -L '%s'"
+	 * GIT_DIFF_OPTS="-c";
+	 */
+	diff_cmd = getenv("GIT_DIFF_CMD") ? : diff_cmd;
+	diff_opts = getenv("GIT_DIFF_OPTS") ? : diff_opts;
+}
+
+/* Help to copy the thing properly quoted for the shell safety.
+ * any single quote is replaced with '\'', and the caller is
+ * expected to enclose the result within a single quote pair.
+ *
+ * E.g.
+ *  original     sq_expand     result
+ *  name     ==> name      ==> 'name'
+ *  a b      ==> a b       ==> 'a b'
+ *  a'b      ==> a'\''b    ==> 'a'\''b'
+ */
+static char *sq_expand(const char *src)
+{
+	static char *buf = NULL;
+	int cnt, c;
+	const char *cp;
+	char *bp;
+
+	/* count bytes needed to store the quoted string. */ 
+	for (cnt = 1, cp = src; *cp; cnt++, cp++)
+		if (*cp == '\'')
+			cnt += 3;
+
+	if (! (buf = malloc(cnt)))
+	    return buf;
+	bp = buf;
+	while ((c = *src++)) {
+		if (c != '\'')
+			*bp++ = c;
+		else {
+			bp = strcpy(bp, "'\\''");
+			bp += 4;
+		}
+	}
+	*bp = 0;
+	return buf;
+}
+
+void show_differences(const char *name, /* filename on the filesystem */
+		      const char *label, /* diff label to use */
+		      void *old_contents, /* contents in core */
+		      unsigned long long old_size, /* size in core */
+		      int reverse /* 0: diff core file
+				     1: diff file core */)
+{
+	FILE *f;
+	char *name_sq = sq_expand(name);
+	const char *label_sq = (name != label) ? sq_expand(label) : name_sq;
+	char *diff_arg = reverse ? diff_arg_reverse : diff_arg_forward;
+	int cmd_size = strlen(name_sq) + strlen(label_sq) * 2 +
+		strlen(diff_cmd) + strlen(diff_opts) + strlen(diff_arg);
+	char *cmd = malloc(cmd_size);
+	int next_at;
+
+	fflush(stdout);
+	next_at = snprintf(cmd, cmd_size, diff_cmd, label_sq, label_sq);
+	next_at += snprintf(cmd+next_at, cmd_size-next_at, "%s", diff_opts);
+	next_at += snprintf(cmd+next_at, cmd_size-next_at, diff_arg, name_sq);
+	f = popen(cmd, "w");
+	if (old_size)
+		fwrite(old_contents, old_size, 1, f);
+	pclose(f);
+	if (label_sq != name_sq)
+		free((void*)label_sq); /* constness */
+	free(name_sq);
+	free(cmd);
+}
+
+void show_diff_empty(const unsigned char *sha1,
+		     const char *name,
+		     int reverse)
+{
+	char *old;
+	unsigned long int size;
+	unsigned char type[20];
+
+	old = read_sha1_file(sha1, type, &size);
+	if (! old) {
+		error("unable to read blob object for %s (%s)", name,
+		      sha1_to_hex(sha1));
+		return;
+	}
+	show_differences("/dev/null", name, old, size, reverse);
+}